Analysis of the causal components of assortative mating in water striders |
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Authors: | L Rowe G Arnqvist |
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Institution: | Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S 1A1, CA Department animal Ecology, University of Ume?, S-901 87 Ume?, Sweden, SE
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Abstract: | Field studies demonstrate that natural populations of a group of water striders (Heteroptera: Gerridae) that share a common
mating system are characterized by weak assortative mating by size and by large sizes of mating males and females relative
to single individuals. This study presents an experimental assessment of the components of mating that may contribute to these
mating patterns. The effects of male and female body size on each of three components of mating were studied in three water
strider species in the laboratory. Large females of all three species mated more frequently, copulated for longer and were
guarded longer than small females. Large males mated more frequently than small males in all three species, and also guarded
females for longer in the two species where the average of mate guarding was long. However, we found an antagonistic effect
of male size on copulation duration: small males copulated for longer than large males in all three species. We show that
the combined effects of these size biases mimic the mating patterns found in the wild, e.g. weak and variable assortative
mating, and stronger and less variable size ratios of mating versus non-mating females relative to males. We suggest that
the antagonistic effects of male size on copulation and guarding duration may be a key source of interpopulational variation
in assortative mating and sexual selection on male size. Further, neither spatial or temporal covariation in size, nor mechanical
constraints, caused the assortative mating observed here in this group of water striders. Some combination of male and female
choice (either active or passive forms) of large mates and male-male exploitation competition for mates play potentially important
roles in producing population level assortative mating in water striders.
Received: 17 March 1995/Accepted after revision: 28 October 1995 |
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Keywords: | Assortative mating Body size Mating behaviour Gerridae Sexual selection |
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