Genomes of the Orestias pupfish from the Andean Altiplano shed light on their evolutionary history and phylogenetic relationships within Cyprinodontiformes.

BACKGROUND: To unravel the evolutionary history of a complex group, a comprehensive reconstruction of its phylogenetic relationships is crucial. This requires meticulous taxon sampling and careful consideration of multiple characters to ensure a complete and accurate reconstruction. The phylogenetic position of the Orestias genus has been estimated partly on unavailable or incomplete information. As a consequence, it was assigned to the family Cyprindontidae, relating this Andean fish to other geographically distant genera distributed in the Mediterranean, Middle East and North and Central America. In this study, using complete genome sequencing, we aim to clarify the phylogenetic position of Orestias within the Cyprinodontiformes order. RESULTS: We sequenced the genome of three Orestias species from the Andean Altiplano. Our analysis revealed that the small genome size in this genus (~ 0.7 Gb) was caused by a contraction in transposable element (TE) content, particularly in DNA elements and short interspersed nuclear elements (SINEs). Using predicted gene sequences, we generated a phylogenetic tree of Cyprinodontiformes using 902 orthologs extracted from all 32 available genomes as well as three outgroup species. We complemented this analysis with a phylogenetic reconstruction and time calibration considering 12 molecular markers (eight nuclear and four mitochondrial genes) and a stratified taxon sampling to consider 198 species of nearly all families and genera of this order. Overall, our results show that phylogenetic closeness is directly related to geographical distance. Importantly, we found that Orestias is not part of the Cyprinodontidae family, and that it is more closely related to the South American fish fauna, being the Fluviphylacidae the closest sister group. CONCLUSIONS: The evolutionary history of the Orestias genus is linked to the South American ichthyofauna and it should no longer be considered a member of the Cyprinodontidae family. Instead, we submit that Orestias belongs to the Orestiidae family, as suggested by Freyhof et al. (2017), and that it is the sister group of the Fluviphylacidae family, distributed in the Amazonian and Orinoco basins. These two groups likely diverged during the Late Eocene concomitant with hydrogeological changes in the South American landscape.

Genomic data support the taxonomic validity of Middle American livebearers Poeciliopsis gracilis and Poeciliopsis pleurospilus (Cyprinodontiformes: Poeciliidae).

Poeciliopsis (Cyprinodontiformes: Poeciliidae) is a genus comprised of 25 species of freshwater fishes. Several well-known taxonomic uncertainties exist within the genus, especially in relation to the taxonomic status of Poeciliopsis pleurospilus and P. gracilis. However, to date, no studies have been conducted to specifically address the taxonomic status of these two species. The goal of this study was to examine the taxonomic validity of P. pleurospilus and P. gracilis using genomic data (ddRADseq) in phylogenetic, population genetic, and species delimitation frameworks. Multiple analyses support the recognition of both taxa as distinct species and also permits us to revise their respective distributions. A species delimitation analysis indicates that P. pleurospilus and P. gracilis are distinct species, each of which consists of two distinct lineages that are geographically structured. Phylogenetic and population genetic analyses provide clear evidence that individuals of P. gracilis are distributed north and west of the Isthmus of Tehuantepec in both Pacific and Atlantic river systems in Mexico, whereas individuals of P. pleurospilus are distributed in both Atlantic and Pacific river systems south and east of the Isthmus of Tehuantepec, from southern Mexico to Honduras.

emNothobranchius/em emnikiforovi/em, a new species of seasonal killifish from the lower Matandu drainage in south-eastern coastal Tanzania (Cyprinodontiformes: Nothobranchiidae).

