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This paper synthesizes the findings from The Last Play, The Fall of R'Thea and Sticklebacks, three immersive storytelling experiences developed by the author and his collaborators over a span of four years. We define 'immersive storytelling' as a time-limited, location-based experience that invites audiences into a fragmented narrative across multiple mediums. Engaging various senses and requiring active participation, the experience adapts to individual choices and uses technology as a tool to expand the narrative spaces. Through this paper, we provide insights into our creative approaches, methodologies, and the lessons learned during the development and production phases and propose an immersive design methodology aimed at guiding future research and practice in crafting immersive experiences. [ABSTRACT FROM AUTHOR]

The adaptation of marine fish to freshwater environments includes prodigious examples of rapid evolution.Given the scarcity of ω‐3 long‐chain polyunsaturated fatty acids (LC‐PUFA) in freshwater, we expect selection to be strong on fish transitioning to freshwater habitats and yet the underlying ecological causes of genomic and phenotypic differentiation are poorly understood for traits associated with lipid content and composition. Threespine stickleback Gasterosteus aculeatus have repeatedly colonized, and adapted to, freshwater habitats across the Northern Hemisphere. These freshwater populations often show elevated copy number of the fatty acid desaturase 2 gene (FADS2), which increases the biosynthetic capacity of LC‐PUFA. The starkly lower content of LC‐PUFA in freshwater compared to marine prey, especially docosahexaenoic acid (DHA), likely imposes strong positive selection on freshwater fish for either increased biosynthesis or greater dietary acquisition of LC‐PUFA. The recently colonized and relatively undisturbed threespine stickleback populations in postglacial coastal lakes of southern Greenland offer an exceptional opportunity to study how variation in the copy number of FADS2 is related to abiotic and biotic conditions of lakes and their morphometry. As expected, given its position on the stickleback X chromosome, we found strong sexual dimorphism in FADS2 copy number in all populations (19 freshwater, 1 marine and 1 brackish), and an increased dimorphism in some freshwater populations. We also found that FADS2 copy number was negatively correlated, for both males and females, with the abundance of copepods, which are a DHA‐rich food source in the zooplankton community. Overall, our results suggest that the prey community context of lakes might influence the process of metabolic adaptation of marine fish colonizing freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Sandy beaches and their surf zones characterise many of the world's open coastlines. They are important breeding, nursery and feeding areas for many species of fish. Despite the commonness and importance of sandy beach surf zones, the dynamics, space occupancy and diversity patterns of residing fish is in many places poorly understood. The aim of this study was to (1) characterise the fish community structure in 11 simple structured sandy surf zones of the northern Baltic Sea and (2) relate variation in fish abundance and community structure to a set of chosen abiotic variables. Using beach seine, weekly or biweekly sampling was conducted at fixed sites at 10 occasions throughout a summer season. A total of 60,006 fish individuals belonging to 20 species were recorded. Changes in abundance and community structure were mainly driven by the variation of only five species reflecting species‐specific recruitment patterns and different spatial responses to abiotic variables. Dominating groups were Gasterosteidae, Ammodytidae and Gobiidae that together formed 86% of the total adult fish catches. Larval numbers were completely dominated by Gobiidae. Multivariate analyses indicated species‐specific responses to measured environmental variables, most important being a combination of wave exposure, beach slope, bottom roughness, and temperature. The present study shows that changes in fish abundance on simple structured sandy sublittoral beaches in the northern Baltic Sea are large over the course of a breeding season. It also reveals that variation in adult and juvenile fish are driven by a set of abiotic factors that influence on the fish assemblage structure through mainly species‐specific, rather than through generic responses. Unravelling the degree to which the sandy shore fish community vary in the northern Baltic Sea will help in managing coastal environments that are increasingly being threatened by many anthropogenic stressors. [ABSTRACT FROM AUTHOR]

Recent discoveries of sex chromosome diversity across the tree of life have challenged the canonical model of conserved sex chromosome evolution and evoked new theories on labile sex chromosomes that maintain less differentiation and undergo frequent turnover. However, theories of labile sex chromosome evolution lack direct empirical support due to the paucity of case studies demonstrating ongoing sex chromosome turnover in nature. Two divergent lineages (viz. WL & EL) of nine-spined sticklebacks (Pungitius pungitius) with different sex chromosomes (linkage group [LG] 12 in the EL, unknown in the WL) hybridize in a natural secondary contact zone in the Baltic Sea, providing an opportunity to study ongoing turnover between coexisting sex chromosomes. In this study, we first identify an 80 kbp genomic region on LG3 as the sex-determining region (SDR) using whole-genome resequencing data of family crosses of a WL population. We then verify this region as the SDR in most other WL populations and demonstrate a potentially ongoing sex chromosome turnover in admixed marine populations where the evolutionarily younger and homomorphic LG3 sex chromosome replaces the older and heteromorphic LG12 sex chromosome. The results provide a rare glimpse of sex chromosome turnover in the wild and indicate the possible existence of additional yet undiscovered sex chromosome diversity in Pungitius sticklebacks. [ABSTRACT FROM AUTHOR]

Assessing social effects on individual behaviour is challenging because knowledge of an individual's social environment is often difficult to gain, especially for animals that form dynamic social groups. We here report on an experiment where the social environment could be manipulated. To this end, we capitalized on the availability of populations of migrant and resident sticklebacks, Gasterosteus aculeatus , that exhibit strong differences in movement tendencies. This allowed us to create mixed shoals with different proportions of migrants and residents, to investigate the occurrence of social effects between migrant and resident fish. In a mesocosm consisting of linearly connected ponds, we found that the overall movement patterns, as quantified by the number of pond transitions, remained consistently higher in migrants than in residents, regardless of the social group composition. The fish's intrinsic movement tendency was the main predictor of the observed variation between populations. However, at the start of the experiment, when social effects were expected to be strongest, residents were more likely to leave the starting pond in the presence of migrants than in their absence. As this increase in movement tendency was not related to the frequency of migrants in the mixed groups it cannot solely be ascribed to social conformity. Additionally, we found an effect of being part of the majority on movement: the first fish to leave the starting pond was almost always a member of the majority group (be it migrants or residents). In conclusion, we found little evidence for social modulation of movement based on differences in the populations' movement tendencies, but rather an effect of being in a majority group. • We experimentally manipulated the social environment under seminatural conditions. • Movements between ponds remained consistently higher in migratory fish. • Residents were more likely to leave the starting pond in the presence of migrants. • Habituation to the experimental set-up likely played a role. • The first fish to leave the starting pond was almost always from the majority group. [ABSTRACT FROM AUTHOR]

Whether populations adapt to similar selection pressures using the same underlying genetic variants depends on population history and the distribution of standing genetic variation at the metapopulation level. Studies of sticklebacks provide a case in point: when colonizing and adapting to freshwater habitats, three-spined sticklebacks (Gasterosteus aculeatus) with high gene flow tend to fix the same adaptive alleles in the same major loci, whereas nine-spined sticklebacks (Pungitius pungitius) with limited gene flow tend to utilize a more heterogeneous set of loci. In accordance with this, we report results of quantitative trait locus (QTL) analyses using a backcross design showing that lateral plate number variation in the western European nine-spined sticklebacks mapped to 3 moderate-effect QTL, contrary to the major-effect QTL in three-spined sticklebacks and different from the 4 QTL previously identified in the eastern European nine-spined sticklebacks. Furthermore, several QTL were identified associated with variation in lateral plate size, and 3 moderate-effect QTL with body size. Together, these findings indicate more heterogenous and polygenic genetic underpinnings of skeletal armour variation in nine-spined than three-spined sticklebacks, indicating limited genetic parallelism underlying armour trait evolution in the family Gasterostidae. Graphical Abstract [ABSTRACT FROM AUTHOR]

