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The viviparity-driven conflict hypothesis postulates that the evolution of matrotrophy (postfertilization maternal provisioning) will result in a shift from a pre- to postcopulatory mate choice and thus accelerate the evolution of postcopulatory reproductive isolation. Here, we perform artificial insemination experiments on Heterandria formosa , a matrotrophic poeciliid fish, to probe for evidence of postcopulatory female choice. We established laboratory populations from Wacissa River (WR) and Lake Jackson (LJ). The WR females normally produce larger offspring than the LJ females. We artificially inseminated females with sperm from each population or from both populations simultaneously. When LJ females were inseminated with sperm from WR and LJ males, they allocated fewer resources to WR-sired offspring than when they were inseminated with WR sperm alone. The LJ females carrying developing offspring sired by males from different populations were thus able to discriminate against non-resident males when allocating resources to developing young. The WR females, which normally produce larger offspring than LJ females, did not discriminate among males from different localities. These findings provide insights into the ability of females from one population to exercise a form of postcopulatory mate selection. [ABSTRACT FROM AUTHOR]

Gill function in gas exchange and ion regulation has played key roles in the evolution of fishes. In this review, we summarize data from the fields of palaeontology, developmental biology and comparative physiology for when and how the gills first acquired these functions. Data from across disciplines strongly supports a stem vertebrate origin for gas exchange structures and function at the gills with the emergence of larger, more active fishes. However, the recent discovery of putative ionocytes in extant cephalochordates and hemichordates suggests that ion regulation at gills might have originated much earlier than gas exchange, perhaps in the ciliated pharyngeal arches in the last common ancestor of deuterostomes. We hypothesize that the ancestral form of ion regulation served a filter-feeding function in the ciliated pharyngeal arches, and was later coopted in vertebrates to regulate extracellular ion and acid–base balance. We propose that future research should explore ionocyte homology and function across extant deuterostomes to test this hypothesis and others in order to determine the ancestral origins of ion regulation in fish gills. [ABSTRACT FROM AUTHOR]

The production of aquatic animals has more than doubled over the last 50 years and is anticipated to continually increase. While fish are recognized as a valuable and sustainable source of nutrition, particularly in the context of human population growth and climate change, the rapid expansion of aquaculture coincides with the emergence of highly pathogenic viruses that often spread globally through aquacultural practices. Here, we provide an overview of the fish virome and its relevance for disease emergence, with a focus on the insights gained through metagenomic sequencing, noting potential areas for future study. In particular, we describe the diversity and evolution of fish viruses, for which the majority have no known disease associations, and demonstrate how viruses emerge in fish populations, most notably at an expanding domestic-wild interface. We also show how wild fish are a powerful and tractable model system to study virus ecology and evolution more broadly and can be used to identify the major factors that shape vertebrate viromes. Central to this is a process of virus-host co-divergence that proceeds over many millions of years, combined with ongoing cross-species virus transmission. [ABSTRACT FROM AUTHOR]

Pampus belongs to the Perciformes, Stromateoidei, and Stromateidae and are widely distributed throughout the Indian Ocean and the Western Pacific. In this study, we employed next-generation sequencing to generate comprehensive genomic data for Pampus punctatissimus and Pampus echinogaster and subsequently compared the obtained genomic information with the published data of Pampus argenteus. P. echinogaster was identified to be the largest genome size (602 Mb), heterozygosity (1.38%), and repetitive sequence ratio (33.06%), while similar genome sizes between P. punctatissimus (540 Mb) and P. argenteus (550 Mb) were observed. A total of 402,921 and 628,298 SSRs were identified for P. punctatissimus and P. echinogaster, respectively. Additionally, 1,876, 638, and 394 single-copy homologous genes were identified from P. punctatissimus, P. echinogaster, and P. argenteus, respectively. The KEGG enrichment results of the unique single-copy genes to the three species were significantly different in genetic information processing, protein processing, and metabolic functions. The complete mitochondrial genomes of P. punctatissimus and P. echinogaster were successfully assembled, and the resulting phylogenetic relationships align with the currently reported taxonomic status of species in the Stromateoidei. Additionally, population size analysis using PSMC revealed that P. punctatissimus experienced one bottleneck effect, while P. echinogaster underwent two bottleneck events during the Pleistocene Glacial Epoch. [ABSTRACT FROM AUTHOR]

Abstract Comparative studies of cancer‐related genes not only provide novel information about their evolution and function but also an understanding of cancer as a driving force in biological systems and species’ life histories. So far, these studies have focused on mammals. Here, we provide the first comparative study of cancer‐related gene copy number variation in fish. Fishes are a paraphyletic group whose last common ancestor is also an ancestor of the tetrapods, and accordingly, their tumour suppression mechanisms should include most of the mammalian mechanisms and also reveal novel (but potentially phylogenetically older) previously undetected mechanisms. We have matched the sequenced genomes of 65 fish species from the Ensemble database with the cancer gene information from the COSMIC database. By calculating the number of gene copies across species using the Ensembl CAFE data (providing species trees for gene copy number counts), we used a less resource‐demanding method for homolog identification. Our analysis demonstrates a masked relationship between cancer‐related gene copy number variation (CNV) and maximum lifespan in fish species, suggesting that a higher number of copies of tumour suppressor genes lengthens and the number of copies of oncogenes shortens lifespan. Based on the positive correlation between the number of copies of tumour suppressors and oncogenes, we show which species have more tumour suppressors in relation to oncogenes. It could be suggested that these species have stronger genetic defences against oncogenic processes. Fish studies could be a largely unexplored treasure trove for understanding the evolution and ecology of cancer, providing novel insights into the study of cancer and tumour suppression, in addition to fish evolution, life‐history trade‐offs, and ecology.

The amygdala, a complex array of nuclei in the forebrain, controls emotions and emotion-related behaviors in vertebrates. Current research aims to understand the amygdala's evolution in ray-finned fish such as zebrafish because of the region's relevance for social behavior and human psychiatric disorders. Clear-cut molecular definitions of the amygdala and its evolutionary-developmental relationship to the one of mammals are critical for zebrafish models of affective disorders and autism. In this review, I argue that the prosomeric model and a focus on the olfactory system's organization provide ideal tools for discovering deep ancestral relationships between the emotional systems of zebrafish and mammals. The review's focus is on the "extended amygdala," which refers to subpallial amygdaloid territories including the central (autonomic) and the medial (olfactory) amygdala required for reproductive and social behaviors. Amphibians, sauropsids, and lungfish share many characteristics with the basic amygdala ground plan of mammals, as molecular and hodological studies have shown. Further exploration of the evolution of the amygdala in basally derived fish vertebrates requires researchers to test these "tetrapod-based" concepts. Historically, this has been a daunting task because the forebrains of basally derived fish vertebrates look very different from those of more familiar tetrapod ones. An extreme case are ray-finned fish (Actinopterygii) like zebrafish because their telencephalon develops through a distinct outward-growing process called eversion. To this day, scientists have struggled to determine how the everted telencephalon compares to non-actinopterygian vertebrates. Using the teleost zebrafish as a genetic model, comparative neurologists began to establish quantifiable molecular definitions that allow direct comparisons between ray-finned fish and tetrapods. In this review, I discuss how the most recent discovery of the zebrafish amygdala ground plan offers an opportunity to identify the developmental constraints of amygdala evolution and function. In addition, I explain how the zebrafish prethalamic eminence (PThE) topologically relates to the medial amygdala proper and the nucleus of the lateral olfactory tract (nLOT). In fact, I consider these previously misinterpreted olfactory structures the most critical missing evolutionary links between actinopterygian and tetrapod amygdalae. In this context, I will also explain why recognizing both the PThE and the nLOT is crucial to understanding the telencephalon eversion. Recognizing these anatomical hallmarks allows direct comparisons of the amygdalae of zebrafish and mammals. Ultimately, the new concepts of the zebrafish amygdala will overcome current dogmas and reach a holistic understanding of amygdala circuits of cognition and emotion in actinopterygians. [ABSTRACT FROM AUTHOR]

