Evidence of incipient speciation in Astyanax scabripinnis species complex (Teleostei: Characidae)

Abstract

Two populations of the Astyanax scabripinnis complex, isolated by a waterfall with over 100 meters depth and inhabiting different altitudes of the same river (1850 m a.s.l. and 662 m a.s.l.) were compared in reproductive data, geometric morphometry, tooth morphology, anal-fin rays counts, and karyotype, in order to test the hypothesis of speciation between the two populations. The results in the geometric morphometry analysis showed differences between the populations. Discriminant function analysis (DFA) and canonical variance analysis revealed sexual dimorphism. Secondary sexual characters, such as hooks in the anal fin rays of the males are absent in the lower altitude population. Both populations had the same macro karyotype structure, except for the absence of B chromosomes in the lower altitude population. The fluorescence in situ hybridization showed differences for both markers (18S rDNA and 5S rDNA), and reproductive data suggests pre-zygotic reproductive isolation among the two populations. The data showed the absence of gene flow, indicating that an incipient speciation process has occurred, which leads the two populations to follow independent evolutionary pathways.Duas populações do complexo Astyanax scabripinnis isoladas por uma queda d´água de mais de 100 metros de altura e localizadas em diferentes altitudes do mesmo rio (662 m e 1850 m a.s.l.) foram comparadas através de dados de reprodução, cariótipo, morfometria geométrica, morfologia dentária, e número de raios da nadadeira anal, de modo a testar a hipótese de especiação entre as duas populações. Os resultados de morfometria geométrica mostraram diferenças entre as populações. A análise da função discriminante (DFA) e a análise de variância canônica (CVA) demonstraram a presença de dimorfismo sexual. Caracteres sexuais secundários, como ganchos em raios da nadadeira anal dos machos, estão ausentes na população de menor altitude. Ambas as populações têm a mesma macro estrutura cariotípica, exceto pela ausência de cromossomos B na população de menor altitude. A hibridação in situ mostrou diferenças para ambos os marcadores (rDNA 18S e rDNA 5S), e os dados de reprodução sugerem isolamento reprodutivo pré-zigótico entre as duas populações. Os dados mostram ausência de fluxo gênico, indicando que ocorreu um processo de especiação incipiente, o que leva as duas populações seguirem vias evolutivas independentes.

Allopatric chromosomal variation in Nematocharax venustus Weitzman, Menezes & Britski, 1986 (Actinopterygii: Characiformes) based on mapping of repetitive sequences

“…However, this characteristic may be an intrapopulation variation found in Jequitinhonha 2, since the double-FISH was obtained for a single individual from this collection site. Other reports of synteny between both families of ribosomal genes are available in some genera of Characiformes, like Astyanax Baird & Girard (Castro et al, 2014b), Prochilodus Agassiz (Vicari et al, 2006), Triportheus Cope (Diniz et al, 2009), and Hoplias Gill (Cioffi et al, 2009b). It should be pointed out that active Ag-NORs in the population from Jequitinhonha 2 were observed only in pair 8.…”

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

“…This regulatory effect could cause, in the case of females, later ovary development, since B+ females presented lower expression of foxl2a compared to a B− female, and extending male spermatogenesis due to the upregulatory effect on dmrt1 expression reported for B+ males of A. scabripinnis [31] (Figure 4). Such an extended reproductive period may contribute to the maintenance of this chromosome and consist of an important adaptive advantage that maintains populations in small high-altitude streams, which are constantly susceptible to intense environmental variations and predation [35,50,51]. Regarding a disproportional sex ratio, our sampling did not demonstate such a difference, mainly because we chose not to do that.…”

Spinal malformations in a naturally isolated Neotropical fish population

“…To produce morphometric data, we considered 14 anatomical landmarks (Fig. 2) distributed throughout the body, according to (Castro et al, 2014). For determination of errors in the landmark points, the procedure was realized in triplicate by the same observer in different moments and tested by a Procrustes ANOVA (p < 0.0001) performed in Morpho J v1.07a (Klingerberg, 2011).…”

“…Figure 2 Anatomical landmarks used in X-ray images for morphometric analysis. 1: Anterior orbital region; 2: Posterior orbital region; 3: Dorsal region of head; 4: Anterior region of dorsal fin insertion; 5: Posterior region of dorsal fin insertion; 6: Dorsal region of beginning of caudal fin; 7: Ventral region of beginning of caudal fin; 8: Posterior region of anal fin insertion; 9: Anterior region of anal fin insertion; 10: Insertion of pectoral fin; 11: Ventral region of head (1-11 based onCastro et al, 2014). 12: First pre-caudal vertebra; 13: First caudal vertebra; 14: Last caudal vertebra (12-14 based onBird & Mabee, 2003), where pre-caudal vertebrae are those posterior to the Weberian apparatus and anterior to caudal vertebrae.…”