Increased adaptability to sudden environmental change can more than make up for the two-fold cost of males^(a)

¹ Current address. Departments of Physics and Biology, Institute in Theory and Modeling of Living Systems, Emory University Atlanta, GA, USA
² Department of Physics, Princeton University - Princeton, NJ, USA

Received: 6 June 2018
Accepted: 31 August 2018

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 favor anisogamy over 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. This advantage in adaptability is particularly effective at maintaining anisogamy against invasion by isogamy. We discuss the extensions to our simple model needed to determine how important this mechanism is to overcoming the two-fold cost in natural populations.