Sex ratios, mating behavior and sexual size dimorphism of the northern water snake, Nerodia sipedon

@article{Weatherhead2004SexRM,
  title={Sex ratios, mating behavior and sexual size dimorphism of the northern water snake, Nerodia sipedon},
  author={Patrick J. Weatherhead and Frances E. Barry and Gregory P. Brown and Mark R. Forbes},
  journal={Behavioral Ecology and Sociobiology},
  year={2004},
  volume={36},
  pages={301-311}
}
Competition among males to mate is generally associated with male-biased size dimorphism. In this study we examine mating behavior in the northern water snake (Nerodia sipedon), a species in which males are much smaller than females despite substantial competition among males to mate. Competition among males was a consequence of a male-biased operational sex ratio due to slightly higher female mortality from a birth sex ratio of 1 : 1, and, in 1 year, more synchronous and longer mating activity… 

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Experimental assessment of ecological and phenotypic factors affecting male mating success and polyandry in northern watersnakes, Nerodia sipedon

Positive size-assortative mating was found, but only when the OSR was female biased, suggesting that smaller males had improved access to females when competition among males was reduced, but that competition with larger males still restricted mating opportunities of small males to less preferred, smaller females.

Male reproductive success and sexual selection in northern water snakes determined by microsatellite DNA analysis

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The opportunity for sexual selection was more than five times higher in males than females, apparently both because bigger females mated with more males and because the larger litters of big females provide paternity opportunities to more males.

DOES LARGE BODY SIZE IN MALES EVOLVE TO FACILITATE FORCIBLE INSEMINATION? A STUDY ON GARTER SNAKES

  • R. ShineR. Mason
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    Evolution; international journal of organic evolution
  • 2005
Even in mating systems where males compete physically and where larger body size confers a significant advantage in male-male competition, the actual selective force for larger bodysize in males may relate to forcible insemination of unreceptive females.

Sex Differences in Body Size and Ectoparasite Load in the Ball Python, Python regius

Sexual dimorphism in body size, body condition (body mass relative to body size), and relative head size was investigated on field-caught Python regius (Togo, western Africa), suggesting that females and males follow different growth trajectories from birth to adulthood.

Intraspecific variation in ejaculate traits of the northern watersnake (Nerodia sipedon)

The lack of condition dependence of most ejaculate traits is consistent with previous studies that indicate that male reproductive effort in this species is generally not energy limited, perhaps because of opportunistic foraging during the mating season.

Reproductive roles predict sexual dimorphism in internal and external morphology of lake whitefish, Coregonus clupeaformis

Male and female lake whitefish had significantly longer jaws and pectoral and pelvic fins, larger hearts, and more muscle than females, and females had relatively heavier livers.

Geographic variation in sexual size dimorphism within a single snake species (Morelia spilota, Pythonidae)

Observations of free-ranging snakes suggest that males do not engage in overt agonistic interactions during the mating season, and that larger body size does not enhance male mating success, which fits well with previous interpretations of the relationship between mating systems and sexual size dimorphism in snakes.
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