Pushing the edge: extended activity as an alternative to risky body temperatures in a herbivorous teiid lizard (Cnemidophorus murinus: Squamata)

Dietary Variation Is Driven by Landscape Heterogeneity in an Insular Omnivorous Endemic Lizard, Revealed by DNA Metabarcoding

Living on islands entails numerous challenges for animals, among which population density approaching the carrying capacity of trophic resources stands out. To overcome this limitation, many insular lizards can supplement their insectivorous diet with increasing portions of plant material. The Madeira wall lizard, Teira dugesii, is a medium-sized lacertid, endemic to the Madeira and Selvagens archipelagos. As common in this family, adults are sexually dimorphic with males being bigger than females. Previous dietary studies on morphological scatology identified a higher proportion of plant over animal prey items, changing according to the location and sex. Here, we used DNA metabarcoding to examine the diet of this lizard species quantifying it at a higher taxonomical resolution and enhancing the detection of soft-body prey that often go undetected in morphology-based studies. In a sample of 151 faecal samples from eight populations including different habitats and altitudes in Madeira, we identified 289 prey items belonging to eight animal and three plant Classes, encompassing 58 distinct orders and 140 families. Of these, 63 were identified up to the species level. The results support a strong trend towards herbivory in this species with plants representing almost 74% of the diet occurrences in contrast to the 26% of animal prey. Remarkably, the plant fraction of the diet remained stable across localities but varied with size and mass in males. As males grew bigger and heavier, they significantly increased their plant matter intake. Likely, larger bodies and abdomens allowed allocating longer and more complex digestive tracts harbouring intestinal flora to better decompose plant organic compounds. This allowed heavier animals to have a richer diet regime. However, diet richness and composition were not affected by either sex or size, while the locality had a significant effect on both diet components likely in response to local variation in prey availability. By including an increasing plant fraction into a primarily insectivorous diet, this insular lizard has not only enlarged its trophic niche but is also able to exploit more efficiently the highly variable resources provided by insular environments.

Warmer isn't always better: Performance eurythermy in a cold-climate gecko

Most aspects of the lives of ectotherms are temperature dependent. Achieving the warmer body temperatures (T_b s) typically required for optimal performance can be particularly challenging for nocturnal ectotherms. Homonota darwinii-the world's southernmost gecko-is broadly distributed in southern Argentina (35-52 °S latitude) where cold climates over parts of its range likely pose an additional performance challenge for this nocturnal lizard. We hypothesized that the southernmost populations of this species would be the most thermally challenged, as evidenced by a decline in temperature-dependent sprint performance with increasing latitude. A temperature-dependent depression in locomotory performance may indicate suboptimal performance in other thermally dependent traits linked to fitness (e.g., foraging efficiency, metabolism). We measured sprint performance at five ecologically relevant T_b s for four populations spanning most of the latitudinal range of H. darwinii. We also recorded annual operative temperatures (T_e s) at each site on the surface and in refuges used by the geckos. Sprint data indicated differences in maximum performance over the range of H. darwinii, but not the latitudinal decline predicted. Instead, sprint performance was likely influenced by climatic variability associated with each site's elevation. Geckos from most populations had a broad range of T_b s over which sprint performance was optimal, albeit twofold to threefold lower than other geckos. This is indicative of eurythermy, the ability to perform well over a wide range of temperatures. We discuss this finding in the context of alternative hypotheses concerning performance tradeoffs in nocturnal ectotherms.

Thermoregulatory performance and habitat selection of the eastern box turtle (Terrapene carolina carolina)

Environmental conditions may affect individual physiological processes that influence short-term performance and ultimately growth, survival and reproduction. As such, habitats selected by animals must provide suitable and adequate resources. Ectothermic species are highly dependent on climatic conditions and ambient temperatures that dictate body temperature regulation and in turn physiological processes. We investigated the thermoregulatory performance, habitat selection, and movements of an ectothermic vertebrate, the Eastern box turtle (Terrapene carolina carolina) to assess the importance of thermoregulatory physiology in habitat selection. We evaluated the relationship between habitat selection and thermoregulatory performance in Southwest Ohio over two active seasons from May until October. We found that T. carolina selected shaded habitats, including evergreen and deciduous forests, as well as herbaceous grasslands, conformed to the ambient temperatures throughout the active season, although these habitats had temperatures below those expected based on thermal optima of box turtles. Further, we found that movement was not correlated with internal body temperature. Our study shows that thermal conditions are not paramount in habitat selection of box turtles, but that cooler temperatures do not have an effect on the extent of their locomotion.