Arnqvist, G., T.M. Jones, and M.A. Elgar (2003) Reversal of sex roles in nuptial

Question

Arnqvist, G., T.M. Jones, and M.A. Elgar (2003) Reversal of sex roles in nuptial feeding. Nature 424: 387.
1) In many species (including some insects, birds, mammals, etc), males provide their mates with food or other resources. In doing so, they help females provide for young, thus enhancing their own reproductive success (they can produce more, healthier offspring). In addition, they are likely to be able to mate with more females and/or better females, because females often carefully select only the best mates. In the case of Zeus bugs, could females that provide resources to males reap similar benefits? What would those benefits be?
2) Explain how the scientists tested their hypothesis that females secrete food for males. What is the sample size used in the first experiment? Break it down by treatment category. Hint:

Explanation / Answer

Scientists have been hard pressed to explain why menopause happens so early in humans - there's no obvious evolutionary advantage to having your reproductive system shut down decades before the rest of your body. Most other long-lived animals keep reproducing until the end. Female turtles can lay fertile eggs at 100. Our primate relatives, too, keep pumping out young until they are near death. Now, scientists are finding clues to our unusual life pattern in killer whales - one of the few other species in which females get decades of so-called post-reproductive life. What they found was a surprising connection between longevity of mothers and their sons. Biologist Emma Foster of Exeter University in England said that females become fertile around 12, have a calf every three to five years, and then stop reproducing in their late 30s and early 40s. After that they can live many years, sometimes to 90 and beyond. "No other animals have such long post-reproductive lives," she said, except for pilot whales and humans. And while there's a small difference between the sexes in human longevity, it's extreme for whales, with females living to 90 and males rarely getting past 40. Scientists have little understanding of why this would be. In puzzling over this anthropologists have proposed what they call the grandmother hypothesis - the possibility that post-menopausal women gain an evolutionary edge by helping their existing children and grandchildren. In Darwinian terms, after all, no matter how many offspring you have, you'll still be a dead end unless your offspring have surviving offspring. Ultimately, according to the hypothesis, grandmotherly support could allow women to pass on more copies of their genes than by investing the same energy in continuing to have their own babies. The other possibility is that menopause is some sort of evolutionary byproduct that can occur in long-lived animals.

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