Energy expenditure of the spotted snow skink, Niveoscincus ocellatus, at two climatic extremes of its distribution range

Of telomeres and temperature: Measuring thermal effects on telomeres in ectothermic animals

Ectotherms are classic models for understanding life-history tradeoffs, including the reproduction-somatic maintenance tradeoffs that may be reflected in telomere length and their dynamics. Importantly, life-history traits of ectotherms are tightly linked to their thermal environment, with diverse or synergistic mechanistic explanations underpinning the variation. Telomere dynamics potentially provide a mechanistic link that can be used to monitor thermal effects on individuals in response to climatic perturbations. Growth rate, age and developmental stage are all affected by temperature, which interacts with telomere dynamics in complex and intriguing ways. The physiological processes underpinning telomere dynamics can be visualized and understood using thermal performance curves (TPCs). TPCs reflect the evolutionary history and the thermal environment during an individual's ontogeny. Telomere maintenance should be enhanced at or near the thermal performance optimum of a species, population and individual. The thermal sensitivity of telomere dynamics should reflect the interacting TPCs of the processes underlying them. The key processes directly underpinning telomere dynamics are mitochondrial function (reactive oxygen production), antioxidant activity, telomerase activity and telomere endcap protein status. We argue that identifying TPCs for these processes will significantly help design robust, repeatable experiments and field studies of telomere dynamics in ectotherms. Conceptually, TPCs are a valuable framework to predict and interpret taxon- and population-specific telomere dynamics across thermal regimes. The literature of thermal effects on telomeres in ectotherms is sparse and mostly limited to vertebrates, but our conclusions and recommendations are relevant across ectothermic animals.

Is Habitat More Important than Phylogenetic Relatedness for Elucidating the Gut Bacterial Composition in Sister Lizard Species?

The gut microbiota influences the phenotype and fitness of a host; however, limited information is currently available on the diversity and functions of the gut microbiota in wild animals. Therefore, we herein examined the diversity, composition, and potential functions of the gut microbiota in three Sceloporus lizards: Sceloporus aeneus, S. bicanthalis, and S. grammicus, inhabiting different habitats in a mountainous ecosystem. The gut bacterial community of S. bicanthalis from alpine grasslands at 4,150‍ ‍m a.s.l. exhibited greater taxonomic, phylogenetic, and functional alpha diversities than its sister species S. aeneus from cornfields and human-induced grasslands at 2,600‍ ‍m‍ ‍a.s.l. Bacteria of the genus Blautia and metabolic functions related to the degradation of aromatic compounds were more abundant in S. bicanthalis than in S. aeneus, whereas Oscillibacter and predicted functions related to amino acid metabolism and fermentation were more abundant in S. aeneus. The structure of the dominant and most prevalent bacteria, i.e., the core microbiota, was similar between the sister species from different habitats, but differed between S. grammicus and S. aeneus cohabiting at 2,600‍ ‍m‍ ‍a.s.l. and between S. grammicus and S. bicanthalis cohabiting at 4,150‍ ‍m a.s.l. These results suggest that phylogenetic relatedness defines the core microbiota, while the transient, i.e., non-core, microbiota is influenced by environmental differences in the habitats. Our comparisons between phylogenetically close species provide further evidence for the specialized and complex associations between hosts and the gut microbiota as well as insights into the roles of phylogeny and ecological factors as drivers of the gut microbiota in wild vertebrates.

Individual telomere dynamics and their links to life history in a viviparous lizard

Emerging patterns suggest telomere dynamics and life history are fundamentally linked in endotherms through life-history traits that mediate the processes underlying telomere attrition. Unlike endotherms, ectotherms maintain the ability to lengthen somatic telomeres throughout life and the link between life-history strategies and ectotherm telomere dynamics is unknown. In a well-characterized model system (Niveoscincus ocellatus), we used long-term longitudinal data to study telomere dynamics across climatically divergent populations. We found longer telomeres in individuals from the cool highlands than those from the warm lowlands at birth and as adults. The key determinant of adult telomere length across populations was telomere length at birth, with population-specific effects of age and growth on adult telomere length. The reproductive effort had no proximate effect on telomere length in either population. Maternal factors influenced telomere length at birth in the warm lowlands but not the cool highlands. Our results demonstrate that life-history traits can have pervasive and context-dependent effects on telomere dynamics in ectotherms both within and between populations. We argue that these telomere dynamics may reflect the populations' different life histories, with the slow-growing cool highland population investing more into telomere lengthening compared to the earlier-maturing warm lowland population.

Temperature and telomeres: thermal treatment influences telomere dynamics through a complex interplay of cellular processes in a cold-climate skink

Telomere dynamics vary fundamentally between endothermic populations and species as a result of differences in life history, yet we know little about these patterns in ectotherms. In ectotherms, the relationships between climate, metabolism and life history suggest that telomere attrition should be higher at relatively high environmental temperatures compared to relatively low environmental temperatures, but these effects may vary between populations due to local adaptation. To address this hypothesis, we sampled reactive oxygen species (ROS) and telomere length of lizards from warm lowland and cool highland populations of a climatically widespread lizard species that we exposed to hot or cold basking treatments. The hot treatment increased relative telomere length compared to the cold treatment independent of climatic origin or ROS levels. Lizards from the cool highland region had lower ROS levels than those from the warm lowland region. Within the highland lizards, ROS increased more in the cold basking treatment than the hot basking treatment. These results are in the opposite direction to those predicted, suggesting that the relationships between temperature, metabolism, ROS and telomere dynamics are not straightforward. Future work incorporating detailed understanding of the thermal reaction norms of these and other linked traits is needed to fully understand these processes.

Thermal biology of the spotted snow skink, Niveoscincus ocellatus, along an altitudinal gradient

Body temperatures in ectotherms are strongly affected by their thermal environment. Ectotherms respond to variation in the thermal environment either by modification of behavioural thermoregulation to maintain their optimal body temperature or by shifting their optimal body temperature. In this study, the body temperatures of males of three populations of spotted snow skinks, Niveoscincus ocellatus, living along an altitudinal gradient (low, mid, and high altitude) were studied in the field and laboratory in spring, summer, and autumn, representing the full activity period of this species. The environmental variation across both sites and seasons affected their field active body temperatures. At the low and mid altitude, N. ocellatus had a higher mean body temperature than at the high altitude. Animals achieved their thermal preference at the low and mid altitude sites in all seasons. At the high altitude, however, N. ocellatus struggled to reach its preferred body temperatures, especially in autumn. The lower body temperature at the high-altitude site is likely due to limited thermal opportunity and/or an effect of avoiding the costs associated with increased intensity of basking.