Despite ongoing efforts to protect species and ecosystems in Cuba, habitat degradation, overuse and introduction of alien species have posed serious challenges to native freshwater fish species. In spite of the accumulated knowledge on the systematics of this freshwater ichthyofauna, recent results suggested that we are far from having a complete picture of the Cuban freshwater fish diversity. It is estimated that 40% of freshwater Cuban fish are endemic; however, this number may be even higher. Partial sequences (652 bp) of the mitochondrial gene COI (cytochrome c oxidase subunit I) were used to barcode 126 individuals, representing 27 taxonomically recognized species in 17 genera and 10 families. Analysis was based on Kimura 2-parameter genetic distances, and for four genera a character-based analysis (population aggregation analysis) was also used. The mean conspecific, congeneric and confamiliar genetic distances were 0.6%, 9.1% and 20.2% respectively. Molecular species identification was in concordance with current taxonomical classification in 96.4% of cases, and based on the neighbour-joining trees, in all but one instance, members of a given genera clustered within the same clade. Within the genus Gambusia, genetic divergence analysis suggests that there may be at least four cryptic species. In contrast, low genetic divergence and a lack of diagnostic sites suggest that Rivulus insulaepinorum may be conspecific with Rivulus cylindraceus. Distance and character-based analysis were completely concordant, suggesting that they complement species identification. Overall, the results evidenced the usefulness of the DNA barcodes for cataloguing Cuban freshwater fish species and for identifying those groups that deserve further taxonomic attention.

Evolution sometimes proceeds by loss, especially when structures and genes become dispensable after an environmental shift relaxes functional constraints. Subterranean vertebrates are outstanding models to analyze this process, and gene decay can serve as a readout. We sought to understand some general principles on the extent and tempo of the decay of genes involved in vision, circadian clock and pigmentation in cavefishes. The analysis of the genomes of two Cuban species belonging to the genus Lucifuga provided evidence for the largest loss of eye-specific genes and non-visual opsin genes reported so far in cavefishes. Comparisons with a recently evolved cave population of Astyanax mexicanus and three species belonging to the Chinese tetraploid genus Sinocyclocheilus revealed the combined effects of the level of eye regression, time and genome ploidy on eye-specific gene pseudogenization. The limited extent of gene decay in all these cavefishes and the very small number of loss of function (LoF) mutations per pseudogene suggest that their eye degeneration may not be very ancient, ranging from early to late Pleistocene. This is in sharp contrast with the identification of several vision genes carrying many LoF mutations in ancient fossorial mammals, further suggesting that blind fishes cannot thrive more than a few million years in cave ecosystems.

Underground environments are increasingly recognized as reservoirs of faunal diversity. Extreme environmental conditions and limited dispersal ability of underground organisms have been acknowledged as important factors promoting divergence between species and conspecific populations. However, in many instances, there is no correlation between genetic divergence and morphological differentiation. Lucifuga Poey is a stygobiotic fish genus that lives in Cuban and Bahamian caves. In Cuba, it offers a unique opportunity to study the influence of habitat fragmentation on the genetic divergence of stygobiotic species and populations. The genus includes four species and one morphological variant that have contrasting geographical distributions. In this study, we first performed a molecular phylogenetic analysis of the Lucifuga Cuban species using mitochondrial and nuclear markers. The mitochondrial phylogeny revealed three deeply divergent clades that were supported by nuclear and morphological characters. Within two of these main clades, we identified five lineages that are candidate cryptic species and a taxonomical synonymy between Lucifuga subterranea and Lucifuga teresinarum. Secondly, phylogeographic analysis using a fragment of the cytochrome b gene was performed for Lucifuga dentata, the most widely distributed species. We found strong geographical organization of the haplotype clades at different geographic scales that can be explained by episodes of dispersal and population expansion followed by population fragmentation and restricted gene flow. At a larger temporal scale, these processes could also explain the diversification and the distribution of the different species.

No abstract