A new genus of Anostomidae (Ostariophysi: Characiformes): Diversity, phylogeny and biogeography based on cytogenetic, molecular and morphological data

Repetitive DNAs and chromosome evolution in Megaleporinus obtusidens and M. reinhardti (Characiformes: Anostomidae)

The high dynamism of repetitive DNAs is a major driver of chromosome evolution. In particular, the accumulation of repetitive DNA sequences has been reported as part of the differentiation of sex-specific chromosomes. In turn, the fish species of the genus Megaleporinus are a monophyletic clade in which the presence of differentiated ZZ/ZW sex chromosomes represents a synapomorphic condition, thus serving as a suitable model to evaluate the dynamic evolution of repetitive DNA classes. Therefore, transposable elements (TEs) and in tandem repeats were isolated and located on chromosomes of Megaleporinus obtusidens and M. reinhardti to infer their role in chromosome differentiation with emphasis on sex chromosome systems. Despite the conserved karyotype features of both species, the location of repetitive sequences - Rex 1, Rex 3, (TTAGGG)n, (GATA)n, (GA)n, (CA)n, and (A)n - varied both intra and interspecifically, being mainly accumulated in Z and W chromosomes. The physical mapping of repetitive sequences confirmed the remarkable dynamics of repetitive DNA classes on sex chromosomes that might have promoted chromosome diversification and reproductive isolation in Megaleporinus species.

Exploring hidden diversity: Molecular insights into the Leporinus species of the rivers of the Brazilian states of Maranhão and Piauí

The present study delved into the world of hidden diversity by examining specimens identified as Leporinus piau from the river basins of the northern Brazilian states of Maranhão and Piauí. Using genetic analyses that combined data from three mitochondrial markers and one nuclear marker, the study identified two well-supported groups, reinforcing the findings of previous publications. The first group, found in samples from the Itapecuru, Mearim, Turiaçu, and Pericumã basins, in Maranhão, appears to represent a relatively ancient diversification and the possibility of concealed cryptic diversity. The second group, comprising specimens from the Parnaíba (Piauí) and Mearim (Maranhão) basins, appears to have resulted from a more recent process of diversification and has a close relationship with Leporinus friderici from the type locality. Our findings not only confirm the existence of a complex scenario of cryptic diversity in the genus Leporinus from the study basins but also underscore the taxonomic inconsistencies within this group of fish. This study offers a comprehensive analysis of the species diversity of the Maranhão and Piauí basins, which are critical regions for the conservation of Amazonian fish, providing valuable insights for the sustainable management and conservation of these fish.

Comparative analysis of transposable elements dynamics in fish with different sex chromosome systems

Transposable elements (TEs) are widespread genomic components with substantial roles in genome evolution and sex chromosome differentiation. In this study, we compared the TE composition of three closely related fish with different sex chromosome systems: Megaleporinus elongatus (Z1Z1Z2Z2/Z1W1Z2W2), Megaleporinus macrocephalus (ZZ/ZW) (both with highly differentiated W sex chromosomes), and Leporinus friderici (without heteromorphic sex chromosomes). We created custom TE libraries for each species using clustering methods and manual annotation and prediction, and we predicted TE temporal dynamics through divergence-based analysis. The TE abundance ranged from 16% to 21% in the three mobilomes, with L. friderici having the lowest overall. Despite the recent amplification of TEs in all three species, we observed differing expansion activities, particularly between the two genera. Both Megaleporinus recently experienced high retrotransposon activity, with a reduction in DNA TEs, which could have implications in sex chromosome composition. In contrast, L. friderici showed the opposite pattern. Therefore, despite having similar TE compositions, Megaleporinus and Leporinus exhibit distinct TE histories that likely evolved after their separation, highlighting a rapid TE expansion over short evolutionary periods.

Speciation in Coastal Basins Driven by Staggered Headwater Captures: Dispersal of a Species Complex, Leporinus bahiensis, as Revealed by Genome-wide SNP Data

Past sea level changes and geological instability along watershed boundaries have largely influenced fish distribution across coastal basins, either by dispersal via palaeodrainages now submerged or by headwater captures, respectively. Accordingly, the South American Atlantic coast encompasses several small and isolated drainages that share a similar species composition, representing a suitable model to infer historical processes. Leporinus bahiensis is a freshwater fish species widespread along adjacent coastal basins over narrow continental shelf with no evidence of palaeodrainage connections at low sea level periods. Therefore, this study aimed to reconstruct its evolutionary history to infer the role of headwater captures in the dispersal process. To accomplish this, we employed molecular-level phylogenetic and population structure analyses based on Sanger sequences (5 genes) and genome-wide SNP data. Phylogenetic trees based on Sanger data were inconclusive, but SNPs data did support the monophyletic status of L. bahiensis. Both COI and SNP data revealed structured populations according to each hydrographic basin. Species delimitation analyses revealed from 3 (COI) to 5 (multilocus approach) MOTUs, corresponding to the sampled basins. An intricate biogeographic scenario was inferred and supported by Approximate Bayesian Computation (ABC) analysis. Specifically, a staggered pattern was revealed and characterized by sequential headwater captures from basins adjacent to upland drainages into small coastal basins at different periods. These headwater captures resulted in dispersal throughout contiguous coastal basins, followed by deep genetic divergence among lineages. To decipher such recent divergences, as herein represented by L. bahiensis populations, we used genome-wide SNPs data. Indeed, the combined use of genome-wide SNPs data and ABC method allowed us to reconstruct the evolutionary history and speciation of L. bahiensis. This framework might be useful in disentangling the diversification process in other neotropical fishes subject to a reticulate geological history.

