Peter A. Zani

Climate Change Trade‐Offs in the Side‐Blotched Lizard (Uta stansburiana): Effects of Growing‐Season Length and Mild Temperatures on Winter Survival

An expanding body of literature has demonstrated that global climate change continues to adversely affect many populations, species, and ecosystems. However, life‐history theory also predicts possible benefits from longer growing seasons and less severe winters, particularly for ectotherms. To test the idea that climate change will have benefits as well as costs, I studied the impacts of growing‐season length on growth and overwintering conditions on survival time using side‐blotched lizards (Uta stansburiana). Experiments in replicate field enclosures revealed that fall growing‐season length has a direct effect on overwintering body size. Laboratory experiments revealed that both size and overwintering temperature have direct effects on winter survival time. Larger lizards are more likely to survive longer regardless of winter temperature. Furthermore, animals in colder (but still mild) winter microenvironments are more likely to survive longer than those in warmer winter environments. These results indicate that warmer winters caused by global climate change have the potential to negatively affect ectotherm populations. However, longer growing seasons may offset losses by allowing additional growth and energy storage. Thus, environmental alterations associated with climate change may be simultaneously beneficial and detrimental, and the long‐term persistence of certain organisms may depend on the relative strength of their effects.

Integrative biology of tail autotomy in lizards.

Self-amputation (autotomy) of the tail is essential for the survival of many lizards. Accordingly, it has garnered the attention of scientists for more than 200 years. Several factors can influence the release of the tail, such as the size, sex, and age of the lizard; type of predator; ecology; and evolutionary history of the lineage. Once lost, the tail will writhe for seconds to minutes, and these movements likely depend on the size and physiology of the tail, habitat of the lizard, and predation pressure. Loss of the tail will, in turn, have impacts on the lizard, such as modified locomotor performance and mechanics, as well as escape behavior. However, the tail is almost always regenerated, and this involves wound healing, altered investment of resources, and tissue differentiation. The regenerated tail generally differs from the original in several ways, including size, shape, and function. Here we summarize recent findings of research pertaining to tail autotomy, and we propose a framework for future investigations.

Effects of night-time warming on temperate ectotherm reproduction: potential fitness benefits of climate change for side-blotched lizards

SUMMARY Temperate ectotherms, especially those at higher latitudes, are expected to benefit from climate warming, but few data yet exist to verify this prediction. Furthermore, most previous studies on the effects of climate change utilized a model of uniform annual change, which assumes that temperature increases are symmetric on diurnal or seasonal time scales. In this study, we simulated observed trends in the asymmetric alteration of diurnal temperature range by increasing night-time temperatures experienced by female lizards during their ovarian cycle as well as by the resulting eggs during their incubation. We found that higher night-time temperatures during the ovarian cycle increased the probability of reproductive success and decreased the duration of the reproductive cycle, but did not affect embryo stage or size at oviposition, clutch size, egg mass or relative clutch mass. Furthermore, higher incubation temperatures increased hatchling size and decreased incubation period but had no effect on incubation success. Subsequent hatchlings were more likely to survive winter if they hatched earlier, though our sample size of hatchlings was relatively small. These findings indicate that higher night-time temperatures mainly affect rate processes and that certain aspects of life history are less directly temperature dependent. As our findings confirm that climate warming is likely to increase the rate of development as well as advance reproductive phenology, we predict that warmer nights during the breeding season will increase reproductive output as well as subsequent survival in many temperate ectotherms, both of which should have positive fitness effects.

Glycogen, not dehydration or lipids, limits winter survival of side-blotched lizards (Uta stansburiana)

