Body size is directly linked to key life history traits such as growth, fecundity, and survivorship. Identifying the causes of body size variation is a critical task in ecological and evolutionary research. Body size variation along altitudinal gradients has received considerable attention; however, the underlying mechanisms are poorly understood. Here, we compared the growth rate and age structure of toad‐headed lizards (Phrynocephalus vlangalii) from two populations found at different elevations in the Qinghai‐Tibetan Plateau. We used mark‐recapture and skeletochronological analysis to identify the potential proximate causes of altitudinal variation in body size. Lizards from the high‐elevation site had higher growth rates and attained slightly larger adult body sizes than lizards from the low‐elevation site. However, newborns produced by high‐elevation females were smaller than those by low‐elevation females. Von Bertalanffy growth estimates predicted high‐elevation individuals would reach sexual maturity at an earlier age and have a lower mean age than low‐elevation individuals. Relatively lower mean age for the high‐elevation population was confirmed using the skeletochronological analysis. These results support the prediction that a larger adult body size of high‐elevation P. vlangalii results from higher growth rates, associated with higher resource availability.

We maintained pregnant Sphenomorphus indicus under four thermal conditions for the whole gestation period to assess the effects of gestation temperature on offspring phenotypes. Parturition occurred between late June and early August, with females at high body temperatures giving birth earlier than those maintained at low body temperatures. Litter size, litter mass, and postpartum body mass did not differ among treatments, and females with relatively higher fecundity produced smaller offspring. Females gave birth to predominantly female offspring (85.7% of the 14 sexed offspring were females) at 24 ° C and to predominantly male offspring (76.5% of the 17 sexed offspring were males) at 28 ° C. Females with the opportunity to regulate body temperature produced a mix of sexes that did not differ from equality. Offspring produced in different treatments differed in head size, hind-limb length, and tympanum length, but not in snout-vent length, tail length, body mass, fore-limb length, and eye length. Offspring produced at 28 ° C were not only smaller in head size, but also shorter in hind-limb length and tympanum length than those offspring produced at lower temperatures. Offspring produced at 28 ° C performed more poorly in the racetrack and grew more slowly than offspring produced in the other three treatments. Taken together, our results show that S. indicus might be a temperature-dependent sex determination species and that offspring phenotypes are impaired at high gestation temperatures but maximized at relatively low gestation temperatures.

Patterns in functional diversity of organisms at large spatial scales can provide insight into possible responses to future climate change, but it remains a challenge to link large-scale patterns at the population or species level to their underlying physiological mechanisms at the individual level. The climate variability hypothesis predicts that temperate ectotherms will be less vulnerable to climate warming compared with tropical ectotherms, due to their superior acclimatization capacity.However, metabolic acclimatization occurs over multiple levels, from the enzyme and cellular level, through organ systems, to whole-organism metabolic rate (from this point forwards biological hierarchy). Previous studies have focused on one or a few levels of the biological hierarchy, leaving us without a general understanding of how metabolic acclimatization might differ between tropical and temperate species. Here, we investigated thermal acclimation of three species of Takydromus lizards distributed along a broad latitudinal gradient in China, by studying metabolic modifications at the level of the whole organism, organ, mitochondria, metabolome, and proteome. As predicted by the climate variability hypothesis, the two temperate species T. septentrionalis and T. wolteri had an enhanced acclimation response at the whole organism level compared with the tropical species T. sexlineatus, as measured by respiratory gas exchange rates. However, the mechanisms by which whole organism performance was modified was strikingly different in the two temperate species: widespread T. septentrionalis modified organ sizes, whereas the narrowly distributed T. wolteri relied on mitochondrial, proteomic and metabolomic regulation. We suggest that these two mechanisms of thermal acclimatization may represent general strategies used by ectotherms, with distinct ecological costs and benefits. Lacking either of these mechanisms of thermal acclimatization capacity, the tropical species is likely to have increased vulnerability to climate change.