Nothobranchius nikiforovi, a new species known from seasonal habitats in the lower Matandu drainage in south-eastern coastal Tanzania is described. It is distinguished from all other congeners, except N. eggersi, by males presenting two colour phenotypes: the blue phenotype having a bright iridescent light blue to blue-green body, with narrow red-brown scale margins creating irregular reticulated pattern, forming chevron-shaped crossbars on the posteroventral portion of body and light blue median fins with red-brown dotted pattern; the red phenotype has a dark red head, light blue dorsal and anal fins proximally and medially, dark red distally, with dark red stripes parallel to the fin rays, and a plain dark red caudal fin. Nothobranchius nikiforovi differs from N. eggersi by male colour pattern, the blue phenotypes having median fins with dark grey distal portion, some of the rays of dorsal and anal fins with white tips (vs. median fins with distinct slender white distal band), and the caudal fin lacking a spotted pattern (vs. dots arranged into irregular curved stripes); the red phenotype with golden stripe between the nape and dorsal-fin origin (vs. light-blue stripe), the dorsal and anal fins with a plain red distal portion and lacking a light distal band (vs. with distinct narrow white distal band), the pelvic fin lacking a distal band (vs. with distinct slender light blue to white distal band), and some morphometric differences. Phylogenetic analyses also support the genetic distinction of the new species from its closest known relative, N. eggersi, and confirm its position in the N. guentheri species group within the Adiniops subgenus.

Two new annual fishes (Cyprinodontiformes: Rivulidae) unexpectedly discovered in the highlands of southern Brazil.

Two new species of Austrolebias are described based on specimens collected from temporary pools located in natural grassland landscape within the Araucaria Forest domain at exceptionally high altitudes (~1000 meters a.s.l.). Austrolebias botocudo sp. n. and Austrolebias nubium sp. n. occur, respectively, in drainages of upper rio Apuaê-Inhandava (upper rio Uruguay basin) and upper rio Taquari-Antas (upper rio Jacuí, Laguna dos Patos basin), in the Meridional Plateau of southern Brazil. Despite an intensive survey conducted in the area, only two populations of each species were recorded. Both new species occurs at altitudes that are among the higher recorded for species of the genus, and both are assigned to the subgenus Acrolebias. The new species described herein are easily distinguished for its congeners by the colour pattern of males, by presence of melanophores irregularly distributed in different parts of the body, contact organs cover the body and anal fins, position of fins related with vertebrae, by preopercular and mandibular series of neuromasts united, by a series of morphometric features and by larger maximum standard length. Austrolebias botocudo and A. nubium are distinguished from each other by colour pattern of males, length of contact organs in the flank and number of contact organs in scales of lateral line, dorsal profile of head, number of neuromasts in the preopercular + mandibular series, body depth in females, and by basihyal cartilage length. Additionally, we discuss the conservation status of the new species, and provided an identification key for the species of the subgenus Acrolebias.

Genetic differentiation among populations of the blackfin goodea Goodea atripinnis (Cyprinodontiformes: Goodeidae): implications for its evolutionary history.

Central Mexico is characterized by a complex topography that is the result of historic and contemporary tectonic and climatic factors. These events have influenced the evolutionary history of numerous freshwater fishes in the region. Nonetheless, recent studies have shown that life-history traits and ecological characteristics of species may influence dispersal capabilities and the degree of genetic connectivity. Goodea (Cyprinodontiformes: Goodeidae) is one of the most widely distributed and environmentally tolerant genera of goodeids. In this study, the authors analysed variation in the mitochondrial cytochrome b gene to evaluate the phylogeographic relationships, genetic structure, genetic diversity and demographic history of Goodea from across its distribution range. They found low genetic differentiation and identified shared haplotypes among several regions. Geographic segregation was found in samples southwest and northeast of the Lower Lerma region, with some internal isolated groups showing phylogeographic differentiation and unique haplotypes. The AMOVA best explained genetic structure when grouped by haplogroups rather than when grouped by recognized biogeographic regions. Several regions showed null genetic diversity, raising the possibility of dispersal mediated by humans. Finally, Bayesian Skyline Plot analysis showed a population expansion for the Southwest haplogroup, except for the Armería population and sub-group II of the Northeast haplogroup. All this suggests a recent colonization of Goodea atripinnis throughout some of the biogeographic regions currently inhabited by this species.

Microanalysis of scale morphology in killifish, Aphaniops hormuzensis inhabiting ecologically diverse environments (Cyprinodontiformes; Aphaniidae).

