磁单极子————观测实验 Nature

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propagates copies of some of its own genes5. It has been proposed that kin selection  — natural selection that increases indirect fitness — can explain why males sometimes reduce the harm incurred by their mates4,6. Specifically, when kin compete, any harm imposed on a female should detrimentally affect the males’ inclusive fitness by reducing the reproductive output of their male relatives. So, by favouring reduced competition between related males, kin selection should limit collateral harm to females. Although sexual cooperation between related males has been extensively studied in vertebrates7,8, the fitness consequences for females have received little attention. In a series of experiments, Carazo et al. paired one female with three males that were unrelated to the female, but that varied in relatedness to one another. The authors found that females paired with male triplets that were full siblings (AAA) had greater lifetime reproductive success than females paired with three males that were unrelated to each other (ABC). This difference was not a result of AAA-treatment females having higher fecun-dity or a longer lifespan, but rather because they exhibited reduced reproductive senes-cence — that is, their rate of offspring produc-tion declined with age more slowly than did that of females exposed to un related males. The researchers show that this pattern was attributable, at least in part, to a significantly slower decline in the survival of offspring as AAA- compared with ABC-treated females aged (Fig. 1). The authors next sought to uncover the mechanisms underlying the reduced repro-ductive senescence of females when paired with brothers, by quantifying how males interact with the female and with one another. Again, females were randomly assigned to AAA or ABC trios of males, with the addition of a third, intermediary treatment of two full siblings and one unrelated male (AAB). As predicted by kin-selection theory, fighting between males was more common in ABC triplets than in either of the other conditions (Fig. 1). ABC males also courted females more intensely than AAA males. However, there were no treatment-related differences in mating rates. These observations suggest that harm to females is mediated by the aggres-sive behaviour of unrelated males towards each other and to females, reinforcing earlier findings9. One might propose that ABC males harm their mates by adjusting the contents of their ejaculate. For example, the seminal-fluid hor-mone Acp70A can reduce female lifespan, and D. melanogaster males are adept at facultatively adjusting both the sperm and seminal-fluid content of their ejaculates10,11. But Carazo et al. ruled out this explanation. They quan-tified female post-mating behaviours that are influenced by ejaculate content (latency to re-mating, and egg-laying rate) and found no differences between females inseminated by AAA compared with ABC males. Thus, the beneficial consequences of kin selection seem to involve pre-mating sexual selection. Nevertheless, another experiment revealed dramatic post-copulatory consequences of male competitive behaviour. By combining two brothers with one unrelated male (AAB), the authors found that the unrelated male did not court or mate more frequently than either of the brothers, yet sired on average twice as many offspring! Although the mechanism underlying this dramatic pattern remains a mystery, the evolutionary implications are clear: the gentler behaviour among brothers that reduces premature ageing of females is evolutionarily unstable. Such kindness will not be rewarded whenever selfish, unrelated males join the group.Drosophila melanogaster has been an impor-tant model system for studying myriad top-ics in evolutionary biology, including sexual selection and sexual conflict, but not kin selection. Natural fruit-fly populations are typically large, and individuals are thought to disperse widely within their environment, so there would presumably be little oppor-tunity for interaction among relatives. Yet Carazo and colleagues’ findings suggest that D. melanogaster populations might occasion-ally be (or have been) structured such that they could be influenced by kin selection. We hope that this surprising and compelling study will tempt more Drosophila biologists to leave the laboratory to explore the ecology of this model system. ■Scott Pitnick is in the Department of Biology, Syracuse University, Syracuse, New York 13244, USA. David W. Pfennig is in the Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.e-mails: sspitnic@syr.edu; dpfennig@unc.edu1. Arnqvist, G. & Rowe, L. Sexual Conflict (Princeton Univ. Press, 2005).2. Morrow, E. H., Arnqvist, G. & Pitnick, S. Behav. Ecol. 14, 802–806 (2003).3. Carazo, P., Tan, C. K. W., Allen, F., Wigby, S. & Pizzari, T. Nature 505, 672–675 (2014).4. Rankin, D. J., Dieckmann, U. & Kokko, H. Am. Nat. 177, 780–791 (2011).5. Hamilton, W. D. J. Theor. Biol. 7, 1–16, 17–52 (1964).6. Pizzari, T. & Gardner, A. Phil. Trans. R. Soc. B 367, 2314–2323 (2012).7. Solomon, N. G. & French, J. A. (eds) Cooperative Breeding in Mammals (Cambridge Univ. Press, 2007).8. Concannon, M. R., Stein, A. C. & Uy, J. A. C. Mol. Ecol. 21, 1477–1486 (2012).9. Partridge, L. & Fowler, K. J. Insect Physiol. 36, 419–425 (1990).10. Lüpold, S., Manier, M. K., Ala-Honkola, O., Belote, J. M. & Pitnick, S. Behav. Ecol. 22, 184–191 (2011).11. Sirot, L. K., Wolfner, M. F. & Wigby, S. Proc. Natl Acad. Sci. USA 108, 9922–9926 (2011).This article was published online on 22 January 2014.Polar explorationMagnetic monopoles — particles carrying a single magnetic charge — have never been seen. Analogues of these entities have now been produced in an ultracold cloud of rubidium atoms. See Letter p.657LINDSAY J. LEBLANCIf …… 此处隐藏：12170字，全部文档内容请下载后查看。喜欢就下载吧 ……