The AUTS2 gene plays major roles during brain development and is associated with various neuropathologies including autism. Data in non-mammalian species are scarce, and the aim of our study was to provide a comprehensive analysis of auts2 evolution in teleost fish, which are widely used for in vivo functional analysis and biomedical purposes. Comparative genomics in 78 species showed that auts2a and auts2b originate from the teleost-specific whole genome duplication (TGD). auts2a, which is highly similar to human AUTS2, was almost systematically retained following TGD. In contrast, auts2b, which encodes for a shorter protein similar to a short human AUTS2 isoform, was lost more frequently and independently during evolution. RNA-seq analysis in 10 species revealed a highly conserved profile with predominant expression of both genes in the embryo, brain, and gonads. Based on protein length, conserved domains, and expression profiles, we speculate that the long human isoform functions were retained by auts2a, while the short isoform functions were retained by auts2a and/or auts2b, depending on the lineage/species. auts2a showed a burst in expression during medaka brain formation, where it was expressed in areas of the brain associated with neurodevelopmental disorders. Together, our data suggest a strong conservation of auts2 functions in vertebrates despite different evolutionary scenarios in teleosts. [ABSTRACT FROM AUTHOR]

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The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is involved in regulating the body's immunity, cell proliferation, differentiation, and apoptosis. Members of the STAT family have been extensively studied in different mammalian species. However, there are few studies on the STAT family genes in farmed economic fish. In this study, eight STAT genes including STAT1a , STAT1b, STAT2 , STAT3 , STAT4 , STAT5a , STAT5b and STAT6 , in blunt snout bream (Megalobrama amblycephala), an economically important fish in China, were identified and characterized. Analyses of gene location, phylogeny and conserved synteny were conducted to infer the evolutionary origin of these STAT family genes. Furthermore, the evolutionary origin model of STATs was constructed based on the 2R hypothesis and teleost genome duplication (TGD) hypothesis, which clarified the evolutionary origin of the eight STATs in blunt snout bream. Besides, expression of the eight STATs was detected in 10 tissues of healthy blunt snout bream, which showed different expression patterns, and all had the highest level in the blood. In addition, expression of the STATs was significantly induced in the spleen, liver, and kidney after infection of Aeromonas hydrophila , suggesting that they play an important role in protecting the host from pathogens. In general, the evolution of cytokine-related genes parallels that of the immune system, which has likely been a main evolutionary driver. Therefore, the evolutionary model of STAT genes, constructed in the non-model organism pioneeringly, may provide some enlightenment for the evolution of the fish STAT family genes and their involvement in the immune function. • Eight STAT genes were identified in blunt snout bream. • An evolutionary model of the STAT family genes was constructed. • Expression of STAT genes was detected in healthy blunt snout bream. • Expression of STAT genes was examined after Aeromonas hydrophila infection. [ABSTRACT FROM AUTHOR]

The cranial neural crest (CNC) arises within the developing central nervous system, but then migrates away from the neural tube in three consecutive streams termed mandibular, hyoid and branchial, respectively, according to the order along the anteroposterior axis. While the process of neural crest emigration generally follows a conserved anterior to posterior sequence across vertebrates, we find that ray-finned fishes (bichir, sterlet, gar, and pike) exhibit several heterochronies in the timing and order of CNC emergence that influences their subsequent migratory patterns. First, emigration of the cranial neural crest in these fishes occurs prematurely compared to other vertebrates, already initiating during early neurulation and well before neural tube closure. Second, delamination of the hyoid stream occurs prior to the more anterior mandibular stream; this is associated with early morphogenesis of key hyoid structures like external gills (bichir), a large opercular flap (gar) or first forming cartilage (pike). In sterlet, the hyoid and branchial CNC cells form a single hyobranchial sheet, which later segregates in concert with second pharyngeal pouch morphogenesis. Taken together, the results show that despite generally conserved migratory patterns, heterochronic alterations in the timing of emigration and pattern of migration of CNC cells accompanies morphological diversity of ray-finned fishes. Image 1 • First comprehensive analysis of cranial neural crest migration in ray-finned fishes. • Unique cranial neural crest migratory patterns among vertebrates. • Heterochronies in neural crest migratory patterns influences craniofacial diversity. [ABSTRACT FROM AUTHOR]

How vertebrates evolved different traits for acid excretion to maintain body fluid pH homeostasis is largely unknown. The evolution of Na+/H+ exchanger (NHE)‐mediated NH4+ excretion in fishes is reported, and the coevolution with increased ammoniagenesis and accompanying gluconeogenesis is speculated to benefit vertebrates in terms of both internal homeostasis and energy metabolism response to acidic stress. The findings provide new insights into our understanding of the possible adaptation of fishes to progressing global environmental acidification. In human kidney, titratable H+ and NH4+ comprise the two main components of net acid excretion. V‐type H+‐ATPase‐mediated H+ excretion may have developed in stenohaline lampreys when they initially invaded freshwater from marine habitats, but this trait is lost in most fishes. Instead, increased reliance on NHE‐mediated NH4+ excretion is gradually developed and intensified during fish evolution. Further investigations on more species will be needed to support the hypothesis. Also see the video abstract here https://youtu.be/vZuObtfm-34. [ABSTRACT FROM AUTHOR]

Morphological transformations can be generated by evolutionary changes in the sequence of developmental events. In this study, we examined the evolutionary dynamics of the developmental sequence on a macroevolutionary scale in teleosts. Using the information from previous reports describing the development of 31 species, we extracted the developmental sequences of 19 landmark events involving the formation of phylogenetically conserved body parts; we then inferred ancestral developmental sequences by two different parsimony‐based methods—event‐pairing and continuous analysis. The phylogenetic comparisons of these sequences revealed event‐dependent heterogeneity in the frequency of sequence changes. Most of the sequence changes occurred as exchanges of temporally neighboring events. These heterochronic changes in developmental sequences accumulated along evolutionary time, but the precise distribution of the changes over the teleostean phylogeny remains unclear due to technical limitations. [ABSTRACT FROM AUTHOR]

Through elasmobranch (sharks and rays) evolutionary history, gigantism evolved multiple times in phylogenetically distant species, some of which are now extinct. Interestingly, the world's largest elasmobranchs display two specializations found never to overlap: filter feeding and mesothermy. The contrasting lifestyles of elasmobranch giants provide an ideal case study to elucidate the evolutionary pathways leading to gigantism in the oceans. Here, we applied a phylogenetic approach to a global dataset of 459 taxa to study the evolution of elasmobranch gigantism. We found that filter feeders and mesotherms deviate from general relationships between trophic level and body size, and exhibit significantly larger sizes than ectothermic‐macropredators. We confirm that filter feeding arose multiple times during the Paleogene, and suggest the possibility of a single origin of mesothermy in the Cretaceous. Together, our results elucidate two main evolutionary pathways that enable gigantism: mesothermic and filter feeding. These pathways were followed by ancestrally large clades and facilitated extreme sizes through specializations for enhancing prey intake. Although a negligible percentage of ectothermic‐macropredators reach gigantic sizes, these species lack such specializations and are correspondingly constrained to the lower limits of gigantism. Importantly, the very adaptive strategies that enabled the evolution of the largest sharks can also confer high extinction susceptibility. [ABSTRACT FROM AUTHOR]

