PhD Oral Exam - Javier Ibarra Issasi, Biology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The drivers of phenotypic diversity have puzzled humanity for centuries. Functional trait approaches have helped advance the mechanistic understanding of the diversity of life forms. Previous work shows that evolutionary history and environmental adaptation contribute to the observed diversity of phenotypes. However, most of our understanding comes from plants and studies that often neglect the influence of intraspecific variability. Using ants as study organisms, my thesis aims to examine the drivers of phenotypic diversity across organizational levels. In Chapter 2, I examined the influence of evolutionary and environmental heterogeneity on the phenotypic diversity of ant lineages. I found a positive relationship between the diversity of climates occupied by ant genera and their phenotypic volume and integration. This indicates that ant morphologies are adaptations to ecological opportunities created by climate diversity. For Chapter 3, I examined geographic variation in community-wide patterns of phenotypic diversity, at different organizational levels (i.e., worker, colony, and species), along a 9° latitude gradient in Quebec, Canada. The results suggest that stressful environmental conditions typical of northern ecosystems exert a strong selection pressure on ant morphology causing shifts in optimal trait values of antennae length and eye size. Specifically, I found that shorter antennae and larger eyes possibly represent adaptations to cold, dry, and open habitats. In Chapter 4, I evaluated the impact of coffee plantation management practices on community-wide patterns of ant phenotypic diversity and composition. I found that intensified monocultures harboured phenotypically distinct ant communities. Moreover, community-wide phenotypic composition was more homogeneous in intensified plantations than in nearby forest patches or shade-grown plantations. This indicates that shade-grown strategies in coffee plantations buffer the impoverishment of ant phenotypic diversity following forest conversion, which could help preserve ecosystem services provided by ants. Overall, my thesis suggests that patterns of ant phenotypic diversity emerged and are maintained by environmental gradients, vary among organizational levels (worker, colony, and species), and are influenced by anthropogenic disturbance across facets (taxonomic, phylogenetic, and functional). These findings have important implications for the understanding of how phenotypically complex organisms respond to climate change and provide important guidance for conservation strategies targeting vulnerable lineages.