The DNA barcode reveals cryptic diversity and a new record for the genus Leporinus (Characiformes, Anostomidae) in the hydrographic basins of central northern Brazil

Leporinus is one of the most speciose genera of the order Characiformes, with 81 valid species distributed throughout much of Central and South America. The considerable diversity of this genus has generated extensive debate on its classification and internal arrangement. In the present study, we investigated the species diversity of the genus Leporinus in central northern Brazil, and conclude that six valid species-Leporinus maculatus, Leporinus unitaeniatus, Leporinus affinis, Leporinus venerei, Leporinus cf. friderici, and Leporinus piau-are found in the hydrographic basins of the Brazilian states of Maranhão, Piauí, and Tocantins. We analyzed 182 sequences of the Cytochrome Oxidase subunit I gene, of which, 157 were obtained from Leporinus specimens collected from the basins of the Itapecuru, Mearim, Turiaçu, Pericumã, Periá, Preguiças, Parnaíba, and Tocantins rivers. The species delimitation analyses, based on the ABGD, ASAP, mPTP, bPTP, and GMYC methods, revealed the presence of four distinct molecular operational taxonomic units (MOTUs), identified as L. maculatus, L. unitaeniatus, L. affinis, and L. piau (from the Parnaíba River). The bPTP method restricted L. venerei to a single MOTU, and confirmed the occurrence of this species in the rivers of Maranhão for the first time. The separation of L. cf. friderici into two clades and the subsequent formation of different operational taxonomic units was consistent with polyphyly in this species, which indicates the existence of cryptic diversity. The arrangement of L. cf. friderici and L. piau in two different clades supports the conclusion that the L. piau specimens from Maranhão were misidentified, based on their morphological traits, reflecting the taxonomic inconsistencies that exist among morphologically similar species. Overall, then, the species delimitation methods employed in the present study indicated the presence of six MOTUs-L. maculatus, L. unitaenitus, L. affinis, L. cf. friderici, L. venerei, and L. piau. In the case of two other MOTUs identified in the present study, one (L. venerei) is a new record for the state of Maranhão, and we believe that the other represents a population of L. piau from the basin of the Parnaíba River.

Paleogene emergence and evolutionary history of the Amazonian fossorial fish genus Tarumania (Teleostei: Tarumaniidae)

Tarumania walkerae is a rare fossorial freshwater fish species from the lower Rio Negro, Central Amazonia, composing the monotypic and recently described family Tarumaniidae. The family has been proposed as the sister group of Erythrinidae by both morphological and molecular studies despite distinct arrangements of the superfamily Erythrinoidea within Characiformes. Recent phylogenomic studies and time-calibrated analyses of characoid fishes have not included specimens of Tarumania in their analyses. We obtained genomic data for T. walkerae and constructed a phylogeny based on 1795 nuclear loci with 488,434 characters of ultraconserved elements (UCEs) for 108 terminals including specimens of all 22 characiform families. The phylogeny confirms the placement of Tarumaniidae as sister to Erythrinidae but differs from the morphological hypothesis in the placement of the two latter families as sister to the clade with Hemiodontidae, Cynodontidae, Serrasalmidae, Parodontidae, Anostomidae, Prochilodontidae, Chilodontidae, and Curimatidae. The phylogeny calibrated with five characoid fossils indicates that Erythrinoidea diverged from their relatives during the Late Cretaceous circa 90 Ma (108–72 Ma), and that Tarumania diverged from the most recent common ancestor of Erythrinidae during the Paleogene circa 48 Ma (66–32 Ma). The occurrence of the erythrinoid-like †Tiupampichthys in the Late Cretaceous–Paleogene formations of the El Molino Basin of Bolivia supports our hypothesis for the emergence of the modern Erythrinidae and Tarumaniidae during the Paleogene.

