Untangling The Roles Of Habitat Heterogeneity And Physiological Polymorphism In Contributing To Thermal Adaptation Of Intertidal Molluscs

The intertidal ecosystem is highly sensitive to clime change and has long served as a typical model system for studying species’ adaptive mechanisms to climate change.The polymorphism of habitat and physiological performance play important roles in adaptation to environment variance of intertidal organisms,and received more and more focus.In the present study,we measured the body temperature in situ and physiological performance of several common molluscs in the intertidal zone and elucidated the roles habitat heterogeneity and physiological polymorphism in governing vulnerability of intertidal molluscs to heat stress in the background of climate change.1.The roles of microclimate and inter-individual variance in governing vulnerability of three intertidal snails to heat stressVulnerability of animals to thermal stress is the result of thermal tolerance,behavioural thermoregulation,and microclimatic conditions.To understand interactions among these variables,we analysed the thermal tolerances of three species of intertidal snails from different latitudes along the Chinese coast(Littoraria sinensis,Littorina brevicula and Nerita yoldii),and estimated potential Tb in different microhabitats at each site.ABTs(sub-lethal thermal tolerance)of some individuals were exceeded at sun-exposed microhabitats in most sites,suggesting physiological impairment for snails.The predictability of extreme temperatures was lowest at the hottest sites,indicating that the effectiveness of behavioural thermoregulation is potentially lowest at these sites.Our result indicated the important roles of interindividual variations(physiological polymorphism)of thermal limits.These results illustrate the critical roles of microclimate and inter-individual variance in governing vulnerability of of intertidal organisms to heat stress.2.Different behavioral and physiological responses to high temperature between two sympatric Cerithidea snailsSmall-scale variation in the thermal environment are potentially an important factor that governs distributions on a local scale.For untangling the roles of behavioral and physiological adaptations on species’ distribution at a small-scale level,we carried out a comparative study of two mudflat snails(genus Cerithidea).These two sympatric snails occupy different microhabitats on the upper intertidal mudflat.Our results indicate that the two Cerithidea congeners show different behavioral and physiological responses to high temperature.Compared to C.largillierti,C.cingulata prefers to bury into the mud,has a higher thermal limit,a higher level of inducible expression of hsp 70 mRNA and high inter-individual variation,implying important roles of behavioral and physiological adaptations to the harsh thermal environment on the open mudflat.These results highlight the importance of behavioral and physiological adaptions in sympatric species’ distributions on the mudflat and help to shed light on the mechanisms of how small-scale differences in the thermal environment shape sympatric species’distributions.3.Temperature variation combines with physiological plasticity to enhance thermal resilience of the intertidal mussel Mytilisepta virgataPredicting the effects of rising temperature on a sessile intertidal species entails measuring both habitat thermal characteristics and the physiological plasticity of the species as it relates to this microhabitat variation;these two types of measurements can generate what is termed a "physiological seascape" for the species.In the present study,we continually monitored the body(operative)temperature of the intertidal mussel M.virgata in both sun-exposed and shaded microhabitats and determined the seasonal variations of cardiac performance of field-acclimatized and laboratory-acclimated mussels from these different microhabitats.With this large,high-resolution dataset,we were able to integrate the effects of synchronization changes in microenvironmental temperatures heat tolerance plasticity and inter-individual variation.The complex physiological seascape that exists in the intertidal zone must be taken into account when predicting effects of changes in environmental temperature,such as those occurring with global climate change.4.Physiological polymorphism across multiple spacial-scales and its effect on thermal adaptation of Mytilisepta virgataLiving in the highly variable thermal environment,intertidal organisms exhibited high variation of thermal performance across multiple spatial scales.To find out the relationship of physiological polymorphism in macro-and micro-scale and their effect on species to adapt the complex environment of intertidal zones,comparative study of M.virgata in both sun-exposed and shaded microhabitats from different latitudes along the Chinese coast were carried on.The seasonal variations of cardiac performance of the field-acclimatized and laboratory-acclimated mussels were determined.The result indicated that the variance in macro-scale was the main component of thermal performance variance and was the result of both local adaptation physiological plasticity,while micro-scale physiological polymorphism was caused by physiological plasticity.Variation of thermal tolerance across multiple spatial and temporal scales and contributing organisms’ adaptation to variable thermal environment.In summary,the combined effect of thermal environment variance across multiple temporal and spatial scales and physiological polymorphism of organisms in the intertidal ecosystem plays an important role in governing vulnerability of intertidal molluscs to heat stress.To accurately assess the ecological effects of climate change on the intertidal ecosystem,habitat heterogeneity and physiological polymorphism across across multiple temporal and spatial scales should be concerned.