Maternal Effects as Adaptations

Edited by:
  • Timothy A. Mousseau &
  • Charles W. Fox
Oxford University Press: 1998. 348 pp£49.50, $65

Mothers love their children, of that we can be sure. Some biologists, who love their mothers as much as anyone, interpret the effects that mothers have on their offspring as adaptations shaped by evolution.

A female parasitoid wasp determines the sex of her haplodiploid offspring by controlling insemination: inseminated eggs become daughters. She lays daughters in large larvae, sons in relatively small ones — the reproductive success of daughters is more dependent on large body size than is that of sons.

A socially dominant red deer hind gives birth to more sons than daughters, probably by selective abortion of female fetuses. Her sons have a better chance of becoming dominant and fathering many grandchildren than do the sons of subordinate females. Subordinate females, on the other hand, have offspring with normal sex ratios. So are maternal effects usually adaptations? The case is clearer for these examples than it is for most of the effects mentioned in this book, and the authors admit as much.

Although there are many such examples, the editors and authors of the book complain that adaptive maternal effects have been neglected and that this must change. How do they arrive at the impression of neglect in the midst of plenty? To an evolutionary quantitative geneticist, taking an effect seriously means studying its genetics. This they do by extending the methods of quantitative genetics to include inter-generational effects of parental phenotypes on offspring phenotypes, and they succeed rather well.

Why did they think that the time was ripe to focus on maternal effects? Here I was less satisfied. Plant and animal breeders have tended to play down maternal effects, and the dominant texts on plant and animal breeding make little mention of them. The neglect has thus not been the fault of evolutionary biologists, but of non-evolutionary quantitative geneticists, who can hardly be blamed for not addressing problems they did not realize they were supposed to solve. I wonder whether one needs a whole book to make that simple point.

Some authors seemed to value complexity for its own sake. Other contributions were more satisfying. Roff's review of methods is clear, useful and concise. The reviews of maternal effects in flowering plants, insects, fish, amphibians and rodents are competent summaries of the state of the art. Denlinger's chapter on the transgenerational control of fly diapause shows how much can be achieved with classical techniques; here the way ahead appears to be molecular rather than quantitative genetics.

In brief, this multi-authored symposium volume has some new, creative contributions to methods, some useful reviews of the state of the art and a few chapters from people who should have done a better job. All the authors are from North America. I hope that this does not declare a prejudice about where significant work is being done.