Differential Expression of Genes Related to Sexual Determination Can Modify the Reproductive Cycle of Astyanax scabripinnis (Characiformes: Characidae) in B Chromosome Carrier Individuals

The species complex Astyanax scabripinnis is one of the most studied with respect to origin, distribution, and frequency of B chromosomes, and is considered a model organism for evolutionary studies. Research using population inferences about the occurrence and frequency of the B chromosome shows seasonal variation between sexes, which is associated with the presence of this supernumerary element. We hypothesized that the B chromosome could influence the sex ratio of these animals. Based on this assumption, the present work aimed to investigate if differences exist among levels of gene expression with qRT-PCR of the amh (associated with testicular differentiation) and foxl2a (associated with ovarian differentiation) genes between B-carrier and non-B-carrier individuals. The results showed that for the amh gene, the difference in expression between animals with B chromosomes was not accentuated compared to that in animals without this chromosome. Expression of foxl2a in B-carrier females, however, was reduced by 73.56% compared to females that lacked the B chromosome. Males had no difference in expression of the amh and foxl2a genes between carriers and non-carriers of the B chromosome. Results indicate that the presence of B chromosomes is correlated with the differential expression of sex-associated genes. An analysis of these results integrated with data from other studies on the reproductive cycle in the same species reveals that this difference in expression may be expanding the reproductive cycle of the species.

Genetic variability in a population of Astyanax scabripinnis: recent bottleneck and the possible influence of individuals with B chromosomes

Access the genetic variability of endangered and isolated populations has become an important conservation tool. Astyanax scabripinnis is a well-known fish model for genetic studies, forming very isolated populations in headwaters. Besides that, this species frequently presents supernumerary chromosomes, which elevates the interest on genetic studies. Genetic diversity of an Astyanax scabripinnis population from the Atlantic Forest (Serra da Mantiqueira region, Brazil) was assessed with microsatellite markers for the first time. Since microsatellite markers are not described for this species, we tested markers described for a related species for transferability to A. scabripinnis. Six polymorphic loci were sufficiently reliable for population genetic analysis. We found that this population passed through a recent bottleneck because of the presence of an excess of heterozygotes, low allelic diversity, heterozygosity excess, and small effective population size. Individuals with and without B chromosomes were previously identified in this population and our study found private alleles in the individuals without B chromosomes. Furthermore, when individuals without B chromosomes were removed from the analysis, the population did not present heterozygosity excess, suggesting that the bottleneck event was driven by individuals with B chromosomes. Our results provide an insight into the value of microsatellite markers as molecular tools and is the first genetic study using molecular data of A. scabripinnis from this area.

A new species of Astyanax Baird & Girard (Characiformes: Characidae) from western Chapada Diamantina, Bahia, Brazil

A new species of Astyanax from the upper rio Paraguaçu basin, Chapada Diamantina, Bahia, Brazil, is described. Astyanax sincora shares characters currently used to define the Astyanax scabripinnis species complex, as highest body depth approximately at vertical through pectoral-fin midlength and a low number of branched anal-fin rays (13–17). It differs from its congeners by a combination of characters, including eight branched dorsal-fin rays, six branched pelvic-fin rays, presence of bony hooks in pectoral and anal fins of males, dark midlateral line or stripe initiating posteriorly to the vertically elongate humeral blotch, and by the presence of 30–35 scales in the median longitudinal series. The generic positioning of the new species and some polymorphic morphological characters in Astyanax are briefly discussed. The degree of completeness of the lateral line in Hyphessobrycon balbus is discussed. [Species Zoobank registration: urn:lsid:zoobank.org:pub:D708FE7E-3FB5-4729-B438-779717F7ED1A]

Two new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Paraguaçu basin, Chapada Diamantina, Bahia, Brazil

Astyanax lorien and A. rupestris are described from tributaries of upper rio Paraguaçu basin, Bahia, Brazil. Both species shares the majority of the characters currently used to define the Astyanax scabripinnis species complex, with highest body depth approximately at vertical through pectoral-fin midlength and a low number of branched anal-fin rays (15–21). Astyanax lorien is distinguished from its congeners by a combination of characters, including presence of small bony hooks on all fins of mature males, a unique vertically elongate humeral blotch, and ventral margin of the third infraorbital close to the horizontal limb of preopercle. Astyanax rupestris is distinguished from its congeners also by a combination of characters, including ventral margin of third infraorbital distinctly separated from horizontal limb of preopercle, leaving a broad area without superficial bones, absence of midlateral stripe on body, absence of blotch on caudal peduncle, and presence of a vertically elongated conspicuous dark humeral blotch, not bordered anteriorly and posteriorly by distinct unpigmented areas. Both species are apparently endemic to the upper portion of the Paraguaçu river basin, within the Chapada Diamantina domain.

Composição e riqueza de peixes em diferentes corpos d’água no parque nacional das Araucárias, Sul do Brasil

O conhecimento das espécies de um determinado ambiente é base para futuros estudos ecológicos, bem como para o auxílio no manejo e conservação de áreas prioritárias. Para tal, esse estudo objetivou inventaria a composição de espécies de peixes em diferentes ambientes aquáticos no Parque Nacional das Araucárias (PNA), Santa Catarina. Foram avaliados 10 pontos amostrais com características distintas (riachos, lago de reservatório, açude e rios de maior porte) ao longo da área do Parque. Para a amostragem diferentes artes de pesca foram empregadas em cinco coletas com periodicidade trimestral. Um total de 1.022 exemplares foi registrado, distribuídos em 22 espécies, sete famílias e quatro ordens, das quais Siluriformes apresentou a maior riqueza para a área de estudo. Astyanax scabripinnis, Oligosarcus brevioris, Hoplias malabaricus e Rhamdia quelen apresentaram a maior amplitude de distribuição, enquanto as demais ficaram restritas a um ou poucos ambientes. Ainda, destaca-se a presença de Crenicichla empheres, espécie considerada endêmica do rio Chapecó, além de Cyprinus carpio, espécies exótica, que foi registrada em um açude no interior do Parque. Ademais, por meio da curva de acumulação, foi possível inferir que as maiores parcelas das espécies presentes na área do PNA foram registradas, haja vista a tendência da curva a atingir a assíntota. Por fim, destaca-se a ocorrência de Crenicichla lepidota, Pareiorhaphis vestigipinnis e Pareiorhaphis steindachneri, para as quais não havia ainda, registros para a bacia do rio Chapecó. Ressalta-se que a presença de algumas espécies possivelmente esteja associada a determinadas características estruturais e ambientais encontradas na área do Parque, reforçando a importância de tais áreas para a manutenção da biota, tal como os peixes.