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Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species. [ABSTRACT FROM AUTHOR]

Populations experiencing negligible predation pressure are expected to evolve higher behavioral activity. However, when sexes have different expected benefits from high activity, the adaptive shift is expected to be sex-specific. Here, we compared movement activity of one cave (lack of predation) and three adjacent surface (high and diverse predation) populations of Asellus aquaticus , a freshwater isopod known for its independent colonization of several caves across Europe. We predicted 1) higher activity in cave than in surface populations, with 2) the difference being more pronounced in males as they are known for active mate searching behavior, while females are not. Activity was assessed both in the presence and absence of light. Our results supported both predictions: movement activity was higher in the cave than in the surface populations, particularly in males. Relaxed predation pressure in the cave-adapted population is most likely the main selective factor behind increased behavioral activity, but we also showed that the extent of increase is sex-specific. [ABSTRACT FROM AUTHOR]

Aggregation (gathering together) and sheltering (hiding in cover) are basic behaviours that can reduce the risk of predation. However, both behaviours have costs, such as increased competition over resources and high prevalence of contact-spread parasites (aggregation) or lost opportunities for foraging and mating (sheltering). Therefore, variation in these behaviours is expected between populations with varying levels of predation risk. We compared aggregation and sheltering in surface- (various predators) and cave-adapted (no predator) populations of the isopod Asellus aquaticus in a common garden experiment. Given that the cave environment is constantly dark, we also tested for population variation in light-induced behavioural plasticity. Variation in sheltering was explained by habitat type: cave individuals sheltered less than surface individuals. We found high between-population variation in aggregation with or without shelters and their light-induced plasticity, which was not explained by habitat type. Cave individuals decreased (habituation) whereas surface individuals increased sheltering with time (sensitization). We suggest that population variation in sheltering is driven by predation, whereas variation in aggregation must be driven by other, unaccounted environmental factors, in a similar manner to light-induced behavioural plasticity. Based on habituation/sensitization patterns, we suggest that predation-adapted populations are more sensitive to disturbance related to routine laboratory procedures. [ABSTRACT FROM AUTHOR]

There is an increasing interest in studying bacterial-fungal interactions (BFIs), also the interactions of Pleurotus ostreatus , a model white-rot fungus and important cultivated mushroom. In Europe, P. ostreatus is produced on a wheat straw-based substrate with a characteristic bacterial community, where P. ostreatus is exposed to the microbiome during substrate colonisation. This study investigated how the bacterial community structure was affected by the introduction of P. ostreatus into the mature substrate. Based on the results obtained, the effect of the presence and absence of this microbiome on P. ostreatus production in an experimental cultivation setup was determined. 16S rRNA gene-based terminal restriction fragment length polymorphism (T-RFLP) and amplicon sequencing revealed a definite succession of the microbiome during substrate colonisation and fruiting body production: a sharp decrease in relative abundance of Thermus spp. and Actinobacteria, and the increasing dominance of Bacillales and Halomonas spp. The introduced experimental cultivation setup proved the protective role of the microbial community against competing fungi without affecting P. ostreatus growth. We could also demonstrate that this effect could be attributed to both living microbes and their secreted metabolites. These findings highlight the importance of bacterial-fungal interactions during mushroom production. [ABSTRACT FROM AUTHOR]

Sex allocation theory predicts that the proportion of daughters to sons will evolve in response to ecological conditions that determine the costs and benefits of producing each sex. All else being equal, the adult sex ratio (ASR) should also vary with ecological conditions. Many studies of subterranean species reported female‐biased ASR, but no systematic study has yet been conducted. We test the hypothesis that the ASR becomes more female‐biased with increased isolation from the surface. We compiled a data set of ASRs of 35 species in the subterranean amphipod Niphargus, each living in one of three distinct habitats (surface‐subterranean boundary, cave streams, phreatic lakes) representing an environmental gradient of increased isolation underground. The ASR was female‐biased in 27 of 35 species; the bias was statistically significant in 12 species. We found a significant difference in the ASR among habitats after correction for phylogeny. It is most weakly female‐biased at the surface‐subterranean boundary and most strongly female‐biased in phreatic lakes. Additional modelling suggests that the ASR has evolved towards a single value for both surface‐subterranean boundary and cave stream‐dwelling species, and another value for 9 of 11 phreatic lake dwellers. We suggest that a history of inbreeding in subterranean populations might lower inbreeding depression such that kin selection favours mating with siblings. This could select for a female‐biased offspring sex ratio due to local mate competition among brothers. The observed patterns in sex ratios in subterranean species make them a group worthy of more attention from those interested in sex allocation theory. [ABSTRACT FROM AUTHOR]

