Evolutionary dynamics of the Trivers–Willard effect : A nonparametric approach





Faculty/Professorship: Foundations in Education  
Author(s): Borgstede, Matthias  
Publisher Information: Bamberg : Otto-Friedrich-Universität
Year of publication: 2021
Pages: 1-10
Source/Other editions: Ecology and evolution (2021), S. 1-10, ISSN 2045-7758
Language(s): English
DOI: 10.20378/irb-51176
Licence: Creative Commons - CC BY - Attribution 4.0 International 
URL: https://fis.uni-bamberg.de/handle/uniba/51333
URN: urn:nbn:de:bvb:473-irb-511764
Abstract: 
The Trivers–Willard hypothesis (TWH) states that parents in good condition tend to bias their offspring sex ratio toward the sex with a higher variation in reproductive value, whereas parents in bad condition favor the opposite sex. Although the TWH has been generalized to predict various Trivers–Willard effects (TWE) depending on the life cycle of a species, existing work does not sufficiently acknowledge that sex-specific reproductive values depend on the relative abundances of males and females in the population. If parents adjust their offspring sex ratio according to the TWE, offspring reproductive values will also change. This should affect the long-term evolutionary dynamics and might lead to considerable deviations from the original predictions.

In this paper, I model the full evolutionary dynamics of the TWE, using a published two-sex integral projection model for the Columbian ground squirrel (Urocitellus columbianus). Offspring sex ratio is treated as a nonparametric continuous function of maternal condition. Evolutionary change is treated as the successive invasion of mutant strategies. The simulation is performed with varying starting conditions until an evolutionarily stable strategy (ESS) is reached.

The results show that the magnitude of the evolving TWE can be far greater than previously predicted. Furthermore, evolutionary dynamics show considerable nonlinearities before settling at an ESS. The nonlinear effects depend on the starting conditions and indicate that evolutionary change is fastest when starting at an extremely biased sex ratio and that evolutionary change is weaker for parents of high condition. The results show neither a tendency to maximize average population fitness nor to minimize the deviation between offspring sex ratio and offspring reproductive value ratio.

The study highlights the importance of dynamic feedback in models of natural selection and provides a new methodological framework for analyzing the evolution of continuous strategies in structured populations.
SWD Keywords: Evolutionäre Spieltheorie ; Eichhörnchen ; Sexualverhalten
Keywords: continuous strategies, evolutionary dynamics, evolutionary invasion analysis, integral projection models, Trivers–Willard hypothesis, two-sex models
DDC Classification: 500 Science  
RVK Classification: WH 5200   
Peer Reviewed: Ja
International Distribution: Ja
Open Access Journal: Ja
Document Type: Article
URI: https://fis.uni-bamberg.de/handle/uniba/51176
Release Date: 11. October 2021

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