Abstract
Extensive chromosome variation involving Robertsonian and non-Robertsonian changes were proposed to explain chromosomal evolution within killifishes of the aplocheiloid group belonging to the order Cyprinodontiforms. In the present work we describe the karyotypes of four Cynolebias species and analyze chromosome changes by means of mitochondrial phylogenetic studies, including 10 taxa of this genus. Diploid numbers varied from 48 to 44 and the number of chromosome arms from 50 to 54. Molecular phylogenetic analyses allow us to corroborate previous hypothesis about chromosome evolution in aplocheiloid fishes. The tree topology based on a combined dataset of mitochondrial cytochrome b and 12S genes shows that recent cladogenetic events within the genus Cynolebias could have occurred by allopatric or ‘in-situ’ differentiation involving chromosomal rearrangements. Our analyses of approximately 10% of mitochondrial genome can be helpful in determining these recent cladogenetic events but it showed limited phylogenetic resolution at intermediate levels of divergence. This can be explained in part by the high levels of DNA sequence divergence (ranging from 0.015 to 0.245) detected at intrageneric level. Different methodological approaches suggest that chromosomal changes in Cynolebias have occurred during their differentiation, supporting the hypothesis that the unresolved basal polytomy could be the result of rapid speciation events, like a true ‘star polytomy’.

Abstract
The annual killifishes of the genus Cynolebias Steindachner, 1876, include one of the well-supported clades composed of the Cynolebias adloffi species complex of the Ban˜ados del Este Biosphere Reserve Site, from the Atlantic coastal wetlands in Uruguay. One member of this clade, Cynolebias charrua, has been considered as an intergradation complex of populations between C. adloffi and C. viarius by showing high levels of morphological variability. Systematic affinities between both taxa have been historically discussed. In the present study, a phylogeographic approach based on mitochondrial cytochrome b haplotype analysis and chromosome data are presented. According to the present data a scenario of a multiple simultaneous speciation process and perhaps reticulation events is possible in the C. adloffi species complex, followed by divergence associated with Quaternary marine transgressions in this region. This hypothetic scenario could explain the remarkable genetic diversity and the lack of phylogenetic resolution among clades in C. charrua, as well as the disconcordance in the phylogenetic relationships among Cynolebias from different data sets. Several parameters of DNA polymorphism and chromosome data have also suggested that populations of C. charrua from southern Laguna Merin, in eastern Uruguay and southern Brazil, could represent a relictual group from a widespread ancestral population. Chromosome rearrangements like pericentric inversions in isolated populations could have triggered cladogenetic events from this highly polymorphic population. Present analysis suggests that the metapopulation could represent the management units in these endangered killifishes and that the populations of C. charrua from the Laguna Merin basin could be included in a high-priority conservation programme

Abstract
Phylogenetic relationships based on 324 base pairs of the mitochondrial cytochrome b gene were examined in 14 species of the genus Cynolebias. The monophyly of the genus relative to three outgroup taxa belonging to the family Rivulidae was supported by the sequence data. Bootstrap values corroborated the existence of intrageneric monophyletic units in both parsimony and Neighbour-joining analyses. These include a Cynolebias bellottii-C. wolterstorffl clade, a C. adloffi-2, C. duraznensis, C. viarius and C adloffi-1 group, and a C. gymnoventris, C. luteoflammulatus pair and the strongly supported assemblage that includes C. prognalhus and C. cheradophilus clade. Phylogenetic relationships remain poorly supported for C. nigripinnis, C. affinis and C. alexandri, and unresolved among the previous ingroup clades. Cytochrome b sequences reveal an unexpectedly high level of divergence among species of the genus Cynolebias. Consequently, cytochrome b shows good resolution of recent cladogenetic events but limited phylogenetic information at deeper nodes. High levels of sequence divergence span a broad range within Cynolebias. The highest sequence divergence (c. 28%) occurred among C. antenori and the remaining species of the genus. The minimum divergence value (4.5%) is exhibited by sympatric species C. cheradophilus and C. prognathus.

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.

Abstract
Among Neotropical fish fauna, the South American killifish genus Austrolebias (Cyprinodontiformes: Rivulidae) constitutes an excellent model to study the genomic evolutionary processes underlying speciation events. Recently, unusually large genome size has been described in 16 species of this genus, with an average DNA content of about 5.95 ± 0.45 pg per diploid cell (mean C-value of about 2.98 pg). In the present paper we explore the possible origin of this unparallel genomic increase by means of comparative analysis of the repetitive components using NGS (454-Roche) technology in the lowest and highest Rivulidae genomes. Here, we provide the first annotated Rivulidae-repeated sequences composition and their relative repetitive fraction in both genomes. Remarkably, the genomic proportion of the moderately repetitive DNA in Austrolebias charrua genome represents approximately twice (45 %) of the repetitive components of the highly related rivulinae taxon Cynopoecilus melanotaenia (25 %). Present work provides evidence about the impact of the repeat families that could be distinctly proliferated among sublineages within Rivulidae fish group, explaining the great genome size differences encompassing the differentiation and speciation events in this family.