Many vocalizing animals produce the discrete elements of their acoustic signals in a specific sequential order, but we know little about the biological relevance of this ordering. For that, we must characterize the degree by which individuals differ in how they organize their signals sequentially and relate these differences to variation in quality and fitness. In this study, we fulfilled these tasks in male collared flycatchers (Ficedula albicollis). We characterized the sequential order of syllables with a network analysis approach and studied the consistency of network variables on distinct time scales (within day, between days, and between years), and assessed their relationship with such quality indicators like age, body condition, arrival date, and fitness related proxies like survival to the next year and pairing success. We found that the syllables were associated nonrandomly with one another and both the frequency differences of consecutive syllables and the number of motif types were higher in the original than in randomized syllable sequences. Average degree and small-worldness showed considerable among-individual differences and decreasing repeatability with increasing time scale. Furthermore, we found relationships between male age and average degree among and within individuals. Accordingly, older males produce syllable sequences by using common syllables less often than younger individuals. However, the network variables showed no relationship with fitness-related variables. In conclusion, the sequential organization of birdsong has the potential to encode individual-specific characteristics, which thus could be used as signal in social interactions and thus potentially could be subject to sexual selection. [ABSTRACT FROM AUTHOR]

We published a study recently testing the link between brain size and behavioural plasticity using brain size selected guppy (Poecilia reticulata) lines (2019, Journal of Evolutionary Biology, 32, 218‐226). Only large‐brained fish showed habituation to a new, but actually harmless environment perceived as risky, by increasing movement activity over the 20‐day observation period. We concluded that "Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level". In a commentary published in the same journal, Haave‐Audet et al. challenged the main message of our study, stating that (a) relative brain size is not a suitable proxy for cognitive ability and (b) habituation measured by us is likely not adaptive and costly. In our response, we first show that a decade's work has proven repeatedly that relative brain size is indeed positively linked to cognitive performance in our model system. Second, we discuss how switching from stressed to unstressed behaviour in stressful situations without real risk is likely adaptive. Finally, we point out that the main cost of behavioural plasticity in our case is the development and maintenance of the neural system needed for information processing, and not the expression of plasticity. We hope that our discussion with Haave‐Audet et al. helps clarifying some central issues in this emerging research field. We tested the link between relative brain size and behavioural plasticity recently (Herczeg et al. 2019, Journal of Evolutionary Biology, 32, 218‐226). In their commentary, Haave‐Audet et al. stated that (i) relative brain size is not a suitable proxy for cognitive ability and (ii) habituation measured by us is likely not adaptive and costly. Here, we show that a positive link between relative brain size and cognitive performance has been repeatedly proven in our system. Then, we argue that habituation in the absence of risk is likely adaptive. Finally, we point out that the costs of capacity, and not the costs of expression, are important for behavioural plasticity in our laboratory experiment. [ABSTRACT FROM AUTHOR]

Understanding how animal personality (consistent between‐individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20 days with video‐aided motion tracking. We found that individuals differed consistently in activity and risk‐taking, as well as in behavioural plasticity. In activity, only the large‐brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk‐taking, we found sensitization (decreased risk‐taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour‐specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level. [ABSTRACT FROM AUTHOR]

Phenotypically plastic changes in response to variation in perceived predation risk are widespread, but little is known about if and how social environment modulates induced responses to predation risk. We investigated the influence of perceived predation risk (i.e. chemical cues from a predator) and social environment (i.e. one, two or 20 individuals reared together) on three-spined stickleback ( Gasterosteus aculeatus) morphology in a factorial common garden experiment. We found that exposure to chemical cues from potential predators did not influence growth or body condition or induce more robust morphological defences (i.e. lateral plate numbers and dorsal spine lengths). However, sticklebacks exposed to predator cues developed longer caudal peduncles and larger eyes as compared with fish from the control treatment. As these responses may improve sticklebacks' ability to avoid piscine predation, they might be adaptive. Social environment/density also influenced expression of some traits, but these effects were independent of predation-risk treatment effects. In general, these results suggest that apart from the classic morphological defence structures, which appear mostly constitutive, three-spined sticklebacks are capable of expressing potentially adaptive morphological responses to chemical cues from potential predators. [ABSTRACT FROM AUTHOR]

