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Population structure and genotype dynamics of ancient asexuals: insights from bdelloid rotifers

Final Activity Report Summary - RotPop (Population structure and genotype dynamics of ancient asexuals: insights from bdelloid rotifers)

I worked on bdelloid rotifer macroecology and evolution, mainly speciation, distribution, phylogeography and population genetics. The main objective of the proposal was to understand if species as independent entities did exist in a group of animals that did not reproduce through sexual recombination, as well as to disentangle which process could drive speciation.

The evolution of distinct species was often considered a property characterising only sexually reproducing organisms. In fact, however, there was little evidence as to whether asexual groups did or did not diversify into species. We showed that a famous group of asexual animals, the bdelloid rotifers, diversified into distinct species broadly equivalent to those found in sexual groups. We surveyed diversity within a single clade, the genus rotaria, from a range of habitats worldwide using deoxyribonucleic acid (DNA) sequences and measurements of jaw morphology from scanning electron microscopy. New statistical methods for the combined analysis of morphology and DNA sequence data confirmed two fundamental properties of species, namely, independent evolution and ecological divergence by natural selection.

Another process could help diversification, namely geographical isolation. Due to high dispersal capabilities of bdelloids through dormant propagules, no geographical limitation was expected. Nevertheless, we discovered that geographical isolation could play a role in bdelloids, in addition to ecological diversification.

Another unexpected result was that different approaches in species’ identification did not always coincide to define unambiguous species groups, but this finding was common in sexual groups as well. One striking difference with sexual animals was the amount of hidden diversity found in bdelloids, which were, for the time being, the animals with the highest amount of cryptic taxa for each traditional species.

The results of our work overall showed that sex was not a necessary condition for speciation and diversification.