The nine-spined stickleback (Pungitius pungitius) has been increasingly used as a model system in studies of local adaptation and sex chromosome evolution but its current reference genome assembly is far from perfect, lacking distinct sex chromosomes. We generated an improved assembly of the nine-spined stickleback reference genome (98.3% BUSCO completeness) with the aid of linked-read mapping. While the new assembly (v8) was of similar size as the earlier version (v7), we were able to assign 4.4 times more contigs to the linkage groups and improve the contiguity of the genome. Moreover, the new assembly contains a ∼22.8 Mb Y-linked scaffold (LG22) consisting mainly of previously assigned X-contigs, putative Y-contigs, putative centromere contigs, and highly repetitive elements. The male individual showed an even mapping depth on LG12 (pseudo X chromosome) and LG22 (Y-linked scaffold) in the segregating sites, suggesting near-pure X and Y representation in the v8 assembly. A total of 26,803 genes were annotated, and about 33% of the assembly was found to consist of repetitive elements. The high proportion of repetitive elements in LG22 (53.10%) suggests it can be difficult to assemble the complete sequence of the species' Y chromosome. Nevertheless, the new assembly is a significant improvement over the previous version and should provide a valuable resource for genomic studies of stickleback fishes. [ABSTRACT FROM AUTHOR]

The three-spined stickleback (Gasterosteus aculeatus) is a teleost fish and a model organism in evolutionary ecology, useful for both laboratory and natural experiments. It is especially valued for the substantial intraspecific variation in morphology, behaviour and genetics. Classic work of Swarup (1958) has described the development in the laboratory of embryos from a single freshwater population, but this was carried out at higher temperature than many stickleback would encounter in the wild and variation between populations was not addressed. Here we describe the development of embryos from two sympatric, saltwater ecotypes of stickleback from North Uist, Scotland raised at 14°C, the approximate temperature of North Uist lochs in the breeding season. The two ecotypes were (a) a large, migratory form in which the adults are completely plated with bony armour and (b) a smaller, low-plated form that is resident year-round in saltwater lagoons. By monitoring embryos every 24-hours post fertilisation, important characteristics of development were observed and photographed to provide a reference for North Uist ecotypes at this temperature. Hatching success was greater than 85% and did not differ between resident and migratory stickleback, but migratory eggs hatched significantly earlier than the resident ecotype. Our work provides a framework that can now be used to compare stickleback populations that may also grow in distinct environmental conditions, to help understand the breadth of normal developmental features and to characterise abnormal development. [ABSTRACT FROM AUTHOR]

Mate choice plays a fundamental role in speciation, yet we know little about the molecular mechanisms that underpin this crucial decision-making process. Stickleback fish differentially adapted to limnetic and benthic habitats are reproductively isolated and females of each species use different male traits to evaluate prospective partners and reject heterospecific males. Here, we integrate behavioural data from a mate choice experiment with gene expression profiles from the brains of females actively deciding whether to mate. We find substantial gene expression variation between limnetic and benthic females, regardless of behavioural context, suggesting general divergence in constitutive gene expression patterns, corresponding to their genetic differentiation. Intriguingly, female gene co-expression modules covary with male display traits but in opposing directions for sympatric populations of the two species, suggesting male displays elicit a dynamic neurogenomic response that reflects known differences in female preferences. Furthermore, we confirm the role of numerous candidate genes previously implicated in female mate choice in other species, suggesting evolutionary tinkering with these conserved molecular processes to generate divergent mate preferences. Taken together, our study adds important new insights to our understanding of the molecular processes underlying female decision-making critical for generating sexual isolation and speciation. [ABSTRACT FROM AUTHOR]

Extreme temperature events, such as heat waves, can have lasting effects on the behavior, physiology, and reproductive success of organisms. Here, we examine the impact of short-term exposure to a simulated heat wave on condition, parental care, and reproductive success in a population of threespine stickleback (Gasterosteus aculeatus), a small fish with exclusive paternal care, currently experiencing regular heat waves. Males were either exposed to a simulated heat wave (23 °C) for 5 d or held at an ideal temperature (18 °C). Following this 5-d treatment, all males were transferred to 18 °C, where they completed a full parenting cycle. Offspring were raised at 18 °C. We found that while mass and body condition were unaffected in males exposed to a heat wave, cortisol responses were dampened across the nesting cycle compared to control males. In addition, heat wave males had longer latency for eggs to hatch, lower hatching success, and showed lower levels of parental care behavior compared to control males. Offspring of heat wave males had lower body condition, affecting swimming performance. Altogether, our results highlight the long-term impact that even short-term events can have on reproductive success, parental behavior, and subsequent generations, providing insight into population responses to rapid environmental change. [ABSTRACT FROM AUTHOR]

An important goal of environmental and comparative physiology research is to identify species or populations that may be susceptible to environmental change such as heat wave events that are predicted to become more frequent and intense in the future. This study tested the hypothesis that fishes inhabiting alkaline lakes face significant physiological challenges, which results in reduced thermal tolerance. Brook stickleback (Culaea inconstans) were collected from an alkaline lake (pH 9.3) in Alberta, Canada and held under neutral conditions in the laboratory. Subsequently, fish were acutely exposed (4 d) to neutral (pH 7) or alkaline (pH 9.5) waters at 10 or 25°C. Exposure to alkaline water reduced critical thermal maximum (CTmax) in stickleback by approximately 1°C, but thermal acclimation capacity ("thermal plasticity") was unaffected by alkaline exposure. Alkaline conditions resulted in physiological disturbances characteristic of exposure to high pH including elevated whole-body ammonia and lactate concentrations. Acute warming to CTmax in alkaline-exposed fish resulted in reductions in whole-body sodium and chloride concentrations. In addition, alkaline exposure compromised recovery from exercise at elevated temperatures. Overall, these results suggest that the physiological disturbances observed in response to alkaline exposure may render fish more susceptible to acute warming, reducing thermal tolerance. [ABSTRACT FROM AUTHOR]

Eco‐evolutionary experiments are typically conducted in semi‐unnatural controlled settings, such as mesocosms; yet inferences about how evolution and ecology interact in the real world would surely benefit from experiments in natural uncontrolled settings. Opportunities for such experiments are rare but do arise in the context of restoration ecology—where different "types" of a given species can be introduced into different "replicate" locations. Designing such experiments requires wrestling with consequential questions. (Q1) Which specific "types" of a focal species should be introduced to the restoration location? (Q2) How many sources of each type should be used—and should they be mixed together? (Q3) Which specific source populations should be used? (Q4) Which type(s) or population(s) should be introduced into which restoration sites? We recently grappled with these questions when designing an eco‐evolutionary experiment with threespine stickleback (Gasterosteus aculeatus) introduced into nine small lakes and ponds on the Kenai Peninsula in Alaska that required restoration. After considering the options at length, we decided to use benthic versus limnetic ecotypes (Q1) to create a mixed group of colonists from four source populations of each ecotype (Q2), where ecotypes were identified based on trophic morphology (Q3), and were then introduced into nine restoration lakes scaled by lake size (Q4). We hope that outlining the alternatives and resulting choices will make the rationales clear for future studies leveraging our experiment, while also proving useful for investigators considering similar experiments in the future. [ABSTRACT FROM AUTHOR]

