Meiotic drive fertility maintained under natural conditions of high sperm competition, a unique example in the stalk-eyed fly, Teleopsis dalmanni

Sperm killer meiotic drivers gain a fitness advantage by increasing their gametic transmission to the next generation. This comes at a fertility cost to the host organism, due to the disabling or loss of non-drive sperm, particularly in species where females permit multiple mating with many males. A classic example is the X-linked driver, SR, in the stalk-eyed fly Teleopsis dalmanni, which destroys non-carrier Y bearing sperm. In the wild, sperm competition is rife as females remate frequently (often several times per day) in a lifespan that lasts months. Here, we allowed drive or wildtype males to mate once with a female who had previously multiply mated over many days with a male of the opposite genotype. In contrast with previous studies, genotype had no effect on reproductive success - drive males were not disadvantaged compared to wildtype males on encountering a female full of rival male sperm. Drive males were also equally successful at resisting paternity gain by a rival male that was allowed a single mating. This unique finding of drive male success under sperm competition is linked to the massive testes enlargement in drive males which boosts sperm production and compensates for the loss of gametes caused during spermatogenesis. This fertility gain contributes to the spread of drive and its high prevalence in wild populations of T. dalmanni.