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Open Access Publications from the University of California

The Effect of Sex Ratio on Copulation, Sperm Transfer, and Sperm Reserves in the Waterstrider, Aquarius remigis

  • Author(s): Houck, Clayton James
  • Advisor(s): Fairbairn, Daphne J
  • et al.

Although male reproductive success is expected to increase with additional copulations and the transfer of numerous or large sperm to females, these may reduce male sperm reserves and affect future reproductive effort. The waterstrider Aquarius remigis Say (Gerridae, Heteroptera) has large sperm (5mm length), copulates frequently (averages one per day) and has a polygynandrous mating system. We test the hypothesis that sperm reserves will decrease as mating opportunities increase by comparing the behavior and sperm reserves of male A. remigis after nine days under three sex ratios (3 males:9 females, 6 males:6 females, 6 males:0 females) and for single copulation trials with two sex ratios (1 male:3 females, 2 males:2 females). We show that males with additional mating opportunities copulate more often and for shorter durations but do not become sperm depleted and frequently have copulations of insufficient duration to result in sperm transfer. The number of sperm transferred was not related to copulation duration, sex ratio, or number of eggs in females. This suggests lack of strategic sperm allocation by males. Multiple mating did not increase female fertility and the number of sperm in female reproductive tracts. Thus, non-virgin females appear to gain no direct benefit from additional sperm transfer, although past research shows females in copula receive less harassment from males. Our results indicate that variation in the success and duration of copulations is best explained by female influence over copulation rather than by male reproductive tactics.

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