Freshwater Fish Genus Research Articles

Recent dispersion routes between freshwater ecoregions evidence headwater captures in southern Brazil: a case study using cryptic species of the neotropical freshwater fish genus Cambeva (Siluriformes: Trichomycteridae)

Recent dispersion routes between freshwater ecoregions evidence headwater captures in southern Brazil: a case study using cryptic species of the neotropical freshwater fish genus Cambeva (Siluriformes: Trichomycteridae)

Wall-following - Phylogenetic context of an enhanced behaviour in stygomorphic Sinocyclocheilus (Cypriniformes: Cyprinidae) cavefishes.

With 75 known species, the freshwater fish genus Sinocyclocheilus is the largest cavefish radiation in the world and shows multiple adaptations for cave-dwelling (stygomorphic adaptations), which include a range of traits such as eye degeneration (normal-eyed, micro-eyed and eyeless), depigmentation of skin, and in some species, the presence of "horns". Their behavioural adaptations to subterranean environments, however, are poorly understood. Wall-following (WF) behaviour, where an organism remains in close contact with the boundary demarcating its habitat when in the dark, is a peculiar behaviour observed in a wide range of animals and is enhanced in cave dwellers. Hence, we hypothesise that wall-following is also present in Sinocyclocheilus, possibly enhanced in eyeless species compared to eye bearing (normal-/micro-eyed species). Using 13 species representative of Sinocyclocheilus radiation and eye morphs, we designed a series of assays, based on pre-existing methods for Astyanax mexicanus behavioural experiments, to examine wall-following behaviour under three conditions. Our results indicate that eyeless species exhibit significantly enhanced intensities of WF compared to normal-eyed species, with micro-eyed forms demonstrating intermediate intensities in the WF distance. Using a mtDNA based dated phylogeny (chronogram with four clades A-D), we traced the degree of WF of these forms to outline common patterns. We show that the intensity of WF behaviour is higher in the subterranean clades compared to clades dominated by normal-eyed free-living species. We also found that eyeless species are highly sensitive to vibrations, whereas normal-eyed species are the least sensitive. Since WF behaviour is presented to some degree in all Sinocyclocheilus species, and given that these fishes evolved in the late Miocene, we identify this behaviour as being ancestral with WF enhancement related to cave occupation. Results from this diversification-scale study of cavefish behaviour suggest that enhanced wall-following behaviour may be a convergent trait across all stygomorphic lineages.

Niche overlap between sympatric cichlid species of the genus Rocio (Cichliformes: Cichlidae) in Guatemala

AbstractRocio is a small genus of Neotropical freshwater fishes that is distributed in Atlantic drainages of northern Middle America. Two species of Rocio, R. spinosissima and R. octofasciata, exhibit sympatry in the Río Dulce basin in eastern Guatemala. Rocio spinosissima is endemic to the Río Dulce basin, while R. octofasciata has a larger geographic range that includes this area. Our goal was to explore the ecological and morphological variation shown by these two closely related species and determine their differences. A combination of field work, analysis of museum specimens, and ecological niche modelling helped to better understand the differences in habitat and environmental characteristics, along with the body shape variation. Local‐scale environmental data suggest that both species inhabit lentic environments, with R. spinosissima using narrower and low canopy‐covered habitats and R. octofasciata inhabiting areas with a larger range of environmental characteristics. Ecological Niche Models indicated that land cover, soil, precipitation, and temperature largely define the distribution of both species. Body shape differs between species, with R. spinosissima exhibiting a rounder and deeper body while R. octofasciata is more elongated. Specimens of R. octofasciata across its distribution also show variation in head shape, mouth position, fin, and caudal peduncle characteristics, possibly as a response to trophic strategies that reduce competition. Similarities in their environments and morphologies allow us to identify broadly overlapping niches in the two species of Rocio, while the fine scale differences documented between species will have conservation implications for the endemic R. spinosissima.

Phylogeography of a widespread Australian freshwater fish, western carp gudgeon (Eleotridae: Hypseleotris klunzingeri): Cryptic species, hybrid zones, and strong intra-specific divergences.

