[en] reproduction ; sexual selection ; sperm storage
[en] In polyandrous insects, postcopulatory sexual selection is a pervasive evolutionary force favouring male and female traits that allow control of offspring paternity. Males may inﬂuence paternity through adaptations for sperm competition, and females through adaptations facilitating cryptic female choice. Yet, the mechanisms are often complex, involving behaviour, physiology or morphology, and they are difﬁcult to identify. In red ﬂour beetles (Tribolium castaneum), paternity varies widely, and evidence suggests that both male and female traits inﬂuence the outcome of sperm competition. To test the role of spermathecal morphology and of sperm storage processes on the outcome of sperm competition, we mated each of 26 virgin females with two males, one of which carrying a phenotypic marker to assign
offspring paternity. We manipulated the interval between mating with the ﬁrst and the second male, to create different conditions of sperm storage (overlapping and non-overlapping) in the female reproductive tract. To investigate the role of sperm storage more closely, we examined the relationship between paternity and spermathecal morphology in a subset of 14 experimental females. In addition, we also characterized variation in spermathecal morphology in three different strains, wildtype, Chicago black and Reindeer. No signiﬁcant inﬂuence of the intermating interval was found on the paternity of the focal male, although the direction of the difference was in the expected direction of higher last male paternity for longer intervals. Moreover, paternity was not signiﬁcantly associated with spermathecal morphology, although spermathecal volume, complexity, and tubule width varied signiﬁcantly and substantially among individuals in all investigated strains.
Swiss National Science Foundation ; Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS