Thermal physiological traits and plasticity of metabolism are sensitive to biogeographic breaks in a rock-pool marine shrimp

Populations of broadly distributed species commonly exhibit latitudinal variation in thermal tolerance and physiological plasticity. This variation can be interrupted when biogeographic breaks occur across the range of a species, which are known to affect patterns of community structure, abundance and recruitment dynamics. Coastal biogeographic breaks often impose abrupt changes in environmental characteristics driven by oceanographic processes and can affect the physiological responses of populations inhabiting these areas. Here, we examined thermal limits, performances for heart rate and plasticity in metabolic rate of the intertidal shrimp Betaeus emarginatus from seven populations along its latitudinal range (~3000 km). The distribution of this species encompass two breaks along the southeastern Pacific coast of Chile: the northern break is characterized by sharp discontinuities in upwelling regimes, and the southern break constitutes a major discontinuity in water conditions (temperature, pH, dissolved oxygen and nutrients), coastline topography and divergence of main oceanographic currents. For B. emarginatus, we found higher plasticity in metabolism at the sites sampled at the biogeographic breaks, and at the site subjected to seasonal upwelling. The variation in metabolic ratewas not consistent with increasing latitude and it was not affected by breaks. The lower and upper thermal limits were lower in populations around breaks, although the optimum temperature decreased towards higher latitudes. Overall, whereas thermal limits and plasticity of metabolism are related to biogeographic breaks, metabolic rate is not related to increasing latitude or the presence of breaks in the sampled range.