Rapid vertebrate speciation via isolation, bottlenecks, and drift.

Speciation is often driven by selective processes like those associated with viability, mate choice, or local adaptation, and "speciation genes" have been identified in many eukaryotic lineages. In contrast, neutral processes are rarely considered as the primary drivers of speciation, especially over short evolutionary timeframes. Here, we describe a rapid vertebrate speciation event driven primarily by genetic drift. The White Sands pupfish (Cyprinodon tularosa) is endemic to New Mexico's Tularosa Basin where the species is currently managed as two Evolutionarily significant units (ESUs) and is of international conservation concern (Endangered). Whole-genome resequencing data from each ESU showed remarkably high and uniform levels of differentiation across the entire genome (global FST ≈ 0.40). Despite inhabiting ecologically dissimilar springs and streams, our whole-genome analysis revealed no discrete islands of divergence indicative of strong selection, even when we focused on an array of candidate genes. Demographic modeling of the joint allele frequency spectrum indicates the two ESUs split only ~4 to 5 kya and that both ESUs have undergone major bottlenecks within the last 2.5 millennia. Our results indicate the genome-wide disparities between the two ESUs are not driven by divergent selection but by neutral drift due to small population sizes, geographic isolation, and repeated bottlenecks. While rapid speciation is often driven by natural or sexual selection, here we show that isolation and drift have led to speciation within a few thousand generations. We discuss these evolutionary insights in light of the conservation management challenges they pose.

A vertebrate adaptive radiation is assembled from an ancient and disjunct spatiotemporal landscape.

To investigate the origins and stages of vertebrate adaptive radiation, we reconstructed the spatial and temporal histories of adaptive alleles underlying major phenotypic axes of diversification from the genomes of 202 Caribbean pupfishes. On a single Bahamian island, ancient standing variation from disjunct geographic sources was reassembled into new combinations under strong directional selection for adaptation to the novel trophic niches of scale-eating and molluscivory. We found evidence for two longstanding hypotheses of adaptive radiation: hybrid swarm origins and temporal stages of adaptation. Using a combination of population genomics, transcriptomics, and genome-wide association mapping, we demonstrate that this microendemic adaptive radiation of novel trophic specialists on San Salvador Island, Bahamas experienced twice as much adaptive introgression as generalist populations on neighboring islands and that adaptive divergence occurred in stages. First, standing regulatory variation in genes associated with feeding behavior (prlh, cfap20, and rmi1) were swept to fixation by selection, then standing regulatory variation in genes associated with craniofacial and muscular development (itga5, ext1, cyp26b1, and galr2) and finally the only de novo nonsynonymous substitution in an osteogenic transcription factor and oncogene (twist1) swept to fixation most recently. Our results demonstrate how ancient alleles maintained in distinct environmental refugia can be assembled into new adaptive combinations and provide a framework for reconstructing the spatiotemporal landscape of adaptation and speciation.

Molecular phylogeny of the Austrolebias/ adloffi/ group (Cyprinodontiformes, Rivulidae), with description of two new endangered and highly endemic species of annual killifishes from the Laguna dos Patos system, southern Brazil.

The Austrolebias adloffi species group encompasses a diverse lineage of annual killifishes that occurs along the Laguna dos Patos/Lagoa Mirim system, in both Brazilian and Uruguayan territories. We herein employ an integrative taxonomy approach to describe two new species of the group, inferring their phylogenetic relationships and evaluating their conservation status. Austrolebias cheffei sp. nov. and Austrolebias lourenciano sp. nov. are herein described from the western portion of the Laguna dos Patos system. Austrolebias cheffei is distinguished from the remaining species of the A. adloffi species group by presenting a yellowish green or yellowish blue dorsal fin, with wide black to dark brown bars extending from the base to the middle portion of the dorsal and anal fins in the males. Austrolebias lourenciano is distinguished from the remaining species of the A. adloffi species group by presenting a yellowish green dorsal fin, with light yellow or light bluish bars forming small triangles, interspersed with small dark brown rows of blotches in the dorsal fin base, and greenish blue anal fin, sometimes with lighter elongated yellowish iridescent blotches, limited to the basal region. According to mitochondrial cytb sequences, both species are reciprocally monophyletic relative to other species of the A. adloffi species group, and present positive barcoding gap values. Interestingly, both new species form a grade that is closely related to Austrolebias aff. minuano 1, an undescribed species that occurs at the opposite margin of the Laguna dos Patos. Among the other evaluated species, A. bagual, A. aff. minuano 1, A. nigrofasciatus, A. pelotapes, A. pongondo, A. arachan, and A. viarius also revealed to be reciprocally monophyletic, whereas A. minuano and A. adloffi revealed to be paraphyletic in regard to A. charrua and A. aff. minuano 2, respectively, and A. nachtigalli is subdivided in two clades, one of which including A. reicherti, which points to the need of a taxonomic review of the group. In addition, we discussed the conservation status of the new species, corrected the type locality of A. pongondo, and provided a dichotomous identification key of the A. adloffi species group.

