Cytogenetic contributions for the study of the Amazonian Engystomops (Anura; Leiuperidae) assessed in the light of phylogenetic relationships

Abstract

Genetic divergence and speciation mechanisms of the Amazonian Engystomops frog have been inferred mainly from mtDNA sequences, microsatellite and male advertisement call. Although many aspects of this divergence remain unclear, cytogenetic analyses of Amazonian Engystomops populations are described and are compared to the relationships inferred from mitochondrial and nuclear DNA sequence data. High cytogenetic variation distinguished karyotypic patterns among the populations, even between populations which had no prezygotic isolation previously inferred from mating call analysis. Interestingly, the Puyo and Acre populations, which are in different clades, showed heteromorphic sex chromosomes (XX/XY), not identified in the other Ecuatorian populations analyzed. The analysis of a specimen collected in a site near Yasuní (Ecuador) which was cytogenetically related to the specimens from Puyo (Ecuador), was also phylogenetically closely related these specimens. In the rhodopsin nucleotide sequences, six polymorphic sites were identified and various specimens were heterozygous for them. All the data presented herein, in conjunction with those previously reported, corroborate the hypothesis that Engystomops petersi is a complex of distinct species. It also indicates that karyotypic evolution patterns may have played a substantial role in the Engystomops speciation and the occurrence of sporadic mating events between divergent evolutive lineages is discussed.

Karyotypic differentiation via 2n reduction and a finding of a case of triploidy in anurans of the genus Engystomops (Anura, Leiuperidae)

“…Based on the interpopulational female mate choice assessed in phonotaxis experiments, Guerra and Ron (2008) proposed that sexual selection is involved in speciation between populations of E. petersi. In addition, a high interpopulational karyological variation was observed and allowed the recognition of three groups in E. petersi (Targueta et al 2010). It supported the hypothesis that selective pressure against hybrids of diverse karyotypic groups could have played a role in the differentiation of some populations, contributing for their reproductive isolation (Targueta et al 2010).…”

“…In addition, a high interpopulational karyological variation was observed and allowed the recognition of three groups in E. petersi (Targueta et al 2010). It supported the hypothesis that selective pressure against hybrids of diverse karyotypic groups could have played a role in the differentiation of some populations, contributing for their reproductive isolation (Targueta et al 2010).…”

“…Despite the high chromosomal variation, all the karyotypes described for E. petersi complex had 2n = 22, as did those found in E. freibergi (Lourenço et al 1999;Targueta et al 2010), in E. pustulosus (León 1970, and in the karyotyped species of Physalaemus (De Lucca et al 1974;Silva et al 1999Silva et al , 2000Amaral et al 2000;Quinderé et al 2009;Tomatis et al 2009;Milani et al 2010;Nascimento et al 2010), which is the sister-group of Engystomops (Ron et al 2006). On the other hand, E. puyango and E. pustulatus showed a karyotype composed of 2n = 20 (Ron et al 2010), raising a question about when the 2n reduction has occurred.…”

“…By comparing the 2n = 20 karyotypes of the species of the Duovox clade with the 2n = 22 karyotypes of E. freibergi, of E. petersi from Puyo (Targueta et al 2010) and of Physalaemus species (De Lucca et al 1974;Silva et al 1999Silva et al , 2000Amaral et al 2000;Quinderé et al 2009;Tomatis et al 2009;Milani et al 2010;Nascimento et al 2010), a great similarity can be identified for the seven first chromosome pairs. Despite that, the chromosomal data already available does not allow us to infer any chromosomal loss or rearrangement that might have resulted in the 2n reduction in the Duovox clade.…”

“…The presence of undescribed cryptic species under the name E. petersi has been considered by some authors, in studies on advertisement call (Guerra and Ron 2008) and on genetics and cytogenetics Targueta et al 2010). Based on the interpopulational female mate choice assessed in phonotaxis experiments, Guerra and Ron (2008) proposed that sexual selection is involved in speciation between populations of E. petersi.…”