Ecologically, Aphaniops hormuzensis populations occupying diverse environments in southern Iran and showed substantial morphological variation across its range. In this study, three different habitats were chosen and identified as group A (sulfur rich spring), group B (salty River), and group C (urban canal), and scale microstructures and scale shape was inspected among three groups. The SEM imaging indicated that lepidonts were more developed on the scale of larger (group C, SL > 30 mm) than younger fish (group A, SL < 30 mm). We tentatively concluded that lepidonts are formed during scale development so that in the earlier stages of fish development, scales probably do not have lepidont. Also, the size and shape of lepidonts vary between the populations, and their shape and orientation within a given species affected by the fish size rather than the local ecological conditions of habitats. The number of radii was relatively higher in group C (12.58 ± 0.66 in males and 13.00 ± 1.89 in females). Similar to what is mentioned before in the case of lepidont, the inter-population variation in the number of radii seems to be influenced by fish size. Group A (SL < 30 mm) had a relatively large focus diameter (0.14 ± 0.02 in males and 0.36 ± 0.44 in females). It is assumed that the focus size is large at the earlier stage of fish development, but later during the fish growth, and by increasing the scale size, the focus diameter is reduced. In conclusion and agreement with previous studies, scale surface morphology and microstructure could be employed to discriminate certain populations, while scale size and J-indices could not help in distinguishing the populations. It is also proposed that the characteristics of scale morphology in the population-level are influenced by the combination of genetic, and environmental factors, as well as fish development.

Description of two new miniature species of Hylopanchax Poll & Lambert, 1965 (Cyprinodontiformes: Procatopodidae), from northeastern Gabon, with an updated diagnosis of the genus based on morphology, colouration and osteology.

Two new species of the lampeye genus Hylopanchax are described from the Ivindo River basin in the Ogowe River drainage. Hylopanchax multisquamatus, new species, and Hylopanchax thysi, new species, differ from congeners by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Hylopanchax multisquamatus is distinguished from congeners by the number of scales on the mid-longitudinal series (27-30 vs. 19-26, respectively) and by the relative anterior/posterior flank scale depth ratio (140%-150% vs. 170%-220%). Hylopanchax thysi is distinguished from all other congeners, except Hylopanchax paucisquamatus, by the presence of vertebrae (30 vs. 31-33) and is further distinguished from H. multisquamatus by the presence of a deeper caudal peduncle and much larger anterior flank scales. It is distinguished from H. paucisquamatus by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Osteological data of Hylopanchax are presented for the first time, and an updated diagnosis based on external morphology, colouration pattern and osteology is provided. An osteological comparison with closely related species belonging to the genera Procatopus, Hypsopanchax and "Hypsopanchax" is presented. (a) A truncate and slightly downward-directed anterior process of the angulo-articular and (b) a guitar-shaped lachrymal with both its anterior and posterior margins sharply curved are here considered as diagnostic features of Hylopanchax.

First record sheds light on the distribution of the cyprinodontiform genus Jenynsia (Günther, 1866) in the High Andean Plateau.

This is the first record of the genus Jenynsia in the High Andean Plateau (HAP). It has been found at elevations between 3400 and 3900 m in three endorreheic systems: Salar Antofalla, Antofagasta de la Sierra and El Peñón, northwestern Argentina, South America. This finding increases the number of known HAP fish genera to five. Furthermore, in contrast to the old Andean species-rich genus Orestias, the presence of Jenynsia obscura populations in young high-altitude, non-marine saline wetlands reported here supports a recent dispersal into the HAP.

A Pleistocene freshwater ichthyofaunal assemblage from central Argentina: What kind of fishes lived in the Pampean lagoons before the extinction of the megafauna?

This study contributes to the knowledge of continental fishes recovered from sedimentary successions corresponding to the Bonaerean Stage/Age (late mid-Pleistocene) in the locality of Centinela del Mar, General Alvarado County, Buenos Aires province, Argentina. At this site we describe fossil fishes from a palaeolagoon, including Corydoras sp., Pimelodella sp., Rhamdia sp., Oligosarcus sp., small undetermined characids, Jenynsia sp. and Odontesthes sp. The recovered ichthyofaunal assemblage comprises at least seven taxa of Paranaean lineage. The taxonomic composition of the palaeoichthyofauna is quite comparable to that presently found in Bonaerean Watercourses of the Atlantic Drainage ecoregion. This suggests that local ichthyofaunal communities have remained relatively stable since the late mid-Pleistocene.