The influence of hypoxia on the cardiac transcriptomes of two estuarine species - C. variegatus and F. grandis.

Increased nutrient loading has led to eutrophication of coastal shelf waters which has resulted in increased prevalence of persistent hypoxic zones - areas in which the dissolved oxygen content of the water drops below 2 mg/L. The northern Gulf of Mexico, fed primarily by the Mississippi River watershed, undergoes annual establishment of one of the largest hypoxic zones in the world. Exposure to hypoxia can induce physiological impacts in fish cardiac systems that include bradycardia, changes in stroke volume, and altered cardiovascular vessel development. While these impacts have been addressed at the functional level, there is little information regarding the molecular basis for these changes. This study used transcriptomic analysis techniques to interrogate the effects of hypoxia exposure on the developing cardiovascular system in newly hatched larvae of two estuarine species that occupy the same ecological niche - the sheepshead minnow (Cyprinodon variegatus) and the Gulf killifish (Fundulus grandis). Results suggest that while differential gene expression is largely distinct between the two species, downstream impacts on pathways and functional responses such as reduced cardiac hypertrophy, modulation of blood pressure, and increased incidence of apoptosis appear to be conserved. Further, differences in the magnitude of these conserved responses may suggest that the length of embryonic development could impart a level of resiliency to hypoxic perturbation in early life stage fish.

Genomic fingerprints of palaeogeographic history: The tempo and mode of rift tectonics across tropical Africa has shaped the diversification of the killifish genus Nothobranchius (Teleostei: Cyprinodontiformes).

This paper reports a phylogeny of the African killifishes (Genus Nothobranchius, Order Cyprinodontiformes) informed by five genetic markers (three nuclear, two mitochondrial) of 80 taxa (seven undescribed and 73 of the 92 recognized species). These short-lived annual fishes occupy seasonally wet habitats in central and eastern Africa, and their distribution coincides largely with the East African Rift System (EARS). The fossil dates of sister clades used to constrain a chronometric tree of all sampled Nothobranchius recovered the origin of the genus at ~13.27 Mya. It was followed by the radiations of six principal clades through the Neogene. An ancestral area estimation tested competing biogeographical hypotheses to constrain the ancestral origin of the genus to the Nilo-Sudan Ecoregion, which seeded a mid-Miocene dispersal event into the Coastal ecoregion, followed closely (~10 Mya) by dispersals southward across the Mozambique coastal plain into the Limpopo Ecoregion. Extending westwards across the Tanzanian plateau, a pulse of radiations through the Pliocene were associated with dispersals and fragmentation of wetlands across the Kalahari and Uganda Ecoregions. We interpret this congruence of drainage rearrangements with dispersals and cladogenic events of Nothobranchius to reflect congruent responses to recurrent uplift and rifting. The coevolution of these freshwater fishes and wetlands is attributed to ultimate control by tectonics, as the EARS extended southwards during the Neogene. Geobiological consilience of the combined evidence supports a tectonic hypothesis for the evolution of Nothobranchius.

Differences in Cell Proliferation and Craniofacial Phenotype of Closely Related Species in the Pupfish Genus Cyprinodon.

