Molecular markers indicate rare sex in a predominantly asexual parasitoid wasp

The parasitoid wasp genus Lysiphlebus (Hymenoptera: Braconidae: Aphidiinae) contains a taxonomically poorly resolved group of both sexual (arrhenotoko us) species and asexual (thelytokous) clones. Maximum-parsimony and maximum -likelihood analyses of mitochondrial DNA sequence data from specimens coll ected across Western Europe showed that asexuality, which does not appear t o be caused by the bacterium Wolbachia, is concentrated in two geographical ly widespread lineages, the older of which diverged from the closest extant sexual taxa approximately 0.5 million years ago. However, the DNA sequence s of a nuclear intron (elongation factor-1 alpha) showed no congruence with this pattern, and a much higher frequency of heterozygotes with very high allelic diversity was observed among the asexual females compared to that a mong females from the sexual species. This pattern is consistent with mater nally inherited asexuality coupled with a history of rare sex with members of several closely related sexual populations or species. Our observations reinforce recent arguments that rare sex may be more important for the pers istence of otherwise asexual lineages than hitherto appreciated.