Biochemische und histologische Untersuchungen physiologischer Anpassungen an Hitzestress bei der mediterranen Landschnecke Xeropicta derbentina

Die Befähigung xerothermophiler Landschnecken selbst unter extrem fordernden Umweltbedingungen zu überleben bedarf einiger Verhaltensadaptionen sowie Anpassungen auf physiologischer und morphologischer Ebene. Im Rahmen dieser Arbeit konnten neue Erkenntnisse über diese adaptiven Mechanismen bei der Schneckenart Xeropicta derbentina gewonnen werden und Anpassungsstrategien für die jeweiligen Lebensphasen der Tiere abgeleitet werden. Aufgrund der Ergebnisse kann für X. derbentina ein annueller Lebenszyklus in Südfrankreich angenommen werden. Daher wurde im Frühjahr noch eine geringe Schalengröße detektiert, assoziiert mit einer dunklen Bänderung der Tiere, welche als Juvenilfärbung interpretiert werden kann und im Laufe des Schalenwachstums über das Jahr hinweg durch verschiedene Schalenfärbungen (Morphen) abgelöst wird. Durch Korrelation des Stressprotein-Levels (Hsp70) mit dem Temperatur-Tagesprofil zeigte sich, dass die Induktion von Hsp70 zwar mit steigenden Umgebungstemperaturen zunimmt, jedoch, vermutlich aufgrund eines bereits hohen konstitutiven Basis-Levels von Hsp70, die Induktion bei juvenilen Tieren weniger stark ausfällt als bei Adulti. Im späten Frühling konnte folgendes Schema identifiziert werden: Große Schnecken mit vornehmlich heller Gehäusefärbung halten sich tagsüber in größerer Höhe über der Bodenoberfläche auf und weisen dabei einen niedrigen Hsp70-Level auf, wohingegen kleine Vertreter mit dunkleren Gehäusen eher in Grundnähe verweilen, dabei jedoch mehr Hsp70 induzieren. Außerdem konnte nach experimentell induziertem Temperaturstress beobachtet werden, dass dunklere Morphen befähigt waren, Hsp70 bis zu einem gewissen Grad höher zu induzieren als hellere Morphen. Zusätzlich kommt es in dieser Lebensphase vermehrt zur Generierung von Lipidperoxiden - hervorgerufen durch oxidativen Stress. Es zeigte sich, dass helle Morphen vor allem in „niedrigen“ Temperaturbereichen einen geringeren Gehalt an Lipidperoxiden aufwiesen als dunkler gefärbte Individuen und daher scheinbar ein wirkungsvolleres antioxidatives Abwehrsystem besitzen. Außerdem offenbarten weitere Untersuchungen, dass X. derbentina bereits einen hohen konstitutiven Level an Katalase besitzt. Im Sommer erreichen die Tiere das Adultstadium und weisen mehrheitlich eine weiße Schalenfärbung auf. Untersuchungen des Hepatopankreas wiesen diesen als ein stark in die Hitzestresssituation involviertes Organ aus. Aufgrund von intraspezifischen Variationen im Hsp70-Induktionsmuster konnten bei Vergleichen mit der jeweiligen populationsspezifischen Integrität des Hepatopankreas drei verschiedene (populationsspezifische) Strategien zur Hitzestressbewältigung bei X. derbentina identifiziert werden. Im Zuge weiterer Hitzeexpositionen wurde deutlich, dass Hsp70 sowie die antioxidativen Enzyme Katalase und Glutathionperoxidase ein effektives Schutzsystem unter physiologisch ungünstigen Temperaturbedingungen bei X. derbentina bilden. Gegen Ende des Jahres fällt die Kapazität der Schnecken zur Induktion von Stressproteinen deutlich ab bzw. bleibt gänzlich aus, was mit dem Alter der Tiere in Verbindung gebracht werden kann. Zum Ende des Jahres sterben die meisten Tiere

Symposium on “Climate Change and Molluscan Ecophysiology” at the 79th Annual Meeting of the American Malacological Society

Climate change has already had many observable effects on Earth. On land, glaciers and snowpacks have shrunk, tropical forests are being replaced by savannahs, and coastal areas have increased risks of flooding (e.g., IPCC 2007, Allan and Soden 2008, Dai 2010, NOAA 2010, Chen et al. 2011). In addition to sea-surface warming, climate change has altered the physical and chemical nature of the marine environment, including ocean acidification and expanding hypoxia. The scope and scale of future environmental change that individuals will undergo on land and in the sea will fundamentally influence the ecological and evolutionary responses of populations and species, dependent on their evolved physiological capacities for environmental tolerance (Parmesan 2006, Hoffmann and Sgrò 2011, Kuntner et al. 2014). Although climate change will affect all organisms, molluscs are unique in many respects, and, given their high diversity and evolutionarily flexible body plan, they provide several established and emerging models systems for comparative physiological study in nearly all types of ecosystems, from rivers to rocky shores and deserts to the deep sea. Moreover, many mollusks play pivotal roles as consumers, predators, and competitors in a diversity of ecosystems and habitats. Mollusks also have great economic importance, with many species of mollusks harvested by humans for food, either from natural populations or from aquaculture. The joint meeting of the American Malacological Society and the World Congress of Malacology in Ponta Delgada, Azores, on July 23rd 2013, brought together malacologists actively pursuing research aimed at addressing the direct and indirect impacts of climate change and the mechanisms mollusks use to compensate for these changes, their natural evolved tolerances, and the energetic, ecological, and biogeographic consequences of compensation. The goal for this symposium was to expose a broad range of malacologists to ecophysiological approaches in the hopes of recruiting and stimulating interest in the emerging questions of this field. Speakers included those whose talks addressed the effects of climate change on mollusks across a wide range of time scales and levels of biological organization, describing the results from recent research as well as considerations of some of the challenges facing ecophysiological research on mollusks in the future.info:eu-repo/semantics/publishedVersio

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

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

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

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

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