Does differential mortality after parental investment affect sex ratio evolution? No

Area of Science:

• Evolutionary biology
• Population dynamics
• Behavioral ecology

Background:

• R. A. Fisher's hypothesis posits equal sex ratios at birth when parental investment is equal.
• Differential mortality post-parental investment was recently suggested to alter sex ratios at birth.
• This contradicts Fisher's classical view on sex ratio evolution.

Purpose of the Study:

• To resolve the disparity between Fisher's hypothesis and recent theoretical models on sex ratio evolution.
• To investigate the impact of differential mortality after parental investment on sex ratio at birth.
• To confirm or refute the influence of post-parental investment mortality on sex ratio evolution.

Main Methods:

• Analysis of a stage- and sex- structured population dynamics model.
• Inclusion of separate union classes for mutant-resident interactions.
• Mathematical modeling to simulate evolutionary trajectories.

Main Results:

• Selection consistently drives populations to an equal sex ratio at birth.
• Differential mortality after parental investment does not affect the sex ratio at birth.
• Fisher's hypothesis is confirmed, with disparities arising from accounting errors in previous models.

Conclusions:

• The sex ratio at birth is robustly equalized by selection, irrespective of post-parental investment mortality.
• Fisher's theory on sex ratio evolution remains valid.
• Accurate accounting of population interactions is crucial for theoretical models.