Intraspecific Variation in Cellular and Biochemical Heat Response Strategies of Mediterranean Xeropicta derbentina [Pulmonata, Hygromiidae]

Abstract

Dry and hot environments challenge the survival of terrestrial snails. To minimize overheating and desiccation, physiological and biochemical adaptations are of high importance for these animals. In the present study, seven populations of the Mediterranean land snail species Xeropicta derbentina were sampled from their natural habitat in order to investigate the intraspecific variation of cellular and biochemical mechanisms, which are assigned to contribute to heat resistance. Furthermore, we tested whether genetic parameters are correlated with these physiological heat stress response patterns. Specimens of each population were individually exposed to elevated temperatures (25 to 52°C) for 8 h in the laboratory. After exposure, the health condition of the snails' hepatopancreas was examined by means of qualitative description and semi-quantitative assessment of histopathological effects. In addition, the heat-shock protein 70 level (Hsp70) was determined. Generally, calcium cells of the hepatopancreas were more heat resistant than digestive cells - this phenomenon was associated with elevated Hsp70 levels at 40°C.We observed considerable variation in the snails' heat response strategy: Individuals from three populations invested much energy in producing a highly elevated Hsp70 level, whereas three other populations invested energy in moderate stress protein levels - both strategies were in association with cellular functionality. Furthermore, one population kept cellular condition stable despite a low Hsp70 level until 40°C exposure, whereas prominent cellular reactions were observed above this thermal limit. Genetic diversity (mitochondrial cytochrome c oxidase subunit I gene) within populations was low. Nevertheless, when using genetic indices as explanatory variables in a multivariate regression tree (MRT) analysis, population structure explained mean differences in cellular and biochemical heat stress responses, especially in the group exposed to 40°C. Our study showed that, even in similar habitats within a close range, populations of the same species use different stress response strategies that all rendered survival possible.

Hsp70 and lipid peroxide levels following heat stress in Xeropicta derbentina (Krynicki 1836) (Gastropoda, Pulmonata) with regard to different colour morphs

“…As reported in other studies related to adaptations of land snails from Southern France to elevated temperatures (Di Lellis et al 2012;Dieterich et al 2012;Köhler et al 2009;Scheil et al 2011;Troschinski et al 2014), X. derbentina reacts to heat stress with a clear Hsp70 induction when being confronted with increasing temperatures. A maximum induction of Hsp70, the intensity of which depended on the identity of the population, was regularly observed between 38°and 40°C in different populations (Di Troschinski et al 2014).…”

“…Therefore, it seems that snails of the colour category 3 are less able to cope with temperatures higher than 43°C, probably as they are no longer able to invest these high energy costs in this protection system. Consequently, at very high temperatures, category 3 snails may show lesions on the cellular level, as described in different studies Scheil et al 2011;Troschinski et al 2014), earlier in comparison to the other morphs. In years with very hot summers, this may be a disadvantage for category 3 snails.…”

“…A maximum induction of Hsp70, the intensity of which depended on the identity of the population, was regularly observed between 38°and 40°C in different populations (Di Troschinski et al 2014). Exceeding these temperatures, a decrease in Hsp70 level was found, with the lowest measured values at 45°C, followed by a second, minor increase in Hsp70 at 48°C (Di Troschinski et al 2014). Both, qualitative and quantitative aspects of these heat stress response kinetics were also recorded for the X. derbentina specimens investigated in the present study.…”

“…The authors speculated on anthropogenic change of environment and the increase in temperature in the sampling region to be possible reasons for these morph frequency changes. For the investigated population of X.derbentina in this study, as well as for other populations of this species in the vicinity investigated so far (Di Köhler et al 2009;Troschinski et al 2014), no historic data about the change in morph frequencies are available. Without long term studies like the above mentioned ones, a possible area effect that may explain the predominant white coloured category 1 snails, remains speculative.…”

“…In case of X. derbentina, analyses of whole body homogenates have shown that the Hsp70 level of individuals depends on the population (Di , the life stage, the season, and the intensity of heat exposure (Dieterich et al 2012) as well as on the total load of heat stress over a given period of time Scheil et al 2011). Furthermore, was been shown that several populations of X. derbentina deriving from the same area have developed different heat response strategies characterized by different levels of Hsp70 (Troschinski et al 2014). …”