In vitro selection of autochthonous bacterium with probiotic potential for the neotropical fish piauçu Megaleporinus microcephalus

ABSTRACT The study aimed to isolate, identify, and apply in vitro tests on bacteria with autochthonous probiotic potential isolated from fifteen healthy specimens of Megaleporinus macrocephalus. The strains were selected from the intestinal tract of fish and inoculated in the Petri plate containing Sharp Man Rogosa Agar (MRS) for (48 hours at 35ºC). They were isolated based on a test of catalase, Gram stain, tolerance to different gradients NaCl (1, 2 and 3%), pH (4, 5, 6, 8 and 9) values and bile salts (2.5 and 5%), in addition to the inhibition zone against pathogens. Of the 42 strains isolated, ST1 and ST9 had higher values (p<0.05) for total viable cells (31.80±0.07 and 32.51±0.05 CFU/mL × 108) respectively. In the resistance tests, strains ST1 and ST9 presented the best results, with emphasis on ST9 in the gradients of pH, high values of bile salts and larger inhibition zones against Aeromonas hydrophila and Aeromonas jandaei. The strains with the best results in the tests, ST1 and ST9, were identified by the MALDI-TOF-MS method as Enterococcus faecium. Thus, the isolated E. faecium bacteria, may be recommended as for probiotic use in farming the M. macrocephalus.

Satellitome analysis illuminates the evolution of ZW sex chromosomes of Triportheidae fishes (Teleostei: Characiformes)

Satellites are an abundant source of repetitive DNAs that play an essential role in the chromosomal organization and are tightly linked with the evolution of sex chromosomes. Among fishes, Triportheidae stands out as the only family where almost all species have a homeologous ZZ/ZW sex chromosomes system. While the Z chromosome is typically conserved, the W is always smaller, with variations in size and morphology between species. Here, we report an analysis of the satellitome of Triportheus auritus (TauSat) by integrating genomic and chromosomal data, with a special focus on the highly abundant and female-biased satDNAs. In addition, we investigated the evolutionary trajectories of the ZW sex chromosomes in the Triportheidae family by mapping satDNAs in selected representative species of this family. The satellitome of T. auritus comprised 53 satDNA families of which 24 were also hybridized by FISH. Most satDNAs differed significantly between sexes, with 19 out of 24 being enriched on the W chromosome of T. auritus. The number of satDNAs hybridized into the W chromosomes of T. signatus and T. albus decreased to six and four, respectively, in accordance with the size of their W chromosomes. No TauSat probes produced FISH signals on the chromosomes of Agoniates halecinus. Despite its apparent conservation, our results indicate that each species differs in the satDNA accumulation on the Z chromosome. Minimum spanning trees (MSTs), generated for three satDNA families with different patterns of FISH mapping data, revealed different homogenization rates between the Z and W chromosomes. These results were linked to different levels of recombination between them. The most abundant satDNA family (TauSat01) was exclusively hybridized in the centromeres of all 52 chromosomes of T. auritus, and its putative role in the centromere evolution was also highlighted. Our results identified a high differentiation of both ZW chromosomes regarding satellites composition, highlighting their dynamic role in the sex chromosomes evolution.

Genomic Differences Between the Sexes in a Fish Species Seen Through Satellite DNAs

Neotropical fishes have highly diversified karyotypic and genomic characteristics and present many diverse sex chromosome systems, with various degrees of sex chromosome differentiation. Knowledge on their sex-specific composition and evolution, however, is still limited. Satellite DNAs (satDNAs) are tandemly repeated sequences with pervasive genomic distribution and distinctive evolutionary pathways, and investigating satDNA content might shed light into how genome architecture is organized in fishes and in their sex chromosomes. The present study investigated the satellitome of Megaleporinus elongatus, a freshwater fish with a proposed Z₁Z₁Z₂Z₂/Z₁W₁Z₂W₂ multiple sex chromosome system that encompasses a highly heterochromatic and differentiated W₁ chromosome. The species satellitome comprises of 140 different satDNA families, including previously isolated sequences and new families found in this study. This diversity is remarkable considering the relatively low proportion that satDNAs generally account for the M. elongatus genome (around only 5%). Differences between the sexes in regards of satDNA content were also evidenced, as these sequences are 14% more abundant in the female genome. The occurrence of sex-biased signatures of satDNA evolution in the species is tightly linked to satellite enrichment associated with W₁ in females. Although both sexes share practically all satDNAs, the overall massive amplification of only a few of them accompanied the W₁ differentiation. We also investigated the expansion and diversification of the two most abundant satDNAs of M. elongatus, MelSat01-36 and MelSat02-26, both highly amplified sequences in W₁ and, in MelSat02-26’s case, also harbored by Z₂ and W₂ chromosomes. We compared their occurrences in M. elongatus and the sister species M. macrocephalus (with a standard ZW sex chromosome system) and concluded that both satDNAs have led to the formation of highly amplified arrays in both species; however, they formed species-specific organization on female-restricted sex chromosomes. Our results show how satDNA composition is highly diversified in M. elongatus, in which their accumulation is significantly contributing to W₁ differentiation and not satDNA diversity per se. Also, the evolutionary behavior of these repeats may be associated with genome plasticity and satDNA variability between the sexes and between closely related species, influencing how seemingly homeologous heteromorphic sex chromosomes undergo independent satDNA evolution.

