Increased adaptability to rapid environmental change can more than make up for the two-fold cost of males

TL;DR

This paper demonstrates through simulations that increased male adaptability in anisogamous populations can offset the inherent reproductive cost of males, enabling faster adaptation to environmental changes.

Contribution

It shows that high variance in male fitness can allow anisogamous populations to outperform isogamous ones despite the two-fold reproductive cost.

Findings

Anisogamous populations can adapt faster due to high male fitness variance.

Male adaptability can overcome the two-fold cost of sex.

Simulations support anisogamy's advantage in changing environments.

Abstract

The famous "two-fold cost of sex" is really the cost of anisogamy -- why should females mate with males who do not contribute resources to offspring, rather than isogamous partners who contribute equally? In typical anisogamous populations, a single very fit male can have an enormous number of offspring, far larger than is possible for any female or isogamous individual. If the sexual selection on males aligns with the natural selection on females, anisogamy thus allows much more rapid adaptation via super-successful males. We show via simulations that this effect can be sufficient to overcome the two-fold cost and maintain anisogamy against isogamy in populations adapting to environmental change. The key quantity is the variance in male fitness -- if this exceeds what is possible in an isogamous population, anisogamous populations can win out in direct competition by adapting faster.