Abstracts (first author)
Selection on penis size, body shape and height in humans: a simple multivariate method to quantify female preferences based on male physical attractiveness
Compelling evidence from many animal taxa indicates that male genitalia are often under post-copulatory sexual selection for characteristics that increase a male’s relative fertilization success under sperm competition. There could, however, also be direct pre-copulatory female mate choice based on male genital traits. Before clothing, the non-retractable human penis would have been conspicuous to potential mates. This, in combination with claims that humans have a large penis for their body size compared to other primates, has generated suggestions that human penis size partly evolved due to female choice. We presented women with digitally projected fully life-size, computer-generated animations of male figures to quantify the (interactive) effects of penis size, body shape and height on female assessment of male sexual attractiveness. We generated 343 male figures that each had one of seven possible values for each of the three test traits (7x7x7 = 343). All seven test values per trait were within two standard deviations of the mean based on a representative sample of males. We calculate response (fitness) surfaces based on the average attractiveness rank each of the 343 male figure received. We also calculated individual response surfaces for 105 women (each women viewed 53 figures). Both methods yielded almost identical results. We discuss our finding in the context of previous studies that have taken a univariate approach to quantify female preferences. We discuss the hypothesis that pre-copulatory sexual selection might play a role in the evolution of genital traits.
The influence of nutrient type on longevity and reproductive senescence in wild and laboratory populations of the Antler Fly (Protopiophila litigata)
Senescence has rarely been shown in systems with high rates of extrinsic (age-independent) mortality such as in wild insects. What is known about senescence is generally based on laboratory model organisms (i.e. exclude extrinsic mortality) or based on studies of wild populations that have not examined senescence experimentally. Thus, we have little information on the extent to which studies in the laboratory correspond to senescence in the wild. The observed patterns of ageing in these systems will be influenced by resource acquisition and allocation to various life-history traits. Theory predicts more rapid ageing in individuals with higher initial mating rates stemming from a trade-off in reproduction vs. somatic maintenance and repair. In turn, the proportion of various energy sources in food, or restriction thereof, may shift the balance in this life history trade-off through their influence on physiological state and condition. Moreover, high-profile effects of caloric restriction in increasing lifespan come from lab populations. Diet manipulations may have much more complex and sex-dependent effects, especially in the wild. Here we take advantage of an extraordinary system - Antler Flies – where extreme site fidelity of males permits estimates of both lifespan and lifetime mating success. We extend previous work demonstrating aging in wild males to address the effects of a diet manipulation and to compare estimates conducted under lab vs. field conditions. Using a factorial design, we estimated senescence in mating rates and probability of survival for males treated with protein, carbohydrates, or water in both lab and field environments. We will discuss the extent to which these resources differentially influence life span, reproductive ageing, and the shape of survival curves. Our results have direct implications for the evolution of demographic patterns and senescence.