Total evidence phylogenetic analysis reveals polyphyly of Anostomoides and uncovers an unexpectedly ancient genus of Anostomidae fishes (Characiformes)

The nearly 150 species of Anostomidae comprise one of the most diverse and taxonomically dynamic families of Neotropical freshwater fishes. A recent revision of the enigmatic and poorly diagnosed genus Anostomoides demonstrated that it contains two valid species, each with complicated taxonomic histories; however, that study did not address their phylogenetic placement. Herein, we integrate molecular and morphological data to demonstrate their distant evolutionary relationship, and thus the polyphyly of Anostomoides. While we reconstruct one of the species in a previously hypothesized placement within a clade also containing Laemolyta, Rhytiodus and Schizodon, the other represents a morphologically and genetically distinctive lineage that diverged early in the history of the family. We describe and illustrate the osteology of this remarkable species, discuss the evolutionary implications of its unique suite of features, and use those characteristics to diagnose a new genus that evolved independently of all other known members of the family for approximately 37 Myr.

Accelerated Diversification Explains the Exceptional Species Richness of Tropical Characoid Fishes

The Neotropics harbor the most species-rich freshwater fish fauna on the planet, but the timing of that exceptional diversification remains unclear. Did the Neotropics accumulate species steadily throughout their long history, or attain their remarkable diversity recently? Biologists have long debated the relative support for these museum and cradle hypotheses, but few phylogenies of megadiverse tropical clades have included sufficient taxa to distinguish between them. We used 1,288 ultraconserved element loci (UCE) spanning 293 species, 211 genera and 21 families of characoid fishes to reconstruct a new, fossil-calibrated phylogeny and infer the most likely diversification scenario for a clade that includes a third of Neotropical fish diversity. This phylogeny implies paraphyly of the traditional delimitation of Characiformes because it resolves the largely Neotropical Characoidei as the sister lineage of Siluriformes (catfishes), rather than the African Citharinodei. Time-calibrated phylogenies indicate an ancient origin of major characoid lineages and reveal a much more recent emergence of most characoid species. Diversification rate analyses infer increased speciation and decreased extinction rates during the Oligocene at around 30 million years ago (Ma) during a period of mega-wetland formation in the proto-Orinoco-Amazonas. Three species-rich and ecomorphologically diverse lineages (Anostomidae, Serrasalmidae, and Characidae) that originated more than 60 Ma in the Paleocene experienced particularly notable bursts of Oligocene diversification and now account collectively for 68% of the approximately 2,150 species of Characoidei. In addition to paleogeographic changes, we discuss potential accelerants of diversification in these three lineages. While the Neotropics accumulated a museum of ecomorphologically diverse characoid lineages long ago, this geologically dynamic region also cradled a much more recent birth of remarkable species-level diversity.

A Pliocene-Pleistocene continental biota from Venezuela

The Pliocene-Pleistocene transition in the Neotropics is poorly understood despite the major climatic changes that occurred at the onset of the Quaternary. The San Gregorio Formation, the younger unit of the Urumaco Sequence, preserves a fauna that documents this critical transition. We report stingrays, freshwater bony fishes, amphibians, crocodiles, lizards, snakes, aquatic and terrestrial turtles, and mammals. A total of 49 taxa are reported from the Vergel Member (late Pliocene) and nine taxa from the Cocuiza Member (Early Pleistocene), with 28 and 18 taxa reported for the first time in the Urumaco sequence and Venezuela, respectively. Our findings include the first fossil record of the freshwater fishes Megaleporinus, Schizodon, Amblydoras, Scorpiodoras, and the pipesnake Anilius scytale, all from Pliocene strata. The late Pliocene and Early Pleistocene ages proposed here for the Vergel and Cocuiza members, respectively, are supported by their stratigraphic position, palynology, nannoplankton, and ⁸⁶Sr/⁸⁸Sr dating. Mammals from the Vergel Member are associated with the first major pulse of the Great American Biotic Interchange. In contrast to the dry conditions prevailing today, the San Gregorio Formation documents mixed open grassland/forest areas surrounding permanent freshwater systems, following the isolation of the northern South American basin from western Amazonia. These findings support the hypothesis that range contraction of many taxa to their current distribution in northern South America occurred rapidly during at least the last 1.5 million years.

Developmental plasticity reveals hidden fish phenotypes and enables morphospace diversification

The establishment of a given phenotype is only one expression from a range of hidden developmental possibilities. Developmental plasticity at hidden reaction norms might elicit phenotypic diversification under new developmental environments. Current discussion benefits from empirical analyses that integrate multiple environmental stimuli to evaluate how plastic responses may shape phenotypic variation. We raised Megaleporinus macrocephalus fish in different environmental settings to address contributions of developmental plasticity for emergence of new phenotypes and subsequent morphospace diversification. Plastic morphotypes were evaluated at two complementary scales, the M. macrocephalus morphospace and the higher taxonomic level of Anostomidae family. Morphospace analyses demonstrated that developmental plasticity quickly releases distinct head morphotypes that were hidden in the parental monomorphic population. Plastic morphotypes occupied discrete and previously unfilled morphospace regions, a result obtained from comparisons with a control population and in analyses including several Anostomidae species. Plastic responses involved adjustments in shape and relative position of head bonesets, and fish raised under specific environmental combinations rescued phenotypic patterns described for different genera. Therefore, developmental plasticity possibly contributes to adaptive radiation in Anostomidae. Results illustrate how plastic responses enable morphospace diversification and contribute to evolution.

