Theory predicts that half of the individuals produced by sexually reproducing species will be male. But in a sizable minority of organisms, females greatly outnumber males, and there are cases in which more males than females are produced. Here a respected geneticist explains why, introducing the strange world of male-killers, parthenogenetic reproduction, and ultra-selfish genes. Written for a broad audience of biologists and students and incorporating a tremendous variety of fascinating examples, this book is the first to synthesize what we know about sex ratio distorters and their evolutionary effects. Michael Majerus begins by characterizing our theoretical and empirical understanding of sexual difference, determination, and conflict. He then focuses on inherited elements that flout the normal Mendelian rules, particularly inherited microorganisms that influence their hosts' sex ratios for their own survival and replication. The Wolbachia bacterium, for example, can turn some male moths into fully functional females. In other species, such as ladybird beetles, ultra-selfish symbionts kill male but not female hosts.
And some inherited microorganisms induce their hosts to reproduce without sex, leading certain wasp and other species to forsake males altogether. Majerus explains how and why such mechanisms distort population sex ratios and describes the consequences for organisms' genetics, ecology, and reproductive behavior. Accessibly integrating a great quantity of research, this book makes the information on sex ratios and their distortion available to researchers and students across biology. It will be welcomed as both text and reference.