Original Paper

Behavioral Ecology and Sociobiology

, Volume 62, Issue 10, pp 1679-1687

First online:

Variation in offspring sex ratio among individual Weddell seal (Leptonychotes weddellii) females of different quality

  • Kelly M. ProffittAffiliated withDepartment of Ecology, Montana State University Email author 
  • , Robert A. GarrottAffiliated withDepartment of Ecology, Montana State University
  • , Jay J. RotellaAffiliated withDepartment of Ecology, Montana State University

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The Trivers–Willard model predicts that in polygynous species, superior-quality females will maximize their fitness by producing male offspring. Using a sample of 1,780 Weddell seal (Leptonychotes weddellii) pups recorded over 31 years, we investigated relationships between offspring sex ratio and maternal age, reproductive experience, an index of maternal lifetime reproductive output, and annual environmental variations. We found evidence that females with higher index of lifetime reproductive output were more likely to produce male than female offspring but found only weak evidence that large-scale environmental variations influenced sex ratios. Our results suggest that mothers manipulate offspring sex to maximize their own fitness, and inherent maternal quality may influence offspring sex. These findings support the Trivers–Willard sex-allocation model.


Sex ratio Trivers–Willard model Lifetime reproductive output Leptonychotes weddellii