Cytogenetic analysis of Hypomasticus copelandii and H. steindachneri: relevance of cytotaxonomic markers in the Anostomidae family (Characiformes)

Recent phylogenetic hypotheses within Anostomidae, based on morphological and molecular data, resulted in the description of new genera (Megaleporinus Ramirez, Birindelli et Galetti, 2017) and the synonymization of others, such as the reallocation of Leporinus copelandii Steindachner, 1875 and Leporinus steindachneri Eigenmann, 1907 to Hypomasticus Borodin, 1929. Despite high levels of conservatism of the chromosomal macrostructure in this family, species groups have been corroborated using banding patterns and the presence of different sex chromosome systems. Due to the absence of cytogenetic studies in H. copelandii (Steindachner, 1875) and H. steindachneri (Eigenmann, 1907), the goal of this study was to characterize their karyotypes and investigate the presence/absence of sex chromosome systems using different repetitive DNA probes. Cytogenetic techniques included: Giemsa staining, Ag-NOR banding and FISH using 18S and 5S rDNA probes, as well as microsatellite probes (CA)₁₅ and (GA)₁₅. Both species had 2n = 54, absence of heteromorphic sex chromosomes, one chromosome pair bearing Ag-NOR, 18S and 5S rDNA regions. The (CA)₁₅ and (GA)₁₅ probes marked mainly the subtelomeric regions of all chromosomes and were useful as species-specific chromosomal markers. Our results underline that chromosomal macrostructure is congruent with higher systematic arrangements in Anostomidae, while microsatellite probes are informative about autapomorphic differences between species.

New records of the occurrence of Megaleporinus macrocephalus () (Characiformes, Anostomidae) from the basins of the Itapecuru and Mearim rivers in Maranhão, Northeastern Brazil

The "piaussu", Megaleporinus macrocephalus is an anostomatid fish species native to the basin of the Paraguay River, in the Pantanal biome of western Brazil. However, this species has now been recorded in a number of other drainages, including those of the upper Paraná, Uruguay, Jacuí, Doce, Mucuri, and Paraíba do Sulrivers. This study presents two new records of the occurrence of M. macrocephalus, in the basins of the Itapecuru and Mearim rivers in the state of Maranhão, in the Brazilian Northeast. The piaussu is a large-bodied fish of commercial interest that is widely raised on fish farms, and its occurrence in the Itapecuru and Mearim rivers is likely the result of individuals escaping from fish tanks when they overflow during the rainy season. Morphological analyses and sequences of the Cytochrome Oxidase Subunit I (COI) gene confirmed the taxonomic identification of the specimens as M. macrocephalus. The COI sequences were 99.66% similar to those of M. macrocephalus deposited in the BOLDSystems database. These records extend the known distribution of M. macrocephalus to the basins of the Itapecuru and Mearim rivers in the Brazilian Northeast, highlighting a new case of introduction of exotic fish species into Brazilian river basins.

Integrative taxonomy reveals a new species of Neotropical headstanding fish in genus Schizodon (Characiformes: Anostomidae)

Abstract Schizodon encompasses approximately 15 species of Neotropical headstanding fishes. Integrative taxonomy, combining molecular and morphometric analyses with traditional taxonomic methods, was used to investigate Schizodon vittatus and its potential new sister species. Molecular differences between the two species in the barcode are greater than intra-specific variation recovered in species of Schizodon, and the two species represent distinct lineages for approximately one million years. The two species are morphologically very similar, and the meristic data showed great overlap. Morphometric analyses also showed overlap among the putative species but indicated differences in caudal-peduncle depth, orbital diameter, and length of anal-fin rays. Color pattern seems to provide a clear diagnostic feature for the two species. Schizodon vittatus usually has four dark brown transversal bars on body, and its sister species has three conspicuous bars, with the fourth, if present, inconspicuous and dorsal to the lateral line. Schizodon vittatus is redescribed based on the type and recently collected specimens, its type locality is revisited, and its known distribution restricted to the Araguaia and Tocantins drainages. The new species, sister to S. vittatus, distributed in the Xingu and Tapajós drainages, is described. A key for the identification of the Amazon clade species of Schizodon is provided.