Understanding the genetic basis for phenotypic differences is fundamental to the study of macroevolutionary patterns of biological diversity. While technological advances in DNA sequencing have made researching genetic variation in wild taxa routine, fully understanding how these variants affect phenotype requires taking the next step to investigate how genetic changes alter cell and tissue interactions that ultimately produce phenotypes. In this article, we investigate a role for cell proliferation as a developmental source of craniofacial diversity in a radiation of 3 species of Cyprinodon from San Salvador Island, Bahamas. Patterns of cell proliferation in the heads of hatching-age fish differ among species of Cyprinodon, and correlate with differences in allometric growth rate among the jaws of 3 distinct species. Regional patterns of cell proliferation in the head are complex, resulting in an unintuitive result in which lower levels of cell proliferation in the posterior head region are associated with the development of relatively larger jaws in one species. We combine these data with previously published morphological and genomic data to show how studying the mechanisms generating phenotype at the cellular and tissue levels of biological organization can help mechanistically link genomic studies with classic morphological studies.

Evidences for genetic differentiation within the highly endemic and endangered annual fish Austrolebias nigrofasciatus (Cyprinodontiformes: Rivulidae).

Samples of Austrolebias nigrofasciatus (n = 103), an endangered species of annual fish endemic to a small area of the Patos-Mirim lagoon system encompassing the São Gonçalo Channel lowlands, were collected from eight isolated temporary ponds, four located at the known distribution range of the species and four located along the Piratini River lowlands, where morphologically different individuals were found. In the laboratory, fragments of the mitochondrial cytochrome c oxidase I (coI), cytochrome b (cytb) and nuclear rhodopsin (rho) genes were amplified, purified and sequenced for 100, 99 and 58 of these individuals, respectively. Samples were further analysed using phylogenetic and phylogeographic methods to evaluate the patterns of genetic diversity and differentiation presented within and between populations, while assessing their evolutionary history, in order to guide the application of further conservation strategies. We found that the four new populations from the Piratini River lowlands encompass a different lineage of A. nigrofasciatus that diverged from that encountered in the São Gonçalo Channel at approximately 0.165 M years before present, during a population expansion and did not yet attain reciprocal monophyly. This divergence was associated with a glacial event that was preceded by an interglacial period putatively associated with the dispersal. Moreover, significant levels of genetic differentiation and a high number of exclusive haplotypes could be encountered even in micro-geographical scales, as in the comparisons between populations located within the same major lineage, indicating each of them may encompass independent management units. Conservation actions are certainly urgent, especially in the face of signs of a recent bottleneck.

Relaxed Selection Limits Lifespan by Increasing Mutation Load.

To uncover the selective forces shaping life-history trait evolution across species, we investigate the genomic basis underlying adaptations to seasonal habitat desiccation in African killifishes, identifying the genetic variants associated with positive and relaxed purifying selection in 45 killifish species and 231 wild individuals distributed throughout sub-Saharan Africa. In annual species, genetic drift led to the expansion of nuclear and mitochondrial genomes and caused the accumulation of deleterious genetic variants in key life-history modulating genes such as mtor, insr, ampk, foxo3, and polg. Relaxation of purifying selection is also significantly associated with mitochondrial function and aging in human populations. We find that relaxation of purifying selection prominently shapes genomes and is a prime candidate force molding the evolution of lifespan and the distribution of genetic variants associated with late-onset diseases in different species. VIDEO ABSTRACT.

Hybrid gene misregulation in multiple developing tissues within a recent adaptive radiation of Cyprinodon pupfishes.