The diverse and changing pigmentation of the skin allows fish to adapt to environmental conditions for survival and communication with conspecifics. However, various physical and chemical environmental factors, including pollutants, affect fish coloration. Therefore, the implementation of an analysis of skin pigmentation has been considered in fish well-being and ecotoxicological studies. A physiological color change is achieved by the motility of melanincontaining organelles: they aggregate into the perikaryon or disperse throughout the cytoplasm of melanophores in response to various stimuli. In our study, we addressed the issue of implementing the analysis of pigment dispersion in melanophores in stickleback skin to assess the response of fish to oxidative stress. We examined pigment dispersion in day and night skin samples collected from the dorsal, lateral and ventral regions. The degree of pigment dispersion we assessed by the melanophore index. The total number of melanophores counted in the defined skin area was significantly higher in the night samples than in the day samples. Only in day samples of dorsal skinwe observed the significant changes in pigment dispersion after exposure to stress: melanin was predominantly in the aggregated state. In the night samples, we did not report any response to stress in any part of the skin. Examination of pigment dispersion in melanophores in stickleback skin can be useful for assessing the welfare of fish and detecting toxic agents in the environment, but under specified conditions: in sticklebacks, it is analysis of dorsal skin during the day. [ABSTRACT FROM AUTHOR]

Ecological disturbances such as fish kills can negatively impact ecosystem processes in coastal lagoons. To gain an understanding of factors causing fish kills, we examined conditions associated with a summertime fish kill in a northeastern Pacific coastal lagoon (Rodeo Lagoon, CA, USA). Examination of available data indicated the fish kill was likely caused by hypoxia involving the following etiology: (1) strong onshore winds (up to 12 m/s) mixed a stratified water column, (2) water column mixing transported nutrients from near the bed into the photic zone, (3) increased nutrient concentrations in the photic zone (> 200%) together with high solar irradiance fueled a phytoplankton bloom, (4) death and decomposition of phytoplankton (72% decrease in abundance) contributed to biological oxygen demand that led to (5) hypoxic conditions (as low as 0.6 mg/L) that caused the fish kill. The event resulted in the death of an estimated 3677 Tidewater Goby (Eucyclogobius newberryi), a species listed as endangered under the US Endangered Species Act, and numerous (but not enumerated) Threespine Stickleback (Gasterosteus aculeatus), unidentified sculpins (Cottidae), and macroinvertebrates (primarily Amphipoda). The processes contributing to the event are likely re-occurring phenomena responsible for observed periodic fish kills. Coastal lagoons with limited freshwater inflows and connection to the Pacific Ocean may retain nutrients and be susceptible to similar events. [ABSTRACT FROM AUTHOR]

Darwin attributed the absence of species transitions in the fossil record to his hypothesis that speciation occurs within isolated habitat patches too geographically restricted to be captured by fossil sequences. Mayr's peripatric speciation model added that such speciation would be rapid, further explaining missing evidence of diversification. Indeed, Eldredge and Gould's original punctuated equilibrium model combined Darwin's conjecture, Mayr's model and 124 years of unsuccessfully sampling the fossil record for transitions. Observing such divergence, however, could illustrate the tempo and mode of evolution during early speciation. Here, we investigate peripatric divergence in a Miocene stickleback fish, Gasterosteus doryssus. This lineage appeared and, over approximately 8000 generations, evolved significant reduction of 12 of 16 traits related to armour, swimming and diet, relative to its ancestral population. This was greater morphological divergence than we observed between reproductively isolated, benthic-limnetic ecotypes of extant Gasterosteus aculeatus. Therefore, we infer that reproductive isolation was evolving. However, local extinction of G. doryssus lineages shows how young, isolated, speciating populations often disappear, supporting Darwin's explanation for missing evidence and revealing a mechanism behind morphological stasis. Extinction may also account for limited sustained divergence within the stickleback species complex and help reconcile speciation rate variation observed across time scales. [ABSTRACT FROM AUTHOR]

Translocation programmes for endangered species typically focus on a single species, but in areas where little native habitat remains, it may be necessary to translocate multiple species to the same sites. Interactions between translocated species, such as predation and competition, are among the factors that need to be considered when planning multispecies translocations. Translocation sites for aquatic species are particularly scarce in southern California, where a limited number of sites exist for historically co‐occurring endangered mountain yellow‐legged frogs Rana muscosa and unarmoured three‐spine sticklebacks Gasterosteus aculeatus williamsoni. To determine how these species would interact if translocated to the same sites, we carried out experiments ex situ with R. muscosa tadpoles and a surrogate subspecies of stickleback (G. a. microcephalus). We found that (1) adult sticklebacks preyed on hatchling tadpoles but did not consume R. muscosa eggs or large tadpoles; (2) tadpoles did not consume stickleback eggs or disturb sticklebacks nests; and (3) both species' microhabitat use shifted slightly when the other was present. Our results suggest that these species can likely be co‐managed successfully, if measures are taken to curb stickleback predation on tadpoles until the R. muscosa population is well established. Using ex situ studies to evaluate species interactions prior to translocation is an approach that could prove useful in other species recovery programmes. Multispecies translocations could make better use of available resources when habitat is limited and promote ecosystem recovery by re‐establishing interactions among native species. [ABSTRACT FROM AUTHOR]

Cooperative behaviours, which benefit a recipient, are widespread in the animal kingdom; yet their evolution is not straightforward. Reciprocity, i.e., cooperating with previously experienced cooperative partners, has been suggested to underly cooperation, but has been contested throughout the years. Once a textbook example of reciprocity was cooperative predator inspection, where one or several individuals leave their group to approach a potential threat. Each can at any point stop or retreat, increasing the risk for its partner. It was suggested that inspecting individuals follow a specific reciprocal strategy called tit‐for‐tat, i.e., cooperating on the first move and then copying the partner's last move. Numerous studies provide evidence to support the claim that fish cooperate to inspect predators, including three‐spined sticklebacks (Gasterosteus aculeatus), guppies (Poecilia reticulata) and minnows (Phoxinus phoxinus). However, over the past few decades some scholars have expressed scepticism whether predator inspection is indeed a cooperative behaviour or rather a case of by‐product mutualism, which describes behaviours that benefit a partner as a corollary of an otherwise selfish behaviour. For instance, it has been shown that pairs of fish moving in unfamiliar environments appear to coordinate movements even in the absence of predators. Many studies have also used coarse measures of overall approach rates towards predators rather than the fine‐grained analyses necessary to infer tit‐for‐tat in cooperative inspections. Now is the time to return to the question of cooperative predator inspection with new tools and approaches to resolve a decades‐old debate. [ABSTRACT FROM AUTHOR]

Additive and dominance genetic variances underlying the expression of quantitative traits are important quantities for predicting short‐term responses to selection, but they are notoriously challenging to estimate in most non‐model wild populations. Specifically, large‐sized or panmictic populations may be characterized by low variance in genetic relatedness among individuals which, in turn, can prevent accurate estimation of quantitative genetic parameters. We used estimates of genome‐wide identity‐by‐descent (IBD) sharing from autosomal SNP loci to estimate quantitative genetic parameters for ecologically important traits in nine‐spined sticklebacks (Pungitius pungitius) from a large, outbred population. Using empirical and simulated datasets, with varying sample sizes and pedigree complexity, we assessed the performance of different crossing schemes in estimating additive genetic variance and heritability for all traits. We found that low variance in relatedness characteristic of wild outbred populations with high migration rate can impair the estimation of quantitative genetic parameters and bias heritability estimates downwards. On the other hand, the use of a half‐sib/full‐sib design allowed precise estimation of genetic variance components and revealed significant additive variance and heritability for all measured traits, with negligible dominance contributions. Genome‐partitioning and QTL mapping analyses revealed that most traits had a polygenic basis and were controlled by genes at multiple chromosomes. Furthermore, different QTL contributed to variation in the same traits in different populations suggesting heterogeneous underpinnings of parallel evolution at the phenotypic level. Our results provide important guidelines for future studies aimed at estimating adaptive potential in the wild, particularly for those conducted in outbred large‐sized populations. [ABSTRACT FROM AUTHOR]

