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Genetic differentiation, behavioural reproductive isolation and mixis cues in three sibling species of Monogonont rotifers

Freshwater biology 2010 v.55 no.12 pp. 2570-2584
Rotifera, females, floodplains, freshwater, genetic variation, habitats, interspecific hybridization, introgression, lakes, males, parthenogenesis, population density, progeny, random amplified polymorphic DNA technique, reproductive isolation, sexual reproduction, sibling species
1. Many aquatic species usually considered to be ‘cosmopolitan' have been identified as cryptic species complexes, based on deep genetic differentiation. However, reproductive isolation among sibling cryptic species has rarely been studied, and interspecific hybridisation is common in some taxa. 2. We investigated isolation mechanisms and possible introgression among three cyclical parthenogenetic rotifer species in the Epiphanes senta complex that are found in very different freshwater habitats: temperate floodplains, subtropical desert rock pools and a tropical alpine lake. Whereas Epiphanes ukera is reproductively isolated from E. chihuahuaensis and E. hawaiiensis, the latter hybridise under laboratory conditions. 3. While reproductive isolation is incomplete, RAPD profiles indicated unique genetic signatures and showed no evidence for introgression, indicating that these three species are diverging and have independent evolutionary trajectories. 4. Testing cues for sexual reproduction in these cyclic parthenogens demonstrated that mixis in E. chihuahuaensis and E. ukera is influenced by population density, whereas E. hawaiiensis females rarely produce mictic offspring regardless of density. Different mixis cues are likely to separate sexual periods and effectively cause reproductive isolation between the species. Epiphanes ukera and E. chihuahuaensis males display mate‐guarding behaviour, and E. ukera males distinguish between conspecific and heterospecific females in mate‐choice experiments. Geographic isolation, along with different cues for mixis induction and mate recognition, acts as reproductive barrier among these sibling species.