Despite belonging to the most abundant and widespread genus of freshwater fishes in the region, the carp gudgeons of eastern Australia (genus Hypseleotris) have proved taxonomically and ecologically problematic to science since the 19th century. Several molecular studies and a recent taxonomic revision have now shed light on the complex biology and evolutionary history that underlies this group. These studies have demonstrated that carp gudgeons include a sexual/unisexual complex (five sexual species plus an assortment of hemiclonal lineages), many members of which also co-occur with an independent sexual relative, the western carp gudgeon (H. klunzingeri). Here, we fill yet another knowledge gap for this important group by presenting a detailed molecular phylogeographic assessment of the western carp gudgeon across its entire and extensive geographic range. We use a suite of nuclear genetic markers (SNPs and allozymes) plus a matrilineal genealogy (cytb) to demonstrate that H. klunzingeri s.l. also displays considerable taxonomic and phylogeographic complexity. All molecular datasets concur in recognizing the presence of multiple candidate species, two instances of historic between-species admixture, and the existence of a natural hybrid zone between two of the three candidate species found in the Murray-Darling Basin. We also discuss the major phylogeographic patterns evident within each taxon. Together, these analyses provide a robust molecular, taxonomic, and distributional framework to underpin future morphological and ecological investigations on this prominent member of regional freshwater ecosystems in eastern Australia.

Species diversity deflation: Insight into taxonomic validity of Garra species (Teleostei: Cyprinidae) from Dhofar Region in the Arabian Peninsula using an integrated morpho-molecular approach

Garra is the most species-rich genus of freshwater fishes in the Arabian Peninsula, including Oman, which has eight recognized, species restricted mainly to the Hajar and Dhofar mountains. Garra species from the Dhofar region in Oman are reviewed based on integrated morphological and molecular (COI) data of newly collected fishes from the type localities of G. sindhae and G. smartae, and a new population from Wadi Laggashalyon. No diagnostic character was found to distinguish the two species and the Laggashalyon population as distinct taxa. Garra dunsirei, another species endemic to a sinkhole at Tawi Attair, a very difficult area to access at a depth of about 211 m, was examined here based on the GenBank data and the diagnostic characters given in the original descriptions of the studied Garra species. In addition, the phylogenetic tree placed the sequenced Omani Garra fishes into nine groups with K2P sequence divergence of 0.8% (G. smartae and G. smartae_Laggasaylon); 1.2% (G. smartae and G. sindhae), and 14.5% (G. Shamal and G. dunsirei) in their COI barcode region. A molecular species delimitation approach using PTP, also detected one entity for Garra species from the Dhofar region (G. dunsirei, G. sindhae and the both populations of G. smartae), which is consistent with our morphological data. Therefore, based on absence of diagnostic characters, low genetic distance, and molecular species delimitation approach, we treat G. sindhae and G. smartae as junior synonyms of G. dunsirei.

Phylogeography of the Chocó Endemic Rainbow Characin (Teleostei: Rhoadsia)

South America's Chocó, part of the North Andean Pacific Slopes–Rio Atrato ecoregion, is a biodiversity hotspot with many disjunct rivers, yet phylogeographic and population genetic studies of the Chocó's aquatic species are scarce. Rhoadsia is a Chocó endemic freshwater fish genus with two recognized species: R. minor from the upper Esmeraldas River drainage and R. altipinna from the lower Guayas River drainage, Ecuador. Little is known about the evolutionary history of Rhoadsia, and due to morphological similarities, the validity of the two nominal species has been questioned. We conducted a phylogeographic study using two mitochondrial genes and 12 microsatellite markers to examine the evolutionary history of Rhoadsia and the validity of its two species. Samples collected in drainages throughout western Ecuador from sea level to 1260 m.a.s.l. were included, as were samples of species in the closely related genera Parastremma and Carlana from Colombia and Central America. Phylogenetic analysis of the mtDNA markers confirmed the reciprocal monophyly of a northern and southern clade, and the presence of mitochondrial haplotypes of both clades in the northern Guayas basin. Structure analysis with the microsatellite markers pointed to introgression at the border between the species ranges as the likely cause of the mixing of mitochondrial haplotypes in the northern Guayas. Bayesian analysis of the microsatellite data revealed the existence of ten populations throughout western Ecuador, divided into three main geographically segregated groups. Group I coincided with the northern distribution of R. minor, while groups II and III seemed to represent geographic subgroups of R. altipinna in the Guayas and southern coastal drainages. Patterns of genetic divergence and diversity support the recognition of multiple evolutionarily significant units within both species and allowed reevaluation of previously reported freshwater biogeographic zones in the Ecuadorian Chocó. This study provides a baseline for future studies examining freshwater biogeographical patterns throughout the Ecuadorian Chocó, as well as a phylogeographic framework to examine the genetic basis of adaptation of morphologically divergent populations of Rhoadsia inhabiting Andean mountain streams in the region.