Fatty acids, and especially long‐chain polyunsaturated fatty acids, are biologically important components in the metabolism of vertebrates, including fish. Essential fatty acids (EFA) are those that in a given animal cannot be synthesized or modified from precursors and must therefore be acquired via the diet. Because EFAs are often unevenly distributed in nature, this requirement may drive species to make behavioral or ecological adaptations to avoid malnutrition. This is especially true for fish like the three‐spined stickleback (Gasterosteus aculeatus L.) of Upper Lake Constance (ULC), whose recent marine ancestors evolved with access to EFA‐rich prey, but which found themselves in an EFA‐deficient habitat. An unexpected and unprecedented ecological shift in the ULC stickleback population from the littoral to pelagic zones in 2012 might be linked to EFA availability, triggering ecological release and enabling them to build a hyperabundant population while displacing the former keystone species, the pelagic whitefish Coregonus wartmanni. To test this hypothesis, sticklebacks from the littoral and pelagic zones of ULC were sampled seasonally in two consecutive years, and their stomach contents and fatty acid profiles were analysed. Pelagic sticklebacks were found to possess significantly higher values of an important EFA, docosahexaenoic acid (DHA), especially during autumn. Evaluation of the DHA supply suggests that sticklebacks feeding in the littoral zone during autumn could not meet their DHA requirement, whereas DHA availability in the pelagic zone was surplus to demand. During autumn, pelagic sticklebacks consumed large amounts of DHA‐rich prey, that is, copepods, whereas littoral sticklebacks relied mainly mostly on cladocerans, which provide much lower quantities of DHA. Access to pelagic zooplankton in 2012 was possibly facilitated by low densities of previously dominant zooplanktivorous whitefish. The present study offers a convincing physiological explanation for the observed expansion of invasive sticklebacks from the littoral to the pelagic zones of Lake Constance, contributing to a phase shift with severe consequences for fisheries. [ABSTRACT FROM AUTHOR]

Determining how environmental conditions contribute to divergence among populations and drive speciation is fundamental to resolving mechanisms and understanding outcomes in evolutionary biology. Postglacial freshwater fish species in the Northern Hemisphere are ideal biological systems to explore the effects of environment on diversification in morphology, ecology, and genetics (ecomorph divergences) within lakes. To date, various environmental factors have been implicated in the presence of multiple ecomorphs within particular lakes or regions. However, concerted evidence for generalizable patterns in environmental variables associated with speciation across geographical regions and across species and genera has been lacking. Here, we aimed to identify key biotic and abiotic factors associated with ecological divergence of postglacial freshwater fish species into multiple sympatric ecomorphs, focusing on species in the well‐studied, widespread, and co‐distributed genera Gasterosteus, Salvelinus, and Coregonus (stickleback, charr, and whitefish, respectively). We found that the presence of multiple sympatric ecomorphs tended to be associated with increasing lake surface area, maximum depth, and nutrient availability. In addition, predation, competition, and prey availability were suggested to play a role in divergence into multiple ecomorphs, but the effects of biotic factors require further study. Although we identified several environmental factors correlated with the presence of multiple ecomorphs, there were substantial data gaps across species and regions. An improved understanding of these systems may provide insight into both generalizable environmental factors involved in speciation in other systems, and potential ecological and evolutionary responses of species complexes when these variables are altered by environmental change. [ABSTRACT FROM AUTHOR]

The rapid expansion of three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758 (Perciformes, Gasterosteida)) in the pelagic zone of Lake Constance, Central Europe, since 2012 contributed to stark ecosystem-wide effects, such as food-web shifts and declines in native biodiversity, including commercially important fish species. Yet, the origin of this invasive pelagic population remains unclear. Using RAD-sequencing of Lake Constance sticklebacks, we show that the pelagic Lake Constance population likely arose recently within the lake, potentially from the littoral population. We did not detect any substantial genome-wide genetic differentiation between individuals from different habitats, supporting a recent origin of the pelagic population and/or ongoing gene flow. This is further supported by minimal differences in meristic and morphometric traits. However, we also identified multiple outlier loci between littoral and pelagic individuals across the genome, potentially suggesting early signs of adaptation despite high connectivity. In this study, we provide an important example of rapid within-lake ecological diversification of an invasive species from standing genetic variation. Ultimately, our findings will have major implications for the management of invasive pelagic stickleback, as they indicate that the stickleback population has to be managed as a whole and that management efforts cannot only focus on the hyper-abundant pelagic population. [ABSTRACT FROM AUTHOR]

Organismal divergence can be driven by differential resource use and adaptation to different trophic niches. Variation in diet is a major factor shaping the gut microbiota, which is crucial for many aspects of their hosts' biology. However, it remains largely unknown how host diet diversity affects the gut microbiota, and it could be hypothesized that trophic niche width is positively associated with gut microbiota diversity. To test this idea, we sequenced the 16S ribosomal RNA gene from intestinal tissue of 14 threespine stickleback populations from lakes of varying size on Vancouver Island, Canada, that have been shown to differ in trophic niche width. Using lake size as a proxy for trophic ecology, we found evidence for higher gut microbiota uniqueness among individuals from populations with broader trophic niches. While these results suggest that diet diversity might promote gut microbiota diversity, additional work investigating diet and gut microbiota variation of the same host organisms will be necessary. Yet our results motivate the question of how host population diversity (e.g., ecological, morphological, genetic) might interact with the gut microbiota during the adaptation to ecological niches. [ABSTRACT FROM AUTHOR]

Shelter is an important resource, serving as protection from rivals, predators and environmental stressors. The physical dimensions of a potential shelter are an important factor that can affect decisions about potential shelter options. Animals must select a shelter that they can fit into and use as a refuge, but beyond that, do they show fine-scale preferences based on shelter dimensions? This question has been actively studied for species whose shelter use is closely connected to their life cycles, such as obligate shell dwellers and nest-inhabiting species. However, preferences and decision making for temporary shelters has received less attention. We tested whether three-spined sticklebacks, Gasterosteus aculeatus , a common laboratory model, exhibit preferences in shelter use (actively entering and spending time within a shelter) between shelters with different dimensions. We used PVC tubes of different dimensions as shelters and conducted a simultaneous choice assay where individual fish were presented with each of three tubes available for use as shelter. The fish showed a clear preference, using larger diameter shelters more frequently than either of the other two options. There was no difference in the number of nonsheltering visits fish made or time to enter a shelter across tube sizes, which suggests an active selection by the fish rather than passive bias. There was no difference in duration of time spent within a shelter, suggesting that despite these preferences, actual benefit derived by the fish may be decoupled from the shelter dimensions. Our results offer opportunities for future research that addresses longer term questions in both behavioural ecology and welfare. What drives the preference for larger diameter tubes, and are there are long-term benefits to shelter with preferred dimensions? Certainly, our results suggest that housing sticklebacks with larger diameter shelters may be a simple and convenient means to improve welfare. • Do three-spined sticklebacks select shelters based on differences in dimensions? • We presented fish with different shelters in a simultaneous choice arena. • Fish showed a higher frequency of shelter use in larger diameter shelters. • Using larger PVC tubes may be a convenient way to improve stickleback housing. [ABSTRACT FROM AUTHOR]