Beyond Pairwise Interactions: Multispecies Character Displacement in Mexican Freshwater Fish Communities.

Competition has long been recognized as a central force in shaping evolution, particularly through character displacement. Yet research on character displacement is biased, as it has focused almost exclusively on pairs of interacting species while ignoring multispecies interactions. Communities are seldom so simple that only pairs of species interact, and it is not clear whether inferences from pairwise interactions are sufficient to explain patterns of phenotypes in nature. Here, we test for character displacement in a natural system of freshwater fishes in western Mexico that contains up to four congeneric species of the genus Poeciliopsis. We analyzed body shape differences between populations with different numbers of competitors while accounting for confounding environmental variables. Surprisingly, we found evidence for convergent character displacement in populations of P. prolifica, P. viriosa, and P. latidens. We also found that the convergence in body shape was not consistently in the same direction, meaning that when three or more competitors co-occurred, we did not find more extreme body shapes compared with when there were only two competitors. Instead, when three or more competitors co-occurred, body shape was intermediate between the shape found with a pair of species and the shape found with no competitor present. This intermediate shape suggests that evolution in multispecies communities likely occurs in response to several competitors rather than to simple pairwise interactions. Overall, our results suggest that competition among multiple species is more complex than simple pairwise competitive interactions.

DNA barcoding and species delimitation of the Old World tooth-carps, family Aphaniidae Hoedeman, 1949 (Teleostei: Cyprinodontiformes).

The fishes, which have currently named Aphanius Nardo, 1827 are the relict of the ancient ichthyofauna of the Tethys Sea. For a long time since 1827, the genus name has been subjected to revision by several researchers using mainly morphological features. Until recently, no comprehensive single- or multi-locus DNA barcoding study has been conducted on whole members of the family Aphaniidae. In the present study, by applying four conceptually different molecular species delimitation methods, including one distance-based method, one network-based and two topology-based methods, we examined a single-locus DNA barcode library (COI) diversity for the 268 sequences within the family Aphaniidae from the Old World (57 sequences are new in the present study and 211 sequences were retrieved from NCBI database). The molecular analyses revealed a clearer picture of intra-family relationships and allowed us to clarify the generic names, and also describe a new genus for the family Aphaniidae. Results supported distinction of three major clades related to three genera within this family: i) the first clade includes the A. mento group which are placed in a new genus, Paraphanius gen. nov., found in the Orontes (= Asi) and Tigris-Euphrates River drainage, the Levant in coastal waters and the Dead Sea basin, western Jordan, and in southern Turkey in the Mediterranean basins as well as in central Turkey. This clade positioned at the base of the phylogenetic tree, (ii) the second clade contains the A. dispar-like brackish water tooth-carps which are transferred to the genus Aphaniops Hoedeman, 1951 (type species, Lebias dispar), distributed in the coastal waters around the Red Sea and the Persian Gulf basins; and (iii) the third clade, the genus Aphanius Nardo, 1827 (type species Aphanius nanus = A. fasciatus) contains all the inland and inland-related tooth-carps, which are mainly distributed in the inland waters in Turkey and Iran and also in the inland-related drainages around the Mediterranean basin.

A new livebearing fish of the genus Limia (Cyprinodontiformes: Poeciliidae) from Lake Miragoane, Haiti.