Testing for hybridization between Nile tilapia (Oreochromis niloticus) and blue spotted tilapia (Oreochromis leucostictus) in the Lake Edward system

Oreochromis is the most important tropical freshwater fish genus for aquaculture purposes, with various introduction and translocation events having played an integral part of its management. Some Oreochromis species such as the Nile tilapia, O. niloticus, are thought to be superior for aquacultural purposes when compared to other species. Hence, understanding the admixed nature of the species within a native system is of key importance for the development of future broodstock. Using a combination of mitochondrial (COI) and nuclear (microsatellites) DNA, we tested for the presence of O. niloticus and O. leucostictus hybrids within the Lake Edward-George system. The present study revealed that, despite their natural overlapping ranges, hybridization between O. niloticus and O. leucostictus appears to be rare within the Lake Edward-George system, suggesting that the native populations of these two species may serve as suitable broodstock to develop future aquaculture strains. Moreover, our study provides the first COI sequences for O. leucostictus from its native range and adds to the growing database of O. niloticus sequences.

Description of a new species of cryptic snubnose darter (Percidae: Etheostomatinae) endemic to north-central Mississippi.

Many subclades within the large North American freshwater fish genus Etheostoma (Percidae) show brilliant male nuptial coloration during the spring spawning season. Traditionally, perceived differences in color were often used to diagnose closely related species. More recently, perceived differences in male nuptial color have prompted further investigation of potential biodiversity using genetic tools. However, cryptic diversity among Etheostoma darters renders male nuptial color as unreliable for detecting and describing diversity, which is foundational for research and conservation efforts of this group of stream fishes. Etheostoma raneyi (Yazoo Darter) is an imperiled, range-limited fish endemic to north-central Mississippi. Existing genetic evidence indicates cryptic diversity between disjunctly distributed E. raneyi from the Little Tallahatchie and Yocona river watersheds despite no obvious differences in male color between the two drainages. Analysis of morphological truss and geometric measurements and meristic and male color characters yielded quantitative differences in E. raneyi from the two drainages consistent with genetic evidence. Morphological divergence is best explained by differences in stream gradients between the two drainages. Etheostoma faulkneri, the Yoknapatawpha Darter, is described as a species under the unified species concept. The discovery of cryptic diversity within E. raneyi would likely not have occurred without genetic tools. Cryptic diversity among Etheostoma darters and other stream fishes is common, but an overreliance on traditional methods of species delimitation (e.g., identification of a readily observable physical character to diagnose a species) impedes a full accounting of the diversity in freshwater fishes in the southeastern United States.

Diversity, phylogeny and biogeography of Systomus (Teleostei, Cyprinidae) in Sri Lanka