Advances in genomic studies have revealed that hybridization in nature is pervasive and raised questions about the dynamics of different genetic and evolutionary factors following the initial hybridization event. While recent research has proposed that the genomic outcomes of hybridization might be predictable to some extent, many uncertainties remain. With comprehensive whole-genome sequence data, we investigated the genetic introgression between 2 divergent lineages of 9-spined sticklebacks (Pungitius pungitius) in the Baltic Sea. We found that the intensity and direction of selection on the introgressed variation has varied across different genomic elements: while functionally important regions displayed reduced rates of introgression, promoter regions showed enrichment. Despite the general trend of negative selection, we identified specific genomic regions that were enriched for introgressed variants, and within these regions, we detected footprints of selection, indicating adaptive introgression. Geographically, we found the selection against the functional changes to be strongest in the vicinity of the secondary contact zone and weaken as a function of distance from the initial contact. Altogether, the results suggest that the stabilization of introgressed variation in the genomes is a complex, multistage process involving both negative and positive selection. In spite of the predominance of negative selection against introgressed variants, we also found evidence for adaptive introgression variants likely associated with adaptation to Baltic Sea environmental conditions. [ABSTRACT FROM AUTHOR]

The article "Dimensionality and Modularity of Adaptive Variation: Divergence in Threespine Stickleback from Diverse Environments" has been corrected to fix an error in the allometric adjustment formula used for measured traits. The corrected analysis shows that integration between trait suites is generally weaker and more variable between populations than previously suggested. The relationships between trait suites and the environment are slightly stronger than previously thought, indicating that morphology in these populations is closely tied to environmental variation. Overall, the conclusion that divergence among populations is too multivariate to be explained by a common genetic line of least resistance remains valid. [Extracted from the article]

Anthropogenic activities increase turbidity in coastal marine environments globally, and turbidity is particularly caused by eutrophication. Turbidity is a measurement of the scattering and absorption of light by suspended matter in water. An increase in turbidity influences visual predators and affects community structures and whole ecosystems. The three-spined stickleback (Gasterosteus aculeatus) is a widespread species in the northern hemispheric Pacific and Atlantic oceans. It is a visual predator and, therefore, a very well-suited species for studying the effects of increasing turbidity on foraging behaviour and activity. Sticklebacks used for this study were from an aquarium in the North Sea Oceanarium. They have been in the aquarium for around two months and were originally collected in a highly eutrophicated marine fjord system. They were individually placed in an observation aquarium, fed with krill, given 10 min to forage, and observed by video cameras. The video films were analysed to study stickleback predation behaviour. Experiments were repeated with four different turbidity treatments, ranging from a mean of 0.034 up to 10 NTU (nephelometric turbidity unit). Bentonite clay was used as a turbidity-increasing substance. A statistically significant difference in foraging behaviour and activity between the turbidity treatments was observed. The test subjects were found to lunge less for prey and had a higher feeding latency with increasing turbidity. Additionally, they were less active with increasing turbidity. The behavioural instability estimated as a variation in feeding latency increased with increasing turbidity but decreased at the highest turbidity value. Our study indicates an effect of turbidity-increasing events on the behaviour of the three-spined stickleback and potentially also other similar visual predators. [ABSTRACT FROM AUTHOR]

Parasites are ubiquitous, yet their effects on hosts are difficult to quantify and generalize across ecosystems. One promising metric of parasitic impact uses the metabolic theory of ecology (MTE) to calculate energy flux, an estimate of energy lost to parasites. We investigated the feasibility of using metabolic scaling rules to compare the energetic burden of parasitism among individuals. Specifically, we found substantial sensitivity of energy flux estimates to input parameters used in the MTE equation when using available data from a model host–parasite system (Gasterosteus aculeatus and Schistocephalus solidus). Using literature values, size data from parasitized wild fish, and a respirometry experiment, we estimate that a single S. solidus tapeworm may extract up to 32% of its stickleback host's baseline metabolic energy requirement, and that parasites in multiple infections may collectively extract up to 46%. The amount of energy siphoned from stickleback to tapeworms is large but did not instigate an increase in respiration rate in the current study. This emphasizes the importance of future work focusing on how parasites influence ecosystem energetics. The approach of using the MTE to calculate energy flux provides great promise as a quantitative foundation for such estimates and provides a more concrete metric of parasite impact on hosts than parasite abundance alone. [ABSTRACT FROM AUTHOR]

Most vertebrate species undergo tooth replacement throughout adult life. This process is marked by the shedding of existing teeth and the regeneration of tooth organs. However, little is known about the genetic circuitry regulating tooth replacement. Here, we tested whether fish orthologs of genes known to regulate mammalian hair regeneration have effects on tooth replacement. Using two fish species that demonstrate distinct modes of tooth regeneration, threespine stickleback (Gasterosteus aculeatus) and zebrafish (Danio rerio), we found that transgenic overexpression of four different genes changed tooth replacement rates in the direction predicted by a hair regeneration model: Wnt10a and Grem2a increased tooth replacement rate, whereas Bmp6 and Dkk2 strongly inhibited tooth formation. Thus, similar to known roles in hair regeneration, Wnt and BMP signals promote and inhibit regeneration, respectively. Regulation of total tooth number was separable from regulation of replacement rates. RNA sequencing of stickleback dental tissue showed that Bmp6 overexpression resulted in an upregulation of Wnt inhibitors. Together, these data support a model in which different epithelial organs, such as teeth and hair, share genetic circuitry driving organ regeneration. [ABSTRACT FROM AUTHOR]

The tradition of stocking whitefish (Coregonus spec.) is widespread throughout Europe and dates back more than a century in some lakes. Despite its broad acceptance as a management action, stocking success is less often studied and might change with shifts in ecosystems. Similar to many other large lakes in Central Europe, Lake Constance is stocked with millions of larvae each year at great cost. The last evaluation of this management practice took place in 2003, and since then several potential impacts on whitefish increased in magnitude (e.g. stickleback invasion, increasing water temperature). Forty‐two million dye‐marked larvae were stocked in 2016 and 36 million in 2018. Recaptures made 1.5 and 3.5 years after stocking revealed that around 20% of the 2016 and 2018 whitefish cohorts consisted of stocked whitefish. This amount is significantly lower than was found in previous experiments. To identify potential factors controlling recruitment, a Beverton‐Holt stock‐recruitment model showed that stocking did not significantly affect year‐class recruitment. We conclude that stocking is no longer cost‐effective, and we recommend that stocking should be reduced in the short term. Furthermore, our results suggest that explanatory variables that previously described recruitment variation of the whitefish population, such as April water temperature, may no longer apply. [ABSTRACT FROM AUTHOR]

Being a group of popular model organisms in eco-evolutionary biology, genetic, and genomic research studies, the genus Pungitius with 12 species is the most species-rich genus in the stickleback family Gasterosteidae including the Caspian nine-spine stickleback, Pungitius platygaster (Kessler, 1859), the only known species from southern Caspian Sea basin. Here, the new data based on morphological and molecular characters of the mtDNA COI barcode region, and current distribution range of P. platygaster is presented. These data confirm the validity of P. platygaster among its congeners, being sister clade to P. hellenicus from Greece. Morphologically, it is distinguished from the other congeneric species by complete pelvic girdle, 8−11 dorsal spines, and presence of large lateral scutes. The Caspian nine-spine stickleback is found in several closely placed freshwater and brackish waterbodies in the southern Caspian Sea. [ABSTRACT FROM AUTHOR]

