Developmental sexual dimorphism and the evolution of mechanisms for adjustment of sex ratios in mammals

Sex allocation theory predicts biased offspring sex ratios in relation to local conditions if they would maximize parental lifetime reproductive return. In mammals, the extent of the birth sex bias is often unpredictable and inconsistent, leading some to question its evolutionary significance. For f...

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Bibliographic Details
Published in:Annals of the New York Academy of Sciences 2017-02, Vol.1389 (1), p.147-163
Main Authors: Cameron, Elissa Z., Edwards, Amy M., Parsley, Laura M.
Format: Article
Language:English
Subjects:
Animals
Biological Evolution
chromosomal sexual dimorphism
Chromosomes
extended evolutionary synthesis
Female
Fertilization
Gene expression
Humans
Male
Mammals - genetics
Ratios
Selection, Genetic
sex allocation
Sex Characteristics
Sex Determination Processes
Sex Ratio
sex‐linked traits
X‐inactivation
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Summary:Sex allocation theory predicts biased offspring sex ratios in relation to local conditions if they would maximize parental lifetime reproductive return. In mammals, the extent of the birth sex bias is often unpredictable and inconsistent, leading some to question its evolutionary significance. For facultative adjustment of sex ratios to occur, males and females would need to be detectably different from an early developmental stage, but classic sexual dimorphism arises from hormonal influences after gonadal development. Recent advances in our understanding of early, pregonadal sexual dimorphism, however, indicate high levels of dimorphism in gene expression, caused by chromosomal rather than hormonal differences. Here, we discuss how such dimorphism would interact with and link previously hypothesized mechanisms for sex‐ratio adjustment. These differences between males and females are sufficient for offspring sex both to be detectable to parents and to provide selectable cues for biasing sex ratios from the earliest stages. We suggest ways in which future research could use the advances in our understanding of sexually dimorphic developmental physiology to test the evolutionary significance of sex allocation in mammals. Such an approach would advance our understanding of sex allocation and could be applied to other taxa.
ISSN:0077-8923
1749-6632
DOI:10.1111/nyas.13288