SUCCESS · Sexual selection under changing conditions and environments

Sexual selection under changing conditions and environments

The main objective of the present proposal was to analyse the potential role of environmental heterogeneity on sexual selection processes. I achieved this question by means of two different approaches: on one side, a correlative approach (analyses of a long-term data-set of red grouse populations) and on the other hand, an experimental field-study (manipulation of the level of aggressiveness in wild red grouse). To accomplish the first objective, I have analysed the long-term dataset of the host group regarding sexual traits and condition in red grouse. This data-set includes measures of more than 1 500 individuals from nine populations over 10 years covering a wide range of environmental conditions in terms of population density, parasite infection and weather conditions. I focused the analyses of this dataset in two ways. First, I studied the effect of environmental conditions in signal reliability. Secondly, I analysed whether sexual ornament expression is affected by environmental heterogeneity. Both expression and reliability are key concepts in sexual selection. Whether environmental conditions affect both signal reliability and expression is needed to improve our knowledge of this evolutionary force. As predicted, I found that environmental heterogeneity affects both signal reliability and expression. I found that adverse environmental conditions increase signal reliability but decrease its expression. In particular, I found that increased levels of intra-sexual competition and high parasite abundances promote and increase in signal reliability. Furthermore, environmental factors such as population density or weather conditions have a negative impact on sexual ornamentation in red grouse. Interestingly, we also found that these patterns are also true for females, a novel aspect as sexual ornamentation in females is a largely neglected topic. The second objective aimed to experimentally test whether environmental conditions affect sexual selection processes. I focused the experimental approach on the level of aggressiveness. Previous experiments showed that males implanted with testosterone increase their aggressive behaviour and sexual displays. As a consequence, manipulations of testosterone at a population level also increase intra-sexual competition. Therefore, I followed such previous experimental designs to achieve the second objective. Briefly, the experiment was carried out by implanting testosterone a subset of males (around 40 %) living in a given area. Then, I compared the individuals living within the treatment-area with individuals living in a neighbouring and non-manipulated control-area. I found that the treatment worked as expected increasing intra-sexual competition in the treatment area. Interestingly, untreated males living in the treatment area have decreased their levels of sexual signalling (comb size) few weeks after the manipulation. I also found higher testosterone levels in untreated males living in the treatment area than in males living in the control area. These results add experimental support to the prediction that environmental heterogeneity in general, and the social context in particular is important in regulating sexual signalling.

Data: CORDIS, © European Union