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Resource transfers and evolution: helpful offspring and sex allocation.
J William Stubblefield1, Steven Hecht Orzack
1Fresh Pond Research Institute Cambridge, MA 02140, USA.
Theoretical Population Biology
|November 21, 2012
Summary
Offspring helping influences sex-ratio evolution in vertebrates. Accounting for age structure reveals optimal strategies shift, favoring the more-helpful sex early and less-helpful sex later, especially with facultative sex-ratio control.
Area of Science:
- Evolutionary biology
- Behavioral ecology
- Population genetics
Background:
- In many vertebrate species, offspring provide crucial assistance to their parents, a phenomenon known as
Purpose of the Study:
- To analyze how sex-biased offspring helping influences sex-ratio evolution.
- To incorporate age-structure into models of sex-ratio evolution, addressing limitations in previous analyses.
- To investigate optimal sex-allocation strategies under varying helping returns and environmental conditions.
Main Methods:
- Theoretical modeling of sex-ratio evolution incorporating age-structure.
- Analysis of optimal investment strategies under fixed and facultative sex-ratio control.
- Examination of nonlinear helping returns and environmental patchiness effects.
- Meta-analysis of empirical data on offspring helping and sex-ratio adjustment.
Main Results:
- The optimal sex-allocation strategy depends on the age-structure and the nature of helping returns.
- When helping returns are linear, facultative control leads to producing the more-helpful sex early and the less-helpful sex later.
- Nonlinear helping returns favor maximizing resource accrual early, then producing the less-helpful sex.
- Population sex ratio consistently favors the more-helpful sex, irrespective of age-dependency, unless environmental patchiness dictates otherwise.
Conclusions:
- Accurate accounting for age-structure is critical for understanding sex-ratio evolution in cooperative breeding systems.
- Parental sex-ratio adjustment strategies are complex and context-dependent, influenced by helping benefits and environmental factors.
- Empirical evidence does not support claims that parents preferentially produce the helpful sex when it is rare.
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