Two new species of calliotropid gastropods, Calliotropis (Riselloidea) faustiankensis sp. nov. and Calliotropis (Riselloidea) lukovensis sp. nov., are described from the Middle Jurassic (Middle Bathonian−Upper Callovian) of Poland. Additionally, new excellently preserved shells of Calliotropis (Riselloidea) biarmata (Münster) allow redefinition of this species. The new morphological information obtained from these three fossil species of Calliotropis in combination with the dataset assembled from 20 extinct and 24 living calliotropids is here summarized in quantitative multivariate and principal component analyses suggesting an onshore-offshore trend in calliotropid gastropod evolution from the Triassic to Recent times. This trend, which is expressed in the morphology of shells, shows that the Mesozoic species are mostly shallow water, while Cenozoic and Recent taxa are mostly deep water. The distinction supports earlier suggestions that the genus Calliotropis can be subdivided into two temporal subgenera belonging to the family Eucyclidae Koken. http://zoobank.org/urn:lsid:zoobank.org:pub:C8362FB8-966A-4322-95D5-7151CED20476 [ABSTRACT FROM AUTHOR]

Evolutionary novelties require rewiring of transcriptional networks and/or the evolution of new gene functions. Sex determination (SD), one of the most plastic evolutionary processes, requires such novelties. Studies on the evolution of vertebrate SD revealed that new master SD genes are generally recruited from genes involved in the downstream SD regulatory genetic network. Only a single exception to this rule is currently known in vertebrates: the intriguing case of the salmonid master SD gene (sdY), which arose from duplication of an immune-related gene. This exception immediately posed the question of how a gene outside from the classical sex differentiation cascade could acquire its function as a male SD gene. Here we show that SdY became integrated in the classical vertebrate sex differentiation cascade by interacting with the Forkhead box domain of the female-determining transcription factor, Foxl2. In the presence of Foxl2, SdY is translocated to the nucleus where the SdY:Foxl2 complex prevents activation of the aromatase (cyp19a1a) promoter in cooperation with Nr5a1 (Sf1). Hence, by blocking a positive loop of regulation needed for the synthesis of estrogens in the early differentiating gonad, SdY disrupts a preset female differentiation pathway, consequently allowing testicular differentiation to proceed. These results also suggest that the evolution of unusual vertebrate master sex determination genes recruited from outside the classical pathway like sdY is strongly constrained by their ability to interact with the canonical gonadal differentiation pathway. [ABSTRACT FROM AUTHOR]

Some hypotheses on the evolution of regeneration in amphibians and reptiles are presented. Amphibian regeneration is derived from metamorphosis present in sarcopterygian fish and amphibians of the Devonian‐Carboniferous. The genetic ability to rebuild organs during metamorphosis was maintained in form of "regeneration" in urodele and anuran tadpoles. Amphibian regeneration may be a consequence of the transition from an aquatic to a terrestrial environment through the evolution of a developmental program for the tadpole stage and replacements of adult organs controlled by the endocrine and immune system. Following metamorphosis, the regeneration program for terrestrial anurans and amniotes was lost or modified, whereas the immune system involved in self‐integrity and microbial protection became in charge of regeneration that was replaced by scarring. Among amniotes only lizards regenerate an organ as large and complex as the tail. It is hypothesized that in Permian captorhinids and in Triassic lizards (eosuchians) a regenerative blastema evolved in relation to autotomy, a unique phenomenon present in these reptiles that enhanced survival against the larger predators of the Permian‐Mesozoic. Appendage regeneration in amphibians and lizards occurs after the migration of activated mesenchymal and epidermal cells in the wounded areas to form soft and hyaluronate‐rich blastemas. Autotomy and production of high hyaluronate levels allows high hydration and immunosuppression, favoring regeneration. It is suggested that a way for regenerative medicine to induce limb regeneration in humans is to develop medical procedures to recreate soft blastemas that can grow, a long and difficult process because it counteracts mammalian evolution toward scarring. Cladogram showing three successive geological periods (arrows) where the evolution of regeneration of body appendages initiated among amphibians and reptiles. [ABSTRACT FROM AUTHOR]

Abstract Tetraspanins are a family of membrane proteins, which play important roles in many aspects of cell biology and physiology via binding other tetraspanins or proteins. In this study, we identified 251 putative tetraspanin genes in 6 teleost fishes. Conserved gene organization and motif distribution suggested their functional relevance existing in each group. Synteny analyses implied conserved and dynamic evolution characteristics of this gene family in several vertebrates. We also found that some recombination events have accelerated the evolution of this gene family. Moreover, a few positive selection sites were identified. Expression patterns of some tetraspanins were further studied under organophosphorus stress using transcriptome sequencing. Functional network analyses identified some interacting genes that exhibited 174 interactions, which reflected the diversity of tetraspanin binding proteins. The results will provide a foundation for the further functional investigation of the tetraspanin genes in fishes. Highlights • Identified tetraspanin genes in the six teleost fishes. • Conserved gene organization and motif compositions in each group. • Identified some positive selection sites. • Different expression profiles implied functional divergence. • Exhibited 174 interactions by functional network analysis. [ABSTRACT FROM AUTHOR]

In fishes, including the jawless lampreys, the most ancient lineage of extant vertebrates, plasma glucose levels are highly variable and regulation is more relaxed than in mammals. The regulation of glucose and lipid in fishes in common with mammals involves members of the glucagon (GCG)-like family of gastrointestinal peptides. In mammals, four peptides GCG, glucagon-like peptide 1 and 2 (GLP1 and GLP2) and glucose-dependent insulinotropic peptide (GIP) that activate four specific receptors exist. However, in lamprey and other fishes the glucagon-like family evolved differently and they retained additional gene family members (glucagon-related peptide, gcrp and its receptor, gcrpr ) that are absent from mammals. In the present study, we analysed the evolution of the glucagon-like system in fish and characterized gene expression of the family members in the European sea bass ( Dicentrarchus labrax ) a teleost fish. Phylogenetic analysis revealed that multiple receptors and peptides of the glucagon-like family emerged early during the vertebrate radiation and evolved via lineage specific events. Synteny analysis suggested that family member gene loss is likely to be the result of a single gene deletion event. Lamprey was the only fish where a putative glp1r persisted and the presence of the receptor gene in the genomes of the elephant shark and coelacanth remains unresolved. In the coelacanth and elephant shark, unique proglucagon genes were acquired which in the former only encoded Gcg and Glp2 and in the latter, shared a similar structure to the teleost proglucagon gene but possessed an extra exon coding for Glp-like peptide that was most similar to Glp2. The variable tissue distribution of the gene transcripts encoding the ligands and receptors of the glucagon-like system in an advanced teleost, the European sea bass, suggested that, as occurs in mammals, they have acquired distinct functions. Statistically significant (p < .05) down-regulation of teleost proglucagon a in sea bass with modified plasma glucose levels confirmed the link between these peptides and metabolism. The tissue distribution of members of the glucagon-like system in sea bass and human suggests that evolution of the brain-gut-peptide regulatory loop diverged between teleosts and mammals despite the overall conservation and similarity of glucagon-like family members. [ABSTRACT FROM AUTHOR]