Unrevealing the Karyotypic Evolution and Cytotaxonomy of Armored Catfishes (Loricariinae) with Emphasis in Sturisoma, Loricariichthys, Loricaria, Proloricaria, Pyxiloricaria, and Rineloricaria

This study provides new insight into the chromosomal diversification in Loricariinae. We analyzed nine species from different Brazilian hydrographic basins, using conventional and molecular cytogenetic methods, aiming to understand the karyotypic diversification, and contribute with cytotaxonomic markers in this group considered one of the most diverse of Loricariidae. Our results evidenced a high karyotypic variability in diploid number (2n) ranging from 2n = 54 (Loricariichthys platymetopon and Loricariichthys anus), 2n = 60 (Rineloricaria reisi and Rineloricaria parva), 2n = 62 (Proloricaria prolixa), 2n = 64 (Loricaria cataphracta complex species), 2n = 66 (Sturisoma barbatum), and 2n = 68 (Pyxiloricaria menezesi). Different patterns of 18S and 5S ribosomal DNA (rDNA) were also identified, while slight divergences in heterochromatin distribution were observed. This high variability is probably related with independent events of Robertsonian translocations, pericentric inversions, and different mechanisms of rDNA sites dispersion (nonreciprocal translocation and transposable element [TEs] co-localization). In addition, our study provides a set of efficient chromosomal markers for the characterization of all analyzed species, and certainly, in future analyzes, will contribute as a useful cytotaxonomic tool in groups where the traditional taxonomy based on morphological data are not sufficient to clarify their relationship.

Karyotypic Diversification in Two Megaleporinus Species (Characiformes, Anostomidae) Inferred from In Situ Localization of Repetitive DNA Sequences

Anostomidae species have conserved diploid numbers (2n = 54), although comparative cytogenetic studies have demonstrated chromosomal rearrangements occurrence among them, especially in repetitive DNA rich regions. The location and distribution of ribosomal DNA (rDNA) and small nuclear RNAs (snRNAs) multigene families are highly dynamic in the genomes of several organisms. In this study, we in situ located the rDNA and snRNA sites in two populations of Megaleporinus obtusidens and a sample of Megaleporinus reinhardti to infer their chromosomal changes in the evolutionary lineages. Both species of Megaleporinus shared 2n = 54 chromosomes with the presence of ZZ/ZW sex chromosome system, but they diverged in relationship to the location of 5S and 45S rDNAs as well as the distribution of snRNAs sites. The characterization of the analyzed sequences revealed the presence of complete rDNA and snRNAs sequences as well as snRNAs containing transposable elements (TEs) and microsatellite repeats. After chromosomal mapping, the sequences encompassing TEs proved to be dispersed through autosomes and accumulated on sex chromosomes. The data demonstrate that intra- and interspecific chromosomal changes occurred involving the multigene family's sites in Megaleporinus karyotypes. Furthermore, we detected TE-like sequences in the differentiation of sex chromosome systems in M. obtusidens and M. reinhardti.

Molecular phylogeny and species delimitation of the genus Schizodon (Characiformes, Anostomidae)

The genus Schizodon is part of a group of headstanders and relatives (Family Anostomidae) that are widespread and ecologically important fishes in South American rivers. Schizodon includes 15 nominal species but their taxonomy has been challenging due to paucity of decisive characters to diagnose species. We present new molecular data to assess species boundaries or molecular operational taxonomic units (MOTUs), and to infer phylogenetic relationships among species. Evidence from two mitochondrial and three nuclear genes was used in these analyses. Mitochondrial DNA data for 112 specimens (from 11 nominal species) supported 13 consensus MOTUs, six of which matched valid nominal species (Schizodon borellii, S. fasciatus, S. intermedius, S. isognathus, S. knerii and S. scotorhabdotus). The nominal species Schizodon vittatus, S. nasutus, and S. dissimilis were subdivided into two MOTUs each, revealing either cryptic species or strong population structuring. In contrast, S. platae and S. jacuiensis constituted a single MOTU, indicating a possible case of synonymy. Our phylogenetic analysis subdivided the genus Schizodon into two large clades that are compatible with observed color patterns and biogeographic distribution. The first clade includes species with three to four conspicuous dark vertical bars on the flanks that originated in the Amazonas region (S. borellii, S. dissimilis, S. intermedius, S. fasciatus, S. scotorhabdotus, S. vittatus, and a cryptic species, Schizodon aff. vittatus). The second clade includes species with a conspicuous dark caudal blotch on the caudal peduncle, with vertical bars absent or inconspicuous, with a biogeographic origin in the La Plata drainage (S. isognathus, S. jacuiensis, S. knerii, S. nasutus and S. platae). Our results reinforce the importance of using molecular analyses to accelerate the study of diversity, particularly in groups with a wide distribution, few variable meristic characters, and high morphological plasticity, which may hide still unknown or underestimated diversity.

A new endangered species of Megaleporinus (Characiformes: Anostomidae) from the Rio de Contas basin, eastern Brazil

A new species of Megaleporinus is described from the Rio de Contas, a coastal drainage of eastern Brazil, and its phylogenetic relationships are studied using molecular data. The new species is unique among Anostomidae by possessing two exclusive features: an irregular dark longitudinal stripe from supracleithrum to second midlateral blotch and anterior cranial fontanel partially closed. In addition, the new species is diagnosed by having three premaxillary teeth, three dentary teeth, 37 or 38 scales in lateral line, 16 scale rows around caudal peduncle, three dark midlateral blotches on body, and red fins in life. The new species is closely related to M. obtusidens from the São Francisco basin, corroborating previous studies that indicated that the latter represents a species complex as currently defined. The new species exhibits the first rib enlarged in mature males, a feature described for some congeners. The new species is herein considered to be Endangered under the IUCN criteria.

