Behavioral Ecology and Sociobiology

, Volume 62, Issue 10, pp 1679–1687

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

  • Kelly M. Proffitt
  • Robert A. Garrott
  • Jay J. Rotella
Original Paper

DOI: 10.1007/s00265-008-0596-2

Cite this article as:
Proffitt, K.M., Garrott, R.A. & Rotella, J.J. Behav Ecol Sociobiol (2008) 62: 1679. doi:10.1007/s00265-008-0596-2


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 

Supplementary material

265_2008_596_MOESM1_ESM.doc (50 kb)
Table S1Candidate a priori models explaining the effects of maternal and environmental characteristics on the odds of producing a male offspring. Covariates evaluated included an index of lifetime reproductive output (iLRO), maternal age (AGE), parity (PARITY), maternal identity (ID), summer sea-ice extent (SumExtent), winter sea-ice extent (WinExtent), southern oscillation (SOI), and year (YEAR) (DOC 51 kb).
265_2008_596_MOESM2_ESM.doc (24 kb)
Table S2Histogram of index of maternal lifetime reproductive output for the 332 mothers included in analysis (DOC 24 kb
265_2008_596_MOESM3_ESM.doc (60 kb)
Table S3Complete model-selection results for a priori models examining variation in Weddell seal offspring sex. Models are presented along with the AICc value, the ΔAICc value, and the Akaike model weight (wi). Covariates evaluated include index of maternal lifetime reproductive output (iLRO), maternal age (AGE), sea-ice extent in the winter prior to conception (WinExtent), sea-ice extent in the summer of breeding and pregnancy (SumExtent), and the southern oscillation index (SOI) in the 3 months prior to conception. The random effects of maternal identity are represented by ID, and the random effects of year are represented by YEAR (DOC 61 kb).
265_2008_596_MOESM4_ESM.doc (30 kb)
Table S4S4 Model-averaged coefficient estimates\(\left( {\widehat{\overline \beta }} \right)\), standard error\(\left( {{\text{SE}}\left( {\widehat{\overline \beta }} \right)} \right)\), and 95% confidence interval (CI) of each fixed covariate explaining variation in offspring sex. Predictor weights (w+(j)) are presented from the overall modeling exercise (DOC 30 KB).

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Kelly M. Proffitt
    • 1
  • Robert A. Garrott
    • 1
  • Jay J. Rotella
    • 1
  1. 1.Department of EcologyMontana State UniversityBozemanUSA

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