Cryptic diversification in ancient asexuals:: evidence from the bdelloid rotifer Philodina flaviceps

Bdelloid rotifers, darwinulid ostracods and some oribatid mites have been called 'ancient asexuals' as they speciated and survived over long-term evolutionary timescale without sexual recombination. Data on their genetic diversification are contrasting: within-species diversification is present mostly at a continental scale in a parthenogenetic oribatid mite, whereas almost no genetic diversification at all seems to occur within darwinulid ostracod species. Strangely enough, no clear data for bdelloid rotifers are available so far. In this paper, we analyse partial COI mtDNA sequences to show that a bdelloid rotifer, Philodina flaviceps, so far considered a single traditional morphological species, has actually been able to diversify into at least nine distinct evolutionary entities, with genetic distances between lineages comparable with those between different traditional species within the same genus. We discovered that local coexistence of such different independent lineages is very common: up to four lineages were found in a same stream, and up to three in a single moss sample of 5 cm(2). In contrast to the large-scale geographic pattern that has recently been reported in the oribatid mite, the spatial distribution of the bdelloid lineages provided evidence of micro-phylogeographic patterns. If the mtDNA diversity indicates that the lineages are independent and represent sympatric cryptic species within P. flaviceps, then the actual bdelloid diversity can be expected to be much greater than that recognized today.