Heteromorphic Sex Chromosomes and Their DNA Content in Fish: An Insight through Satellite DNA Accumulation in Megaleporinus elongatus

The repetitive DNA content of fish sex chromosomes provides valuable insights into specificities and patterns of their genetic sex determination systems. In this study, we revealed the genomic satellite DNA (satDNA) content of Megaleporinuselongatus, a Neotropical fish species with Z1Z1Z2Z2/Z1W1Z2W2 multiple sex chromosomes, through high-throughput analysis and graph-based clustering, isolating 68 satDNA families. By physically mapping these sequences in female metaphases, we discovered 15 of the most abundant satDNAs clustered in its chromosomes, 9 of which were found exclusively in the highly heterochromatic W1. This heteromorphic sex chromosome showed the highest amount of satDNA accumulations in this species. The second most abundant family, MelSat02-26, shared FISH signals with the NOR-bearing pair in similar patterns and is linked to the multiple sex chromosome system. Our results demonstrate the diverse satDNA content in M. elongatus, especially in its heteromorphic sex chromosome. Additionally, we highlighted the different accumulation patterns and distribution of these sequences across species by physically mapping these satDNAs in other Anostomidae, Megaleporinusmacrocephalus and Leporinusfriderici (a species without differentiated sex chromosomes).

Range distribution and contributions to taxonomy of Elops smithi (ELOPIFORMES: ELOPIDAE)

This study presents the first record of Elops smithi for northern Brazil. The evidence suggests this species is being misidentified incorrectly as Elops saurus in estuaries of the Western Atlantic Ocean. Here, morphological, molecular, and cytogenetic evidence identified all ladyfish specimens from one estuary in the region as E. smithi. Thus, at least Elops smithi occurs in the northern coast of Brazil and it is recommended that specimens from this region identified as E. saurus be further investigated with genetic and cytogenetic tools in order to assure a correct species identification.

Origin and evolution of sound production in Serrasalmidae

Among piranhas, sound production is known in carnivorous species, whereas herbivorous species were thought to be mute. Given that these carnivorous sonic species have a complex sonic apparatus, we hypothesize that intermediate forms could be found in other serrasalmid species. The results highlight the evolutionary transition from a simple sound-producing mechanism without specialized sonic structures to a sonic mechanism involving large, fast-contracting sonic muscles. Hypaxial muscles in basal herbivores primarily serve locomotion, but some fibres cause sound production during swimming accelerations, meaning that these muscles have gained a dual function. Sound production therefore seems to have been acquired through exaptation, i.e. the development of a new function (sound production) in existing structures initially shaped for a different purpose (locomotion). In more derived species (Catoprion and Pygopristis), some fibres are distinguishable from typical hypaxial muscles and insert directly on the swimbladder. At this stage, the primary function (locomotion) is lost in favour of the secondary function (sound production). In the last stage, the muscles and insertion sites are larger and the innervation involves more spinal nerves, improving calling abilities. In serrasalmids, the evolution of acoustic communication is characterized initially by exaptation followed by adaptive evolution.

Satellitome landscape analysis of Megaleporinus macrocephalus (Teleostei, Anostomidae) reveals intense accumulation of satellite sequences on the heteromorphic sex chromosome

The accumulation of repetitive DNA sequences on the sex-limited W or Y chromosomes is a well-known process that is likely triggered by the suppression of recombination between the sex chromosomes, which leads to major differences in their sizes and genetic content. Here, we report an analysis conducted on the satellitome of Megaleporinus macrocephalus that focuses specifically on the satDNAs that have been shown to have higher abundances in females and are putatively located on the W chromosome in this species. We characterized 164 satellite families in M. macrocephalus, which is, by far, the most satellite-rich species discovered to date. Subsequently, we mapped 30 satellites, 22 of which were located on the W chromosome, and 14 were shown to exist only on the W chromosome. Finally, we report two simple, quick and reliable methods that can be used for sex identification in M. macrocephalus individuals using fin clips or scales, which could be applicable to future studies conducted in the field of aquaculture.

