Nicholas Wu

Seasonality is a fundamental challenge for life on Earth and energy storage prior to colder and drier periods by fattening is a common strategy for survival. Fattening should reflect a trade-off between an expected seasonal energy deficit and the costs of increased body mass, which are particularly important to flying endotherms. We examined body mass change (ΔM), a proxy of fat storage, among bat populations over low productivity periods with global variation in yearly average and seasonality of local climates. We found that ΔM increased with decreasing mean annual surface temperature (MAST) but ΔM also increased at higher MAST with higher seasonality of rainfall. Seasonal use of body energy reserves by bats is predicted to be widespread in warm, seasonal climates at low latitudes but is poorly studied compared to cold temperate regions. In colder climates only, females lost less mass than males over winter, supporting the 'thrifty females' hypothesis, and ΔM has increased with year of study in warm climates, possibly linked to effects of global climate change on their energetics. Our quantitative synthesis highlights how intrinsic and environmental factors shape seasonal fattening in bats, and its global importance for survival in this diverse and widespread mammal group.

Compared with the risks associated with climate warming and extremes, the risks of climate-induced drying to animal species remain understudied. This is particularly true for water-sensitive groups, such as anurans (frogs and toads), whose long-term survival must be considered in the context of both environmental changes and species sensitivity. Here, we mapped global areas where anurans will face increasing water limitations, analysed ecotype sensitivity to water loss and modelled behavioural activity impacts under future climate change scenarios. Predictions indicate that 6.6–33.6% of anuran habitats will become arid like by 2080–2100, with 15.4–36.1% exposed to worsening drought, under an intermediate- and high-emission scenario, respectively. Arid conditions are expected to double water loss rates, and combined drought and warming will double reductions in anuran activity compared with warming impacts alone by 2080–2100. These findings underscore the pervasive synergistic threat of warming and environmental drying to anurans.

Certain lizards are known to run bipedally. Modelling studies suggest bipedalism in lizards may be a consequence of a caudal shift in the body centre of mass, combined with quick bursts of acceleration, causing a torque moment at the hip lifting the front of the body. However, some lizards appear to run bipedally sooner and for longer than expected from these models, suggesting positive selection for bipedal locomotion. While differences in morphology may contribute to bipedal locomotion, changes in kinematic variables may also contribute to extended bipedal sequences, such as changes to the body orientation, tail lifting and changes to the ground reaction force profile. We examined these mechanisms among eight Australian agamid lizards. Our analysis revealed that angular acceleration of the trunk about the hip, and of the tail about the hip were both important predictors of extended bipedal running, along with increased temporal asymmetry of the ground reaction force profile. These results highlight important dynamic movements during locomotion, which may not only stabilize bipedal strides, but also to de-stabilize quadrupedal strides in agamid lizards, in order to temporarily switch to, and extend a bipedal sequence.

Burrowing is an important form of locomotion in reptiles, but no study has examined the energetic cost of burrowing for reptiles. This is significant because burrowing is the most energetically expensive mode of locomotion undertaken by animals and many burrowing species therefore show specialisations for their subterranean lifestyle. We examined the effect of temperature and substrate characteristics (coarse sand or fine sand) on the net energetic cost of burrowing (NCOB) and burrowing rate in two species of the Egernia group of skinks (Liopholis striata and Liopholis inornata) compared with other burrowing animals. We further tested for morphological specialisations among burrowing species by comparing the relationship between body shape and retreat preference in Egernia group skinks. For L. striata and L. inornata, NCOB is 350 times more expensive than the predicted cost of pedestrian terrestrial locomotion. Temperature had a positive effect on burrowing rate for both species, and a negative effect on NCOB for L. striata but not L. inornata. Both NCOB and burrowing rate were independent of substrate type. Burrows constructed by skinks had a smaller cross-sectional area than those constructed by mammals of comparable mass, and NCOB of skinks was lower than that of mammals of similar mass. After accounting for body size, retreat preference was significantly correlated with body shape in Egernia group skinks. Species of Egernia group skinks that use burrows for retreats have narrower bodies and shorter front limbs than other species. We conclude that the morphological specialisations of burrowing skinks allow them to construct relatively narrow burrows, thereby reducing NCOB and the total cost of constructing their burrow retreats.