Several hypotheses predict a relationship between parasite burden and risk-taking behavior, but the underlying causal mechanisms are poorly understood due to the scarcity of experimental studies and the neglected focus on immune defense. Here, in 3 sets of field studies on the collared flycatcher, Ficedula albicollis, we investigated how among-male variation in flight initiation distance (FID, the distance at which an individual flee a potential predator) is linked to among-male variation in health status. First, we correlatively assessed the relationship between FID and the prevalence of haemosporidian blood parasites. We found no difference in risk-taking behavior between parasitized and nonparasitized individuals rejecting a hypothesis that predicts that malaria infection status affects the costs of predator avoidance. Second, we performed an immune challenge experiment, in which randomly chosen birds were injected with a novel antigen (sheep red blood cell) and their change in FID was compared with birds that received a placebo treatment. This experiment revealed no evidence for the immunological treatment affecting risk-taking behavior, thus we failed to obtain support for the hypothesis that posits that immediate health status mediates decisions about when to flee a predator. Finally, we detected a negative relationship between the number of alleles of the major histocompatibility complex and FID. This result, in concordance with the above negative results, supports the "avoidance" hypothesis that states that only individuals with efficient immune defense machinery are able to bear the costs of risktaking that can emerge through the increased infection rates of risk-taker individuals. [ABSTRACT FROM AUTHOR]

The existence of behavioral syndromes in animals implies that the same innate characteristic of individuals (i.e. temperament) is manifested in different ecological situations, which leads to behavioral correlations. Relying on a statistical synthesis over the published evidence, we found that strength of correlation between exploration, aggression and risk taking varies and depends on the overlap in the context of the behavioral assays. Therefore, the role of animal temperament driving behavioral correlations may be less important than initially thought.Behavioral syndromes predict that individuals display behaviors consistently across different ecological situations, resulting in correlations among functionally different individual-specific behaviors (e.g., activity, exploration, aggression, and risk taking). Such consistencies can arise because of the common innate government of traits (i.e., temperament). However, different behaviors can be mediated by different selection regimes and/or measured with different errors. Furthermore, contextual overlap among traits may also vary. These possibilities can cause dissimilarities in the pair-wise relationship between particular traits. To determine the relationships among the most studied behaviors, we performed a modern meta-analysis, in which we assessed the strength of correlations in each possible combination of traits. Relying on data from 81 scientific papers, we found that the correlations among behaviors were generally weak and that they varied in magnitude across comparisons (e.g., novel environment exploration and activity: r = 0.345; novel object exploration and activity: r = 0.074). The partial correlations among traits revealed that certain relationships (e.g., novel environment exploration/activity and the novel object exploration/risk taking) were independent of the covariation with other traits, whereas certain relationships (e.g., aggression/novel environment exploration) consistently weakened after controlling for covariance. Some relationships were affected by contextual overlap: the effect sizes were systematically higher when the behaviors were assayed in the same experimental compartment (e.g., same test room or aquarium). Different correlations are unlikely to emerge due to differences in repeatabilities that are associated with the measurement of different traits, as we found that averaged repeatabilities vary around the same intermediate magnitude for each behavior. We suggest that the most commonly assessed behavioral traits do not necessarily form equally independent domains. [ABSTRACT FROM AUTHOR]

Environmental differences among populations are expected to lead to local adaptation, while spatial or temporal environmental variation within a population will favour evolution of phenotypic plasticity. As plasticity itself can be under selection, locally adapted populations can vary in levels of plasticity. Nine-spined stickleback ( Pungitius pungitius) originating from isolated ponds (low piscine predation risk, high competition) vs. lake and marine populations (high piscine predation risk, low competition) are known to be morphologically adapted to their respective environments. However, nothing is known about their ability to express phenotypic plasticity in morphology in response to perceived predation risk or food availability/competition. We studied predator-induced phenotypic plasticity in body shape and armour of marine and pond nine-spined stickleback in a factorial common garden experiment with two predator treatments (present vs. absent) and two feeding regimes (low vs. high). The predation treatment did not induce any morphological shifts in fish from either habitat or food regime. However, strong habitat-dependent differences between populations as well as strong sexual dimorphism in both body shape and armour were found. The lack of predator-induced plasticity in development of the defence traits (viz. body armour and body depth) suggests that morphological anti-predator traits in nine-spined stickleback are strictly constitutive, rather than inducible. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••-••. [ABSTRACT FROM AUTHOR]

Adaptation to novel environments can be based either on standing genetic variation or variation attributable to new mutations. When standing genetic variation for a functional adaptation is lacking, and variation due to new mutations is not yet available, adaptation is possible only through alternative functional solutions. Reduction in the number of bony lateral plates as an adaptation to freshwater colonization by marine threespine sticklebacks ( Gasterosteus aculeatus) has occurred in numerous independent cases through allelic substitution in the ectodysplasin-a ( Eda) gene. Studying the phenotypic and genetic variation in plate number and size in five marine and six freshwater threespine stickleback populations, we found that when variation in Eda was limiting (i.e., alleles associated with the low-plate morph were missing or in extremely low frequency), plate number reduction did not take place in freshwater populations, but reduced lateral plate coverage was achieved by a reduction in the size of lateral plates. Our results suggest that this phenotypically and genetically discrete "small-plated" threespine stickleback-which is the dominant form in three northern European freshwater populations-may be functionally equivalent to the low-plated morph and hence, serve as an example of convergent evolution toward functional similarity in the face of genetic constraints. [ABSTRACT FROM AUTHOR]