Ichthyofauna from floodplain lakes of Reserva de Desenvolvimento Sustentável Piagaçu-Purus (RDS-PP), lower rio Purus

Abstract: The ichthyofauna of the rio Purus has been little investigated, especially in its lower portion, characterized by diverse aquatic environments, especially in flooded areas. We inventoried the ichthyofauna of floodplain lakes with different management efforts in Reserva de Desenvolvimento Sustentável Piagaçu-Purus (RDS-PP), which represent important resource for commercial fishing in North region, in the first illustrated inventory of the fish fauna from lower rio Purus. We surveyed 20 lakes, classified as open access (eight lakes) and protected (12 lakes) during 2009 low water levels. A total of 2,299 individuals were collected, represented by seven orders, 25 families and 74 species. Characiformes was the most representative order in number of species and families, followed by Siluriformes, Cichliformes, Gymnotiformes, Clupeiformes, and Osteoglossiformes. Most abundant and frequent species were Pygocentrus nattereri, Triportheus angulatus, Serrasalmus sp. "2n=58", Pterygoplichthys gibbiceps, and Osteoglossum bicirrhosum. Protected lakes presented higher species richness compared to open access lakes. Similarly, protected lakes possessed 26 species occurring exclusively, with emphasis on Colossoma macropomum, an important species for fisheries due to its commercial importance. We added 44 new records of fish species for the lower rio Purus. Our results indicate the potential efficiency of zoning systems of open access and protected lakes established by local population and ruled by RDS-PP for fisheries management. Therefore, we strongly suggest its maintenance for conservation of ichthyofauna of floodplain lakes of lower rio Purus.

New species of Leporinus (Characiformes: Anostomidae) from the highlands of the Guiana Shield in Venezuela

ABSTRACT A new species of Leporinus is described using morphological data and compared to all other species of the family. Specimens were illustrated using digital photograph, measured using digital calipers, and had teeth, scales, and fin rays counted under a stereomicroscope. The new species is distinguished from all other Anostomidae, except Anostomus anostomus, A. brevior, A. ternetzi, Hypomasticus despaxi, Leporinus arcus, and L. striatus, by having four dark longitudinal stripes on body. The new species is distinguished from aforementioned species by having terminal mouth with four teeth on the premaxilla, 12 series of scales around caudal peduncle, and 34 to 36 scales in the lateral line. The new species is remarkably similar to Leporinus arcus, which occurs on the opposite side of Guyana Shield highlands. The new species and L. arcus are possibly closely related to Leporinus gomesi, L. granti, L. lebaili, L. melanostictus, L. nijsseni, and L. santosi.

Peixes da planície de inundação do alto rio Paraná e áreas adjacentes: revised, annotated and updated

ABSTRACT The book “Peixes da planície de inundação do alto rio Paraná e áreas adjacentes” represents the most cohesive data compilation for the rio Paraná floodplain. However, considering the dynamicity of the taxonomy of freshwater fishes, several new records and taxonomic changes occurred along the past years. Therefore, the results of that publication were revisited, providing an update of the species list, their taxonomic status, records and geographic distribution, and also new keys for genera and species. The species included were those recorded in the rio Paraná basin, from the mouth of the rio Paranapanema to the Itaipu Reservoir, following the general methodology presented in the book. A total of 10 orders, 41 families, 126 genera, and 211 species were registered, with an increase of one order, six families, 14 genera, and 29 species when compared to the book. Additionally, four new genera recently described, five synonymization proposals, 14 new identifications, four new combinations, 12 new species recently described, 34 new records, and nine misidentified species were recorded. These results are associated with the redirection of human and financial resources to that area, which enabled monitoring and intensive exploration of its watercourses; as well as training of taxonomists, and new taxonomic resolutions.

Molecular Evidences of a Hidden Complex Scenario in Leporinus cf. friderici

The megadiversity of the neotropical ichthyofauna has been associated to recent diversification processes, reflecting in subtle or lacking morphological differentiation between species, challenging the classical taxonomic identification. Leporinus friderici occurs in several river basins of South America, and its nominal taxonomic validity has been questioned. Its wide distribution within the Brazilian Shield suggests that this species could be genetically structured among the hydrographic basins, despite a sharp morphological similarity. In this study, we performed phylogenetic analyses, based on three nuclear (recombination activating gene 1, RAG1, recombination activating gene 2, RAG2, and myosin heavy chain 6 cardiac muscle alpha gene, Myh6) and two mitochondrial (COI and Cytochrome b, Cytb) markers, in specimens morphologically similar to L. friderici and related species from different hydrographic basins in South America. Our phylogenetic tree identified four well-supported clades, which point out to the existence of taxonomic inconsistencies within this fish group. A clade named L. cf. friderici sensu stricto included eight Molecular Operational Taxonomic Units recently diversified in the Brazilian Shield basins. These results were also confirmed by a single-gene species delimitation analysis. It is suggested that this clade includes a species complex, characterizing taxonomic uncertainties. Another clade recovered only L. friderici from the Suriname rivers, validating this nominal species in its type locality. A third no-named clade, characterized by deeper species divergence, recovered five different nominal species interleaved with other undescribed forms previously also recognized as L. cf. friderici, indicating taxonomic errors. The fourth clade only included L. taeniatus. Our results showed a complex scenario involving the morphotype L. cf. friderici and allowed us to address aspects related to evolutionary diversification of this fish group and historical processes involved with, highlighting the importance of revealing hidden biodiversity for the taxonomy and conservationist action plans of these fish.

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.