SUMMARY Climate change is causing winters to become milder (less cold and shorter). Recent studies of overwintering ectotherms have suggested that warmer winters increase metabolism and decrease winter survival and subsequent fecundity. Energetic constraints (insufficient energy stores) have been hypothesized as the cause of winter mortality but have not been tested explicitly. Thus, alternative sources of mortality, such as winter dehydration, cannot be ruled out. By employing an experimental design that compared the energetics and water content of lizards that died naturally during laboratory winter with those that survived up to the same point but were then sacrificed, we attempt to distinguish among multiple possible causes of mortality. We test the hypothesis that mortality is caused by insufficient energy stores in the liver, abdominal fat bodies, tail or carcass or through excessive water loss. We found that lizards that died naturally had marginally greater mass loss, lower water content, and less liver glycogen remaining than living animals sampled at the same time. Periodically moistening air during winter reduced water loss, but this did not affect survival, calling into question dehydration as a cause of death. Rather, our results implicate energy limitations in the form of liver glycogen, but not lipids, as the primary cause of mortality in overwintering lizards. When viewed through a lens of changing climates, our results suggest that if milder winters increase the metabolic rate of overwintering ectotherms, individuals may experience greater energetic demands. Increased energy use during winter may subsequently limit individual survival and possibly even impact population persistence.

Characterization and Quantification of the Neutral Lipids in the Lizard Uta stansburiana stansburiana by HPTLC-Densitometry

Abstract We performed high-performance thin-layer chromatography (HPTLC) to characterize and quantify the various neutral lipid classes in organs (livers, abdominal fat bodies, and tails) of 6 male and 6 female northern side-blotched lizards (Uta stansburiana stansburiana) with a range of body sizes (from young-of-the-year to adult). We determined the percentage of each organ that was comprised of free sterols, free fatty acids, triacylglycerols, methyl esters, and steryl esters. Regardless of lizard sex or body size, the greatest concentrations of neutral lipids in all organs examined were triacylglycerols. Statistical analyses revealed that the organs of females contained roughly twice the percentage of triacylglycerols compared to males. No other neutral lipid amounts were significantly different between the sexes. We detected only one significant relationship based on size: larger lizards contained more steryl esters in their livers than smaller lizards. Our results are consistent with previous studies showing that females contain more energy reserves (particularly triacylglycerols) than males. This is the first report of the use of TLC or HPTLC with densitometry to analyze any type of analytes in lizard samples.

Characterization and Quantification of the Polar Lipids in the Lizard Uta stansburiana by HPTLC-Densitometry

Abstract Silica gel high-performance thin-layer chromatography (HPTLC) with chloroform-methanol-water (65:25:4) mobile phase and cupric sulfate-phosphoric acid detection reagent was used to characterize and quantify various polar lipid classes in organs (livers, abdominal fat bodies, and tails) of 6 male and 6 female side-blotched lizards (Uta stansburiana) with a range of body sizes (from young-of-the-year to adult). The percentage of phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin, sulfatides, and cerebrosides (C) in each organ was determined. No significant statistical differences were detected between the sexes. Across all three organs, PC was the primary polar lipid class, and the liver contained the most polar lipids. C was the most prevalent polar lipid class in the liver, PC in the tail, and PC and PE in the abdominal fat body. This is the first report of the use of TLC or HPTLC with densitometry to analyze polar lipids in lizard samples.

The effect of diapause on neutral lipids in the pitcher-plant mosquito Wyeomyia smithii as determined by HPTLC-densitometry

Diapause in insects typically results in metabolic adjustments that may include the levels of feeding and activity, metabolic rate, and the accumulation and utilization of reserves. The objective of this study was to characterize and quantify the various neutral lipid classes in the pitcher-plant mosquito (Wyeomyia smithii) that are associated with photoperiod-induced diapause. We used high-performance thin-layer chromatography (HPTLC) with 10 cm × 20 cm silica gel plates, petroleum ether-diethyl ether-glacial acetic acid 80:20:1 as the mobile phase, and 5% ethanolic phosphomolybdic acid solution as detection reagent to determine the percentage of replicate larvae samples (consisting of 16–31 larvae) that contained free sterols (FS), free fatty acids (FFA), triacylglycerols (TG), methyl esters (ME), and steryl esters (SE). Irrespective of the growth treatment (shortdays or long-days), the greatest concentrations of neutral lipids in all samples examined were TG. The effects of day length were such that during long-day (diapause terminating) conditions larvae contained less TG, more FS, and more FFA than larvae exposed to short-day (diapause inducing) conditions. Furthermore, the effects of body mass affected our results such that larger larvae contained more TG when in diapause, but less TG when not in diapause. Both ME and SE were only found in trace amounts in the short-day mosquitoes and not at all in long-day group. Our results are consistent with previous research that suggests TGs are important storage lipids during insect diapause.