PhD Oral Exam - Érik Plante, 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

Abstract Developmental basis of ant caste structure across environments Érik Plante, Ph.D. Concordia University, 2026 Environmental variation shapes morphological complexity by influencing how developmental systems generate phenotypes. Yet, how environmental cues influence phenotypic evolution through developmental systems remains incompletely understood. Eusocial insect colonies are superorganisms that can produce distinct castes from alternative developmental trajectories within a shared genome in response to environmental cues. This makes them a powerful system for studying how development mediates ecological responses in integrated biological systems. This thesis examines how environmental conditions shape ant caste structure, how environmental factors relate to phenotypic variation among castes, and how developmental systems influence phenotypic variation. In Chapter 2, I use the carpenter ant Camponotus herculeanus to show that caste structure varies across a broad environmental gradient, with harsher environments associated with fewer energetically costly major workers. A common garden experiment shows that colonies can plastically adjust caste structure. In Chapter 3, I analyze over a thousand ant species and show that the body sizes of the queen and worker castes relate differently to environmental factors on a global scale. This indicates decoupling in how environmental variation relates to phenotypic variation between castes. In Chapter 4, I target DNA methyltransferases during larval development in the carpenter ant Camponotus floridanus and show that experimental perturbation of these pathways is associated with changes in worker size and head-to-body scaling. Together, these results suggest that developmental systems influence how environmental variation is translated into phenotypic diversity in eusocial organisms, affecting both caste structure and the evolution of caste-specific phenotypes. They further suggest that epigenetic regulation may facilitate the developmental transitions underlying the evolution of worker polymorphism.