Randy Thornhill - US grants

The goal of this one-day symposium is to bring together a diverse and multidisciplinary group of scientists, all of whom are actively investigating the role of parasite infection as a driving force in sexual selection. 'Sexual selection' is the term used by biologists to refer to changes in gene frequencies resulting from competition among members of one sex for mates. Specifically, research to be presented in this symposium is aimed at assessing the extent to which variation among individual traits evaluated during mate choice accurately reflects variation among those same individuals in resistance to parasite infection and disease. Sexual selection is known to have been of great importance in shaping the physiology, morphology and behavior of a wide range of vertebrate species, including humans; hence this very basic genetic process is of considerable interest in its own right. However, the research to be presented in this symposium is also likely to contribute to our understanding of other equally important genetic and behavioral process, most especially processes affecting the transmission (and control) of parasites and disease among both humans and animals. Hence, from the standpoint of human welfare the value of the proposed symposium may lie in its contribution to the emerging synthesis of epidemiology with the closely-related disciplines of population genetics and behavioral ecology. The proposed symposium will be held in conjunction with the 1988 meetings of the American Society of Zoologists (ASZ) and will provide the first opportunity for behavioral ecologists involved in research on sexual selection to interact with parasitologists and other scientists knowledgeable about host- parasite coevolution. It is anticipated that papers presented in the symposium will be published in the American Zoologist or other appropriate outlet, thereby making results of the symposium accessible to a larger audience than simply those individuals attending the 1988 ASZ meetings.

Sexual selection is the cause behind the evolution of elaborate male ornaments in birds (e.g. the large comb and colorful feathers of a domestic chicken rooster). However, exactly how sexual selection works to produce such structures is not understood. Work to date indicates that the size of the comb and the degree of development of other ornaments of jungle fowl roosters (ancestors of domestic chickens) determine their sexual attractiveness to hens and their ability to dominate other roosters. Work to date indicates that ornaments are sensitive indicators of a male's resistance of disease. Thus the investigators have discovered l) a previously unknown relationship between health of males and ornamentation and 2) that sexual selection favors disease-resistant roosters. This first finding has important implications for the poultry industry since jungle fowl and domestic chickens are the same species. The disease resistance, by artificial selection on the basis of male ornaments, disease resistance, and sexual selection in the red jungle fowl.

Recent research indicates that women's mating preferences change across the menstrual cycle. Women's preference for the scent of men who exhibit developmental instability, as revealed by low fluctuating asymmetry, is enhanced in the days leading to ovulation, as is women's preference for masculine male faces. A working interpretation of the findings is that women experience heightened attraction to indicators of benefits that could be heritably passed on to their offspring when they are fertile. Traits that indicate such benefits could be ones that may be generally associated with health (e.g., low fluctuating asymmetry), complement a female's set of genes (e.g., complementary major histocompatibility complex [MHC] alleles), or diversify offspring (e.g., diverse MHC alleles). The research is designed to test four hypotheses: 1) If women's preferences shift during the fertile period toward indicators of heritable benefits, which in-pair partners may not possess, women should experience greater attraction to men other than their primary partners during these days. Overall, women should not experience the same increase in attraction to their primary partners during this period. 2) Men may have evolved to be more attentive of their partners during these times. 3 & 4) Women's greater interest in men other than a primary partner and men's increased attention to their partners may be conditional; it may depend on whether a primary partner possesses heritable benefits (e.g., low fluctuating asymmetry, complementary MHC alleles, diverse MHC alleles). Six studies will assess these predictions in two cultures. One set of studies will assess changes in a sample of 200 romantically involved U.S. college students. The other set will examine the changes in a remote village on the Caribbean island of Dominica. The latter study will also examine whether female or male partner cortisol or the male partner's testosterone change across women's cycle. The aim of this program of research is to increase our understanding of the factors that affect partner choice, the dynamics and stability of relationships, and fertility.