Thermal tolerance and climate warming sensitivity in tropical snails

Abstract

Tropical ectotherms are predicted to be especially vulnerable to climate change because their thermal tolerance limits generally lie close to current maximum air temperatures. This prediction derives primarily from studies on insects and lizards and remains untested for other taxa with contrasting ecologies. We studied the HCT (heat coma temperatures) and ULT (upper lethal temperatures) of 40 species of tropical eulittoral snails (Littorinidae and Neritidae) inhabiting exposed rocky shores and shaded mangrove forests in Oceania, Africa, Asia and North America. We also estimated extremes in animal body temperature at each site using a simple heat budget model and historical (20 years) air temperature and solar radiation data. Phylogenetic analyses suggest that HCT and ULT exhibit limited adaptive variation across habitats (mangroves vs. rocky shores) or geographic locations despite their contrasting thermal regimes. Instead, the elevated heat tolerance of these species (HCT = 44.5 ± 1.8°C and ULT = 52.1 ± 2.2°C) seems to reflect the extreme temperature variability of intertidal systems. Sensitivity to climate warming, which was quantified as the difference between HCT or ULT and maximum body temperature, differed greatly between snails from sunny (rocky shore; Thermal Safety Margin, TSM = −14.8 ± 3.3°C and −6.2 ± 4.4°C for HCT and ULT, respectively) and shaded (mangrove) habitats (TSM = 5.1 ± 3.6°C and 12.5 ± 3.6°C). Negative TSMs in rocky shore animals suggest that mortality is likely ameliorated during extreme climatic events by behavioral thermoregulation. Given the low variability in heat tolerance across species, habitat and geographic location account for most of the variation in TSM and may adequately predict the vulnerability to climate change. These findings caution against generalizations on the impact of global warming across ectothermic taxa and highlight how the consideration of nonmodel animals, ecological transitions, and behavioral responses may alter predictions of studies that ignore these biological details.

Plasticity of foot muscle and cardiac thermal limits in the limpet Lottia limatula from locations with differing temperatures

“…Foot muscle CT max was defined as the temperature at which the organism loses its neuromuscular ability to grasp a vertical surface. Fallen limpets are more susceptible to predation or being washed away by waves, which have negative fitness consequences (Marshall et al 2015); thus, this is an ecologically important metric. Other studies on mollusks and limpets have referred to the temperature of neuromuscular failure or detachment from substratum as the onset of heat coma temperature (HCT) or non-lethal thermal tolerance (Clarke et al 2000, Sokolova & Pörtner 2003, Denny et al 2006, Miller et al 2015, Chapperon et al 2016.…”

Heat-resistant cytosolic malate dehydrogenases (cMDHs) of thermophilic intertidal snails (genus Echinolittorina): protein underpinnings of tolerance to body temperatures reaching 55°C

“…Many intertidal organisms encounter intensive thermal stresses, especially species with limited abilities to regulate body temperature behaviorally (Harley, 2011;Walters et al, 2012;Seabra et al, 2016). Previous studies have shown that many intertidal organisms currently live close to their upper thermal limits and thus are likely to be significantly challenged by future increases in temperature (Stillman, 2002;Somero, 2012;Dong et al, 2015;Marshall et al, 2015). Thus, the rocky intertidal zone is an ideal model system for investigating the relationships between conditions of thermal exposure and adaptation, as well as for elucidating the susceptibility of organisms to the impact of climate change (Mislan et al, 2014).…”

Contemporary climate‐driven range shifts: Putting evolution back on the table

“…In general, phylogenetic signal of thermal tolerance, particularly upper thermal tolerance, is high for ectothermic species (reviewed in Hoffmann, Chown, & Clusella-Trullas, 2013). For example, Drosophila exhibit quite high phylogenetic signal in upper thermal tolerance (Kellermann et al, 2012), as do snails (Marshall, Rezende, Baharuddin, Choi, & Helmuth, 2015) and lizards (Clusella-Trullas, Blackburn, & Chown, 2011;Grigg & Buckley, 2013). Intertidal crabs also show high phylogenetic signal in upper thermal tolerance, but low signal in lower thermal tolerance (Faria et al, 2017).…”