A broad portfolio of phenotypic diversity in natural organisms can buffer against exploitation and increase species persistence in disturbed ecosystems. The study of genomic variation that accounts for ecological and evolutionary adaptation can represent a powerful approach to extend understanding of phenotypic variation in nature. Here we present a chromosome-level reference genome assembly for Chinook salmon (Oncorhynchus tshawytscha; 2.36 Gb) that enabled association mapping of life-history variation and phenotypic traits for this species. Whole-genome re-sequencing of populations with distinct life-history traits provided evidence that divergent selection was extensive throughout the genome within and among phylogenetic lineages, indicating that a broad portfolio of phenotypic diversity exists in this species that is related to local adaptation and life-history variation. Association mapping with millions of genome-wide SNPs revealed that a genomic region of major effect on chromosome 28 was associated with phenotypes for premature and mature arrival to spawning grounds and was consistent across three distinct phylogenetic lineages. Our results demonstrate how genomic resources can enlighten the genetic basis of known phenotypes in exploited species and assist in clarifying phenotypic variation that may be difficult to observe in naturally occurring organisms. [ABSTRACT FROM AUTHOR]

The Notacanthiformes is an ancient group of deep-sea ray-finned fishes comprising 27 species in two families; Halosauridae and Notacanthidae. Although many studies have tried to reconstruct the phylogenetic relationships among the major clades of Elopomorpha, little is known about the evolutionary history of notacanthiforms. Molecular and morphological data were used to test previous hypotheses regarding the phylogenetic relationships among notacanthiform taxa, and to unravel the origin and evolution of this group. The molecular analyses of notacanthids showed similar results to those previously obtained employing osteological data, which proposed the existence of the Lipogenyinae ( Lipogenys ) and Notacanthinae ( Notacanthus  +  Polyacanthonotus ) subfamilies. Nevertheless, when the external morphology data is considered Lipogenys is more related to Notacanthus than Polyacanthonotus . The analyses could not fully resolve the inner relationships of the halosaurids. The time-calibrated tree of the order Notacanthiformes shows a long process of diversification spanning from the upper Cretaceous, to 50 million years after the K-Pg extinction, with the gradual emergence of all the modern families and genera of the group. This is the first specific phylogeny of the order Notacanthiformes, combining different analyses and data in order to obtain a wider perspective of the evolution and diversification of this group of fishes. [ABSTRACT FROM AUTHOR]

Abstract: Aim: To present an updated database of fish species recorded on south‐western Atlantic reef environments and to explore the ecological drivers of the structure, the latitudinal gradient of biodiversity and the centre of endemism in this peripheral province. Location: South‐western Atlantic (SWA): Brazilian and Argentinian Provinces. Methods: A database composed of 733 fish species along 23 locations in the SWA (00°55′ N to 43°00′ S) was compiled based on primary data, literature and museum records. Cluster and beta diversity analyses were carried out to evaluate faunal overlaps among locations and subprovinces. “Target‐area‐distance effect” and “stepping stones dispersal” hypotheses for assemblage composition were tested through Mantel tests. Relationships between the distribution patterns and ecological traits of reef fish species were investigated through generalized linear mixed‐effect models. Results: Out of the 733 fish species, 405 are SWA resident reef fishes, of which 111 (27%) are endemics and 78 are threatened with extinction. Cluster analysis detected six subprovinces in the SWA structured following the target‐area‐distance model, and with no evidence for a latitudinal gradient in diversity. The greatest overall richness and endemic species richness were found in the east–south‐eastern region. Depth range, habitat use and body size were the main drivers of SWA reef fish assemblage structure. Main conclusions: The Brazilian and Argentinian coasts constitute different provinces structured by oceanographic barriers and environmental filters. Similarities among oceanic islands indicate connectivity driven by stochastic and ecological factors. Species richness and endemism indicate that peripheral provinces may also bear centres of origin and biodiversity, patterns driven by parapatric/ecological speciation and the overlap between tropical and subtropical reef fish species. Ecological drivers of reef fish distribution, such as habitat specialization and body size, support hypotheses of speciation in the periphery. New approaches for spatial planning, marine protected areas and off‐reserve marine management are essential for the conservation and sustainability of SWA reef fishes. [ABSTRACT FROM AUTHOR]

We have analyzed the partial sequences of the mitochondrial COI gene along with the amino acid sequences of cytochrome oxidase subunit I, encoded by this gene region, in representatives of 11 genera of salmonoid fish. For amino acid sequences, two alternative networks are constructed with outgroups represented by either Esocoidei or Osmeroidei as the supposed ancestral groups. This way, Osmeroidei appear to be closer to the salmonoid fish than Esocoidei, and their presence in the network as an outgroup explains the available data on the morphology and karyology of salmonoids much better. A number of the results of this study are fundamentally new. In particular, the slowing down of the molecular evolution of the grayling (Thymallidae) is shown. We conclude that the charr (Salvelinus) is one of the modern genera of salmonoids closest to their ancestor. The hypothesis of the phylogenetic proximity of the genera Brachymystax, Hucho, and Salmo has been confirmed. We also discuss the possibility that it is namely the changes in the amino acid sequence of cytochrome oxidase subunit I that lead to postzygotic reproductive isolation between taxa. [ABSTRACT FROM AUTHOR]

A critical analysis of literature data on the distribution, morphology, and phylogeography of the Arctic lamprey (Lethenteron camtschaticum) and five species of marine and anadromous fish such as navaga (Eleginus navaga), pollock (Theragra chalcogramma), rainbow smelt (Osmerus mordax dentex), Pacific herring (Clupea pallasii), and pond smelt (Hypomesus olidus) has been performed. The results show that all these species have colonized Northern European seas, distributing along the Arctic coastline of Eurasia after the glacier retreat. The reasons that the dispersal of these species in the Atlantic Ocean may be impeded (preference for a cold environment, competition, and decrease of the evolutionary potential) are discussed. [ABSTRACT FROM AUTHOR]

As one of the most basal living vertebrates, lampreys represent an excellent model system to study the evolution of thyroid hormone (TH) signaling. The lamprey hypothalamic-pituitary-thyroid and reproductive axes overlap functionally. Lampreys have 3 gonadotropin-releasing hormones and a single glycoprotein hormone from the hypothalamus and pituitary, respectively, that regulate both the reproductive and thyroid axes. TH synthesis in larval lampreys takes place in an endostyle that transforms into typical vertebrate thyroid tissue during metamorphosis; both the endostyle and follicular tissue have all the typical TH synthetic components found in other vertebrates. Furthermore, lampreys also have the vertebrate suite of peripheral regulators including TH distributor proteins (THDPs), deiodinases and TH receptors (TRs). Although at the molecular level the components of the lamprey thyroid system are ancestral to other vertebrates, their functions have been largely conserved. TH signaling as it relates to lamprey metamorphosis represents a particularly interesting phenomenon. Unlike other metamorphosing vertebrates, lamprey THs increase throughout the larval period, peak prior to metamorphosis and decline rapidly at the onset of metamorphosis; patterns of deiodinase activity are consistent with these increases and declines. Moreover, goitrogens (which suppress TH levels) initiate precocious metamorphosis, and exogenous TH treatment blocks goitrogen-induced metamorphosis and disrupts natural metamorphosis. Despite this clear physiological difference, TH action via TRs is consistent with higher vertebrates. Based on observations that TRs are upregulated in a tissue-specific fashion during morphogenesis and the finding that lamprey TRs upregulate genes via THs in a fashion similar to higher vertebrates, we propose the following hypothesis for further testing. THs have a dual role in lampreys where high TH levels promote larval feeding and growth and then at the onset of metamorphosis TH levels decrease rapidly; at this time the relatively low TH levels function via TRs in a fashion similar to that of other metamorphosing vertebrates. [ABSTRACT FROM AUTHOR]

