MULTIFACETED DRIVERS OF PERFORMANCE VARIATION IN ANIMAL POPULATIONS: INVASIVE PREDATOR, RESOURCE AVAILABILITY AND HYBRIDIZATION

The biodiversity on Earth is dramatically affected by global changes. To understand biodiversity loss and determine priorities for conservation, it is important to assess whether and how individuals can adapt to a continuous and drastic environmental change. Phenotypic variation is a key process that allow populations to withstand environmental changes by increasing survival and fitness, and can be related to both adaptations and phenotypic plasticity. For this reason, studies on phenotypic variation, and its associated fitness, analysing response to different stressors are needed. This thesis investigated phenotypic variability, through the study of performance variation, in response to three of the most pressing issue of global change: alien species, resource availability and hybridization. The first study (Chapter 2) focused on phenotypic variation of a native species in response to an alien predator. Italian agile frog embryos developed faster when exposed to the predator in laboratory condition and when collected in alien crayfish-invaded sites. This ontogenetic shift can be interpreted as a local adaptation to the alien predator and suggests that frogs are able to recognise the predatory risk. If these responses are effective, escape strategies against the invasive predator may improve the survival of frog populations. The second study (Chapter 3) analysed how sexually selected traits vary across different degree of resource availability. We assessed the existence of condition- and context-dependent sexual dimorphism (SD) within and among populations in the Italian wall lizard. Body condition and ecosystem productivity were the main drivers of body size SD variation, and body condition was also the main driver for head shape SD. The expression of SD in the Italian wall lizard is strictly related to the changes in resource availability. The third study (Chapter 4) evaluated how hybridization affects hybrid performance and the main drivers of performance differences between hybrid and their parents, using the meta-analytic approach to obtain generalizable conclusions. The averaged hybrid performance was similar to the 2 fitness of parental lineages, however both the level of genetic divergence between parental lineages and the approach used to identify hybrids affected hybrid performance. Performance was lower for hybrids between distantly related lineages and the use of imprecise approaches for hybrid identification (e.g. morphology-based) can bias assessments of performance. Altogether, the analyses performed show how alien species, resource availability and hybridization can drastically modify the phenotypic variability of animal populations. The presence of an alien predator induced plastic and adaptive phenotypic changes in a threatened frog that could increase the survival of the populations. Resource availability determined the degree of expression of sexually selected traits among and within lizard populations. Finally, hybridization can decrease hybrid performance when epistatic interactions occurred in individuals. Here, I demonstrated that animal responses to different stressors are particularly varied and articulate. Future challenges should focus on the combined effects of several stressors on animal phenotype. The conclusions of this thesis represent a step toward a better knowledge of the impact of global changes on phenotypic traits variation related to performance in animals.