9Thermal reaction norms are fundamental relationships for geographic comparisons of organism 10 response to temperature. They are shaped by an organism's environmental history and provide 11 insights into both the global patterns of thermal sensitivity and the physiological mechanisms 12 underlying temperature response. In this study we conducted the first measure of the thermal 13 reaction norm for feeding, comparing the radula rasping rate of two tropical and one polar limpet 14 species. The consistency of thermal response was tested through comparisons with limpet duration 15 tenacity. Feeding and duration tenacity of limpets are ecologically important muscular mechanisms 16 that rely on very different aspects of muscle physiology, repeated concentric (shortening) and 17 isometric (fixed length) contraction of muscles, respectively. In these limpets the thermal reaction 18 norms of feeding limpets were best described by a single break point at a maximum temperature 19 with linear declines at higher (S. atra) or lower temperatures (N. concinna and C. radiata) rather 20 than a bell shaped curve. The thermal reaction norms for duration tenacity were similar in the two 21 tropical limpets. However, the rasping rate in Antarctic Nacella concinna, increased linearly with 22 temperature up to a maximum at 12.3°C (maximal range 8.5 to 12.3°C) when feeding stopped. In 23 contrast duration tenacity in N. concinna, was maximal at 1.0°C (-0.6 to 3.8°C), and linearly 24 decreased with increasing temperature. The thermal reaction norms of muscular activity were 25 therefore inconsistent within and between species, indicating that different mechanisms likely 26 underlie different aspects of species sensitivities to temperature. 27 28

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