The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness.

Jussi Lehtonen

doi:10.3390/cells10030573

Abstract

The evolution of anisogamy or gamete size dimorphism is a fundamental transition in evolutionary history, and it is the origin of the female and male sexes. Although mathematical models attempting to explain this transition have been published as early as 1932, the 1972 model of Parker, Baker, and Smith is considered to be the first explanation for the evolution of anisogamy that is consistent with modern evolutionary theory. The central idea of the model is ingenious in its simplicity: selection simultaneously favours large gametes for zygote provisioning, and small gametes for numerical competition, and under certain conditions the outcome is anisogamy. In this article, I derive novel analytical solutions to a 2002 game theoretical update of the 1972 anisogamy model, and use these solutions to examine its robustness to variation in its central assumptions. Combining new results with those from earlier papers, I find that the model is quite robust to variation in its central components. This kind of robustness is crucially important in a model for an early evolutionary transition where we may only have an approximate understanding of constraints that the different parts of the model must obey.

Highlights

In 1972 Geoff Parker, Robin Baker and Vic Smith [1] published a theoretical explanation for the evolution of anisogamy, explaining why so much of life is organized around a reproductive system with gametes of two different sizes such as eggs and sperm
Given that the biological definition of the sexes is based on a difference in gamete size, the theory is an explanation for the evolutionary origin of females and males in an ancestral, broadcast spawning population
This transition has major consequences for subsequent evolution, and is a part of the so-called ‘sexual cascade’ [2] where the asymmetry in gamete size is thought to play a central role in driving sex-specific selection [3,4,5,6]

Summary

Introduction

Tomer Avidor-Reiss, Eduardo R.In 1972 Geoff Parker, Robin Baker and Vic Smith [1] published a theoretical explanation for the evolution of anisogamy (see Table 1 for definitions), explaining why so much of life is organized around a reproductive system with gametes of two different sizes such as eggs and sperm. The fitness functions for the two mating types are wx ( x, y) = n( x ) g( x ) f ( x, y) wy ( x, y) = n(y) g(y) f ( x, y) where n, g, and f are functions for gamete size-number trade-off, gamete survival, and zygote survival, respectively.

Results

Conclusion