AbstractThe South and South‐East Asian freshwater fish genus Systomus (Cyprinidae) comprises 17 valid species. Six nominal species, including three endemics, have been reported from Sri Lanka, a continental island separated from India by a shallow‐shelf sea. The species diversity of Systomus on the island has until now not been assessed; neither has an evaluation been made of their phylogenetic history. Here, based on an analysis of the nuclear recombination activating protein 1 (rag1), and mitochondrial cytochrome c oxidase subunit 1 (cox1) and cytochrome b (cytb) gene markers, and a morphological examination of 143 specimens from 49 locations in Sri Lanka, we reassess the diversity of Systomus on the island and analyse patterns of their evolution and biogeography. Divergence‐time estimates, based on a substitution rate calibration, date the basal split between Systomus and its sister group, the Afrotropical small barbs, to 30.0 Ma (95% highest posterior density: 25.4–35.2 Ma). The species of Systomus belong to two distinct clades. The first includes the Sri Lankan endemics S. asoka, S. martenstyni and S. pleurotaenia, which comprise an insular diversification following the immigration of a common ancestor during the Oligocene. The second, which includes the remaining species of Indian, Sri Lankan and South‐East Asian Systomus, has a crown age dating to the Late Miocene. Morphological and molecular species delimitation analyses failed to validate the two nominal species, S. spilurus and S. timbiri, previously reported from Sri Lanka: both are considered synonyms of S. sarana, as are the nomina S. chryseus, S. chrysopoma, S. laticeps, S. rufus, S. pinnauratus and S. subnasutus. Four genetically and geographically discrete lineages of S. sarana occur in the island, and three in India. Molecular species delimitation analysis suggests these all belong to a single species, S. sarana. The genetically distinct Sri Lankan populations of S. sarana result from Plio‐Pleistocene dispersal or vicariance events between India and Sri Lanka—as a result of emergence and inundation of the now submerged isthmus connecting the two landmasses—as well as autochthonous insular diversification.

Assessing phylogeographic variation in the Rosyside Dace (Teleostei, Leuciscidae), a widespread morphologically variable taxon

AbstractClinostomus (Leuciscidae) is a wide‐ranging freshwater fish genus that occurs throughout eastern North America and southern portions of Canada with two species currently recognized: C. elongatus and C. funduloides. A previous taxonomic study of C. funduloides recognized two subspecies (estor and funduloides) and one diagnosed, but undescribed subspecies based on morphological characteristics and geographic distribution. In this study, we used three molecular markers (cytochrome b, S7 intron 1 and growth hormone intron 4) to test the three lineage hypothesis and evaluate genetic variation of C. funduloides across the range using Bayesian inference. Our results indicate that C. funduloides is not monophyletic, as individuals of C. elongatus nest within C. funduloides in both the mtDNA and nDNA phylogenetic analyses, although the position of C. elongatus varies between data sets. In addition, some of the recovered clades are deeply divergent from one another, further supporting the distinctiveness of many of the populations. Overall, these results suggest that subspecies designations are not warranted and a taxonomic revision is needed as Clinostomus is likely more diverse than is currently recognized.

Incipient genetic divergence or cryptic speciation? Procamallanus (Nematoda) in freshwater fishes (Astyanax)

AbstractHosts provide the main environmental traits parasites have to deal with, resulting in covariation between both associates at both micro‐ and macro‐evolutionary scales; phylogenetic analyses of highly host‐specific parasites have shown that parasite and host phylogeny might be highly congruent, and adaptation of a host species to new environments may lead to concordant changes of their parasites. Procamallanus (Spirocamallanus) neocaballeroi is a highly host‐specific parasitic nematode of the Neotropical freshwater fish genus Astyanax in Mexico. One of the host species of the nematode is the emblematic Mexican tetra, A. mexicanus, which exhibits two contrasting phenotypes, a cave‐dwelling morph (with troglomorphic features), and the surface‐dwelling morph; other congeneric species inhabit rivers and lakes, and some of them occur in sympatry, displaying trophic specializations. Here, we explored the hypothesis that contrasting environments (surface rivers vs cave rivers), and host morphological divergence (sympatric ecomorphs in a lacustrine environment) might result in the divergence of their parasites, even though the hosts maintain a cohesive genetic structure as the same species. To test the hypothesis, several populations of Astyanax spp. were sampled to search for P. (S.) neocaballeroi. The nematode was found in 10 of the 52 sampled sites; two localities corresponded to cave populations. The phylogenetic analysis based on COI sequences yielded three major lineages for P. (S.) neocaballeroi. We found no concordance between the three lineages and the habitat where they occur in Astyanax mexicanus, even considering those living in drastic environmental conditions (caves), or between these lineages and lacustrine ecomorphs of Astyanax aeneus and A. caballeroi occurring in sympatry. Instead, genetic lineages of the nematode exhibit a clearer pattern of host species association and geographical distribution; our results showed that P. (S.) neocaballeroi is experiencing an incipient divergence although the morphological study of lineages shows no conspicuous differences.

