The Evolution of the Thermal Niche Across Locally Adapted Populations of the Copepod Tigriopus californicus

Abstract

Local adaptation to different thermal environments is often expected to result in trade-offs in other measures of performance, thermal or otherwise. Populations of the copepod Tigriopus californicus found along the Pacific coast of North America have previously been shown to display patterns consistent with local adaptation and thermal trade-offs. Much of the work on this species has focused on performance at high and moderate temperatures with the lower thermal performance explored to a lesser degree. In this study, measures of both high and low thermal performance are examined for a set of eight T. californicus populations spanning a range from Central Baja California, Mexico to the State of Washington, USA. High temperature survival decreases with increasing latitude while chill coma recovery improves with increasing latitude. Comparisons of these measures among populations along with previous results suggest that there is a shift in the thermal niche in this species rather than other forms of trade-offs such as specialist/generalist trade-offs.