Genetic incompatibilities constitute the final stages of reproductive isolation and speciation, but little is known about incompatibilities that occur within recent adaptive radiations among closely related diverging populations. Crossing divergent species to form hybrids can break up coadapted variation, resulting in genetic incompatibilities within developmental networks shaping divergent adaptive traits. We crossed two closely related sympatric Cyprinodon pupfish species-a dietary generalist and a specialized molluscivore-and measured expression levels in their F1 hybrids to identify regulatory variation underlying the novel craniofacial morphology found in this recent microendemic adaptive radiation. We extracted mRNA from eight day old whole-larvae tissue and from craniofacial tissues dissected from 17-20 day old larvae to compare gene expression between a total of seven F1 hybrids and 24 individuals from parental species populations. We found 3.9% of genes differentially expressed between generalists and molluscivores in whole-larvae tissues and 0.6% of genes differentially expressed in craniofacial tissue. We found that 2.1% of genes were misregulated in whole-larvae hybrids whereas 19.1% of genes were misregulated in hybrid craniofacial tissues, after correcting for sequencing biases. We also measured allele specific expression across 15,429 heterozygous sites to identify putative compensatory regulatory mechanisms underlying differential expression between generalists and molluscivores. Together, our results highlight the importance of considering misregulation as an early indicator of genetic incompatibilities in the context of rapidly diverging adaptive radiations and suggests that compensatory regulatory divergence drives hybrid gene misregulation in developing tissues that give rise to novel craniofacial traits.

Synchronic historical patterns of species diversification in seasonal aplocheiloid killifishes of the semi-arid Brazilian Caatinga.

The Caatinga is the largest nucleus of seasonally dry tropical forests in South America, but little is known about the evolutionary history and biogeography of endemic organisms. Evolutionary diversification and distribution of terrestrial vertebrates endemic to the Caatinga have been explained by palaeogeographical Neogene episodes, mostly related to changes in the course of the São Francisco River, the largest river in the region. Our objective is to estimate the timing of divergence of two endemic groups of short-lived seasonal killifishes inhabiting all ecoregions of the Caatinga, testing the occurrence of synchronic events of spatial diversification in light of available data on regional palaeogeography. We performed independent time-calibrated phylogenetic molecular analyses for two clades of sympatric and geographically widespread seasonal killifishes endemic to the Caatinga, the Hypsolebias antenori group and the Cynolebias alpha-clade. Our results consistently indicate that species diversification took place synchronically in both groups, as well as it is contemporary to diversification of other organisms adapted to life in the semi-arid Caatinga, including lizards and small mammals. Both groups originated during the Miocene, but species diversification started between the Late Miocene and Early Pliocene, when global cooling probably favoured the expansion of semi-arid areas. Synchronic diversification patterns found are chronologically related to Tertiary palaeogeographical reorganizations associated to continental drift and to Quaternary climatic changes, corroborating the recent proposal that South American biodiversity has been continuously shaped between the Late Paleogene and Pleistocene.

Molecular phylogeny and timing of diversification in South American Cynolebiini seasonal killifishes.

The rich biological diversity of South America has motivated a series of studies associating evolution of endemic taxa with the dramatic geologic and climatic changes that occurred during the Cainozoic. The organism here studied is the killifish tribe Cynolebiini, a group of seasonal fishes uniquely inhabiting temporary pools formed during the rainy seasons. The Cynolebiini are found in open vegetation areas inserted in the main tropical and subtropical South American phytogeographical regions east of the Andes. Here, we present the first molecular phylogeny sampling all the eight genera of the Cynolebiini, using fragments of two mitochondrial and four nuclear genes for 35 species of Cynolebiini plus 19 species as outgroups. The dataset, 4448bp, was analysed under Bayesian and maximum likelihood approaches, providing a relatively well solved tree, which retrieves high support values for the Cynolebiini and most included clades. The resulting tree was used to estimate the time of divergence in included lineages using two cyprinodontiform fossils to calibrate the tree. We further investigated historical biogeography through the likelihood-based DEC model. Our estimates indicate that divergence between the clades comprising New World and Old World aplocheiloids occurred during the Eocene, about 50Mya, much more recent than the Gondwanan fragmentation scenario assumed in previous studies. This estimation is nearly synchronous to estimated splits involving other South American and African vertebrate clades, which have been explained by transoceanic dispersal through an ancient Atlantic island chain during the Palaeogene. We estimate that Cynolebiini split from its sister group Cynopoecilini in the Oligocene, about 25Mya and that Cynolebiini started to diversify giving origin to the present genera during the Miocene, about 20-14Mya. The Cynolebiini had an ancestral origin in the Atlantic Forest and probably were not present in the open vegetation formations of central and northeastern South America until the Middle Miocene, when expansion of dry open vegetation was favoured by cool temperatures and strike seasonality. Initial splitting between the genera Cynolebias and Simpsonichthys during the Miocene (about 14Mya) is attributed to the uplift of the Central Brazilian Plateau.

