Abstract
View Large Image | Download PowerPoint SlideMichael Majerus wraps up Sex Wars: Genes, Bacteria, and Biased Sex Ratios, with a quote from the White Queen of Lewis Carroll's Through the Looking Glass: ‘Why, sometimes I've believed as many as six impossible things before breakfast’ [1xCarroll, L. See all References][1]. However, even Alice's hallucinatory world pales before the improbable routes by which sex can be determined, switched, or used as a weapon by selfish genetic entities. Majerus provides a fascinating tour of his own Wonderland, replete with feminizers and male-killers, distorters and ultra-selfish elements. And, of course, the Red Queen keeps running. It's a twisted place, but one in which we, as evolutionary biologists, geneticists and ecologists, increasingly dwell. To keep it all straight, we need more thorough and scholarly works like Sex Wars.To understand the flavour of Sex Wars, one must read the complete title – the part about genes, bacteria and sex ratios. Majerus’ mid-weight book (280 pp) is not the racy account of the sexual conflict literature that one might expect from the abbreviated title. It is an academic work about sex ratio, ultra-selfish genes and their carriers. For example, Sex Wars only reluctantly reaches into the entangled bank of theories for the origin of sex itself or the evolution of gender. Rather Sex Wars unabashedly emphasizes the research systems that the author is a leading authority in, particularly the Lepidoptera, ladybird beetles (Coleoptera) and their endosymbionts, of which Wolbachia is the undisputed star (more on this later).It is a good thing that the second part of Sex Wars moves to Majerus’ pet organisms for two reasons. First, in contrast to the competent but rather processional primer on sex ratio, the sexes, and sex-determining systems that constitutes part one, the latter half of the book exudes enthusiasm. Thus, whereas the first 100 or so pages will be of great use to a new student of the area, the more advanced reader will only begin to gasp later on. I am not, however, aware of a finer concise description of mechanisms of sex determination published anywhere than is housed in the third chapter of Sex Wars.Second, although appearing in 2003, references cited in this book stop at the end of the last millennium. The broader area of sexual conflict is evolving so rapidly that a three-year publication delay would be fatal to any book on that topic. Sex Wars avoids this problem by summarizing a specialized literature that has a massive anchor of established theory with empirical support, yet remains cutting edge. This balance enables Majerus to summarize, for example, not only the prodigious literature on male-killing symbionts, but also to speculate on the connections between male-killers, aposematism and enhanced colour polymorphism. The argument, which weaves behavioural ecology, population dynamics and mutualistic endosymbionts into the fabric of comparative beetle biology is typical of Majerus’ lucidly integrative mind and of this book.The character that pops up like the Cheshire Cat throughout Sex Wars is Wolbachia, a Rickettsian bacterium with a talent for manipulation of its host. Most modern evolution texts feature a Wolbachia story but none lays out the incredible diversity of roles that this genus of microbe plays: Wolbachia feminize male crustaceans, serve as mutualistic symbionts in nematodes, induce parthenogenesis in some arthropods (particularly Hymenoptera), and kill males in many insect species. Is Wolbachia special? asks Majerus, or is it just the Drosophila of the endosymbiont world? Should we expect to find many other microbes as diversified and devious as Wolbachia? By considering only the studies that have worked backwards from an anomalous pattern of host phenotypes to their inducers, Majerus suggests that they (or the Rickettsiaceae broadly) are unique. Whereas feminizers and male-killers are relatively diverse, only Wolbachia also induces cytoplasmic incompatibility or parthenogenesis. The mechanics of chromosome–microbe interaction offer clues as to why this adaptability might be present in Wolbachia, and Sex Wars offers an excellent summary of the ways in which this sex ratio distorter operates.On a more pedagogical level, Majerus manages to sneak in a few suggestions for how we, as scientists, should conduct ourselves. He suggests that timidity in the face of ‘sound-bite’ media limits our intellectual progress. The six impossible things that he believes include an expanded role in male reproductive physiology and a greatly enlarged phylogenetic footprint for male-killers and other ultra-selfish agents. By deftly assembling what is known about these sex-ratio distorters and speculating on what is to come, this book should help to point the way forward for the legions of scientists exploring intra- and intergenomic conflict. The White and Red Queens seem to have their opposite kings in check.
Published Version
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