Population Genetic Structure of Astyanax scabripinnis (Teleostei, Characidae) from an Urban Stream

Despite the great anthropogenic interference on urban streams, information is still scarce about the genetic variability and structure of native fish populations inhabiting such streams. In the present study, random amplified polymorphic DNA (RAPD) markers were used to analyze genetic variability and structure of populations assigned to the Neotropical fish species Astyanax scabripinnis from an urban stream located in Londrina, Paraná State, southern Brazil. Thirty individuals of this species were collected from three sites throughout the upper Cambé stream. A total of 10 primers amplified 159 loci, of which 128 (80.5%) were polymorphic. Each of the three populations showed very similar proportions of polymorphic loci, which ranged from 63.5 to 64.8%. Unbiased genetic distances varied from 0.0612 to 0.0646. Theta_p-test values indicated moderate to high genetic differentiation among individuals from different localities. The number of migrants varied from 1.34 to 1.46, suggesting a low gene flow between populations. The genetic similarity among all individuals studied ranged from 0.424 to 0.848. The results suggest that populations of A. scabripinnis in Cambé stream are undergoing genetic differentiation.     

Genetic divergence between cave and surface populations of Astyanax in Mexico (Characidae,Teleostei)

A study of genetic diversity at microsatellite loci and the mitochondrial DNA (mtDNA) cytochrome b gene was carried out to assess genetic relationships among four Mexican cave (Pachon, Sabinos, Tinaja, Chica) and four surface populations of Astyanax fasciatus (Characidae) from northeast Mexico and the Yucatan. With the exception of Chica, the cave populations were all characterized by extremely low microsatellite variability, which most likely resulted from bottleneck events. Population analyses of the microsatellite data indicated no measurable levels of gene flow between all cave and surface populations (F(ST) > 0.0707). Phylogenetic analyses of mtDNA data showed that only two cave populations - Sabinos and Tinaja - group together to the exclusion of surface populations. From the microsatellite data these cave populations cluster with the Pachon cave fish population. The mtDNA thus appears to have been replaced in Pachon because of introgressive hybridization. It is likely that these three cave populations have descended from a surface ancestor in common with current surface populations, rather than evolving recently from one of the extant surface populations. Like Pachon, the Chica population clustered with the surface populations according to mtDNA data, but was not clearly associated with either the surface or the other cave populations according to the microsatellite data. Our data indicate that the Chica population evolved recently from a surface population, and subsequently hybridized with a phylogenetically older cave population. In conclusion, both the microsatellite and mtDNA data suggest multiple origins of cave populations and the Chica and Sabinos/Tinaja/Pachon were founded after at least two independent invasions from surface populations.     

Cytotaxonomy of Astyanax (Characiformes,Characidae) from the Upper Iguaçu River Basin: confirmation of the occurrence of distinct evolutionary units

Taxonomic studies of the genus Astyanax from the Iguaçu River (Brazil) indicate that they may be differentiated into 11 distinct species, some of which have not been formally described and named so for. This study focuses on three of these species, Astyanax sp. B, Astyanax sp. C and Astyanax sp. D from the Upper Iguaçu River Basin. Comparative cytogenetic analyses of C‐banding, Ag‐NORs (silver nitrate stained nucleolar organizer region) and 18S and 5S rDNA corroborate that they are distinct species. A diploid number of 50 chromosomes and similar karyotypic formulae were observed in the three taxa, with the exception of Astyanax sp. D that differs in the number of submetacentric and subtelocentric chromosomes. However, the NOR silver‐staining pattern, the heterochromatic bands (C‐bands) and the mapping of the 18S and 5S rDNA sites in the chromosomes showed divergences between all three species under study, supporting the occurrence of distinct evolutionary units.     

Population genetic patterns revealed by microsatellite data challenge the mitochondrial DNA based taxonomy of Astyanax in Mexico (Characidae, Teleostei)

Astyanax has become an important model system for evolutionary studies of cave animals. We investigated correlations of population genetic patterns revealed by microsatellite data and phylogeographic patterns shown by mitochondrial DNA sequences in Mexican cave and surface fish of the genus Astyanax (Characidae, Teleostei) to improve the understanding of the colonization history of this neotropical fish in Central and North America and to assess a recent taxonomic classification. The distribution of nuclear genotypes is not congruent with that of the mitochondrial clades. Admixture analyses suggest there has been nuclear gene flow between populations defined by different mitochondrial clades. The microsatellite data indicate that there was mitochondrial capture of a cave population from adjacent populations. Furthermore, gene flow also occurred between populations belonging to different nuclear genotypic clusters. This indicates that neither the nuclear genotypic clusters nor the mitochondrial clades represent independent evolutionary units, although the mitochondrial divergences are high and in a range usually characteristic for different fish species. This conclusion is supported by the presence of morphologically intermediate forms. Our analyses show that the Trans-Mexican Volcanic Belt limited gene flow, but has been crossed by Astyanax several times. In Yucatán, where obvious geographic barriers are missing, the incongruence between the distribution of nuclear and mitochondrial markers reflects random colonization events caused by inundations or marine transgressions resulting in random phylogeographic breaks. Thus, conclusions about the phylogeographic history and even more about the delimitation of species should not be based on single genetic markers.     