The spatial and temporal variability in the dietary preferences of juvenile three-spined stickleback Gasterosteus aculeatus were studied across the typical coastal habitats of Keret Archipelago, Kandalaksha Bay(the White Sea). The sampling of fish using a beach seine was conducted in the late July–early August period and in late August. Additionally, zooplankton samples were collected to conduct a quantitative assessment of the abundance of potential prey items. The similarity percentage (SIMPER) analysis was applied to the data obtained from the stomach content and revealed the five planktonic taxa most prominently contributing to the diet of juvenile sticklebacks. Among these, the copepod Temora longicornis was the most important prey item at marine sites, while Acartia longiremis dominated the diet of fish in the marine lagoon. The calculation of the selectivity index revealed that some taxa (such as A. longiremis) were always avoided by juvenile fish, whereas the selectivity of some taxa increased in late August. In general, juvenile sticklebacks demonstrated a pronounced individual variation in their selectivity, even when a particular prey item was selected positively during the whole period of study. Our data highlight that despite the predominant consumption of easily available prey by juvenile sticklebacks, they demonstrate taxonomic- and size-specific prey selectivity. [ABSTRACT FROM AUTHOR]

Multiple indicators have been used to assess the degree of exposure of fish to anthropogenic chemicals in their stream habitats. We hypothesized that brook stickleback (Culaea inconstans) in a headwater stream receiving urban and agricultural runoff (South Fork Whitewater River, SFWR) would exhibit poorer condition, reduced reproductive fitness, and a greater left side to right side morphological asymmetry (i.e., fluctuating asymmetry or FA) than fish from a nearby headwater stream with a forested drainage basin (Garvin Brook). Male and female fish were collected from both streams just prior to spawning in 2013–2015. In 2013 and 2014, fish were assessed for overall condition (Fulton's K), internal measures of condition (hepatosomatic index, HSI) and reproductive fitness (gonadosomatic index [GSI], total oocyte count, and oocyte mass). In 2015, measurements of head length, jaw length, eye diameter, pectoral fin length, and pelvic fin length were made on both sides of each fish for assessing degree of FA. We observed declining condition with fish size, increased liver size, and reduced oocyte counts and oocyte size in female brook stickleback in SFWR relative to those from Garvin Brook. SFWR females had significantly higher FA than Garvin females for all structures assessed, except pelvic fin length. FA also was slightly higher for all structures in SFWR males compared to Garvin males, but differences were not significant. A composite FA index combining all measurements from an individual fish into a single value displayed highly significant differences for female fish (SFWR FA >> Garvin FA), but not for male fish (SFWR FA = Garvin FA). Exposure of brook stickleback to reduced water quality in SFWR during early development appears to increase morphological asymmetry in female (but not male) fish, and continuing exposure to compromised water quality throughout life impacts both general condition and reproductive fitness of stickleback, especially older female fish, in SFWR. [ABSTRACT FROM AUTHOR]

Although studies on fish cognition are increasing, consideration of how methodological details influence the ability to detect and measure performance is lagging. Here, in two separate experiments the authors compared latency to leave the start position, latency to make a decision, levels of participation and success rates (whether fish entered the rewarded chamber as first choice) across different physical designs. Experiments compared fish performance across (a) two sizes of T‐mazes, large and standard, and a plus‐maze, and (b) open choice arenas with either two or four doors. Fish in T‐mazes with longer arms took longer to leave the start chamber and were less likely to participate in a trial than fish in T‐mazes with shorter arms. The number of options, or complexity, in a maze significantly impacted success but did not necessarily impact behavioural measures, and did not impact the number of fish that reached a chamber. Fish in the plus‐maze had similar latencies to leave the start box and time to reach any chamber as fish in the same‐sized T‐maze but exhibited lower overall success. Similarly, in an open choice arena, increasing the number of options – doors to potential reward chambers − resulted in lower probability of success. There was an influence of reward position in the choice arena, with rewarded chambers closest to the sides of the arena resulting in lower latencies to enter and higher probability of decision success. Together the results allow the authors to offer practical suggestions towards optimal maze design for studies of fish cognition. [ABSTRACT FROM AUTHOR]

Many fresh and coastal waters are becoming increasingly turbid because of human activities, which may disrupt the visually mediated behaviours of aquatic organisms. Shoaling fish typically depend on vision to maintain collective behaviour, which has a range of benefits including protection from predators, enhanced foraging efficiency and access to mates. Previous studies of the effects of turbidity on shoaling behaviour have focussed on changes to nearest neighbour distance and average group‐level behaviours. Here, we investigated whether and how experimental shoals of three‐spined sticklebacks (Gasterosteus aculeatus) in clear (<10 Nephelometric Turbidity Units [NTU]) and turbid (~35 NTU) conditions differed in five local‐level behaviours of individuals (nearest and furthest neighbour distance, heading difference with nearest neighbour, bearing angle to nearest neighbour and swimming speed). These variables are important for the emergent group‐level properties of shoaling behaviour. We found an indirect effect of turbidity on nearest neighbour distances driven by a reduction in swimming speed, and a direct effect of turbidity which increased variability in furthest neighbour distances. In contrast, the alignment and relative position of individuals was not significantly altered in turbid compared to clear conditions. Overall, our results suggest that the shoals were usually robust to adverse effects of turbidity on collective behaviour, but group cohesion was occasionally lost during periods of instability. [ABSTRACT FROM AUTHOR]

Host-associated microbiota can influence host phenotypic variation, fitness and potential to adapt to local environmental conditions. In turn, both host evolutionary history and the abiotic and biotic environment can influence the diversity and composition of microbiota. Yet, to what extent environmental and host-specific factors drive microbial diversity remains largely unknown, limiting our understanding of host-microbiome interactions in natural populations. Here, we compared the intestinal microbiota between two phylogenetically related fishes, the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius) in a common landscape. Using amplicon sequencing of the V3-V4 region of the bacterial 16S rRNA gene, we characterised the a and β diversity of the microbial communities in these two fish species from both brackish water and freshwater habitats. Across eight locations, a diversity was higher in the nine-spined stickleback, suggesting a broader niche use in this host species. Habitat was a strong determinant of β diversity in both host species, while host species only explained a small fraction of the variation in gut microbial composition. Strong habitat-specific effects overruled effects of geographic distance and historical freshwater colonisation, suggesting that the gut microbiome correlates primarily with local environmental conditions. Interestingly, the effect of habitat divergence on gut microbial communities was stronger in three-spined stickleback than in nine-spined stickleback, possibly mirroring the stronger level of adaptive divergence in this host species. Overall, our results show that microbial communities reflect habitat divergence rather than colonisation history or dispersal limitation of host species. [ABSTRACT FROM AUTHOR]

In many animal species, alternative reproductive tactics can result in alloparenting: adult individuals providing care for juveniles that are not genetically their own progeny. In species with parental care, males may exhibit ‘‘sneaking’’ behavior and fertilize eggs in the nest of another male, or nesting males may commit egg theft from a more successful male, possibly to help attract females. Alloparenting may have important consequences for both male and female reproductive output and mate choice, but rates of such non-paternity in natural populations are poorly understood in many taxa, as are the ecological factors that might influence these rates. Here, we quantified the frequency of non-paternity between males and the eggs in their nests within 15 natural populations of Threespine Stickleback, and tested whether the frequency of mismatch was predicted by characteristics of the lake (lake size and nest density) or features of individual males (body size and diet) or their chosen nest location (depth and presence of vegetation). The frequency of non-paternity was relatively high across all lakes (23–66%) but was not explained by lake-level characteristics (lake area or nest density). Alloparenting was more likely for individual males with more benthic diets (as measured by stable isotopes) and for males whose nests were closer to vegetation, although this effect varied across lakes. Our results suggest that individual-level characteristics of the male and nest influence the frequency of alloparenting, and that variation among individuals and populations should be considered in studies of the genetics and evolutionary consequences of alternative reproductive tactics. [ABSTRACT FROM AUTHOR]

