Introduction to Vertebrate Sex Ratio Adjustment

Abstract

What if we had the ability to design our children before they are born, to give them traits that would maximize their chances of thriving in the environment where they will live, or even to change our own traits as we pass through different life stages to maximize our own chances of surviving or reproducing? As it turns out, humans and other animals may be able to do just that, and without the use of fancy technology. The term “sex allocation” describes the distribution of resources between male and female reproductive function, and there is evidence in every vertebrate class that animals, including humans, have the ability to allocate sex according to the environmental and social conditions that surround them. For some species, this may mean producing more male or female offspring in response to social or environmental triggers. For others, it may mean choosing whether to produce sperm or eggs in a current reproductive attempt. In all cases, the ability to control whether individuals function as males or females can provide potent survival and reproductive benefits that may significantly influence fitness potentials at both the individual and population levels. Despite over a century of research focusing on theories and mechanisms of sex allocation in a variety of species, there are still many questions that have yet to be answered. In this introduction, I will highlight those questions and why it is important that we use comparative approaches, by examining mounting evidence that is emerging across all vertebrate classes, in our quest for answers.