Date of Completion

7-22-2020

Embargo Period

7-21-2024

Keywords

evolutionary ecology, phenotypic plasticity, macrophysiology, copepod, thermal adaptation, Acartia tonsa, tolerance, trade off

Major Advisor

Hans Dam

Associate Advisor

Ann Bucklin

Associate Advisor

Carl Schlichting

Associate Advisor

Senjie Lin

Field of Study

Oceanography

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Understanding the mechanisms that allow organisms to cope with spatial and temporal variation is a fundamental challenge for modern biology. In this dissertation I examine spatial and temporal patterns in two adaptive mechanisms, genetic differentiation and phenotypic plasticity, in the widespread copepod Acartia tonsa. Live populations of A. tonsa were collected from sites across a large latitudinal temperature gradient. Common garden laboratory experiments revealed local adaptation of both thermal tolerance and phenotypic plasticity at the sampling range extremes. However, there was also a remarkable lack of differentiation between populations over a large area. DNA barcoding suggests this lack of divergence is likely to due to constraint by gene flow. Additionally, distinct sex-specific differences in thermal tolerance were observed, with males exhibiting lower tolerances than females. Rapid changes in both thermal tolerance and the strength of phenotypic plasticity were observed during laboratory evolution of several of these populations, possibly due to a trade-off between tolerance and plasticity. In Long Island Sound, a highly seasonal estuary, thermal tolerance varied over the course of the year in both resident species of Acartia copepods. Common garden experiments showed that the seasonal variation observed in Acartia tonsa likely reflects genetic differences between generations. Another key finding is that the evolution of plasticity across both spatial and temporal temperature gradients is best explained by a trade-off with thermal tolerance, suggesting a unifying hypothesis regarding the evolution of plasticity in marine copepods.

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Available for download on Sunday, July 21, 2024

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