Limia islai, a new species of livebearing fish, is described from Lake Miragoane in south-western Haiti on Hispaniola. The new species has a conspicuous barred pattern consisting of several (4-12) black bars along the body, ray 4p serrae of the gonopodium in males with 10 segments and origin of dorsal fin in females slightly behind the origin of the anal fin. Although the new species colour pattern is similar to that of the humpbacked limia Limia nigrofasciata Regan 1913, L. islai sp. nov. has exclusive morphological features, such as slender body, lack of hump anterior to dorsal fin in males and presence of specific features in the gonopodial suspensory, which allow an unambiguous diagnosis from L. nigrofasciata. L. islai further differs from L. nigrofasciata in reproductive behaviour since L. islai males rely on sneak copulations and gonopodial thrusting, whereas L. nigrofasciata display an elaborate courtship behaviour. The new species is also genetically distinct in both nuclear (Rh, Myh6) and mitochondrial (12S, ND2, D-loop, Cytb) genes from other species in the genus showing reciprocal monophyly. The description of this new Limia species from Lake Miragoane confirms this lake as an important centre of endemism for the genus, with a total of eight endemic species described so far.

Chromosomal Markers Are Useful to Species Identification in Rivulidae (Cyprinodontiformes, Aplocheiloidei), Including the Resolution of Taxonomic Uncertainties in a Vulnerable Species Complex.

Killifishes are a unique and diversified fish group composed of several annual species inhabiting ephemeral pools in tropical and subtropical regions. Moreover, many genera have probably undergone fast speciation with a high number of short-ranged species of controversial taxonomy. This is the case of the "Hypsolebias flavicaudatus" complex (Aplocheiloidei, Rivulidae) that includes nine recently described taxa of remarkable morphological similarity, endemic to Brazil. Considering the potential of cytotaxonomy of killifishes, as presently revised, we performed cytogenetic analyses in two sister species within this complex (H. flagellatus and H. janaubensis), including the first mapping of ribosomal genes in Hypsolebias. Despite sharing 48 chromosomes and similar distribution of heterochromatin and 5S rDNA, their karyotype formula probably differed as a result of pericentric inversions. In addition, H. flagellatus presented a single pair bearing 18S rDNA and GC-rich regions, while multiple GC-rich and 18S signals (up to 28 chromosomes) were detected in H. janaubensis. These results reinforce the dynamism of karyotype evolution in annual killifishes favored by population isolation and small effective size. Thus, cytogenetic variation seems to be closely associated with speciation in Aplocheiloidei, representing a useful tool for identifying similar species in Hypsolebias complex, which are vulnerable to extinction.

Are Extreme Anatomical Modifications Required for Fish to Move Effectively on Land? Comparative Anatomy of the Posterior Axial Skeleton in the Cyprinodontiformes.

Many teleost fishes with no apparent modifications for life on land are able to produce effective terrestrial locomotor behaviors, including a ballistic behavior called the "tail-flip" jump. Cyprinodontiformes (killifishes, Teleostei: Atherinomorpha) that live at the water's edge vary in morphology and inclination to emerge onto land. Do fish with an amphibious predisposition have extensive modification of the propulsive region of the body when compared to fully aquatic relatives? We quantified body shape and anatomy of the caudal peduncle and tail (the propulsive organ on land and in water) in 11 cyprinodontiform species and two outgroup taxa (Atherinomorpha). We hypothesized that amphibious species would have longer, "shallower" bodies (larger body fineness ratios), deeper (proportionally larger) caudal peduncles, and more robust bones in the tail fin (larger ossified area of the hypural/epural bones) to facilitate locomotor movements on land. We found no evidence of convergence in body shape or skeletal anatomy among species known to make voluntary sojourns onto land. In fact, deep-bodied species, shallow-bodied species, and species with intermediate morphologies all are able to emerge from the water and move on land. It is possible that there are as-yet-undocumented subtle soft-tissue (muscle, tendon, and ligament) modifications that enhance terrestrial locomotor performance in species known to spend large periods of time on land. However, it is also possible that extreme anatomical changes are not required for aquatic cyprinodontiform species to produce effective locomotor movements when they emerge out of the water and move across the land. Anat Rec, 2019. © 2019 American Association for Anatomy.

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.

Phylogeographic evidence that the distribution of cryptic euryhaline species in the Gambusia punctata species group in Cuba was shaped by the archipelago geological history.