Development and evolution of melanophore patterns in fishes of the genus Danio (Teleostei: Cyprinidae)

Pigmentation patterns in vertebrates have become an important model for those interested in mechanisms of pattern determination. I present detailed information on the development of melanophore patterns in the zebrafish, Danio rerio, five close relatives of that species, and an outgroup. The comparison of the ontogeny of melanophore patterns in this group is an important first step towards understanding the developmental basis of the interspecific variation. Pigment patterns in this group range from no distinct patterning at all to stripes of differing numbers and widths to reticulated stripes. Species examined form identical larval patterns and follow a common sequence of events from which different elements are eliminated or altered to produce the variety of patterns seen in the group. As flexion is completed, melanophores move from larval positions onto the flanks of the fish. In D. rerio, D. rerio ‘leo,’ D. kerri, and D. malabaricus, xanthophores become established on the body of the fish as the melanophores move; erythrophores become established on the flanks of D. albolineatus and D. sp. cf. aequipinnatus. An increase in melanophore number, begun at this time, continues at a higher rate in D. rerio, D. kerri, D. sp. cf. aequipinnatus and Tanichthys albonubes than in the other three species. This results in a greater number of melanophores on adults in those species with a higher rate of melanophore increase. No distinct pattern forms, except on the caudal peduncle, in D. albolineatus. In all other Danio species, melanophore stripes form first below then above the horizontal myoseptum. Additional stripes are added first below then above these initial two stripes. D. kerri develops fewer, wider melanophore stripes than D. rerio. After initial stripe formation, D. malabaricus and D. sp. cf. aequipinnatus both developed vertical pattern elements and reticulations in the melanophore pattern. Differences in patterns between species are similar in several cases to described mutants of the zebrafish, suggesting that some aspects of interspecific pigmentation pattern variation may be under relatively simple genetic control. J. Morphol. 241:83–105, 1999. © 1999 Wiley‐Liss, Inc.     

Toward a population genetic framework of developmental evolution: the costs,limits, and consequences of phenotypic plasticity

Adaptive phenotypic plasticity allows organisms to cope with environmental variability, and yet, despite its adaptive significance, phenotypic plasticity is neither ubiquitous nor infinite. In this review, we merge developmental and population genetic perspectives to explore costs and limits on the evolution of plasticity. Specifically, we focus on the role of modularity in developmental genetic networks as a mechanism underlying phenotypic plasticity, and apply to it lessons learned from population genetic theory on the interplay between relaxed selection and mutation accumulation. We argue that the environmental specificity of gene expression and the associated reduction in pleiotropic constraints drive a fundamental tradeoff between the range of plasticity that can be accommodated and mutation accumulation in alternative developmental networks. This tradeoff has broad implications for understanding the origin and maintenance of plasticity and may contribute to a better understanding of the role of plasticity in the origin, diversification, and loss of phenotypic diversity.     

Cytogenetic characterization of a supernumerary chromosome segment and of B-chromosomes in Astyanax scabripinnis (Teleostei, Characidae)

The chromosome complement of a local population of Astyanax scabripinnis in Brazil was investigated with emphasis on the study of the heterochromatin attached to the A-chromosomes and present in the macro B-chromosome. Analysis after C-banding, silver and CMA₃ staining, incorporation of 5-bromo-2′-deoxyuridine and chromosome digestion with nine restriction endonucleases revealed that the heterochromatin in the B-chromosomes was different from that found in the A-chromosomes. A polymorphism due to the presence of a supernumerary heterochromatic chromosome segment was observed in the population investigated. Some aspects related to the origin of the heterochromatin polymorphism in Astyanax scabripinnis are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gonadal morphology and difference in reproductive development of two isolated populations of Astyanax rivularis (Teleostei,Characidae)

Individuals of the same species may present different reproductive tactics depending on the environment in which they develop and mature. The present study aimed to define the gonadal development phases of males and females of Astyanax rivularis and to carry out a comparative analysis of the reproductive development of specimens captured in two isolated environments of the São Francisco River basin in Serra da Canastra, Brazil (Point 1: low vegetation and river showing calm and crystalline waters with small well formations; Point 2: current waters, and well-established areas of arboreal vegetation). Thus, the gonads of A. rivularis specimens were collected, fixed and processed with techniques for light microscopy. Five maturation phases of the females' reproductive cycle were established: immature, developing, spawning capable, regressing and regenerating. Three maturation phases of the males' reproductive cycle were observed: spawning capable, regressing, and regenerating. There are differences in the phases of gonadal development of A. rivularis between the two sampling points so that, possibly, animals upstream of the waterfall demonstrate a delay in the reproductive cycle in relation to animals downstream.     

