Male-mediated early maturation unlikely to evolve via adaptive evolution

Area of Science:

• Primate reproductive strategies
• Mammalian reproductive endocrinology
• Evolutionary biology

Background:

• The Vandenbergh effect describes accelerated female maturation due to novel male exposure.
• In geladas, this effect was hypothesized as an adaptation to counter male infanticide.
• An alternative hypothesis suggests it's a nonadaptive byproduct of the Bruce effect (maternal spontaneous abortion).

Purpose of the Study:

• To test the adaptive 'optimal timing hypothesis' versus the nonadaptive 'Bruce effect by-product hypothesis' for male-mediated maturation in geladas.
• To investigate the evolutionary basis and adaptive significance of the Vandenbergh effect.

Main Methods:

• Comparative analysis of male-mediated maturation and hormonal changes in geladas and baboons.
• Utilizing observational data and theoretical modeling (individual-based model).
• Derivation of the selection coefficient for male-mediated maturation.

Main Results:

• Male-mediated maturation and associated hormonal changes were absent in baboons, a species lacking the Bruce effect.
• An individual-based model indicated that male-mediated maturation is unlikely to evolve through adaptive selection in either geladas or baboons.
• The selection coefficient for male-mediated maturation is likely very small, suggesting minimal adaptive benefits.

Conclusions:

• Male-mediated maturation in geladas is concluded to be a byproduct of the Bruce effect.
• The study posits that the Vandenbergh effect may be nonadaptive in a broader mammalian context.
• Findings challenge the adaptive explanations for male-mediated maturation in primates.