Effects Of Thermal Stress On Physiological Performance And Energy Metabolism Of Intertidal Gastropods

Investigating effects of thermal stress on physiological responses and energy metabolism of intertidal organisms is crucial for understanding how they adapt to the thermal stress and for providing theoretical basis for predicting their responses to future climate change.In the present study,we conducted eco-physiological studies on several rocky intertidal gastropods.We found distinct physiological responses to thermal stress among species,and revealed their adaptation of energy metabolism to thermal stress.1.Effects of high temperature on physiological responses of two high-intertidal snailsIntertidal species frequently encounter extensive thermal stress,and physiological response is an important adaptation to this harsh thermal regime.In the present study,we investigated physiological responses of two high-intertidal congeners of Echinolittorina to thermal stress after common garden exposure(25?,60 days).Analysis of heart rate showed no significant differences of sublethal temperature(ABT)between populations in each species,indicating both species currently suffer from intensive thermal stress across their biogeographic range.Higher shore snail E malaccana showed significantly higher lethal temperature(FLT),larger difference between the FLT and ABT(FLT-ABT),and higher coefficients of variation in ABT and FLT than E.radiata.These results indicated that higher shore species is more thermally tolerant,and its larger anaerobic capacity and greater individual physiological variability might be crucial for coping with extreme stress and future climate change 2.De novo assembly and annotation of the Echinolittorina malaccana genomeIllumina next-generation sequencing generated 26.09 Gb high quality reads(clean data)of E.malaccana.The estimated genome size was 1.08 Gb.The reads were de novo assembled into 312,533 scaffolds(>500 bp)with N50 of 8,271 bp.The total length of scaffolds was 1,015 Mb.Repeat elements occupied 13.99%of the genome.20,163 gene models were retrieved from 26,218 scaffolds(>10 kb),and 20,156 gene models were functionally annotated.This study provided valuable resources for better understanding the evolutionary adaptation of intertidal gastropod in the future3.Transcriptional responses of Echinolittorina snail to thermal stressTo understand roles of modulation of gene expression in the thermal adaptation of intertidal gastropods,we examined the transcriptomic profiles of two Echinolittorina species at different temperatures(25,37,45 and 52?)after common garden exposure(25? 60 days).The results showed that most defensive genes(e.g.molecular chaperones and inhibitors of apoptosis)were constitutively expressed during metabolic depression(37?45?),which is an energy conservation leading to sufficient energy for frequent and unpredictable extreme stress.However,more hsp genes were up-regulated in lower shore snail E.radiata during this period,indicating its higher thermal sensitivity.Under extreme stress(52 0C),most metabolic genes were down-regulated to minimize energy expenditure and most defensive genes were further up-regulated(>1,000 times).Down-regulation of genes in the ubiquitin-proteasome proteolytic pathway indicated the capacity to protect against extreme stress was relatively limited in E.radiata.Our study revealed that higher shore E.malaccana has stronger metabolic depression,ensuring sufficient energy to cope with more frequent extreme stress in the field.Furthermore,different thermal sensitivity between populations in each species indicated local environments have driven population divergence in transcriptional response to thermal stress.These findings give an insight into how intertidal snails cope with extreme stress and their potential evolutionary adaptation to a warming climate.4.Physiological response of Cellana toreuma to thermal stress under warming and ocean acidificationPhysiological plasticity has been suggested an important strategy for organism to adapt to changing microclimates.Here,we evaluated the importance of physiological plasticity for coping with ocean acidification and elevated temperatures,of the intertidal limpets C.toreuma.Limpets were acclimated under combinations of different temperatures(20 and 24?)andpCO2 concentrations(400 and 1,000 ppm)for 7 days.Analysis of heart rate showed significantly higher temperature coefficients(Q10)for limpets at 20? than at 24? and lower post-acclimation thermal sensitivity of limpets at 400 ppm than at 1,000 ppm.Expression of hsp70 linearly increased with the rising temperatures,with the largest slope occurring in limpets acclimated under a future scenario(24? and 1,000 ppm).These results suggested that limpets showed increased sensitivity and stress response under future conditions.Furthermore,the increased variation in physiological response under the future scenario indicated that some individuals have higher physiological plasticity to cope with these conditions.While short-term acclimation to reduced pH seawater decreases the ability of partial individuals against thermal stress,physiological plasticity and variability seem to be crucial in allowing some intertidal animals to survive in a rapidly changing environment.5.Effects of temperature on population dynamics of three intertidal gastropods and their physiological mechanismsPhysiological adaptation of intertidal species to thermal stress determines their distribution and population dynamics.Here,in situ research on three gastropods with different vertical positions revealed distinct physiological response to thermal stress(15?40?).The limpet Lottia luchuana occurring highest on the shore exhibited constitutional expression of hsp70 with rising temperatures,which is a "preparative defense" strategy for protecting them against high frequency of extreme and unpredictable heat stress.Two lower-occurring species expressed inducible hsp 70,with an onset of expression at 30? for higher shore S.japonica and 27? for lower shore C.toreuma.Because of the trade-off between energy costs of maintenance and costs allocated to production in S.japonica,the relative expression levels of hsp70 in S.japonica was nearly 10 times lower than C.toreuma.Such energy allocation strategy explains high mortality of S.japonica adults observed in summer.Furthermore,the expression of hsp70 at relatively higher temperature in the sun-exposed shore population indicated the effect of thermal history on the thermal sensitivity of these two species to thermal stress.In conclusion,physiological responses to thermal stress and population dynamics are reflection of energy allocation strategies and thermal history.