Determining Management Units in Southeastern Brazil: The Case of Astyanax bimaculatus (Linnaeus, 1758) (Teleostei: Ostariophysi: Characidae)

Characterization, management and protection of biodiversity are the most prominent challenges in conservation biology. Analyses on molecular similarity (Random Amplified Polymorphic DNA-Polymerase Chain Reaction, RAPD-PCR) and morphologic patterns (morphometric and meristic characters) were performed to evaluate the existence of population structuring in the Doce river basin, in a widespread small-sized characin, Astyanax bimaculatus. Three hundred (300) individuals were collected from six locations isolated by waterfalls or dams, in the Doce river basin, Minas Gerais State, Brazil. Genetic differentiation among tributaries was significant (p<0.00001) and accounted for 21% of total variance (p<0.00001). Only the Grande waterfall of the Casca river was an effective factor for differentiation of populations (p<0.00001), and meristic characters were also consistent with molecular data. We concluded that genetic and morphologic variation of this species was not necessarily associated with waterfalls and that molecular and meristic data are effective predictors of population divergence in this basin. The consequences of these findings for the protection and management of aquatic biodiversity were discussed.     

Delimiting species using multilocus data: diagnosing cryptic diversity in the southern cavefish, Typhlichthys subterraneus (Teleostei: Amblyopsidae)

A major challenge facing biodiversity conservation and management is that a significant portion of species diversity remains undiscovered or undescribed. This is particularly evident in subterranean animals in which species delimitation based on morphology is difficult because differentiation is often obscured by phenotypic convergence. Multilocus genetic data constitute a valuable source of information for species delimitation in such organisms, but until recently, few methods were available to objectively test species delimitation hypotheses using genetic data. Here, we use recently developed methods for discovering and testing species boundaries and relationships using a multilocus dataset in a widely distributed subterranean teleost fish, Typhlichthys subterraneus, endemic to Eastern North America. We provide evidence that species diversity in T. subterraneus is currently underestimated and that the picture of a single, widely distributed species is not supported. Rather, several morphologically cryptic lineages comprise the diversity in this clade, including support for the recognition of T. eigenmanni. The high number of cryptic species in Typhlichthys highlights the utility of multilocus genetic data in delimiting species, particularly in lineages that exhibit slight morphological disparity, such as subterranean organisms. However, results depend on sampling of individuals and loci; this issue needs further study.     

Chromosomal location and distribution of As51 satellite DNA in five species of the genus Astyanax (Teleostei, Characidae, Incertae sedis)

Constitutive heterochromatin makes up a substantial portion of the genome of eukaryotes and is composed mainly of satellite DNA repeating sequences in tandem. Some satellite DNAs may have been derived from transposable elements. These repetitive sequences represent a highly dynamic component of rapid evolution in genomes. Among the genus Astyanax , the As51 satellite DNA is found in species that have large distal heterochromatic blocks, which may be considered as derived from a transposable DNA element. In the present study, As51 satellite DNA was mapped through in situ fluorescent hybridization in the chromosomes of five species of the genus. The possible roles of this type of saltatory DNA type in the genome of the species are discussed, along with its use for the phylogenetic grouping of the genus Astyanax , together with other shared chromosomal characters. However, the number of As51 clusters is presented as a homoplastic characteristic, thereby indicating evident genomic diversification of species with this type of DNA.     

Convergent evolution of the lateral line system in Apogonidae (Teleostei: Percomorpha) determined from innervation

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.     

Description of Dendrorchis retrobiloba n. sp. (Digenea: Gorgoderidae) from Astyanax fasciatus (Teleostei: Characidae) from Southern Uruguay, with an emended diagnosis of the genus Dendrorchis

To date, the monospecific Dendrorchis is represented by D. neivai, reported from Brazil and parasitizing Brycon lundi. Dendrorchis retrobiloba n. sp. is described from the swim bladder of Astyanax fasciatus from Ca?ada del Dragón stream in Montevideo, southern Uruguay (34 degrees 47'S, 56 degrees 14'W), and the emended diagnosis of Dendrorchis is given. The diagnosis of Dendrorchis has been modified to include the following characters: Phyllodistominae with flattened body, wider in the region posterior to acetabulum. Intestinal ceca sinuous or not. Testes branched or with superficial lobes. Ovary with deep or superficial lobes. Seminal receptacle present or absent. Vitellaria ellongate or pyriform. Uterus extends to posterior region and to portion of body anterior to acetabulum. Eggs oval, variable size, thin-shelled, without opercula. Dendrorchis retrobiloba n. sp. differs from D. neivai by having pyriform vitellaria, ovary larger than the testes and not deeply lobed, wider distribution of the uterus, smaller egg size, testes with superficial lobes, oral sucker wider than the acetabulum, shorter esophagus, 2 terminal lobes at the posterior end of the body, and much smaller body length. Despite being found in different hosts, both species of Dendrorchis parasitize the swim bladder of freshwater Characidae.     

Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): tools for understanding karyotypic evolution

Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C‐banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter‐individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached. This revised version was published online in July 2006 with corrections to the Cover Date.     

Developmental constraints in regressive evolution: studies of the expression of the γs-crystallin gene in the developing lens of cave-dwelling Astyanax fasciatus (Cuvier, 1819) (Teleostei, Characidae) by in situ hybridization

The early morphogenesis of the lens and the expression of the γs-crystallin gene was studied in epigean Astyanax fasciatus and its cave-dwelling derivative. At early stages, the lens of the cave fish develops in a way that is similar to the epigean form. Later, the developmental timing is delayed and growth ceases in the cave-fish lens. With the beginning of cytodifferentiation, the development of the lens breaks down. Crystallin lens fibres are not produced at any time and the γs-crystallin gene, which is transcribed during a limited period in the lens of epigean fishes, is not active in cave specimens. This study confirms earlier immunofluorescence observations that demonstrated the lack of crystallin proteins in the cave-fish lens, but is in contrast to results on the blind mole rat, which showed a persistence of functioning crystallins in the degenerated lens of this species. The significance of developmental constraints in regressive evolution is discussed.     

A new cavefish of Sinocyclocheilus (Teleostei: Cypriniformes: Cyprinidae) from the Nanpanjiang River in Guizhou,China

A new species, Sinocyclocheilus xingyiensis, is described based on specimens collected from a karst cave in Guizhou Province, China. The authors used an integrated taxonomic approach, including morphological and molecular data, to identify the new species as a member of the Sinocyclocheilu angularis group, and it can be distinguished from all other members of this group by a combination of the following features: two pairs of long barbels and long pectoral fins, 42–46 lateral-line scales, 7 (13–14) on outer (inner) side of the first gill arch and 35 (14–15 + 4 + 16 − 17) vertebrae. Phylogenetic analyses based on the cytochrome b (cyt b) gene fragment suggest that S. xingyiensis is a sister lineage to Sinocyclocheilus flexuosdorsalis. The genetic distance (Kimura 2-parameter) between the S. xingyiensis and S. angularis groups of Sinocyclocheilus species based on cyt b gene fragment ranged from 1.2% to 15.4%.     

Oxygen consumption of Astyanax fasciatus (Characidae,Pisces): a comparison of epigean and hypogean populations

Synopsis The standard and routine oxygen consumptions of Astyanax fasciatus from one surface population (Rio Teapao) and three cave populations (Chica, Micos and Pachon caves: sAnoptichthys jordani, the Micosfish and Anoptichthys antrobius) were determined individually over 24 hours by the use of a flow-through respirometer and polarographic oxygen electrodes. The phylogenetically oldest Pachon fish had a significantly lower standard metabolic rate (0.230 ± 0.036 mg O₂ g^-1 h^-1) than the epigean Teapao fish, the hybrid Chica fish and the phylogenetically younger Micos fish (0.314 ± 0.081 mg O₂g-^-1h^-1, 0.284 ± 0.048 mg O₂g^-1h^-1, 0.277 ± 0.063 mg O₂g^-1h^-1). No significant differences could be determined among the latter three populations. A significant difference in routine metabolic rate existed only between the Pachon fish (0.309 ± 0.0.56 mg O₂g^-1h^-1) and the Teapao fish (0.415 ± 0.071 mg O₂g^-1h^-1). The Chica fish (0.356 ± 0.084 mg O₂g^-1h^-1) and the Micos fish (0.355 ± 0.080 mg O₂ g^-1h^-1) could not be separated from either the Teapao or the Pachon fish, but a decreasing trend from the surface population through the Chica and the Micos to the Pachon population was obvious. During a starvation period of 29 days the metabolic rate of epigean Teapao and hypogean Pachon fish decreased significantly by 32.5% and 34.8% (standard oxygen consumption rate) and 27.5% and 28.2% (routine oxygen consumption rate), respectively. Body mass loss during the starvation period was 16.3% for the Teapao fish and 9.5% for the Pachon fish.