Sexually-antagonistic effects in red deer

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Evolutionary biologists are continually puzzled by the following problem: natural selection should remove genetic variation that affects the fitness of individuals, yet, when measured, there is often quite a lot of genetic variation for fitness. One possible explanation for the persistence of genetic variation in a population is that, in those species which have two sexes, the genes (alleles) that make a successful male are different from those that make a successful female. A particular gene may be good for males but not be good for females, so that a male with this gene would be relatively successful / and father many offspring / but his daughters would not be. We call this phenomenon sexual antagonism. As a consequence of the opposing selection in males and females, different versions of the gene will be maintained in the population. Sexually-antagonistic effects are likely to be especially important in a species experiencing extensive sexual selection, in which one sex (usually males) is bigger than females, and has developed weaponry such as antlers or horns or spectacular colouration, characteristics which enhance mating success. Sexually-antagonistic effects have been well-explored using theoretical models, and there is empirical support for their existence from laboratory studies of fruit flies, but they have rarely been investigated in nature. In this study we will investigate sexually-antagonistic selection in a wild population of a sexually-dimorphic mammal, red deer. The data set is particularly useful for this study because we have records on the individual life histories, including all breeding attempts, of several thousand deer measured across 34 years. In many cases we also have their skull, jaws, leg bones and cast antlers. Most individuals have been sampled for DNA profiling, from which pedigrees (or family trees) of individuals can be constructed, stretching for up to ten generations of deer. We also have blood samples and can collect faecal samples in which we can measure hormone levels, and finally we have information about the density and weather conditions in which each animal has lived. Long-term studies of individually-recognised wild animals such as these are an important source of information on many aspects of ecology and evolutionary biology. In the first and major part of the study we will use our pedigree information to test for sexually-antagonistic genetic effects. In particular, we will test whether successful males have less successful female relatives, whereas successful females have less successful male relatives. Theoretical models predict that the genes underlying sexually-antagonistic selection will be concentrated on the X chromosome, and we will investigate this question using the known differences in the inheritance of X chromosomes from different ancestors. We will then measure the selection pressures associated with sexually-antagonistic effects. We will test the hypothesis that males with especially 'masculine' body proportions should have higher breeding success than males whose body proportions are more similar to those of females, and vice versa. Because we are working on a wild population experiencing natural environmental conditions, we can also determine the extent to which all these pressures are affected by variation in environmental and ecological conditions. Finally, we will explore one possible mechanism for these effects, via an investigation of associations between testosterone levels and differences in morphology and breeding success, in both males and females.