Host-associated microbiota can influence host phenotypic variation, fitness and potential to adapt to local environmental conditions. In turn, both host evolutionary history and the abiotic and biotic environment can influence the diversity and composition of microbiota. Yet, to what extent environmental and host-specific factors drive microbial diversity remains largely unknown, limiting our understanding of host-microbiome interactions in natural populations. Here, we compared the intestinal microbiota between two phylogenetically related fishes, the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius) in a common landscape. Using amplicon sequencing of the V3-V4 region of the bacterial 16S rRNA gene, we characterised the α and β diversity of the microbial communities in these two fish species from both brackish water and freshwater habitats. Across eight locations, α diversity was higher in the nine-spined stickleback, suggesting a broader niche use in this host species. Habitat was a strong determinant of β diversity in both host species, while host species only explained a small fraction of the variation in gut microbial composition. Strong habitat-specific effects overruled effects of geographic distance and historical freshwater colonisation, suggesting that the gut microbiome correlates primarily with local environmental conditions. Interestingly, the effect of habitat divergence on gut microbial communities was stronger in three-spined stickleback than in nine-spined stickleback, possibly mirroring the stronger level of adaptive divergence in this host species. Overall, our results show that microbial communities reflect habitat divergence rather than colonisation history or dispersal limitation of host species.

A central focus of modern fisheries management is eradicating invaders that threaten imperiled native fishes. However, vast landscapes and limited funding and personnel resources demand a prioritized approach to management. Brook Stickleback Culaea inconstans (Kirtland, 1840) is an aquatic invasive species in Wyoming, USA, that may pose a risk to native biodiversity. Our aim was to evaluate Brook Stickleback's invasive potential in the North Platte River drainage. We updated the current distribution of Brook Stickleback, evaluated for possible range expansion, and determined landscape-level habitat drivers and occurrence potential for streams across the North Platte River drainage. Additionally, we examined Brook Stickleback's spatial overlap with native nongame fishes. At the landscape scale, Brook Stickleback preferred low-gradient streams with moderate disturbance risk. Though we did not find evidence of current Brook Stickleback range expansion 61% of streams in the drainage have landscape-level environmental characteristics that are likely suitable for Brook Stickleback, creating potential for future expansion. Brook Stickleback overlapped spatially with 13 native nongame species, though spatial overlap was less common than expected for species with similar habitat preferences. Our work serves as a case study of the factors to consider when assessing a species' invasive potential in a previously unstudied region. [ABSTRACT FROM AUTHOR]

Accurately quantifying an animal's movement is crucial for developing a greater empirical and theoretical understanding of its behaviour, and for simulating biologically plausible movement patterns. However, we have a relatively poor understanding of how animals move at fine temporal scales and in three-dimensional environments. Here, we collected high temporal resolution data on the three-dimensional spatial positions of individual three-spined sticklebacks (Gasterosteus aculeatus), allowing us to derive statistics describing key geometric characteristics of their movement and to quantify the extent to which this varies between individuals. We then used these statistics to develop a simple model of fish movement and evaluated the biological plausibility of simulated movement paths using a Turing-type test, which quantified the association preferences of live fish towards animated conspecifics following either 'real' (i.e., based on empirical measurements) or simulated movements. Live fish showed no difference in their response to 'real' movement compared to movement simulated by the model, although significantly preferred modelled movement over putatively unnatural movement patterns. The model therefore has the potential to facilitate a greater understanding of the causes and consequences of individual variation in movement, as well as enabling the construction of agent-based models or real-time computer animations in which individual fish move in biologically feasible ways. [ABSTRACT FROM AUTHOR]

Pelvic spine polymorphism occurs in several species in the stickleback family (Gasterosteidae). Given the similar phenotypic polymorphisms in multiple stickleback species, we sought to determine the extent of parallelism in the ecological correlates of pelvic spine reduction. Based on a metabarcoding analysis of brook stickleback gut contents in two polymorphic populations, we found that significant diet differences were associated with pelvic spine reduction, but we found no clear or consistent trend supporting a tendency for benthic feeding in pelvic‐reduced brook sticklebacks. These results contrast with those found in threespine sticklebacks where pelvic spine reduction is often associated with a benthic diet. Hence, we found non‐parallel consequences of spine polymorphism across species. Furthermore, a difference in gill raker morphology has been frequently observed between ecomorphs with different diets in many fish species. However, we found no evidence of any difference in gill raker morphology associated with pelvic spine polymorphism in brook sticklebacks. [ABSTRACT FROM AUTHOR]

The analysis of otolith Sr isotope ratios (87Sr/86Sr) is a powerful method to study fish migration in freshwater areas. However, few studies have applied this method to study fish movement in brackish‐water environments. Furthermore, despite the fact that habitat differentiation has been shown to drive genetic differentiation and reproductive isolation among stickleback fish, no studies have used the otolith 87Sr/86Sr ratios to analyze habitat differentiation between stickleback ecotypes and species. In this study, we analyzed the otolith 87Sr/86Sr ratios of three sympatric stickleback species of the genus Pungitius in the Shiomi River on Hokkaido Island, Japan: P. tymensis, the brackish‐water type of the P. pungitius–P. sinensis complex, and the freshwater type of the P. pungitius–P. sinensis complex. First, we created a mixing equation to depict the relationship between habitat salinity and the 87Sr/86Sr ratios of river water. We found that the otolith 87Sr/86Sr ratios differed significantly among the three species, indicating that the three species utilize habitats with different salinities: P. tymensis and the brackish‐water type inhabit freshwater and brackish‐water environments, respectively, with the freshwater type using intermediate habitats. In addition, we found that some freshwater individuals moved to habitats with higher salinities as they grew. Our study demonstrates that the analysis of otolith 87Sr/86Sr ratios is a useful method for studying the habitat use of fish in brackish‐water environments and habitat differentiation among closely related sympatric and parapatric species. [ABSTRACT FROM AUTHOR]

Crossovers in meiosis have an important role in sexual reproduction in ensuring the segregation of chromosomes and shuffling of genetic material. Despite their profound importance, little is known about heritability and repeatability of the crossover rate in the wild. We studied crossover rate variation in outbred nine- (Pungitius pungitius) and three-spined (Gasterosteus aculeatus) stickleback populations to estimate its heritability (h 2) and repeatability (R). Based on crossover rate interpreted from parent–F1-offspring linkage maps created from single nucleotide polymorphism data, the repeatability of crossover rate was moderate at best, but higher in females (R = 0.24 and R = 0.33) than in males (R = 0.017 and R = 0.11) in both species. Owing to the low degree and variance of parental relatedness and low sample sizes, heritabilities could not be estimated with confidence. However, given that R sets the upper limit to h 2, the heritability of crossover rate is indicated to be low in males. A review and comparison with the previously reported repeatability and heritability estimates revealed that the repeatabilities in stickleback females were relatively high, whereas those in males were very low. Collectively, our results and review of earlier estimates suggest low evolvability of the crossover rate. [ABSTRACT FROM AUTHOR]

