SPM Journal Club: Sons, daughters and demography - Sex-specific vital rates and life history choices

Traditional population models are often limited to the female half of the population, but acknowledgement of the importance of males is spreading. There are fundamental differences between male and female demographies, and these differences can strongly affect population dynamics and provide important insights into the evolution of life histories.

In this upcoming session, we will be discussing a recent paper dealing with sex-specific demography and its abilities to inform life history theory:

http://www.nature.com/nature/journal/v526/n7572/abs/nature14968.html

 

 

Abstract

The Trivers–Willard theory proposes that the sex ratio of offspring should vary with maternal condition when it has sexspecific influences on offspring fitness. In particular, mothers in good condition in polygynous and dimorphic species are predicted to produce an excess of sons, whereas mothers in poor condition should do the opposite. Despite the elegance of the theory, support for it has been limited. Here we extend and generalize the Trivers–Willard theory to explain the disparity between predictions and observations of offspring sex ratio. In polygynous species, males typically have higher mortality rates, different agespecific reproductive schedules and more riskprone life history tactics than females; however, these differences are not currently incorporated into the Trivers–Willard theory. Using twosex models parameterized with data from freeliving mammal populations with contrasting levels of sex differences in demography, we demonstrate how sex differences in life history traits over the entire lifespan can lead to a wide range of sex allocation tactics, and show that correlations between maternal condition and offspring sex ratio alone are insufficient to conclude that mothers adaptively adjust offspring sex ratio.

 

Published Mar. 14, 2016 11:15 AM - Last modified Mar. 14, 2016 11:15 AM