Darwin was the first to suggest that sexual selection (that is, mate choice and competition for mates) could be a selective pressure shaping the evolution of populations. At the time his Victorian colleagues scorned the idea that female animals could be "smart" enough to be choosy about their mates. Over the past three decades or so a resurgence of empirical interest in sexual selection has demonstrated the ubiquity and influence of sexual selection on the behavior and morphology of animals and plants.
My current studies of sexual selection in the Wild Turkey build on my previously published work (see curriculum vita for references to these publications).
The wild turkey (Meleagris gallopavo) is a highly polygynous, sexually-dimorphic species, well suited to testing the intraspecific predictions and assumptions of 'good genes' models of female choice. I (Buchholz 1995, 1996, 1997) tested alternative hypotheses for the maintenance of 'fleshy' ornamentation in males of this species. In addition to uncovering a non-sexual function for the brightly colored, bare head of the male wild turkey (which is crucial for maintaining sublethal body temperatures under warm ambient conditions and during physical exertion), my work also demonstrated that one aspect of male head ornamentation, the frontal process, or snood is subject to both intersexual and intrasexual selection. Captive female wild turkeys prefer to mate with long snooded males, and during dyadic interactions, male turkeys deferred to males with relatively longer snoods. These results were demonstrated using both live males and controlled artificial models of males.
Why should turkeys pay such close attention to the length of a male's snood? Data on the parasite burdens of free-living wild turkeys revealed a negative correlation between snood length and infection with intestinal coccidia, Eimeria spp., a deleterious protozoan parasite. That is, in the wild the long snooded males preferred by females and avoided by males seemed to be resistant to coccidia infection. I have suggested that this is a case of female choice for male 'good genes'. Females may be choosing coccidia-resistant males as mates so that their own offspring will inherit resistance genes and be more likely to survive. I hypothesized that coccidia-free males were probably more dominant than infected males. If so, selection should favor males who can assess the quality of their competitors before fighting, and thus avoid wasting energy in fights that they are likely to lose (Buchholz 1997).
The interpretations of the adaptive significance of the turkey's snood hinge strongly on the negative correlation between snood length and coccidia load obtained from the field captures. However, the causal relationship between parasite burden and snood length (or mate choice) have not yet been demonstrated, nor has the mechanism by which these parasites limit ornament growth been shown. These factors would need to be demonstrated clearly in order to understand the results of earlier studies showing female preference for male ornamentation in turkeys.
My current projects involve a series of surveys and controlled experiments for elucidating these questions:
a. What is the genetic basis for helminth (tapeworm and nematode) resistance in free living wild turkeys, and the heritability of resistance to coccidia infection in captive birds? (in collaboration with Ann Findley, Steve Hecht, Mary Jones)
b. What is the impact of coccidia infection on the immunocompetence, endocrinology, general condition, mating success and dominance interactions of captive wild turkeys? (in collaboration with Rebecca Holberton)
c. What are the competitive interactions
among the seven species of turkey coccidia, and can these species be identified
students, post-docs and other collaborators should feel free to contact
me about sexual selection research.
Graduate student Mary Jones is documenting the genetic diversity of
free-living and gamefarm wild turkeys
Conservation Biology Avian Research Facility Teaching Curriculum Vita