Mutation rate is a fundamental parameter in population genetics. Apart from being an important scaling parameter for demographic and phylogenetic inference, it allows one to understand at what rate new genetic diversity is generated and what the expected level of genetic diversity is in a population at equilibrium. However, except for well-established model organisms, accurate estimates of de novo mutation rates are available for a very limited number of organisms from the wild. We estimated mutation rates (µ) in two marine populations of the nine-spined stickleback (Pungitius pungitius) with the aid of several 2- and 3-generational family pedigrees, deep (>50×) whole-genome resequences and a high-quality reference genome. After stringent filtering, we discovered 308 germline mutations in 106 offspring translating to µ = 4.83 × 10−9 and µ = 4.29 × 10−9 per base per generation in the two populations, respectively. Up to 20% of the mutations were shared by full-sibs showing that the level of parental mosaicism was relatively high. Since the estimated µ was 3.1 times smaller than the commonly used substitution rate, recalibration with µ led to substantial increase in estimated divergence times between different stickleback species. Our estimates of the de novo mutation rate should provide a useful resource for research focused on fish population genetics and that of sticklebacks in particular. [ABSTRACT FROM AUTHOR]

Rapid evolution of similar phenotypes in similar environments, giving rise to in situ parallel adaptation, is an important hallmark of ecological speciation. However, what appears to be in situ adaptation can also arise by dispersal of divergent lineages from elsewhere. We test whether two contrasting phenotypes repeatedly evolved in parallel, or have a single origin, in an archetypal example of ecological adaptive radiation: benthic–limnetic three-spined stickleback (Gasterosteus aculeatus) across species pair and solitary lakes in British Columbia. We identify two genomic clusters across freshwater populations, which differ in benthic–limnetic divergent phenotypic traits and separate benthic from limnetic individuals in species pair lakes. Phylogenetic reconstruction and niche evolution modeling both suggest a single evolutionary origin for each of these clusters. We detected strong phylogenetic signal in benthic–limnetic divergent traits, suggesting that they are ancestrally retained. Accounting for ancestral state retention, we identify local adaptation of body armor due to the presence of an intraguild predator, the sculpin (Cottus asper), and environmental effects of lake depth and pH on body size. Taken together, our results imply a predominant role for retention of ancestral characteristics in driving trait distribution, with further selection imposed on some traits by environmental factors. [ABSTRACT FROM AUTHOR]

Fins are major functional appendages of fish that have been repeatedly modified in different lineages. To search for genomic changes underlying natural fin diversity, we compared the genomes of 36 percomorph fish species that span over 100 million years of evolution and either have complete or reduced pelvic and caudal fins. We identify 1,614 genomic regions that are well-conserved in fin-complete species but missing from multiple fin-reduced lineages. Recurrent deletions of conserved sequences in wild fin-reduced species are enriched for functions related to appendage development, suggesting that convergent fin reduction at the organismal level is associated with repeated genomic deletions near fin-appendage development genes. We used sequencing and functional enhancer assays to confirm that PelA , a Pitx1 enhancer previously linked to recurrent pelvic loss in sticklebacks, has also been independently deleted and may have contributed to the fin morphology in distantly related pelvic-reduced species. We also identify a novel enhancer that is conserved in the majority of percomorphs, drives caudal fin expression in transgenic stickleback, is missing in tetraodontiform, syngnathid, and synbranchid species with caudal fin reduction, and alters caudal fin development when targeted by genome editing. Our study illustrates a broadly applicable strategy for mapping phenotypes to genotypes across a tree of vertebrate species and highlights notable new examples of regulatory genomic hotspots that have been used to evolve recurrent phenotypes across 100 million years of fish evolution. [ABSTRACT FROM AUTHOR]

Freshwater populations of threespine stickleback (Gasterosteus aculeatus) have diverged from their marine ancestor and show extensive variation among populations throughout most of their range. However, phenotypes of freshwater populations from the east coast of North America do not appear to demonstrate extensive variability observed throughout the rest of the species' range. The relatively young age of east coast North American populations may explain the apparent lack of freshwater variability. On the other hand, populations in this part of the species' range have not received the same level of attention as populations throughout the rest of its range have, and the low level of variability observed may simply reflect a lack of data for this region. We examined morphological traits (including linear measurements of body armor and body shape) of stickleback from 52 locations representing marine and freshwater populations along the west coast of Newfoundland, Canada. We found that variability in morphological traits among freshwater populations was much more extensive than previously assumed and similar to patterns observed for populations in mainland British Columbia, Alaska, and western Europe. [ABSTRACT FROM AUTHOR]

Inbreeding depression refers to the reduced fitness of offspring produced by genetically‐related individuals and is expected to be rare in large, outbred populations. When it occurs, marked fitness loss is possible as large populations can carry a substantial load of recessive harmful mutations which are normally sheltered at the heterozygous state. Using experimental cross data and genome‐wide identity‐by‐descent (IBD) relationships from an outbred marine nine‐spined stickleback (Pungitius pungitius) population, we documented a significant decrease in offspring survival probability with increasing parental IBD sharing associated with an average inbreeding load (B) of 10.5. Interestingly, we found that this relationship was also underlined by a positive effect of paternal inbreeding coefficient on offspring survival, suggesting that certain combinations of parental inbreeding and genetic relatedness among mates may promote offspring survival. Our results demonstrate the potential for substantial inbreeding load in an outbred population and emphasize the need to consider fine‐scale genetic relatedness in future studies of inbreeding depression in the wild. [ABSTRACT FROM AUTHOR]

The presence of endocrine‐active chemicals (EACs) in the environment continues to cause concern for wildlife given their potential for adverse effects on organisms. However, there is a significant lack of understanding about the potential effects of EACs on populations. This has real‐world limitations for EAC management and regulation, where the aim in environmental risk assessment is to protect populations. We propose a methodological approach for the application of modeling in addressing the population relevance of EAC exposure in fish. We provide a case study with the fungicide prochloraz to illustrate how this approach could be applied. We used two population models, one for brown trout (Salmo trutta; inSTREAM) and the other for three‐spined stickleback (Gasterosteus aculeatus) that met regulatory requirements for development and validation. Effects data extracted from the literature were combined with environmentally realistic exposure profiles generated with the FOCUS SW software. Population‐level effects for prochloraz were observed in some modeling scenarios (hazard‐threshold [HT]) but not others (dose–response), demonstrating the repercussions of making different decisions on implementation of exposure and effects. The population responses, defined through changes in abundance and biomass, of both trout and stickleback exposed to prochloraz were similar, indicating that the use of conservative effects/exposure decisions in model parameterization may be of greater significance in determining population‐level adverse effects to EAC exposure than life‐history characteristics. Our study supports the use of models as an effective approach to evaluate the adverse effects of EACs on fish populations. In particular, our HT parameterization is proposed for the use of population modeling in a regulatory context in accordance with Commission Regulation (EU) 2018/605. Environ Toxicol Chem 2023;42:1624–1640. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Totally, 134 individuals of Gasterosteus aculeatus from the Lake Atanasovsko Wetland, Bulgaria, were examined for helminth parasites. Five helminth species were identified: the trematode Posthodiplostomum brevicaudatum (metacercariae), the monogenean Gyrodactylus arcuatus, the trypanorhynch cestode Progrillotia dasyatidis (plerocerci) and third-stage larvae of the ascaridoid nematodes Contracaecum sp. and Hysterothylacium sp. Of them, G. arcuatus was the most prevalent species, with prevalence (P%) 68.66, followed by P. brevicaudatum (P% 22.39). The remaining species were weakly represented: Hysterothylacium sp. (P% 4.48), P. dasyatidis (P% 3.73) and Contracaecum sp. (P% 0.75). The present study is the first record of G. aculeatus as a host of a species of Contracaecum from the Black Sea basin. Gyrodactylus arcuatus is a new record for the Bulgarian fauna. [ABSTRACT FROM AUTHOR]