The Cyprinodon variegatus genome reveals gene expression changes underlying differences in skull morphology among closely related species.

BACKGROUND: Understanding the genetic and developmental origins of phenotypic novelty is central to the study of biological diversity. In this study we identify modifications to the expression of genes at four developmental stages that may underlie jaw morphological differences among three closely related species of pupfish (genus Cyprinodon) from San Salvador Island, Bahamas. Pupfishes on San Salvador Island are trophically differentiated and include two endemic species that have evolved jaw morphologies unlike that of any other species in the genus Cyprinodon. RESULTS: We find that gene expression differs significantly across recently diverged species of pupfish. Genes such as Bmp4 and calmodulin, previously implicated in jaw diversification in African cichlid fishes and Galapagos finches, were not found to be differentially expressed among species of pupfish. Instead we find multiple growth factors and cytokine/chemokine genes to be differentially expressed among these pupfish taxa. These include both genes and pathways known to affect craniofacial development, such as Wnt signaling, as well as novel genes and pathways not previously implicated in craniofacial development. These data highlight both shared and potentially unique sources of jaw diversity in pupfish and those identified in other evolutionary model systems such as Galapagos finches and African cichlids. CONCLUSIONS: We identify modifications to the expression of genes involved in Wnt signaling, Igf signaling, and the inflammation response as promising avenues for future research. Our project provides insight into the magnitude of gene expression changes contributing to the evolution of morphological novelties, such as jaw structure, in recently diverged pupfish species.

Parallel evolution of genes controlling mitonuclear balance in short-lived annual fishes.

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.

Diversity and status of Mexican killifishes.

The name killifish refers to the oviparous secondary freshwater fishes in the order Cyprinodontiformes. Killifishes are abundant in Mexico and are represented by four extant families, Rivulidae, Profundulidae, Fundulidae and Cyprinodontidae, comprising > 50 species in a wide variety of habitats. This paper reviews the current classification of the killifishes of Mexico, as well as aspects of their distribution, biology, ecology and current population conservation status.

The genetic architecture of novel trophic specialists: larger effect sizes are associated with exceptional oral jaw diversification in a pupfish adaptive radiation.

The genetic architecture of adaptation is fundamental to understanding the mechanisms and constraints governing diversification. However, most case studies focus on loss of complex traits or parallel speciation in similar environments. It is still unclear how the genetic architecture of these local adaptive processes compares to the architecture of evolutionary transitions contributing to morphological and ecological novelty. Here, we identify quantitative trait loci (QTL) between two trophic specialists in an excellent case study for examining the origins of ecological novelty: a sympatric radiation of pupfishes endemic to San Salvador Island, Bahamas, containing a large-jawed scale-eater and a short-jawed molluscivore with a skeletal nasal protrusion. These specialized niches and trophic traits are unique among over 2000 related species. Measurements of the fitness landscape on San Salvador demonstrate multiple fitness peaks and a larger fitness valley isolating the scale-eater from the putative ancestral intermediate phenotype of the generalist, suggesting that more large-effect QTL should contribute to its unique phenotype. We evaluated this prediction using an F2 intercross between these specialists. We present the first linkage map for pupfishes and detect significant QTL for sex and eight skeletal traits. Large-effect QTL contributed more to enlarged scale-eater jaws than the molluscivore nasal protrusion, consistent with predictions from the adaptive landscape. The microevolutionary genetic architecture of large-effect QTL for oral jaws parallels the exceptional diversification rates of oral jaws within the San Salvador radiation observed over macroevolutionary timescales and may have facilitated exceptional trophic novelty in this system.

Inferring Evolution of Habitat Usage and Body Size in Endangered, Seasonal Cynopoeciline Killifishes from the South American Atlantic Forest through an Integrative Approach (Cyprinodontiformes: Rivulidae).