Heat tolerance at the immobile embryonic stage is expected to be critical in determining species vulnerability to climate change. However, how the mean and developmental plasticity of embryonic heat tolerance vary geographically, and how these geographic variations affect species' vulnerability under climate change remain unknown. We experimentally determined the mean and developmental plasticity of embryonic acute heat tolerance (EAHT, i.e., heat shock temperature at which embryonic heartbeats ceased) for three latitudinally distributed populations of an oviparous lacertid lizard. The experimental results suggested that the mean EAHT decreased with decreasing latitude and that the reaction norms of EAHT in relation to developmental temperatures showed “flat,” “bell‐shaped,” and “decreasing” patterns at high, medium, and low latitudes, respectively. Based on the means and plasticity of EAHT and weather data across China, we project that the heat stress frequency would increase from the present to the future and increase toward low latitudes. Furthermore, heat stress becomes more extensive with the incorporation of developmental plasticity. Incorporating the mean EAHT during the embryonic development season, heat stress frequency, and climate variables in a species distribution model projects that suitable habitats could move northward in response to ongoing climate change and shrink due to the loss of southern habitat. Moreover, even lizards within the areas that are predicted to remain highly suitable are expected to experience increases in heat stress over time, particularly at medium and low latitudes. Our study reveals geographic variation in the mean and developmental plasticity of EAHT and highlights its importance for predicting species vulnerability and range shifts in response to climate change.

Parental effects may produce adaptive or maladaptive plasticity that either facilitates persistence or increases the extinction risk of species and populations in a changing climate. However, empirical evidence of transgenerational adaptive plastic responses to climate change is still scarce. Here we conducted thermal manipulation experiments with a factorial design in a Chinese lacertid lizard (Takydromus septentrionalis) to identify the fitness consequences of parental effects in response to climate warming. Compared to present climate conditions, a simulated warming climate significantly advanced the timing of oviposition, depressed the immune capability of post-partum females, and decreased the hatching success of embryos, but did not affect female reproductive output (clutch size and egg mass). These results indicate that maternal warming negatively affects female health, and embryonic hatchability. More interestingly, we found that offspring from parents exposed to warming environments survived well under a simulated warming climate, but not under a present climate scenario. Accordingly, our study demonstrates anticipatory parental effects in response to a warming climate in an ectothermic vertebrate. However, the fitness consequences of this parental effect will depend on future climate change scenarios.Electronic supplementary materialThe online version of this article (10.1186/s12983-018-0296-3) contains supplementary material, which is available to authorized users.

No abstract

BackgroundEctothermic animals living in cold (high latitude or high elevation) regions are predicted to grow slower due to limited thermal opportunities for activity and food resources than those living in warm regions. However, the Qinghai toad-headed lizards (Phrynocephalus vlangalii) grow faster and reach a larger adult size at a high-elevation site than at a low-elevation site. In this study, we aimed to identify the genetic and environmental causes of this between-population difference in growth rate by conducting mark-recapture and common garden experiments on juvenile growth rate, and investigating the thermal environment, lizard body temperature, potential prey availability at the two elevation sites.ResultsCompared with low-elevation individuals, high-elevation juvenile lizards had higher growth rates in the field, but grew at similar rates in the laboratory. High-elevation lizards had higher active body temperatures than low-elevation lizards despite similar air temperatures in the period of field investigation. The high-elevation site had relatively more and larger preys than the low-elevation site.ConclusionsInter-population difference in growth rate of P. vlangalii may primarily result from developmental plasticity in response to the difference in environmental resources, rather than genetic differentiation. The higher growth rate of high-elevation lizards is likely associated with higher potential food availability and higher active body temperatures.

Viviparous Phrynocephalus lizards (Agamidae) are mainly restricted to the Qinghai-Tibet Plateau of China. In this study, we used Phrynocephalus vlangalii females kept under seven thermal regimes for the whole gestation period to test the hypothesis that viviparity in high-altitude Phrynocephalus lizards is adaptive because embryos cannot fully develop without maternal thermoregulation. All females at 24 °C and 93% of the females at 28 °C failed to give birth or produced stillborns, and proportionally fewer females gave birth at 29 or 35 °C than at 32 °C. Though the daily temperatures encountered were unsuitable for embryonic development, 95% of the females in nature and 89% of the females thermoregulating in the laboratory gave birth. There was no shift in the thermal preferences of females when they were pregnant. Although thermal conditions inside natural burrows were unsuitable for embryonic development, mass and sprint speed were both greater in neonates produced in nature. Our data show that (1) long-term exposure of P. vlangalii embryos to temperatures outside the range of 29-35 °C may result in the failure of development, but daily or short-term exposure may not necessarily increase embryonic mortality; (2) low gestation temperatures slow but do not arrest embryonic development, and females produce high-quality offspring in the shortest possible time by maintaining gestation temperatures close to the upper thermal limit for embryonic development; and (3) viviparity is currently adaptive at high elevations because embryos in nature cannot fully develop without relying on maternal thermoregulation. Our data validate the hypothesis tested.