In our comparative studies of thermal tolerance limits of porcelain crabs from across a wide range of thermal habitats, it has become clear that these crabs adapted their thermal physiology to match the heat waves they experience during low tide (Stillman and Somero 2000, Stillman 2002, 2003, 2004). To understand the adaptive mechanisms that organisms have used in response to life in thermal extreme habitats, we have used functional genomics to examine changes in gene expression during thermal acclimatization (Stillman and Tagmount 2009), acclimation (Ronges et al.) and response to thermal stress (e.g., Stillman, Teranishi and Stillman 2007 , Garland et al 2015). These studies have been helpful to identify regions of the genome that are likely candidates for adaptive selection, and provide hypotheses for mechanisms associated with enhancing thermal tolerance.

Evidence suggests that organisms can shift their thermal adaptation across life-stages (Uno and Stillman 2020 , Miller et al 2013,) or across generations (Tanner et al 2020) to match habitat temperature variation. We have also been engaged in studies of thermal tolerance of molluscs, including populations of sea hares (Tanner et al 2020), nudibranchs (Armstrong et al 2019), snails (Rais et al 2010) and limpets from across locations with varying thermal habitat conditions (Wang et al 2019), which show that there can be significant levels of physiological variation in thermal tolerance among pupulations. Previous work in coral reefs of Ofu, American Samoa have also found evidence for thermal adaptation of corals to extreme thermal habitats (Barshis et al 2010,2018)