Towards an understanding of seasonal ecophysiology in north-temperate fish

Northern organisms exhibit a range of physiological, behavioural, and ecological strategies to both survive and exploit seasonal cycles in biotic and abiotic conditions. However, our baseline understanding of these seasonally motivated strategies in northern freshwater fishes remains quite limited, regardless of its potential utility for predicting responses to shifting seasonal environments. In this dissertation, I investigated how fish respond to the highly seasonal energetic demands associated with reproduction across populations and environmental conditions. Specifically, I asked: How does the seasonal phenology of abiotic cues: (i) shape the allocation of energy to reproduction, (ii) combine with biotic factors to motivate flexible digestive capacity, (iii) facilitate the availability of novel and potentially critical resources, and (iv) motivate individuals to express coordinated phenotypic flexibility across multiple organ systems and populations? First, in Ch. 2, I used existing data from field and experimental studies on pumpkinseed sunfish (Lepomis gibbosus) to investigate how early spring warming affects the reproductive process. Here, independently cued development of the liver mediated observed reproductive allocation. Earlier warming interrupted liver development and the transfer of hepatic material and energy to the gonad (termed the “hepato-gonadal shunt”), a process putatively present in 20 other north-temperate fish species. Then, I conducted biweekly field sampling across five pumpkinseed populations to investigate how seasonal patterning in foraging, structural modifications, and energy accumulation across multiple somatic tissues shape reproductive outcomes. In Ch. 3, I identified seasonal digestive flexibility as a consistent pattern across pumpkinseed populations that responded to elevated energetic demands associated with reproduction. In Ch. 4, I used diet data to evaluate the potential for invasive terrestrial invertebrates to subsidize fish populations, identifying novel population- and water level-dependent trophic interactions. Finally, in Ch. 5, I evaluated the contributions of seasonal somatic flexibility to reproductive outcomes. Here, the extent of observed somatic flexibility mediated population-level reproductive allocation. Altogether, the capacity for flexibility and reproductive investment varied among fish populations and appeared sensitive to the timing of spring warming. These findings contribute to our understanding of both recruitment variation among northern freshwater fishes and their sensitivity to changes in seasonality due to climate change.

Department dc:contributor.department

Ecology and Evolutionary Biology

Year dc:date.issued

2025

Author dc:creator

• Fernandes, Timothy

Advisor dc:contributor.advisor

• McMeans, Bailey C.

• Aqautic ecology
• Ecophysiology
• Fish reproduction
• Seasonality

Statement dc:rights

• Attribution 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by/4.0/

Handle dc:identifier.uri

https://hdl.handle.net/1807/142662

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/142662