The evolution of polyandry II: post–copulatory defenses against genetic incompatibility

TLDR

The hypothesis that females mate with multiple males to hedge against genetic incompatibility relies on the existence of post‑copulatory mechanisms that protect reproductive investment from maternal‑paternal genome conflicts. The study proposes that sperm accumulation in the female tract enables direct assessment of genetic compatibility at molecular and cellular levels. Sperm competition and female sperm choice within the reproductive tract allow polyandrous females to reduce fertilization by incompatible sperm, and multiple paternity enables resource reallocation from defective to viable offspring. These mechanisms are especially critical for viviparous species, where the close immunological link between mother and embryo heightens vulnerability to genetic incompatibility from intragenomic conflict and suborganismal processes.

Abstract

Fundamental to the recently–proposed hypothesis that females mate with more than one male as a hedge against genetic incompatibility is the premise that mechanisms are available to polyandrous females which enable them to safeguard their reproductive investment against the threat of incompatibility between maternal and paternal genomes. Accumulation of sperm from several males shifts the arena for sexual selection from the external environment to the female reproductive tract where, we suggest, interactions at the molecular and cellular levels provide females with direct mechanisms for assessing genetic compatibility. We present examples from the literature to illustrate how sperm competition and female choice of sperm can enable polyandrous females to minimize the risk of fertilization by genetically–incompatible sperm. Polyandry and multiple paternity also create the opportunity to reduce the cost of genetic incompatibility by reallocation of maternal resources from defective to viable offspring. This is likely to be a critically important post–copulatory mechanism for viviparous females whose intimate immunological relationship with developing embryos makes them particularly vulnerable to genetic incompatibility arising from intragenomic conflict and other processes acting at the suborganismal level.