|Letters Sexual conflict and female choice William G. Eberhard1 and Carlos Cordero2 1Smithsonian Tropical Research Institute, and Escuela de Biolog??a, Universidad de Costa Rica, Ciudad Universitaria, Costa Rica 2Instituto de Ecolog??a, Universidad Nacional Auto?noma de Me?xico, Apdo. Post. 70-275, Circuito Exterior, Ciudad Universitaria, Coyoaca?n 04510, Distrito Federal, Mexico Chapman et al. [1] nicely summarize some recent thinking about male?female conflict, but repeat a widespread inconsistency between old and new versions of sexual conflict, and give an overly optimistic impression of support for new models of antagonistic coevolution. They define conflict broadly as ?differences in the evolutionary interests between males and females?. Such conflict is hardly a new idea. Traditional darwinian sexual selection by female choice [2] inevitably involves male? female conflicts of interest. Chapman et al.?s characteriz- ation of the traditional view as ?one of cooperation and harmony between the sexes? misreads history. This broad definition contrasts with how the authors propose to distinguish sexual conflict from other models of sexual selection. Here, they emphasize the truly new, but much narrower conflict hypothesis: ?the force driving the evolution of the [female] preference is better described as a general female avoidance of male-imposed costs, rather than, as in traditional direct models, acquisition of benefits from preferred males?. Inconsistent use of old, broad definitions, and new, narrow definitions has plagued recent literature on sexual conflict. How strong is the support for the new, narrower idea of sexual conflict? Some impressions of conflict, based on observing female ?resistance? behavior, or from document- ing reproductive costs to females, are misleading [3,4]. A female can gain by being ?manipulated? by a male if her indirect gains via increased manipulative abilities of her male offspring are greater than the male-imposed reduction in her own reproduction; under some conditions, female susceptibility to males can be advantageous [4,5]. Chapman et al. argue that such ?indirect benefits [to the female] are expected to be a weak force in the face of direct selection on preference?, but cite only a theoretical model as evidence. The track record of quantitative conclusions based on mathematical models of sexual selection is rather dismal [2]. Recall, for instance, the now discarded dogma that Fisherian female choice was unlikely because quantitative models had ?proven? that there is little or no heritable variability for sexually selected traits in males. The conflicting demonstrations regarding the feasibility of handicap models constitute another example. In addition, empirical evidence indicates that indirect benefits to the female are not necessarily small [6]. Thus, the studies that Chapman et al. cite as documenting the overall cost of manipulation for females, none of which took this possible indirect benefit into account, fail to demonstrate a net cost rather than a net benefit. A second weakness is that costs and benefits cited by Chapman et al. were measured under captive rather than field conditions. It is trite, but nevertheless true [4], that fitness measures made in captivity do not reliably document selection in nature. For instance, reductions in female lifespan in the lab [7] might be irrelevant in nature if females die at earlier ages under natural conditions. Ecological realism is especially important for traits possibly involved in male?female conflict [1], because the demonstration of conflict depends on precise quanti- tative balancing of costs and benefits. Finally, Chapman et al. do not discuss morphological evidence from many other species that speaks strongly against the importance of new male?female conflict models [8?11]. References 1 Chapman, T. et al. (2003) Sexual conflict. Trends Ecol. Evol. 18, 41?47 2 Andersson, M. (1994) Sexual Selection, Princeton University Press 3 Eberhard, W.G. (2002) Female resistance or screening? Male force versus selective female cooperation in intromission in sepsid flies and other insects. Rev. Biol. Trop. 50, 485?505 4 Cordero, C. and Eberhard, W.G. (2003) Female choice of antagonistic male adaptations: a critical review of some current research. J. Evol. Biol. 16, 1?6 5 Kokko, H. (2001) Fisherian and ?good genes? benefits of mate choice: how (not) to distinguish between them. Ecol. Lett. 4, 322?326 6 M?ller, A.P. and Jennions, M. (2001) How important are direct fitness benefits of sexual selection? Naturwissenschaften 88, 401?415 7 Chapman, T. et al. (1995) Cost of mating in Drosophila melanogaster females is mediated by male accessory gland products. Nature 373, 241?244 8 Eberhard, W.G. (1985) Sexual Selection and Animal Genitalia, Harvard University Press 9 Eberhard, W.G. (2001) The functional morphology of species-specific clasping structures on the front legs of male Archisepsis and Palaeosepsis flies (Diptera, Sepsidae). Zool. J. Linn. Soc. 133, 335?368 10 Huber, B.A. (1998) Spider reproductive behaviour: a review of Gerhardt?s work from 1911?1933, with implications for sexual selection. Bull. Br. Arachnol. Soc. 11, 81?91 11 Eberhard, W.G. (1997) Sexual selection by cryptic female choice in insects and arachnids. In Evolution of Mating Systems in Insects and Arachnids (Choe, J.C. and Crespi, B.J., eds) pp. 32?57, Cambridge University Press Corresponding author: William G. Eberhard (archisepsis@biologia.ucr.ac.cr). TREE 122 Update TRENDS in Ecology and Evolution Vol.not known No.not known Month 0000 1 ARTICLE IN PRESS http://tree.trends.com 0169-5347/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0169-5347(03)00180-0