Sperm competition or sperm selection: no evidence for female influence over paternity in yellow dung flies Scatophaga stercoraria |
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| Authors: | L W Simmons P Stockley R L Jackson G A Parker |
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| Institution: | (1) Department of Environmental and Evolutionary Biology, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK, GB;(2) Department of Zoology, The University of Western Australia, Nedlands, WA 6009, Australia, AU |
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| Abstract: | Recent studies of non-random paternity have suggested that sperm selection by females may influence male fertilization success.
Here we argue that the problems originally encountered in partitioning variation in non-random mating between male competition
and female choice are even more pertinent to interpreting patterns of non-random paternity because of intense sperm competition
between males. We describe an experiment with the yellow dung fly, Scatophaga stercoraria, designed to partition variance in the proportion of offspring sired by the second male, P
2, between males and females, and to control for sperm competition. Large males were shown to have a higher P
2 than small males but P
2 was independent of the size of the female’s first mate. This result might suggest an absolute female preference for large
males via sperm selection. However, large males have a higher constant rate of sperm transfer and displacement. After controlling
for this effect of sperm competition, large males did not achieve higher paternity than small males. We argue that a knowledge
of the mechanism of sperm competition is essential so that male effects can be controlled before conclusions are made regarding
the influence of sperm selection by females in generating non-random paternity.
Received: 4 April 1995 / Accepted after revision: 17 October 1995 |
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| Keywords: | Sperm competition Sperm selection Scatophaga stercoraria Non-random paternity |
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