Interpopulation differences in body size are of common occurrence in vertebrates, but the relative importance of genetic, maternal, and environmental effects as causes of observed differentiation have seldom been assessed in the wild. Gigantism in pond nine-spined sticklebacks ( Pungitius pungitius Linnaeus, 1758) has been repeatedly observed, but the quantitative genetic basis of population divergence in size has remained unstudied. We conducted a common garden experiment - using 'pure' and reciprocal crosses between two populations ('giant' pond versus 'normal' marine) - to test for the relative importance of additive genetic, non-additive genetic, and maternal effects on body size after 11 months of growth in the laboratory. We found that body size difference between the two populations in laboratory conditions owed mainly to additive genetic effects, and only to a minor degree to maternal effects. Furthermore, the weak maternal effects were seen only in the offspring of 'giant' mothers, and appeared to be mediated through differences in egg size. Thus, the results suggest that gigantism in pond populations of P. pungitius is based on the effects of additively acting genes, rather than to direct environmental induction, or maternal or non-additive gene action. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••-••. [ABSTRACT FROM AUTHOR]

The transition from marine to freshwater life in the threespine stickleback ( Gasterosteus aculeatus) is accompanied by complex morphological changes-including reduction in bony armor and change in body shape-but experimental evidence for the selective agents behind these evolutionary transitions is sparse. We investigated whether selection by predatory fish affects threespine stickleback morphology differentially when refuge is absent (pelagic lifestyle-ancestral condition) or present (benthic lifestyle-derived condition). Our results show that selection favors low numbers of lateral plates in habitats with refuge, whereas fully plated individuals have a selective advantage in habitats without refuge. We also found that a decrease in the length of the caudal peduncle increased survival probability, irrespective of habitat. The effect of spine lengths on survival was evident only in a multivariate analysis of selection, implying that it is essential to account for phenotypic and genetic correlations between traits before drawing conclusions about the effects of selection on single traits. Apart from uncovering targets and patterns of predator-induced selection on threespine stickleback morphology, our results provide direct evidence to support the hypothesis that differences in antipredator strategies in pelagic versus benthic sticklebacks could play a role in the repeated, independent cases of plate number reduction following freshwater colonization in this species. [ABSTRACT FROM AUTHOR]

The relaxation of predation and interspecific competition are hypothesized to allow evolution toward “optimal” body size in island environments, resulting in the gigantism of small organisms. We tested this hypothesis by studying a small teleost (nine-spined stickleback, Pungitius pungitius) from four marine and five lake (diverse fish community) and nine pond (impoverished fish community) populations. In line with theory, pond fish tended to be larger than their marine or lake conspecifics, sometimes reaching giant sizes. In two geographically independent cases when predatory fish had been introduced into ponds, fish were smaller than those in nearby ponds lacking predators. Pond fish were also smaller when found in sympatry with three-spined stickleback ( Gasterosteus aculeatus) than those in ponds lacking competitors. Size-at-age analyses demonstrated that larger size in ponds was achieved by both increased growth rates and extended longevity of pond fish. Results from a common garden experiment indicate that the growth differences had a genetic basis: pond fish developed two to three times higher body mass than marine fish during 36 weeks of growth under similar conditions. Hence, reduced risk of predation and interspecific competition appear to be chief forces driving insular body size evolution toward gigantism. [ABSTRACT FROM AUTHOR]

In ectotherms, the main behavioural option for thermoregulation is the adjustment of daily and seasonal activity to the thermal quality of the environment. While active, ectotherms thermoregulate by shuttling in between thermally differing microhabitat patches. Here, we focused on the question of whether other behavioural or physiological processes could force ectotherms to maintain activity during thermally unfavourable periods, when accurate thermoregulation is impossible. Using laboratory experiments and field data we compared the thermoregulation of male adders ( Vipera berus) between two periods in spring when (1) only males and (2) also females and juveniles had terminated their winter hibernation. We found that males thermoregulated actively both in the lab and in the field. Accurate thermoregulation was only possible during the second period because of the low thermal quality of the environment. Male adders maintained a lower mean body temperature in the field than in the laboratory within both periods, and in addition their body temperature during the first period was on average 4 °C lower than during the second period. The thermal qualities of the natural basking sites showed a similar pattern. We discuss the results in the context of a potential trade-off between spermiogenesis and thermoregulation, where the benefits of early spermiogenesis coupled with inaccurate thermoregulation are higher than the associated costs. The results support the contention that the earlier spring emergence of the male compared with female adders is explainable by natural selection favouring early initiation of spermiogenesis, and hence sex differences in phenology. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 19–27. [ABSTRACT FROM AUTHOR]