The family of secretory calcium-binding phosphoproteins (SCPPs) have been considered vital to skeletal tissue mineralization. However, most previous SCPP studies focused on phylogenetically distant animals but not on those closely related species. Here we provide novel insights into the coevolution of SCPP genes and fish scales in 10 species from Otophysi. According to their scale phenotypes, these fishes can be divided into three groups, i.e., scaled, sparsely scaled, and scaleless. We identified homologous SCPP genes in the genomes of these species and revealed an absence of some SCPP members in some genomes, suggesting an uneven evolutionary history of SCPP genes in fishes. In addition, most of these SCPP genes, with the exception of SPP1, individually form one or two gene cluster(s) on each corresponding genome. Furthermore, we constructed phylogenetic trees using maximum likelihood method to estimate their evolution. The phylogenetic topology mostly supports two subclasses in some species, such as Cyprinus carpio, Sinocyclocheilus anshuiensis, S. grahamin, and S. rhinocerous, but not in the other examined fishes. By comparing the gene structures of recently reported candidate genes, SCPP1 and SCPP5, for determining scale phenotypes, we found that the hypothesis is suitable for Astyanax mexicanus, but denied by S. anshuiensis, even though they are both sparsely scaled for cave adaptation. Thus, we conclude that, although different fish species display similar scale phenotypes, the underlying genetic changes however might be diverse. In summary, this paper accelerates the recognition of the SCPP family in teleosts for potential scale evolution. [ABSTRACT FROM AUTHOR]

The parathyroid hormone (PTH) family is a group of structurally-related secreted peptides involved in bone mineral homeostasis and multitude of developmental processes in vertebrates. These peptides mediate actions through PTH receptors (PTHRs), which belong to the transmembrane G protein-coupled receptor group. To date, genes encoding for PTH and PTHR have only been identified in chordates, suggesting that this signaling pathway may be an evolutionary innovation of our phylum. In vertebrates, we found up to six PTH and three PTHR different paralogs, varying in number between mammals and teleost fishes due to the different rounds of whole-genome duplication and specific gene losses suffered between the two groups of animals. The diversification of the PTH gene family has been accompanied by both functional divergence and convergence, making sometimes difficult the comparison between PTH peptides of teleosts and mammals. Here, we review the roles of all Pth peptides in fishes, and based on the evolutionary history of PTH paralogs, we propose a new and simple nomenclature from PTH1 to PTH4. Moreover, the recent characterization of the Pth4 in zebrafish allows us to consider the prominent role of the brain-to-bone signaling pathway in the regulation of bone development and homeostasis. Finally, comparison between PTH peptides of fish and mammals allows us to discuss an evolutionary model for PTH functions related to bone mineral balance during the vertebrate transition from an aquatic to a terrestrial environment. [ABSTRACT FROM AUTHOR]

The evolutionary effects of harvest on wild fish populations have been documented around the world; however, sublethal selective pressures can also cause evolutionary changes in phenotypes. For migratory fishes, passage facilities may represent instances of nonlethal selective pressure. Our analysis of 6 years of passage data suggests that certain fish passage facilities on the Penobscot River have been exerting selective pressure against large-bodied, anadromous Atlantic salmon ( Salmo salar). At the second and third dams in the river, a 91-cm salmon was 21%-27% and 12%-16% less likely to pass than a 45-cm salmon, respectively. Fish size positively influences egg survival and number and is a heritable trait. Therefore, in a wild-reproducing population, exclusion of large fish from spawning areas may have population-level impacts. In the Penobscot River, most returning adults derive from a hatchery program that collects its broodstock after passing the first dam in the river. Analysis of fork lengths of salmon returning to the Penobscot River from 1978 to 2012 provided mixed support for evolution of size at maturity in different age classes in a pattern that may be expected from interactions with conservation hatchery operations. Additionally, slow-maturing and iteroparous individuals that represent the largest salmon size classes were essentially lost from the population during that time, and Penobscot River fish have shorter fork lengths at maturity than Atlantic salmon in undammed systems. [ABSTRACT FROM AUTHOR]

The current molecular understanding of the aging process derives almost exclusively from the study of random or targeted single-gene mutations in highly inbred laboratory species, mostly invertebrates. Little information is available as to the genetic mechanisms responsible for natural lifespan variation and the evolution of lifespan, especially in vertebrates. Here, we investigated the pattern of positive selection in annual (i.e., short-lived) and nonannual (i.e., longer-lived) African killifishes to identify a genomic substrate for evolution of annual life history (and reduced lifespan). We identified genes under positive selection in all steps of mitochondrial biogenesis: mitochondrial (mt) DNA replication, transcription from mt promoters, processing and stabilization of mt RNAs, mt translation, assembly of respiratory chain complexes, and electron transport chain. Signs of paralleled evolution (i.e., evolution in more than one branch of Nothobranchius phylogeny) are observed in four out of five steps. Moreover, some genes under positive selection in Nothobranchius are under positive selection also in long-lived mammals such as bats and mole-rats. Complexes of the respiratory chain are formed in a coordinates multistep process where nuclearly and mitochondrially encoded components are assembled and inserted into the inner mitochondrial membrane. The coordination of this process is named mitonuclear balance, and experimental manipulations of mitonuclear balance can increase longevity of laboratory species. Our data strongly indicate that these genes are also casually linked to evolution lifespan in vertebrates. [ABSTRACT FROM AUTHOR]

Parasite diversity and abundance (parasite load) vary greatly among host species. However, the influence of host traits on variation in parasitism remains poorly understood. Comparative studies of parasite load have largely examined measures of parasite species richness and are predominantly based on records obtained from published data. Consequently, little is known about the relationships between host traits and other aspects of parasite load, such as parasite abundance, prevalence and aggregation. Meanwhile, understanding of parasite species richness may be clouded by limitations associated with data collation from multiple independent sources. We conducted a field study of Lake Tanganyika cichlid fishes and their helminth parasites. Using a Bayesian phylogenetic comparative framework, we tested evolutionary associations between five key host traits (body size, gut length, diet breadth, habitat complexity and number of sympatric hosts) predicted to influence parasitism, together with multiple measures of parasite load. We find that the number of host species that a particular host may encounter due to its habitat preferences emerges as a factor of general importance for parasite diversity, abundance and prevalence, but not parasite aggregation. In contrast, body size and gut size are positively related to aspects of parasite load within, but not between species. The influence of host phylogeny varies considerably among measures of parasite load, with the greatest influence exerted on parasite diversity. These results reveal that both host morphology and biotic interactions are key determinants of host-parasite associations and that consideration of multiple aspects of parasite load is required to fully understand patterns in parasitism. [ABSTRACT FROM AUTHOR]

Glycoprotein hormones (GpH) interact very specifically with their receptors to mediate hypothalamic-pituitary-peripheral gland endocrine signaling. Vertebrates typically have three functionally distinct GpH endocrine signaling complexes: follicle-stimulating hormone, luteinizing hormone, and thyroid-stimulating hormone, and their receptors. Each hormone consists of a common α subunit bound to one of three different β subunits. Individual hormone subunits and receptors are present in genomes of early metazoans, and a subset of hormone subunits and receptors has been recently characterized in sea lamprey. However, it remains unclear when the full complement of hormone and receptor protein families first appeared, and when specificity of interactions between GpH hormones and receptors first evolved. Here we present phylogenetic analyses showing that the elephant shark ( Callorhinchus milii ) genome contains sequences representing the current diversity of all hormone subunits and receptors in these co-evolving protein families. We examined specificity of hormone and receptor interactions using functional assays testing reporter gene activation by elephant shark follicle-stimulating hormone, luteinizing hormone, and thyroid-stimulating hormone receptors. We show highly specific, dose-responsive hormone interactions for all three complexes. Our results suggest that co-evolution of specificity between proteins in these endocrine signaling complexes occurred prior to the divergence of Chondrichthyes from the chordate lineage. [ABSTRACT FROM AUTHOR]

