Within- and between-site genetic differentiation calculated for <i>Xeropicta derbentina</i> populations (1–7) from Southern France based on the COI gene.

<p>On diagonal line: nucleotide diversity (π); above diagonal: haplotype divergence (H_MH) based on the Morisita-Horn index; below diagonal: pairwise fixation index (F_ST).</p

Digestive gland of <i>Xeropicta derbentina</i> in different reaction states.

<p><b>A.</b> Digestive gland of a control animal. a. indicates tight lumina, b. a smooth base of the tubule and c. shows an oval-shaped nucleus and regular vacuolization of the digestive cells. <b>B.</b> Digestive gland of a control animal. a. shows a calcium cell with dense cytoplasm and round nucleus. b. indicates an irregular vacuolization of the digestive cells with partially fused vacuoles. <b>C.</b> Digestive gland in state of reaction. a. indicates dark nuclei and an irregular cytoplasm of the calcium cells. Also hypertrophy of the calcium cells occurs. <b>D.</b> Digestive gland in state of reaction. a. shows enlarged lumina of the tubule and b. shows pronounced and ruptured apices of the digestive cells. <b>E.</b> Digestive gland in state of destruction. a. indicates a very irregular cytoplasm with bright spots in the calcium cells. b. shows cell fragments in the lumen of the tubule. Cell borders are disengaged. <b>F.</b> Digestive gland in state of destruction showing necrosis. The arrow indicates ruptured cell apices. Cell borders are disengaged.</p

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

<div><p>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 <i>Xeropicta derbentina</i> 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.</p></div

Results of the MRT analyses of PCoA transformed physiological heat stress response data (Hsp70 and histology) constrained with population structure information of <i>Xeropicta derbentina</i> under four temperature conditions.

<p>R²: cross-validated proportion of variance explained by the primary grouping (i.e., first split of the tree); P1–P7: populations studied; π: nucleotide diversity; H_MH3: axis 3 of transformed haplotype diversity; F_ST1, F_ST2: axes 1 and 2 of transformed pairwise fixation index; (+): positive correlation; (−): negative correlation; improved histopathology (i); deteriorated histopathology (d).</p

The condition of the digestive cells of the hepatopancreas.

<p>Mean assessment values for each population at elevated temperature. Shown are means and SD; <i>n</i> = 8. Asterisks show significant differences of the respective exposure groups compared to the control at 25°C after Bonferroni correction: 0.0025<<i>P</i>≤0.0125: (*) and 0.00025<<i>P</i>≤0.0025 (**).</p

Relative Hsp70 level of different populations after exposure to elevated temperature for 8 h.

<p>Shown are means and SD; <i>n</i> = 10. Asterisks show significant differences of the respective exposure groups compared to the control at 25°C after Bonferroni correction: 0.0017<<i>P</i>≤0.0083: (*) and 0.00017<<i>P</i>≤0.0017 (**).</p

Maximum levels of Hsp70 induction in different populations after exposure to elevated temperature regimes.

<p>The maximum induction was calculated as the ratio vs. the Hsp70 induction at the control temperature (25°C).</p

Correlation of relative Hsp70 level vs. histopathological mean assessment values.

<p>Data obtained for the populations of the respective exposure groups (25, 33, 40, 43 and 48°C) are framed, respectively. <b>A.</b> Relative Hsp70 level vs. condition of the tubules. <b>B.</b> Relative Hsp70 level vs. condition of the digestive cells. <b>C.</b> Relative Hsp70 level vs. condition of the calcium cells.</p