Differing patterns of hsp70 gene expression in invasive and native kelp species: evidence for acclimation-induced variation

Abstract

Temperature is one of the primary factors determining the geographic boundaries of seaweeds. Thus, investigations of how seaweeds cope with temperature stress and what affects their ability for range expansion are particularly important when studying invasive species. In physiological ecology, an established index of thermotolerance is the up-regulation of heat shock genes and subsequent synthesis of heat shock proteins (Hsps). The goal of this study was to examine the up-regulation of the hsp70 gene to assess physiological tolerances of the Eastern Pacific invasive kelp, Undaria pinnatifida, as compared to a potentially competing native kelp, Egregia menziesii. Individuals of both species were collected from six known Undaria invasion sites on the west coast of North America and held in the laboratory for 1--2 weeks for acclimation at 10{\textdegree}C. Samples were then heat shocked at 7 temperatures for 1 h. RNA was extracted, reverse transcribed, and amplified in quantitative PCR reactions to determine relative amounts of hsp70 transcript. Results indicate that the native Egregia may be locally adapted to different thermal regimes across latitude, while the invasive Undaria populations exhibit similar expression profiles across latitude but differ by habitat.