Commensal microorganisms inhabit every mucosal surface of teleost fish. At these surfaces, microorganisms directly and indirectly shape the teleost immune system. This review provides a comprehensive overview of how the microbiota and microbiota-derived products influence both the mucosal and systemic immune system of fish. The cross talk between the microbiota and the teleost immune system shifts significantly under stress or disease scenarios rendering commensals into opportunists or pathogens. Lessons learnt from germ-free fish models as well as from oral administration of live probiotics to fish highlight the vast impact that microbiota have on immune development, antibody production, mucosal homeostasis, and resistance to stress. Future studies should dissect the specific mechanisms by which different members of the fish microbiota and the metabolites they produce interact with pathogens, with other commensals, and with the teleost immune system. [ABSTRACT FROM AUTHOR]

In the current model, the most anterior part of the forebrain (secondary prosencephalon) is subdivided into the telencephalon dorsally and the hypothalamus ventrally. Our recent study identified a new morphogenetic unit named the optic recess region ( ORR) between the telencephalon and the hypothalamus. This modification of the forebrain regionalization based on the ventricular organization resolved some previously unexplained inconsistency about regional identification in different vertebrate groups. The ventricular-based comparison also revealed a large diversity within the subregions (notably in the hypothalamus and telencephalon) among different vertebrate groups. In tetrapods there is only one hypothalamic recess, while in teleosts there are two recesses. Most notably, the mammalian and teleost hypothalami are two extreme cases: the former has lost the cerebrospinal fluid-contacting ( CSF-c) neurons, while the latter has increased them. Thus, one to one homology of hypothalamic subregions in mammals and teleosts requires careful verification. In the telencephalon, different developmental processes between Sarcopterygii (lobe-finned fish) and Actinopterygii (ray-finned fish) have already been described: the evagination and the eversion. Although pallial homology has been long discussed based on the assumption that the medial-lateral organization of the pallium in Actinopterygii is inverted from that in Sarcopterygii, recent developmental data contradict this assumption. Current models of the brain organization are largely based on a mammalian-centric point of view, but our comparative analyses shed new light on the brain organization of Osteichthyes. [ABSTRACT FROM AUTHOR]

Summary Venom systems have evolved on multiple occasions across the animal kingdom, and they can act as key adaptations to protect animals from predators [ 1 ]. Consequently, venomous animals serve as models for a rich source of mimicry types, as non-venomous species benefit from reductions in predation risk by mimicking the coloration, body shape, and/or movement of toxic counterparts [ 2–5 ]. The frequent evolution of such deceitful imitations provides notable examples of phenotypic convergence and are often invoked as classic exemplars of evolution by natural selection. Here, we investigate the evolution of fangs, venom, and mimetic relationships in reef fishes from the tribe Nemophini (fangblennies). Comparative morphological analyses reveal that enlarged canine teeth (fangs) originated at the base of the Nemophini radiation and have enabled a micropredatory feeding strategy in non-venomous Plagiotremus spp. Subsequently, the evolution of deep anterior grooves and their coupling to venom secretory tissue provide Meiacanthus spp. with toxic venom that they effectively employ for defense. We find that fangblenny venom contains a number of toxic components that have been independently recruited into other animal venoms, some of which cause toxicity via interactions with opioid receptors, and result in a multifunctional biochemical phenotype that exerts potent hypotensive effects. The evolution of fangblenny venom has seemingly led to phenotypic convergence via the formation of a diverse array of mimetic relationships that provide protective (Batesian mimicry) and predatory (aggressive mimicry) benefits to other fishes [ 2, 6 ]. Our results further our understanding of how novel morphological and biochemical adaptations stimulate ecological interactions in the natural world. [ABSTRACT FROM AUTHOR]

The output of the cerebellar cortex is mainly released via cerebellar nuclei which vary in number and complexity among gnathostomes, extant vertebrates with a cerebellum. Cartilaginous fishes, a basal gnathostome lineage, show a conspicuous, well-organized cerebellar nucleus, unlike rayfinned fishes. To gain insight into the evolution and development of the cerebellar nucleus, we analyzed in the shark Scyliorhinus canicula (a chondrichthyan model species) the developmental expression of several genes coding for transcription factors (ScLhx5, ScLhx9, ScTbr1, and ScEn2) and the distribution of the protein calbindin, since all appear to be involved in cerebellar nuclei patterning in other gnathostomes. Three regions (subventricular, medial or central, and lateral or superficial) became recognizable in the cerebellar nucleus of this shark during development. Present genoarchitectonic and neurochemical data in embryos provide insight into the origin of the cerebellar nucleus in chondrichthyans and support a tripartite mediolateral organization of the cerebellar nucleus, as previously described in adult sharks. Furthermore, the expression pattern of ScLhx5, ScLhx9, and ScTbr1 in this shark, together with that of markers of proliferation, migration, and early differentiation of neurons, is compatible with the hypothesis that, as in mammals, different subsets of cerebellar nucleus neurons are originated from progenitors of 2 different sources: the ventricular zone of the cerebellar plate and the rhombic lip. We also present suggestive evidence that Lhx9 expression is involved in cerebellar nuclei patterning early on in gnathostome evolution, rather than representing an evolutionary innovation of the dentate nucleus in mammals, as previously hypothesized. [ABSTRACT FROM AUTHOR]

The streams draining of into San Francisco Bay, California, have been impacted by habitat alteration for over 150 years, and roads, dams, water diversions, and other impediments now block the paths of many aquatic migratory species. These changes can affect the genetic structure of fish populations, as well as driving adaptive evolution to novel environmental conditions. Here, we determine the evolutionary relationships of San Francisco Bay Area steelhead/rainbow trout ( Oncorhynchus mykiss) populations and show that (i) they are more closely related to native coastal steelhead than to the California Central Valley lineage, with no evidence of introgression by domesticated hatchery rainbow trout, (ii) populations above and below barriers within watersheds are each other's closest relatives, and (iii) adaptive genomic variation associated with migratory life-history traits in O. mykiss shows substantial evolutionary differences between fish above and below dams. These findings support continued habitat restoration and protection of San Francisco Bay Area O. mykiss populations and demonstrate that ecological conditions in novel habitats above barriers to anadromy influence life-history evolution. We highlight the importance of considering the adaptive landscape in conservation and restoration programs for species living in highly modified habitats, particularly with respect to key life-history traits. [ABSTRACT FROM AUTHOR]