Morphometric variations of rasbora lateristriata bleeker population in different habitat: based on truss character analysis

Rasbora lateristriata is an alternative source of protein for the people around the river and fish consumption in Indonesia. Rasbora lateristriata also an economically fish in the streams so that people make it a prime target of the catch. Rasbora lateristriata, Bleeker called yellow Rasbora is a genus of freshwater fish from the family of Cyprinidae and is often found living in groups based on small rivers with a temperature range between 22-24 ° C, pH 6.0 -6.5. The purpose of this study was to determine the method Truss morphometric variation in the upstream, branch, middle and downstream and analyze the effects of water quality to morphometric character of Rasbora lateristriata population as scientific information in the conservation of fish. Morphometric variation of R. lateristriata based on Truss morphometric characters found their closeness between the four populations character of R lateristriata with the degree of similarity that upstream populations with 100% similarity, branch with 60% similarity, middle and downstream with 75%. Morphometric similarity value of R. lateristriata in the Sungi river area of ??77.5%.

A molecular phylogeny of the genus Laubuka (Teleostei: Cyprinidae) in Sri Lanka reveals multiple origins and a cryptic species

The freshwater-fish genus Laubuka contains ∼13 species distributed through the lowlands of tropical South and South-east Asia. Four of these species (Laubuka lankensis, L. varuna, L. ruhuna, and L. insularis) are reported as endemic to Sri Lanka, a remarkable datum given the island’s small size. We sampled populations of Laubuka at 56 locations in 14 of the island’s principal river basins and analysed their morphological, meristic, phylogenetic, and phylogeographic relationships using the mitochondrial genes cytochrome b and cytochrome c oxidase subunit 1 and the nuclear recombination activating protein 1. We investigated the geographic structure, and delineated species using molecular species delimitation methods and morphological analysis within the general lineage concept of species. Molecular and morphological analyses failed to identify L. ruhuna and L. insularis as distinct species; we show them to be synonyms of L. varuna and L. lankensis, respectively. Taxonomic inflation in previous literature is attributed as a result of limited sampling and negligence of size allometry. Additionally, a third, cryptic species discovered in this study is described as L. hema sp. nov. which is evidently confined to the headwaters of the Gal basin in eastern Sri Lanka. Phylogenetic and haplotype network analyses suggest phylogeographic structure within both the southwest-endemic L. varuna and the dry-zone endemic L. lankensis, but the former shows strong phylogeographic structure between adjacent basins. The Sri Lankan species of Laubuka do not form a monophyletic group: they stem from two dispersal or vicariance events, one involving the lineage that led to L. varuna in south-western Sri Lanka, and the other, of [L. lankensis + L. hema] in the dry zone. http://zoobank.org/urn:lsid:zoobank.org:pub:D2A29329-E0E7-447E-B316-81049212CCCBhttp://zoobank.org/urn:lsid:zoobank.org:act:920E5DC0-CEDC-4243-98C7-12CCF829CBCD

Pattern and timing of diversification in the African freshwater fish genus Distichodus (Characiformes: Distichodontidae)

BackgroundDistichodus is a clade of tropical freshwater fishes currently comprising 25 named species distributed continent-wide throughout the Nilo-Sudan and most Sub-Saharan drainages. This study investigates the phylogenetic relationships, timing of diversification, and biogeographic history of the genus from a taxonomically comprehensive mutilocus dataset analyzed using Maximum Likelihood and Bayesian methods of phylogenetic inference, coalescence-based species-tree estimation, divergence time estimation, and inference of geographic range evolution.ResultsAnalyses of comparative DNA sequence data in a phylogenetic context reveal the existence of two major clades of similar species-level diversity and provide support for the monophyletic status of most sampled species. Biogeographic reconstruction on a time-scaled phylogeny suggest that the origins of the genus date back to the late Oligocene and that current geographic distributions are the result of a Congo Basin origin followed by dispersal and range expansion into adjacent ichthyofaunal provinces at different times during the evolutionary history of the group.ConclusionsWe present the most comprehensive phylogenetic, chronological, and biogeographic treatment yet conducted for the genus. The few instances of species paraphyly (D. teugelsi, D. fasciolatus) revealed by the resulting phylogenies are likely a consequence of post-divergence introgressive hybridization and/or incomplete lineage sorting due to recent speciation. Historical biogeographic findings are both in agreement and conflict with previous studies of other continent-wide African freshwater fish genera, suggesting a complex scenario for the assemblage of Africa’s continental ichthyofaunal communities.

