DO GROUP DYNAMICS SHAPE HOW FISH SENSE AND RESPOND TO WARMING TEMPERATURES?

Master of Science (Biology) candidate: Jacob Mercer

20 November 2026

1:00 PM Atlantic

Hybrid Defence

KCIC Acadia Room

Join: https://teams.microsoft.com/meet/2761956801056784?p=l6a4W0YwxUuNgOJW6V
Meeting ID: 276 195 680 105 678 4
Passcode: 8Th9FV23

Thesis Committee:

Drs. Garett Allen (Acadia) & Dr. Suzie Currie (UBC), Supervisors
Dr. Laura Ferguson, Internal Examiner
Dr. Andy Turko, Univ. of Guelph, External Examiner
Dr. Peter Ludlow, Chair of the defence

Abstract

Social context is a crucial component of an animal’s environment that may influence their response to environmental challenges such as warming, especially in ectothermic fishes that exhibit a broad range of social behaviours. Mangrove rivulus (Kryptolebias marmoratus) are amphibious fish that exist naturally in diffuse groups and exhibit aggressive behaviours. My overarching hypothesis was that social grouping (trios) and environmental complexity (e.g., access to a shelter) will affect how fish respond to acute warming through changes in temperature sensing. I used an isogenic lab population of mangrove rivulus (Kryptolebias marmoratus) to test this hypothesis. Capitalizing on the fish’s propensity to voluntarily emerge from water, I observed that individual fish without shelter emerged at significantly warmer temperatures (39.4 ± 0.17°C) than fish in trios without shelter (38.7 ± 0.07°C, p < 0.001). Shelter presence conferred a modest, but statistically insignificant decrease in emersion temperature in single fish (38.9 ± 0.12°C, p = 0.095) but not in trios (38.6 ± 0.09°C, p > 0.05). These differences in emersion temperatures in isolated and grouped fish were not associated with patterns of intraspecific aggression, activity, or whole-body cortisol before or during warming. To assess whether this higher temperature threshold in individual fish is linked to changes in thermal perception, I used a specific chemical agonist of the thermosensing transient receptor potential vanilloid 1 (TRPV1) channel, capsaicin (the active compound in chili peppers) to induce emersion with chemical heat. Fish in trios without shelter emerged at modestly lower capsaicin concentrations (1.1 ± 0.09 mM mg-1) than individual fish without shelter (1.55 ± 0.16 mM mg-1, p < 0.051). These results suggest that fish in trios are more sensitive to warming, at least partly through more sensitive TRPV1 channels. My thesis highlights the importance of group dynamics in shaping how fish will respond to environmental challenge.

About Jacob…

Jacob Mercer is an MSc student in Biology at Acadia University studying fish behaviour and physiology under the co-supervision of Dr. Suzie Currie and Dr. Garett Allen. His research focuses on how group dynamics influence thermal perception and response in the amphibious mangrove rivulus (Kryptolebias marmoratus) killifish. Jacob completed his BSc (Honours) at Memorial University of Newfoundland, with his honours research focusing on how temperature and body size affect covering behaviour in green sea urchin (Strongylocentrotus droebachiensis). In his free time, Jacob snorkels and practices underwater photography of coastal aquatic life with the goal of uploading observations to iNaturalist to inform species distribution and conservation efforts.