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Thesis defences

PhD Oral Exam - Brendan Joyce, Biology

Phenotypic Plasticity of the Teleost Brain: Relationships Between Predation Pressure, Personality, and Stress Coping Style


Date & time
Monday, February 6, 2023
12 p.m. – 2 p.m.
Cost

This event is free

Organization

School of Graduate Studies

Contact

Daniela Ferrer

Where

Richard J. Renaud Science Complex
7141 Sherbrooke W.
Room SP 4578.03

Wheel chair accessible

Yes

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

Teleosts exhibit extensive, ongoing neuroproliferation within their brains even as adults, which facilitates indeterminate growth and permits them to recover from injuries to their central nervous system which would be catastrophic in higher vertebrates. As a result, the brains of teleosts show considerable phenotypically plasticity, adopting different morphologies in response to stimuli from the environment. This plasticity manifests as differential regional growth rates within the brain, with the balance between the rates of neuroproliferation and apoptosis determining if a region grows or shrink. Their adaptive plasticity is constrained by the elevated metabolic cost of neural tissue, which penalizes excess investment in underutilized parts of the brain but also permits patterns of investment to change, leading to substantial intraspecific variation in brain morphology. The plasticity which leads to the morphological variation seen within species can exceed that seen between species and presents both obstacles to and opportunities for those who study teleosts or used them as model species. In this thesis I set out to explore the potential ramifications of neuroplasticity in the teleost brain.

I begin with a review of the literature (Chapter 1), identifying factors known to influence brain morphology and to identify the predominate methods and model species used to measure it. In Chapter 2, I tested the impact of exposure to predation risk on the brain morphology of juvenile Atlantic salmon (Salmo salar) and adult northern redbelly dace (Chrosomus eos). I found that gross brain morphology can change in under 14 days of elevated predation risk. Chapter 3 expands on this, finding that predation pressure lead to smaller hypothalami and bolder individuals. I also demonstrate that hypothalamic size correlates with shyness (i.e. risk averse phenotypes). In Chapter 4, I used predation induced brain morphology to test how olfactory and hypothalamic investment influence anti-predator behaviour in proactive and reactive individuals. Finally, in Chapter 5 I conclude with an experimental validation of the methodology used for quantifying brain morphology (cross sectional area); I tested its performance against the widely used ellipsoid estimation; in most circumstances they were found to perform comparably. Together, my research provides strong evidence that short-term exposures to local stressors (i.e. predation, captivity) lead to predictable changes in brain morphology; changes that correlate well with studies of behavioural phenotypes.

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