Cynopoecilines comprise a diversified clade of small killifishes occurring in the Atlantic Forest, one of the most endangered biodiversity hotspots in the world. They are found in temporary pools of savannah-like and dense forest habitats, and most of them are highly threatened with extinction if not already extinct. The greatest gap in our knowledge of cynopoecilines stems from the absence of an integrative approach incorporating molecular phylogenetic data of species still found in their habitats with phylogenetic data taken from the rare and possibly extinct species without accessible molecular information. An integrative analysis combining 115 morphological characters with a multigene dataset of 2,108 bp comprising three nuclear loci (GLYT1, ENC1, Rho), provided a robust phylogeny of cynopoeciline killifishes, which was herein used to attain an accurate phylogenetic placement of nearly extinct species. The analysis indicates that the most recent common ancestor of the Cynopoecilini lived in open vegetation habitats of the Atlantic Forest of eastern Brazil and was a miniature species, reaching between 25 and 28 mm of standard length. The rare cases of cynopoecilines specialized in inhabiting pools within dense forests are interpreted as derived from four independent evolutionary events. Shifts in habitat usage and biogeographic patterns are tentatively associated to Cenozoic paleogeographic events, but the evolutionary history of cynopoecilines may be partially lost by a combination of poor past sampling and recent habitat decline. A sharp evolutionary shift directed to increased body size in a clade encompassing the genera Campellolebias and Cynopoecilus may be related to a parallel acquisition of an internally-fertilizing reproductive strategy, unique among aplocheiloid killifishes. This study reinforces the importance of adding morphological information to molecular databases as a tool to understand the biological complexity of organisms under intense pressure from loss of habitat.

The complete mitochondrial genome of the Warm Springs pupfish, Cyprinodon nevadensis pectoralis.

In this article we report the complete mitochondrial genome of the Warm Springs pupfish, Cyprinodon nevadensis pectoralis. The genomic DNA of a single female individual was extracted and sequenced on the Illumina HiSeq2000 platform. It contains 16,499 bp and a total of 37 genes, divided into 22 tRNA genes, 2 rRNA genes and 13 protein-coding genes. It exhibits 94% sequence similarity with the other published mitochondrion in its genus, C. rubrofluviatilis. A Tamura-Nei maximum-likelihood tree constructed from mitochondrial sequences shows expected phylogenetic relationships between C. nevadensis and sister taxa.

The complete mitochondrial genome of the killifish Orestias sp. (Cyprinodontiformes, Cyprinodontidae) from the high Andean range.

The killifish genus Orestias is endemic to freshwater ecosystems in the High Andes of Peru, Bolivia and Chile. Phylogenetic and phylogeographic studies with partial mitochondrial genes have failed to resolve relationship among species, needing more comprehensive approaches. In this study, we described the complete mitochondrial genome of Orestias sp. from Lirima, northern Chile, with the aim to provide useful data for phylogenetic purposes and species delimitation. The mitochondrial genome was assembled with 2.6 million of reads obtained through an Ion Torrent (chip 318) sequencer. The circular sequence of 16,617 bp showed the following nucleotide composition: A, 26.7%, C, 27.1%, G, 17.0%, and T, 29.2%. Gene composition and structure were similar to other fish sequences available, and comprised 13 protein-coding genes, 12S and 16S rRNA, 22 tRNA genes, and a control region.

The complete mitochondrial genome of the endemic and threatened killifish Orestias ascotanensis Parenti, 1984 (Cyprinodontiformes, Cyprinodontidae) from the High Andes.

The killifish Orestias ascotanensis is endemic to the small isolated springs of Ascotán salt pan in the Central High Andes, Chile. Due to small populations, mining activity, and increasing aridity, this species is catalogued in danger of extinction. The complete mitochondrial genome of O. ascotanesis was assembled with an Ion Torrent sequencer (chip 318) that produced 2.61 million of reads. The 16 617 bp of the entire genome consisted of 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes, and a control region, showing that the gene composition and arrangement match to that reported for most fishes.