• Information of genome size (GS) is important for various genomic and evolutionary studies. • The study generated new GS records of 43 fish species and revalidated 8 species. • The GS ranged from 0.58 pg in banded gourami to 1.92 pg in scribbled goby. • GS was found to be associated with body length, but no relationship noticed with the chromosome number. Precise estimation of genome size (GS) is vital for various genomic studies, such as deciding genome sequencing depth, genome assembly, biodiversity documentation, evolution, genetic disorders studies, duplication events etc. Animal Genome Size Database provides GS of over 2050 fish species, which ranges from 0.35 pg in pufferfish (Tetraodon nigroviridis) to 132.83 pg in marbled lungfish (Protopterus aethiopicus). The GS of majority of the fishes inhabiting waters of Indian subcontinent are still missing. In present study, we estimated GS of 51 freshwater teleost (31 commercially important, 7 vulnerable and 13 ornamental species) that ranged from 0.58 pg in banded gourami (Trichogaster fasciata) to 1.92 pg in scribbled goby (Awaous grammepomus). Substantial variation in GS was observed within the same fish orders (0.64–1.45 pg in cypriniformes, 0.70–1.41 pg in siluriformes and 0.58–1.92 pg in perciformes). We examined the relationship between the GS, chromosome number and body length across all the fishes. Body length was found to be associated with GS, whereas no relationship was noticed between the GS and the chromosome number. The analysis using ancestral information revealed haploid chromosome number 25, 27 and 24 for the most recent common ancestor of cypriniformes, siluriformes and perciformes, respectively. The study led to generation of new records on GS of 43 fish species and revalidated records for 8 species. The finding is valuable resource for further research in the areas of fish genomics, molecular ecology and evolutionary conservation genetics. [ABSTRACT FROM AUTHOR]

As highlighted by many of the papers in this issue, research on the genomic basis of adaptive phenotypic variation in natural populations has made spectacular progress in the past few years, largely due to the advances in sequencing technology and analysis. Without question, the resulting genomic data will improve the understanding of regions of the genome under selection and extend knowledge of the genetic basis of adaptive evolution. What is far less clear, but has been the focus of active discussion, is how such information can or should transfer into conservation practice to complement more typical conservation applications of genetic data. Before such applications can be realized, the evolutionary importance of specific targets of selection relative to the genome-wide diversity of the species as a whole must be evaluated. The key issues for the incorporation of adaptive genomic variation in conservation and management are discussed here, using published examples of adaptive genomic variation associated with specific phenotypes in salmonids and other taxa to highlight practical considerations for incorporating such information into conservation programmes. Scenarios are described in which adaptive genomic data could be used in conservation or restoration, constraints on its utility and the importance of validating inferences drawn from new genomic data before applying them in conservation practice. Finally, it is argued that an excessive focus on preserving the adaptive variation that can be measured, while ignoring the vast unknown majority that cannot, is a modern twist on the adaptationist programme that Gould and Lewontin critiqued almost 40 years ago. [ABSTRACT FROM AUTHOR]

Teleost fishes are prominent vertebrate models of evolution, illustrated among old-world radiations by the Cichlidae of East African Great Lakes and new-world radiations by the circumpolar Arctic charr Salvelinus alpinus. Herein, we describe variation in lake charr S. namaycush morphology, life history, physiology and ecology, as another example of radiation. The lake charr is restricted to northern North America, where it originated from glacial refugia and diversified in large lakes. Shallow and deepwater morphs arose in multiple lakes, with a large-bodied shallow-water 'lean' morph in shallow inshore depths, a small-bodied mid-water ' humper' morph on offshore shoals or banks, a robust, large-bodied moderate to deep-water ' redfin'; morph and a large-bodied deep-water ' siscowet' morph at depths > 100 m. Eye position, gape size, and gillraker length and spacing adapted for feeding on different-sized prey, with piscivorous morphs (leans, siscowets and presumably redfins) reaching larger asymptotic size than invertivorous morphs (humpers). Lean morphs are light in colour, whereas deepwater morphs are drab and dark, although the pattern is reversed in dark tannic lakes. Morphs shift from benthic to pelagic feeding at a length of 400-490 mm. Phenotypic differences in locomotion, buoyancy and lipid metabolism evolved into different mechanisms for buoyancy regulation, with lean morphs relying on hydrodynamic lift and siscowet morphs relying on hydrostatic lift. We suggest that the Salvelinus genus, rather than the species S. alpinus, is a diverse genus that should be the subject of comparative studies of processes causing divergence and adaptation among member species that may lead to a more complete evolutionary conceptual model. [ABSTRACT FROM AUTHOR]

Jacalin-related lectins are a type of carbohydrate-binding proteins, which are distributed across a wide variety of organisms and involved in some important biological processes. The evolution of this gene family in fishes is unknown. Here, 47 putative jacalin genes in 11 fish species were identified and divided into 4 groups through phylogenetic analysis. Conserved gene organization and motif distribution existed in each group, suggesting their functional conservation. Some fishes have eleven jacalin genes, while others have only one or zero gene in their genomes, suggesting dynamic changes in the number of jacalin genes during the evolution of fishes. Intragenic recombination played a key role in the evolution of jacalin genes. Synteny analyses of jacalin genes in some fishes implied conserved and dynamic evolution characteristics of this gene family and related genome segments. Moreover, a few functional divergence sites were identified within each group pairs. Divergent expression profiles of the zebra fish jacalin genes were further investigated in different stresses. The results provided a foundation for exploring the characterization of the jacalin genes in fishes and will offer insights for additional functional studies. [ABSTRACT FROM AUTHOR]

In March 1800, Alexander von Humboldt observed the extraordinary spectacle of native fisherman collecting electric eels (Electrophorus electricus) by "fishing with horses" [von Humboldt A (1807) Ann Phys 25:34-43]. The strategy was to herd horses into a pool containing electric eels, provoking the eels to attack by pressing themselves against the horses while discharging. Once the eels were exhausted, they could be safely collected. This legendary tale of South American adventures helped propel Humboldt to fame and has been recounted and illustrated in many publications, but subsequent investigators have been skeptical, and no similar eel behavior has been reported in more than 200 years. Here I report a defensive eel behavior that supports Humboldt's account. The behavior consists of an approach and leap out of the water during which the eel presses its chin against a threatening conductor while discharging high-voltage volleys. The effect is to short-circuit the electric organ through the threat, with increasing power diverted to the threat as the eel attains greater height during the leap. Measurement of voltages and current during the behavior, and assessment of the equivalent circuit, reveal the effectiveness of the behavior and the basis for its natural selection. [ABSTRACT FROM AUTHOR]

Temperature tolerances (including lethal limits) and associated rates of thermal acclimation of fish are critical information in predicting fish responses to global climate changes. In this study, a partial sequence of the heat shock protein 70 gene (HSP70) from the fish species Channa striatus was isolated and characterized. Evolutionary process that led to the diversity of HSP70 specific to vertebrates was also analysed. Results revealed that HSP70 is highly homologous in other fish families. The conservation of the HSP 70 gene among fish families could be driven by forces of natural selection due to climatic change. We exposed C. striatus to heat shock (32 °C) and cold shock (16 °C) respectively, in order to examine the differences of temperatures in influencing the expression patterns of HSP70. We revealed that expression of HSP70 was higher at 32 °C than at 16 °C in most of the organs. Specifically, occurrence of chaperone activity of HSP70 was found at low temperature. Therefore, this fish was postulated that to seems to be able to survive at lower temperature compared to higher temperature indicating there is force of natural selection acting towards this HSP 70 gene. This will demonstrate the effect of global warming towards the fish survivability. [ABSTRACT FROM AUTHOR]

The first report of the genus Jenynsia occurring in marine waters is presented here. The evolution of high salinity tolerance within Anablepidae is discussed and a hypothesis is proposed that this characteristic is a plesiomorphic trait in Jenynsia which was probably present in the common ancestor of the Anablepidae. [ABSTRACT FROM AUTHOR]

