9.8 Testing Trivers-Willard in red deer

There are other aspects of “condition” than nutritional status. For example, in the case of the Scottish red deer, maternal condition doesn’t predict the sex ratio of her offspring, but social status (in this case, dominance over other females) does. Consider the following data:

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So, what does a female achieve through these biased sex ratios? Is her fitness (or lifetime reproductive success, LRS) better off when she has sons (if high-ranking) or daughters (if low-ranking)? The figure below depicts the lifetime reproductive success (LRS) of the sons and daughters of red deer mothers, based on the mother’s social status.

Lifetime reproductive success (LRS) of sons and daughters of red deer hinds in relation to their mother’s social rank. See text for details (blue are males, orange are females). The slope shown is the reduced major axis.

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The Evolution and Biology of Sex by Sehoya Cotner and Deena Wassenberg is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.