Evol Ecol Res 4: 259-273 (2002) Full PDF if your library subscribes.
The effect of sexual size dimorphism on mating behaviour in two dung flies with contrasting dimorphism
Alexandre Ding* and Wolf U. Blanckenhorn
Zoological Museum, University of Zurich, Winterthurstrasse 190, CH-8057 Zurich, Switzerland
Author to whom all correspondence should be addressed.
There is a fundamental conflict between the sexes over the frequency and duration of mating; therefore, control of the mating process is important for both. The relative size of the mates may influence who has greater behavioural control over the outcome of mating. In the yellow dung fly Scathophaga stercoraria, males are on average larger, whereas in Sepsis cynipsea, males are smaller. We manipulated larval environments to phenotypically reverse the natural sexual size dimorphism of both dung fly species and investigate the effects of sexual size dimorphism on mating behaviour. We expected that reversal of sexual size dimorphism would at least partly lead to a shift in the relative control of the outcome of mating from one sex to the other, as evident in qualitative or quantitative changes in various aspects of mating behaviour and ultimately mating success. As both species have common behaviour components, we also expected this shift to reveal more similarities between the two species, which have otherwise evolved quite different mating systems. We found little evidence for this in either species in our laboratory study. We conclude that reversal of sexual size dimorphism did not lead to a shift in control, perhaps because males and females control the mating process at different levels. Male Scathophaga stercoraria exert behavioural control because they are larger, whereas females have some internal control through cryptic choice. In Sepsis cynipsea, the larger females have behavioural control over mating, whereas males may control fertilization by internally injuring their mates. Overall, our results suggest that the mating system, and the mating conflict, are long-term, ‘hard-wired’ consequences of evolutionary shifts in sexual size dimorphism.
Keywords: body size, dung flies, mating behaviour, mating system, Scathophaga stercoraria, Sepsis cynipsea, sexual conflict, sexual size dimorphism.
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