Female choice, female reluctance to mate and sexual selection on body sizein the dung fly Sepsis cynipsea

Wu. Blanckenhorn et al., Female choice, female reluctance to mate and sexual selection on body sizein the dung fly Sepsis cynipsea, ETHOLOGY, 106(7), 2000, pp. 577-593
Citations number
Categorie Soggetti
Animal Sciences","Neurosciences & Behavoir
Journal title
ISSN journal
0179-1613 → ACNP
Year of publication
577 - 593
SICI code
We investigated the mechanisms of sexual selection in the common dung fly S epsis cynipsea and how these affect selection on body size at the populatio n level. Because of the presumed costs associated with mating, we predicted that there would be a decrease in the general reluctance of females to mat e with any particular male at higher male densities at the mating site, a f resh cow pat, resulting in indirect female choice and a decrease in the str ength of sexual selection. In contrast, classical direct female choice and male-male competition should result in increased selection intensities beca use more opportunities for choice and competition exist at higher densities . Female reluctance to mate and female assessment of males are expressed in prominent female behaviour to repel mates in several insect species, inclu ding S. cynipsea. Laboratory pair-wise choice experiments showed that large males were more likely to obtain copulations, which also ensued more promp tly, suggesting female assessment of male quality (direct female choice). T here was a basic influence of male activity but little further effect of ma le scramble competition on the outcome of mating. Another laboratory experi ment showed a decrease in female shaking duration per male, associated with an asymptote in the shaking duration per female, as male density and haras sment increased, but did not show the increase in mating frequency predicte d by the female reluctance hypothesis. A study estimating sexual selection differentials in the field showed that directional selection for larger mal es was present overall and was negatively related to seasonally mediated va riation in male density. Our study suggests that direct female choice in co mbination with indirect female choice (due to an interaction of female relu ctance to mate and male persistence) is most consistent with the behavioura l and selection patterns observed in S. cynipsea, but male effects cannot b e definitively excluded.