Corley, LS; Cotton, S; McConnell, E; Chapman, T; Fowler, K; Pomiankowski, A; (2006) Highly variable sperm precedence in the stalk-eyed fly, Teleopsis dalmanni. BMC EVOL BIOL , 6 , Article 53. 10.1186/1471-2148-6-53.

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Abstract

Background: When females mate with different males, competition for fertilizations occurs after insemination. Such sperm competition is usually summarized at the level of the population or species by the parameter, P-2, defined as the proportion of offspring sired by the second male in double mating trials. However, considerable variation in P-2 may occur within populations, and such variation limits the utility of population-wide or species P-2 estimates as descriptors of sperm usage. To fully understand the causes and consequences of sperm competition requires estimates of not only mean P-2, but also intra-specific variation in P-2. Here we investigate within-population quantitative variation in P-2 using a controlled mating experiment and microsatellite profiling of progeny in the multiply mating stalk-eyed fly, Teleopsis dalmanni.Results: We genotyped 381 offspring from 22 dam-sire pair families at four microsatellite loci. The mean population-wide P-2 value of 0.40 was not significantly different from that expected under random sperm mixing (i.e. P-2 = 0.5). However, patterns of paternity were highly variable between individual families; almost half of families displayed extreme second male biases resulting in zero or complete paternity, whereas only about one third of families had P-2 values of 0.5, the remainder had significant, but moderate, paternity skew.Conclusion: Our data suggest that all modes of ejaculate competition, from extreme sperm precedence to complete sperm mixing, occur in T. dalmanni. Thus the population mean P-2 value does not reflect the high underlying variance in familial P-2. We discuss some of the potential causes and consequences of post-copulatory sexual selection in this important model species.

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