Opening the Trojan horse: phylogeny of Astyanax, two new genera and resurrection of Psalidodon (Teleostei: Characidae)

AbstractThe freshwater fish genus Astyanax is one of the most diverse among the Characidae. The genus is defined by a combination of character states that are widely distributed in Characidae. In addition, the genus has the broadest geographical distribution in the family, being found in a great variety of environments of the Neotropical region. Although phylogenetic relationships were treated only partially, many authors agree that the genus is not monophyletic. In this contribution, we study the phylogenetic relationships of Astyanax in the context of the family Characidae, by combining morphological and molecular data. A total of 520 morphological characters, nine molecular markers and 608 taxa are analysed, of which 98 belong to Astyanax. According to our results, Astyanax is not monophyletic. We recovered species attributed to Astyanax in different subfamilies: Gymnocharacinae (including the type species), Stevardiinae and Tetragonopterinae. Among the species recovered in Gymnocharacinae, most (including the type species, the resurrected Psalidodon, and the new genus Andromakhe gen. nov.) were recovered in Gymnocharacini, while the remaining ones were recovered in Probolodini (transferred to Deuterodon or the new genus Makunaima gen. nov.).

Evolutionary Dynamics of Multigene Families in Triportheus (Characiformes, Triportheidae): A Transposon Mediated Mechanism?

Triportheus (Characiformes, Triportheidae) is a freshwater fish genus with 18 valid species. These fishes are widely distributed in the major river drainages of South America, having commercial importance in the fishing market, mainly in the Amazon basin. This genus has diverged recently in a complex process of speciation carried out in different river basins. The use of repetitive sequences is suitable to trace the genomic reorganizations carried out along the speciation process. In this work, the 5S rDNA multigene family has been characterized at molecular and phylogenetic level. The results showed that other multigene family has been found within the Non Transcribed Spacer (NTS): the U1 snRNA gene. Double-FISH with 5S and U1 probes were also carried out, confirming the close linkage between these two multigene families. Moreover, evidences of different Transposable Elements (TE) were detected within the spacer, thus suggesting a transposon-mediated mechanism of 5S-U1 evolutionary pathway in this genus. Phylogenetic analysis demonstrated a species-specific grouping, except for T. pantanensis, T. aff. rotundatus and T. trifurcatus. The evolutionary model of the 5S rDNA in Triportheus species has been discussed. In addition, the results show new clues for the speciation and evolutionary trend in these species, which could be suitable to use in other Characiformes species.

Distribution and genetic diversity of two species ofPelasgusminnows (Leuciscidae) in southern Greece

PelasgusKottelat & Freyhof 2007 (Leuciscidae) is a freshwater fish genus endemic to the Southern Balkans. The distribution of most of its species is insufficiently known.Pelasguswas molecularly studied only marginally, and the genetic diversity of individual species or populations, crucial for their conservation, is completely unknown. We studied distribution and genetic diversity ofPelasgus stymphalicus(Valenciennes 1844) andPelasgus marathonicus(Vinciguerra 1921), two widespread species from southern Greece. Our data, based oncytochrome bsequences, confirmed that a number of populations whose taxonomic status had been uncertain, belong to one of these species. The distribution range ofP. stymphalicusincludes the Ionian mainland, from the Acheloos to Mornos rivers, and most of the Peloponnese, excluding the Evrotas and the headwaters of Alfios. The native range ofPelasgus marathonicusis the western Aegean mainland, from rivers near Athens to the Xerias river in the Pagasitikos Gulf. AMOVA showed that the genetic variance is slightly higher among than between populations. HighFSTvalues indicated a pronounced genetic differentiation of the populations in both species. There was a high proportion of private haplotypes and a very small number of shared haplotypes between populations in both species, which indicates uniqueness of each population and their susceptibility to human-induced changes.

