PUB - Publikationen an der Universität Bielefeld

This work focuses on two aspects of the variation in phenotypic plasticity in the alpine grasshopper Gomphocerus sibiricus, a widespread species inhabiting alpine regions. This species presents various traits which make it very amenable to assess how the interaction between genotype and environment drives phenotypic expression of important ecological and reproductive traits. Of special interest are the remarkable sexual traits present in the male, which are employed during the various stages of female attraction and courtship ritual. These traits constitute ideal targets to study individual condition and its effects on trait expression, since sexual traits are considered to be highly sensitive to condition, making them signals of male quality for the female. First I assessed the effect which background colour and ambient temperature can have on the occurrence of colour morph switches and developmental darkening in Gomphocerus sibiricus (Chapter 2). This species presents a notorious green-brown colour polymorphism, and some species have the ability to switch between these two morphs in order to adapt to their environment. The analyses uncovered that while this species is not capable of switch between the aforementioned morphs, the nymphae are capable, under certain conditions, of darkening or lightening their colour morph. This finding hints at a possible strategy to maintain a good energy budget in an environment whose climatic conditions are in constant change and which are likely to hinder daily activity patterns due to reduced thermoregulation capacity. In Chapter 3 I focused on the effect of individual condition on trait expression, and I specifically set out to test if sexually selected traits in G. Sibiricus are more strongly affected than non-sexually selected traits when condition is impaired. In order to test condition I employed an LPS-based immune challenge on three cohorts of nymphae, and I measured several traits of both types. I expected to observe a stronger decrease in size of sexual versus non-sexual traits in individuals whose condition was impaired due to the immune challenge. Still this was not observed, and instead traits showed an overall similar effect, with a trend for sexually selected traits to grow bigger than non-sexually selected traits. Based on personal observations in the field as well as similar approaches to test condition dependence in similar species, I discussed the significance of these findings for the evolution of the conspicuous sexual traits in this species. On my final assessment I used a theoretical approach to analyse the relation between genetic quality and both sexual and non-sexual traits using a meta-analytic method. According to theory, sexually selected traits are expected to show higher inbreeding depression than non-sexually selected traits. The results of my meta-analysis encountered that contrary to the expectation, sexually selected traits show less inbreeding depression than non-sexually selected traits. I discussed a possible scenario for the evolution of sexually selected traits where their ability to signal individual quality is directly related to how little cheater males in poor condition have noticed their function as signals to attract females. It is these traits which still retain their function as signals of good quality the ones which would present higher inbreeding depression than non-sexually selected traits. On the other hand, those traits which were noticed by males in poor condition, cheater males, would be expressed by these males in spite of their poor condition because of the advantage that they provide to attract females.