Background: An emerging cavefish model, the cyprinid genus Sinocyclocheilus, is endemic to the massive southwestern karst area adjacent to the Qinghai-Tibetan Plateau of China. In order to understand whether orogeny influenced the evolution of these species, and how genomes change under isolation, especially in subterranean habitats, we performed whole-genome sequencing and comparative analyses of three species in this genus, S. grahami, S. rhinocerous and S. anshuiensis. These species are surface-dwelling, semi-cave-dwelling and cave-restricted, respectively. Results: The assembled genome sizes of S. grahami, S. rhinocerous and S. anshuiensis are 1.75 Gb, 1.73 Gb and 1.68 Gb, respectively. Divergence time and population history analyses of these species reveal that their speciation and population dynamics are correlated with the different stages of uplifting of the Qinghai-Tibetan Plateau. We carried out comparative analyses of these genomes and found that many genetic changes, such as gene loss (e.g. opsin genes), pseudogenes (e.g. crystallin genes), mutations (e.g. melanogenesis-related genes), deletions (e.g. scale-related genes) and down-regulation (e.g. circadian rhythm pathway genes), are possibly associated with the regressive features (such as eye degeneration, albinism, rudimentary scales and lack of circadian rhythms), and that some gene expansion (e.g. taste-related transcription factor gene) may point to the constructive features (such as enhanced taste buds) which evolved in these cave fishes. Conclusion: As the first report on cavefish genomes among distinct species in Sinocyclocheilus, our work provides not only insights into genetic mechanisms of cave adaptation, but also represents a fundamental resource for a better understanding of cavefish biology. [ABSTRACT FROM AUTHOR]

In fish, the determination of sex can be controlled by genetic factors, environmental factors or a combination of both. The presence of heteromorphic sex-related chromosomes is widely acknowledged as strongly indicative of genetic control of sex determination (GSD) acting over other sex control systems. Heteromorphic sex-related chromosomes have been observed in a minority of teleosts (approximately 4 %). However, when looking at the fishes of the suborder Notothenioidei the frequency of sex-related chromosomes increases substantially, reaching 26.67 % of the cytogenetically studied species. Noteworthy, sex chromosomes were observed only in cold-adapted species which live in the Antarctic coastal waters, whereas morphologically differentiated sex chromosomes were never observed in the temperate non-Antarctic notothenioid families. Recent evidence suggests that the sex-linked chromosomes across the Antarctic notothenioid families may not share a common origin, but likely originated more than once during notothenioid evolutionary history, thus implying the presence of selection pressures operating toward fixation of GSD system. On the whole, the cytogenetic evidences suggest the Antarctic-specific fixation of differentiated heteromorphic sex-related chromosomes and of a prominent GSD across Antarctic notothenioids that may be an additional manifestation of notothenioid evolution in thermally stable cold environment. [ABSTRACT FROM AUTHOR]

Extreme novelties in the shape and size of paired fins are exemplified by extinct and extant cartilaginous and bony fishes. Pectoral fins of skates and rays, such as the little skate (Batoid, Leucoraja erinacea), show a strikingly unique morphology where the pectoral fin extends anteriorly to ultimately fuse with the head. This results in a morphology that essentially surrounds the body and is associated with the evolution of novel swimming mechanisms in the group. In an approach that extends from RNA sequencing to in situ hybridization to functional assays, we show that anterior and posterior portions of the pectoral fin have different genetic underpinnings: canonical genes of appendage development control posterior fin development via an apical ectodermal ridge (AER), whereas an alternative Homeobox (Hox)-Fibroblast growth factor (Fgf)-Wingless type MMTV integration site family (Wnt) genetic module in the anterior region creates an AER-like structure that drives anterior fin expansion. Finally, we show that GLI family zinc finger 3 (Gli3), which is an anterior repressor of tetrapod digits, is expressed in the posterior half of the pectoral fin of skate, shark, and zebrafish but in the anterior side of the pelvic fin. Taken together, these data point to both highly derived and deeply ancestral patterns of gene expression in skate pectoral fins, shedding light on the molecular mechanisms behind the evolution of novel fin morphologies. [ABSTRACT FROM AUTHOR]

Lampreys, one of the two surviving groups of ancient vertebrates, have become important models for study in diverse fields of biology. Lampreys (of which there are approximately 40 species) are being studied, for example, (a) to control pest sea lamprey in the North American Great Lakes and to restore declining populations of native species elsewhere; (b) in biomedical research, focusing particularly on the regenerative capability of lampreys; and (c) by developmental biologists studying the evolution of key vertebrate characters. Although a lack of genetic resources has hindered research on the mechanisms regulating many aspects of lamprey life history and development, formerly intractable questions are now amenable to investigation following the recent publication of the sea lamprey genome. Here, we provide an overview of the ways in which genomic tools are currently being deployed to tackle diverse research questions and suggest several areas that may benefit from the availability of the sea lamprey genome. [ABSTRACT FROM AUTHOR]

Some lamprey genera include forms that have significantly different life cycles (the most well known are the 'anadromous' and 'resident,' or the 'parasitic' and 'nonparasitic' forms). The analysis of data on the genetic characteristics of these forms shows that, in some cases, the nonparasitic lampreys inde-pendently derived from the parasitic ones in different aqueous systems. These data, together with the results of morphological analysis as well as data on the distribution, ecology, hybridization, and observations of joint spawning of parasitic and nonparasitic forms, show that these forms belong to the same species (except the resident forms that were isolated long ago). [ABSTRACT FROM AUTHOR]

Among-individual diet variation is common in natural populations and may occur at any trophic level within a food web. Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations. In this study we investigate the relationships between trophic position (the population's range and average) and among-individual diet variation. We test for diet variation among individuals and across size classes of Eurasian perch ( Perca fluviatilis), a widespread predatory freshwater fish that undergoes ontogenetic niche shifts. Second, we investigate among-individual diet variation within fish and invertebrate populations in two different lake communities using stable isotopes. Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations. We show that among-individual diet variation is highest at intermediate trophic positions, and that this high degree of among-individual variation likely causes an increase in the range of trophic positions among individuals. We also found that phenotypic divergence was negatively related to trophic position in a population. This study thus shows that trophic position is related to and may be important for among-individual diet variation as well as to phenotypic divergence within populations. [ABSTRACT FROM AUTHOR]

Although confined to fresh water, non-parasitic species of lampreys and the landlocked parasitic sea lamprey, all of which were derived relatively recently from anadromous ancestors, still develop chloride cells, whose function in their ancestors was for osmoregulation in marine waters during the adult parasitic phase. In contrast, such cells are not developed by the non-parasitic least brook lamprey Lampetra aepyptera, which has been separated from its ancestor for >2 million years, nor by the freshwater parasitic species of the genus Ichthyomyzon. The length of time that a non-parasitic species or landlocked parasitic form or species has spent in fresh water is thus considered the overriding factor determining whether chloride cells are developed by those lampreys. [ABSTRACT FROM AUTHOR]

To understand the function of myoglobin (Mb) and cytoglobin (Cygb) in channel catfish Ictalurus punctatus in response to heat stress, mb and cygb genes were identified and characterized in this study. These genes were widely expressed in all the tested tissues, but strong tissue preferences were observed, with the mb gene being expressed most highly in the heart, cygb1 most highly expressed in the intestine and cygb2 most highly expressed in the brain. After heat-stress challenge, mb and cygb genes were up-regulated in almost all tested tissues. In general, such up-regulation was more dramatic in the tolerant group than in the intolerant group, suggesting that higher expression of mb and cygb genes contributed to greater tolerance of I. punctatus to heat stress. [ABSTRACT FROM AUTHOR]