Testing the validity of two putative sympatric species from Sinocyclocheilus (Cypriniformes: Cyprinidae) based on mitochondrial cytochrome b sequences.

There are over 60 species within the freshwater fish genus Sinocyclocheilus (Cypriniformes: Cyprinidae) distributed throughout the Yunnan-Guizhou Plateau and its surrounding areas in China. In recent years, the increasing number of new species described has raised some controversy about the validity of several species within this genus, notably the putative sympatric species pair S. qiubeiensis and S. jiuchengensis. To test the validity of S. qiubeiensis and S. jiuchengensis, we analyzed the complete sequences of the mitochondrial cytochrome b (CYTB) gene of 20 identified species and one outgroup species. Phylogenetic relationships were reconstructed using CYTB with maximum likelihood (ML) and Bayesian inference (BI) methods. Our phylogenetic results showed that all individuals of S. qiubeiensis and S. jiuchengensis clustered in one clade with strong support. In addition, the genetic distance between the two species was 0.11%, within the range observed at the intraspecific level. The most recent common ancestor of S. qiubeiensis and S. jiuchengensis dated back to 0.13 million years ago, indicating little time for complete speciation to have occurred. These results clearly support the viewpoint that S. jiuchengensis is a synonym of S. qiubeiensis.

Correlated evolution of thermal niches and functional physiology in tropical freshwater fishes.

The role of ecology in phenotypic and species diversification is widely documented. Nonetheless, numerous nonadaptive processes can shape realized niches and phenotypic variation in natural populations, complicating inferences about adaptive evolution at macroevolutionary scales. We tested for evolved differences in thermal tolerances and their association with the realized thermal niche (including metrics describing diurnal and seasonal patterns of temperature extremes and variability) across a genus of tropical freshwater fishes reared in a standardized environment. There was limited evolution along the thermal niche axis associated with variation in maximum temperature and in upper thermal limits. In contrast, there was considerable diversification along the first major axis of the thermal niche associated with minimum temperatures and in lower thermal limits. Across our adaptive landscape analyses, 70% of species exhibited evidence of divergence in thermal niches. Most importantly, the first two major axes of thermal niche variation were significantly correlated with variation in lower thermal limits. Our results indicate adaptation to divergent thermal niches and adaptive evolution of related functional traits, and highlight the importance of divergence in lower thermal limits for the evolution of tropical biodiversity.

Revealing Hidden Diversity of the Underestimated Neotropical Ichthyofauna: DNA Barcoding in the Recently Described Genus Megaleporinus (Characiformes: Anostomidae).

Molecular studies have improved our knowledge on the neotropical ichthyofauna. DNA barcoding has successfully been used in fish species identification and in detecting cryptic diversity. Megaleporinus (Anostomidae) is a recently described freshwater fish genus within which taxonomic uncertainties remain. Here we assessed all nominal species of this genus using a DNA barcode approach (Cytochrome Oxidase subunit I) with a broad sampling to generate a reference library, characterize new molecular lineages, and test the hypothesis that some of the nominal species represent species complexes. The analyses identified 16 (ABGD and BIN) to 18 (ABGD, GMYC, and PTP) different molecular operational taxonomic units (MOTUs) within the 10 studied nominal species, indicating cryptic biodiversity and potential candidate species. Only Megaleporinus brinco, Megaleporinus garmani, and Megaleporinus elongatus showed correspondence between nominal species and MOTUs. Within six nominal species, a subdivision in two MOTUs was found, while Megaleporinus obtusidens was divided in three MOTUs, suggesting that DNA barcode is a very useful approach to identify the molecular lineages of Megaleporinus, even in the case of recent divergence (< 0.5 Ma). Our results thus provided molecular findings that can be used along with morphological traits to better define each species, including candidate new species. This is the most complete analysis of DNA barcode in this recently described genus, and considering its economic value, a precise species identification is quite desirable and fundamental for conservation of the whole biodiversity of this fish.