Female distribution affects mate searching and sexual selection in male northern water snakes (Nerodia sipedon)

Gregory P. Brown, Patrick J. Weatherhead

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)

Abstract

Mating systems and sexual selection are assumed to be affected by the distribution of critical resources. We use observations of 312 mating aggregations to compare mate-searching success of male northern water snakes (Nerodia sipedon) in two marshes in which differences in mating substrate availability resulted in more than fourfold differences in female dispersion. Reproductive males had significantly larger home ranges where females were dispersed than where females were clumped. The number of females encountered by males increased significantly with male home range size where females were dispersed, and decreased significantly where females were clumped. Where females were clumped, males were more likely to encounter other males when they located females. We found no evidence in either population that mate searching was energetically expensive or that males with relatively more energy had larger home ranges. However, males with greater fat reserves at the start of the season participated in more mating aggregations when females were dispersed, suggesting that fat reserves could affect a male’s willingness to attempt mating or to persist in aggregations. When females were dispersed there was weak stabilizing selection acting to maintain male body size (β=–0.14), but strong directional selection favoring larger (β=0.50) and fatter (β=0.37) males. Over 7 years, the intensity of selection favoring larger males varied substantially (β=0.14–1.15), but that variation was not related to variation in the operational sex ratio. We found no evidence of directional selection on either body size (β=0.05) or fat reserves (β=0.10) of males when females were spatially clumped. Overall, the distribution of females had a pronounced effect on male behavior, on the factors that affected male success in locating females, and probably on the extent of sperm competition once females had been located.

Original languageEnglish
Pages (from-to)9-16
Number of pages8
JournalBehavioral Ecology and Sociobiology
Volume47
Issue number1-2
DOIs
Publication statusPublished - Dec 1999
Externally publishedYes

Keywords

  • Mate searching
  • Sexual dimorphism
  • Spatial patterns
  • Sexual selection
  • Northern water snakes
  • Nerodia sipedon

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