The main drivers of diversification of freshwater fishes in Cuba are not yet well understood. For example, salt tolerance was thought as the main factor involved in the diversification of Gambusia punctata species group in this archipelago. However, evidence from a recent DNA barcoding survey suggested the presence of cryptic species and no correlation between species delimitation and level of salinity. In this study, we analyzed the cryptic diversification of G. punctata species group in Cuba, based on a comprehensive sampling of its distribution and including habitats with different salinity levels. We evaluated the patterns of molecular divergence of the samples by sequencing a set of mitochondrial DNA (mtDNA) regions and genotyping nine nuclear microsatellite loci. We also used cytochrome b gene (cytb) partial sequences and these microsatellite loci to analyze population structure inside putative species. Five mtDNA well-differentiated haplogroups were found, four of them also identified by the analysis of the microsatellite polymorphism which corresponds to two already recognized species, G. punctata, and G. rhizophorae, and three putative new species. The extent of hybrid zones between these groups is also described. In each group, populations inhabiting environments with contrasting salinity levels were identified, indicating a generalized trait not specific to G. rhizophorae. The geographic distribution of the groups suggested a strong association with major relict territories of the Cuban Archipelago that was periodically joined or split-up by changes in seawater levels and land uplifts. Salinity tolerance might have facilitated sporadic and long-distance oversea dispersal but did not prevent speciation in the Cuban archipelago.

Independent Origin of XY and ZW Sex Determination Mechanisms in Mosquitofish Sister Species.

Fish are known for the outstanding variety of their sex determination mechanisms and sex chromosome systems. The western (Gambusia affinis) and eastern mosquitofish (G. holbrooki) are sister species for which different sex determination mechanisms have been described: ZZ/ZW for G. affinis and XX/XY for G. holbrooki Here, we carried out restriction-site associated DNA (RAD-) and pool sequencing (Pool-seq) to characterize the sex chromosomes of both species. We found that the ZW chromosomes of G. affinis females and the XY chromosomes of G. holbrooki males correspond to different linkage groups, and thus evolved independently from separate autosomes. In interspecific hybrids, the Y chromosome is dominant over the W chromosome, and X is dominant over Z. In G. holbrooki, we identified a candidate region for the Y-linked melanic pigmentation locus, a rare male phenotype that constitutes a potentially sexually antagonistic trait and is associated with other such characteristics, e.g., large body size and aggressive behavior. We developed a SNP-based marker in the Y-linked allele of GIPC PDZ domain containing family member 1 (gipc1), which was linked to melanism in all tested G. holbrooki populations. This locus represents an example for a color locus that is located in close proximity to a putative sex determiner, and most likely substantially contributed to the evolution of the Y.

Profundulus chimalapensis, una nueva especie de pez ciprinodóntido (Cyprinodontiformes: Profundulidae) del Río Coatzacoalcos, México / Profundulus chimalapensis, a new species of cyprinodontid fish (Cyrpinodontiformes: Profundulidae) from the Coatzacoalcos River, Mexico

Introducción: El género Profundulusse considera endémico de la región Mesoamericana, desde el centro-sur del estado de Guerrero hasta la parte central de Honduras, habita principalmente en las cuencas superiores y cabeceras de los ríos de la vertiente Pacífica, con una menor diversidad en la Atlántica. Objetivo: En este trabajo, basado en la comparación morfológica, proponemos una nueva especie, Profundulus chimalapensis sp. nov., confinada a México. Métodos: Se recolectaron ejemplares en los tributarios de la cuenca superior del Río Coatzacoalcos y se depositaron en colecciones de referencia. Se tomaron datos morfológicos (conteos, mediciones y características esqueléticas) y se compararon con especies relacionadas. Resultados: La nueva especie se diferencia de sus congéneres por tener la siguiente combinación de caracteres: 12-15 radios en la aleta dorsal, 14-17 radios anales y 13-16 pectorales; banda de color oscuro en los costados; aleta anal con un margen distal claro; margen anterior y posterior del proceso alveolar del premaxilar cóncavo; procesos epióticos cortos y anchos; base de la aleta anal grande, su longitud igual o mayor a la del pedúnculo caudal. Conclusión: La descripción de esta nueva especie de Profundulus de la vertiente atlántica del Istmo de Tehuantepec, sugiere que esta área ha sido un centro de especiación para el género.

