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1 June 2006 SEXUAL CONFLICT: A NEW PARADIGM?
TAMÁS SZÉKELY
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Sexual Conflict. Göran Arnqvist and Locke Rowe. Princeton University Press, Princeton, NJ, 2005. 360 pp., illus. $39.50 (ISBN 0691122180 paper).

I'm watching a breeding colony of southern elephant seals on a remote island in the Falklands. The harem master is an impressive behemoth, and as he makes his way through his courtiers to clash with rival males, some of his females and their pups are inevitably crushed. This does not seem to bother the master, since his main raison d'être is to sire the pups that will be born a year later. Females, which have only about a fifth of his mass, are powerless to fight him off to save themselves and the pups. A short distance away, southern giant petrels breed on the same beach. Giant petrels pair for life, and they raise their single offspring by sharing the incubation, brooding, and feeding of their young for a staggering 6 months.

So why and how did nature produce some species in which males and females have severe conflicts over reproduction, such as elephant seals, whereas in others, such as giant petrels, cooperation prevails? In Sexual Conflict, Göran Arnqvist and Locke Rowe offer some illumination, and in so doing they make a major contribution to the field of sexual selection. This is a wonderful book, packed with exciting natural history, distilled interpretation of recent experimental studies, and straightforward explanations of complicated mathematical models. If you want to learn how male bedbugs rape females (and fellow males), examine the tactics of penis fencing in marine flatworms, or discover the tricks a promiscuous penduline tit uses to cheat its mate, this is the source to turn to. These and other intricate examples illustrate that nature produces many bizarre examples of sexual conflict in which the interests of males and females are strikingly divergent.

Reproduction is an uneasy alliance between the sexes, a game of tug of war. For a viable embryo, both a male and a female gamete are needed, though to achieve fertilization the sexes (and indeed hermaphrodites) use different means. For males, often the best strategy is to pursue matings persistently, whereas for females selective resistance may be the winning card. It is important, however, to realize that males and females are tied together in more than an allegorical way: If males harm females—for instance, by developing brutal intromittent organs—not only will the female's reproductive success in a population be reduced, but so will that of an average male.

Sexual conflict is becoming a major concept in evolutionary biology for two main reasons. First, teasing apart the male and female perspectives is genuinely fascinating. Unlike some other relationships involving conflict, such as predator–prey and host–parasite interactions, sexual conflict has fighting teams (labeled “males” and “females”) that share the vast majority of their genes. Second, sexual conflict can be studied at several levels using a variety of research tools and model organisms, from genes through individuals to macroevolution. Thus researchers use advanced techniques borrowed from molecular genetics, population genetics, behavioral ecology, and comparative phylogenetics. Indeed, as Arnqvist and Rowe argue, a single type of methodology is unlikely to be successful for revealing the details, directions, and intensity of sexual conflict.

The concept of sexual conflict goes back to seminal papers by Robert Trivers and Geoffrey Parker in the early 1970s, but present-day students can draw on recent rapid advances in genetics, behavioral biology, and phylogenetics. For instance, clever genetic techniques allow researchers to speed up sperm competition in fruit flies and pit the resulting supercompetitive males against unaltered populations of females. The unlucky females are likely to die, an unfortunate side effect of the enhanced seminal fluids produced by supercompetitive males. These achievements warrant a full-fledged new paradigm that cuts through the boundaries of traditional biological disciplines, although only time will tell how far we can push the Trivers–Parker paradigm. It seems certain, however, that Arnqvist and Rowe's well-balanced and carefully worded book is a landmark, and it is likely to recruit new fans to the sexual conflict camp.

Two major challenges, in my view, remain to be tackled. First, we need a full understanding of the costs and benefits of mating, for both sexes. There are convincing demonstrations that mating is costly for females. However, gaining access to the females and achieving copulation may be exceedingly costly for males as well; for example, bull elephant seals can rarely sustain their bloody fights with rivals beyond a single breeding season. Second, we need to find out why life histories, physiology, and ecology appear to make some species more prone to conflicting interests than others, so that many exhibit overt sexual conflicts, like the elephant seals, whereas others, like petrels, become cooperative. Are the effects of ecology and life history unidirectional, leading to the presence or absence of sexual conflict? Or does strife between the sexes feed back to ecology and life history, amplifying or dampening their effects? The balance between conflict and cooperation may lie at the heart of success (or failure) of alleles, individuals, and populations.

Although I enjoyed this book from cover to cover, some explanatory notes or boxes on the details of the major research techniques would have been a welcome addition. Researchers on sexual conflict use vastly different techniques, so brief descriptions of the principal ones would be especially valuable for postgraduates and for those whose research background is in just one field.

Nevertheless, I expect that Sexual Conflict will be popular among postgraduates, evolutionary biologists, and behavioral ecologists. I have already found it excellent material for my final-year undergraduate course on sexual conflict. And though the book is aimed primarily at professional biologists, I hope and expect the fascinating examples on the behavior and natural history of various beasts will appeal also to the general public.

TAMÁS SZÉKELY "SEXUAL CONFLICT: A NEW PARADIGM?," BioScience 56(6), 539-540, (1 June 2006). https://doi.org/10.1641/0006-3568(2006)56[539:SCANP]2.0.CO;2
Published: 1 June 2006
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