Burst speciation processes and genomic expansion in the neotropical annual killifish genus Austrolebias (Cyprinodontiformes, Rivulidae)

Abstract

The extent to which genome sizes and other nucleotypic factors influence the phyletic diversification of lineages has long been discussed but remains largely unresolved. In the present work, we present evidence that the genomes of at least 16 species of the neotropical rivulid killifish genus Austrolebias are unusually large, with an average DNA content of about 5.95 ± 0.45 picograms per diploid cell (mean C-value of about 2.98 pg). They are thus larger than the genomes of very nearly all other diploid, i.e. non-(paleo) polyploid species of actinopterygian fishes so far reported. Austrolebias species appear to be conventional diploids in all other respects and there is no reason to believe that they arise from polyploid ancestors. The genome sizes reported for other rivulid killifishes, including a putative sister group, are considerably smaller and fall within the range typical of most other cyprinodontoid species. Therefore, it appears that the ancestor(s) of contemporary Austrolebias have undergone one or more episodes of genome expansion encompassing sudden speciation process during the Pleistocene. In addition, these findings are consistent with the hypothesis of a positive correlation between species richness and genome size.

Next-generation sequencing detects repetitive elements expansion in giant genomes of annual killifish genus Austrolebias (Cyprinodontiformes, Rivulidae)

“…Two different species were included in the present comparative genomic analysis: A. charrua (specimen 2870) which shows an average value of nuclear DNA content of 6.16 ± 0.28 pg/diploid cell and the sister genus C. melanotaenia (specimen R447) with a nuclear DNA content of 2.72 ± 0.06 pg/diploid cell (García et al 2014). Fishes were sacrificed with an overdose of 2 %-phenoxyethanol and fixed in 95 % ethanol.…”

“…The killifish live in temporary seasonal habitats and each generation should be completed in few months, depending on environmental stochasticity (Wourms 1967). Recently, unusually large genome size, with an average DNA content of about 5.95 ± 0.45 pg per diploid cell (mean C-value of about 2.98 pg), has been described in almost 16 species (García et al 2014). Austrolebias species appear to be conventional diploids in all other respects and there is no reason to believe they arise from polyploid ancestors.…”

“…The analysis of the genome structure in nearly related genera, will allow an insight into the evolution of genome size and their peculiar landscape. Therefore, in this work we present the first comparative analysis, using NGS (454-Roche) technology, of the repetitive component in the genome of Austrolebias charrua and Cynopoecilus melanotaenia with the highest and lowest values of nuclear DNA content respectively (García et al 2014). Here, we provide the first annotated Rivulidae-repeated sequence composition and their relative repetitive fraction in both genomes.…”

Contrasting morphology with population genetics approach: An insight to revision of the Neotropical annual fish “Austrolebias robustus” species group based on a taxonomic integrative framework

“…In fact, spectacular species radiation has been reported for Austrolebias from the Pampas (Costa, ; Costa et al., ), where high morphological diversity was described among Austrolebias species groups (Loureiro & de Sá, ). Additionally, the burst speciation process in this genus has included an unusually large genome size increase within the aplocheiloids (García et al., ), associated with the explosive expansion of the transposable elements (TEs) representing more than 45% of the Austrolebia s genomes (García, Ríos, & Gutiérrez, ). Previous phylogenetic analyses, based on mitochondrial (García et al., ) and nuclear (Costa et al., ) genes, proposed that Austrolebias is a monophyletic entity, including different species groups that underwent sudden cladogenetic events since the Quaternary (García, Alvarez‐Valin, & Gómez, ; García et al., ).…”

“…Previous phylogenetic analyses, based on mitochondrial (García et al., ) and nuclear (Costa et al., ) genes, proposed that Austrolebias is a monophyletic entity, including different species groups that underwent sudden cladogenetic events since the Quaternary (García, Alvarez‐Valin, & Gómez, ; García et al., ). Several such events occurred among and within different species groups, associated with high levels of chromosomal divergence (García, ; García et al., , ). Whereas sympatric species are easily recognizable by morphological features often related to feeding specializations (Costa, ), the genus contains some assemblages of allopatric cryptic species only identifiable by details of their morphology (Costa, ; Costa et al., ).…”