Introduction: The genus Profundulus is considered a Mesoamerican endemic fish which spreading occurs, from the center-south of the state of Guerrero, Mexico, to the central part of Honduras. They mainly inhabit the upper basins and headwaters of the rivers of the Pacific slope, with less diversity in the Atlantic. Objective: This paper, based on morphological comparison we propose a new species, Profundulus chimalapensis sp. nov., confined to Mexico. Methods: Specimens were collected in the tributaries of the upper basin of the Coatzacoalcos River and were deposited in scientific collections. Morphological data (counts, measurements and skeletal features) were taken and compared with related species. Results: The new species differs from its congeners by having the following combination of characters: 12-15 dorsal-fin rays, 14-17 anal- and 13-16 pectoral-fin rays; dark colored stripe on the flanks; anal fin with a clear distal margin; anterior and posterior margin of the alveolar process of the premaxilla concave; pair of short and wide epiotic processes; and large anal fin base, equal to or greater than length of caudal peduncle. Conclusion: The description of this new Profundulus species from Atlantic side of the Isthmus of Tehuantepec suggests that this area has been a center of speciation for the genus.

Transcriptome-Based SNP Discovery and Validation in the Hybrid Zone of the Neotropical Annual Fish Genus Austrolebias.

The genus Austrolebias (Cyprinodontiformes: Rivulidae) represents a specious group of taxa following annual life cycles in the neotropical ichthyofauna. They live in temporary ponds and each generation must be completed in a few months, depending on environmental stochasticity. Annual fish survive the dry season through diapausing eggs buried in the substrate of these ponds. A hypothesized bimodal hybrid zone between two taxa of the genus, A. charrua and A. reicherti from Dos Patos Merin lagoon system, was recently proposed based on genetics and morphological analyses. However, hundreds of additional nuclear molecular markers should be used to strongly support this hypothesized bimodal pattern. In the present paper, we conducted RNA-seq-based sequencing of the transcriptomes from pools of individuals of A. charrua, A. reicherti and their putative natural hybrids from the previously characterized hybrid zone. As a result, we identified a set of 111,725 SNP (single nucleotide polymorphism) markers, representing presumably fixed allelic differences among the two species. The present study provided the first panel of 106 SNP markers as a single diagnostic multiplex assay and validated their capacity to reconstruct the patterns of the hybrid zone between both taxa. These nuclear markers combined with Cytb gene and morphological analyses detected a population structure in which some groups among the hybrid swarms showed different level of introgression towards one or the other parental species according to their geographic distribution. High-quality transcriptomes and a large set of gene-linked SNPs should greatly facilitate functional and population genomics studies in the hybrid zone of these endangered species.

Molecular and morphological convergence to sulfide-tolerant fishes in a new species of Jenynsia (Cyprinodontiformes: Anablepidae), the first extremophile member of the family.

Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sulfide springs. In this paper, we described a new fish species of the genus Jenynsia, Anablepidae, from a sulfide spring in Northwestern Argentina, the first in the family known from such extreme environment. Jenynsia sulfurica n. sp. is diagnosable by the lack of scales on the pre-pelvic area or the presence of a single row of scales, continuous or not, from the isthmus to the bases of the pelvic fins. Additionally, it presents a series of morphological and molecular characteristics that appear convergent with those seen in other fish species (e.g., Poeciliids) inhabiting sulfide springs. Most notably, J. sulfurica has an enlarged head and postorbital area compared to other fish of the genus and a prognathous lower jaw with a hypertrophied lip, thought to facilitate respiration at the air-water interface. Analyses of cox1 sequence showed that J. sulfurica has two unique mutations resulting in amino acid substitutions convergent to those seen in Poeciliids from sulfide springs and known to provide a physiological mechanism related to living in sulfide environments. A phylogenetic analysis, including molecular and morphological characters, placed J. sulfurica as sister taxa to J. alternimaculata, a species found in nearby, non-sulfide habitats directly connected to the sulfide springs. Thus, it can be inferred that the selection imposed by the presence of H2S has resulted in the divergence between these two species and has potentially served as a barrier to gene flow.