Exposure to thermal extremes favours higher solar reflectivity in intertidal gastropods

<p>During low tides, intertidal animals can be exposed to temperature extremes that can be near or exceed the animals' thermal limits. Reflectance of solar radiation could be critical to prevent overheating for animals that remain exposed to the sun; however, most studies ignore near-infrared (NIR) wavelengths that comprise approximately half of solar energy.  Here, we conduct a phylogenetically controlled analysis to test whether the reflectivity of intertidal gastropod species is associated with solar exposure. For nineteen gastropod species, we quantified UV, visible and NIR reflectance and documented microhabitat at low tide. Gastropods from exposed microhabitats had greater total reflectivity than those from sheltered microhabitats. The difference between microhabitats was greater for dry shells than wet shells, for which evaporative cooling may be a more important means of reducing heat gain. Dry shells from exposed microhabitats had higher reflectivity in NIR wavelengths even after controlling for UV-visible reflectivity, supporting selection for thermal benefits independent of visual benefits such as camouflage. Based on a heating rate experiment and thermal imaging, gastropods with high shell reflectivity had a lower heating rate in natural conditions than those with low shell reflectivity. Together, these studies show that reflectivity can play a crucial role in thermoregulation in extreme environments.</p>