Shu-Ran Li

Different mechanisms lead to convergence of reproductive strategies in two lacertid lizards (Takydromus wolteri and Eremias argus)

Life history traits may vary within and among species. Rarely, however, are both variations examined concurrently to identify the life history adaptation. We found that female body size, offspring number and size, and incubation period showed convergent evolution in two lacertid lizards (Takydromus wolteri and Eremias argus) that occur sympatrically in high-latitude and low-latitude localities. Females from the high-latitude population were larger and produced larger clutches than those from the low-latitude population. In both species, the incubation period was shorter for the high-latitude population than for the low-latitude population. However, the physiological mechanism underlying the shorter incubation period differed between the species. These results suggest that: (1) sympatric lizards may adopt similar reproductive strategies in response to their common environments, and (2) embryonic development of the two species follows different pathways for adaptation to low temperatures. This study highlights the importance of understanding the adaptive evolution of life history in response to environmental changes at the embryonic life stages.

Maternal Thermal Environment Induces Plastic Responses in the Reproductive Life History of Oviparous Lizards

Adaptive plasticity may shift phenotypic traits close to a new optimum for directional selection and probably facilitates adaptive evolution in new environments. However, such plasticity has rarely been reported in life-history evolution, despite overwhelming evidence of life-history variation both among and within species. In this study, the temperatures experienced by gravid females of Scincella modesta were manipulated to identify maternally induced plasticity in reproductive traits and the significance of such changes in the evolution of life history. Consistent with the geographic pattern of life history, the study demonstrated that low temperatures delayed egg oviposition, resulting in a more advanced embryonic developmental stage at oviposition and shorter incubation periods compared with warm temperatures. In addition, females maintained at low temperatures produced larger eggs and hence heavier hatchlings than those at warm temperatures. This study demonstrated that environmental temperatures can induce plastic responses in egg retention and offspring size, and these maternally mediated changes in reproductive life history seem to be adaptive in the light of latitudinal clines of these traits in natural populations.

Low precipitation aggravates the impact of extreme high temperatures on lizard reproduction

Extreme high temperatures are occurring more frequently with ongoing anthropogenic climate warming, but the experimental tests of the effects of high temperatures on terrestrial vertebrates in natural conditions are rare. In this study, we investigated the effects of extreme high temperatures on female reproduction and offspring traits of multi-ocellated racerunners (Eremias multiocellata) kept in field enclosures in the desert steppe of Inner Mongolia. Our studies indicate that high temperatures significantly affect the gestation period and reproductive output of females and the offspring sex ratio, but have little impact on offspring body size and mass. More interestingly, we found that the effect of extreme high temperatures on female reproductive output was not consistent between two consecutive years that differed in precipitation. Low precipitation may aggravate the impact of climate warming on lizards and negatively affect the survival of lizards in the desert steppe. Our results provide evidence that temperature interacts with precipitation to determine the life history of lizards, and they suggest that a drier and hotter environment, such as the future climate in arid mid-latitude areas, will likely impose severe pressure on lizard populations, which are an important component of the food web in desert areas around the world.

Female lizards choose warm, moist nests that improve embryonic survivorship and offspring fitness

The fitness consequence of maternal nest-site choice has attracted increasing scientific attention, but field studies identifying the long-term effects of nest-site choice on offspring survival and reproductive success are still rare in vertebrates. To investigate the consequences of nest-site choice in lizards, we quantified the thermal and hydric conditions of nest sites that were chosen by female toad-headed agama (Phrynocephalus przewalskii) in the desert steppe of northern China. We also determined the effect of nest-site choice on embryonic development and survival and on offspring growth, survival, and maturity by comparing the embryos and offspring from maternally and randomly chosen nest sites. We found that female toad-headed agama chose warm and moist nest sites that improved the developmental rate and survivorship of embryos and promoted the post-hatching growth, sexual maturity, reproduction, and fitness of offspring, thereby improving their reproductive success. Such studies on short-lived lizards across multiple stages of embryonic and postembryonic ontogeny are critical for fully understanding the fitness consequences of nest-site choice. This article is protected by copyright. All rights reserved.

Thermal ecology of three coexistent desert lizards: Implications for habitat divergence and thermal vulnerability

How ectotherms exploit thermal resources has important implications for their habitat utilization and thermal vulnerability to climate warming. To address this issue, we investigated thermal relations of three sympatric lizard species (Eremias argus, Eremias multiocellata, and Phrynocephalus przewalskii) in the desert steppe of Inner Mongolia, China. We determined the thermoregulatory behavior, body temperature (Tb), operative temperature (Te), selected body temperature (Tsel), and critical thermal maximum (CTmax) of adult lizards. Based on these physiological parameters, we quantified the accuracy and effectiveness of thermoregulation as well as thermal-safety margin for these species. The three species were accurate and effective thermoregulators. The P. przewalskii preferred open habitats, and had a higher Tb than the two Eremias lizards, which preferred shade habitats and shuttled more frequently between the shade and sun. This indicated that the three sympatric lizards have different thermoregulatory behavior and thermal physiology, which might facilitate their coexistence in the desert steppe ecosystem. In addition, the P. przewalskii had higher Tsel and CTmax, and a wider thermal-safety margin than the two Eremias lizards, suggesting that the two Eremias lizards would be more vulnerable to climate warming than P. przewalskii.

The effects of light exposure during incubation on embryonic development and hatchling traits in lizards.

Light is an environmental factor that is known to profoundly affect embryonic development in some oviparous vertebrates, but such effects are unstudied in reptiles. We investigated the light sensitivity of lizard embryos by examining the thickness and light transmittance of eggshells as well as the effect of light on embryonic development and hatchling traits in four lizard species, the Chinese skink (Plestiodon chinensis), the northern grass lizard (Takydromus septentrionalis), the oriental leaf-toed gecko (Hemidactylus bowringii) and the Japanese gecko (Gekko japonicus). The eggshells were thinner and thus had higher light transmittance in Chinese skink than the other three species. Light exposure during incubation significantly accelerated the embryonic development in all species, with higher light intensity resulting in faster embryonic development. Interestingly, light stimulation negatively influenced hatchling size and survival in skinks, but had no effect in lacertids and geckos. This interspecific discrepancy not only relates to the differences in thickness and light transmittance of eggshells, but might also reflect the differences in the reproductive habits of these species. Given the diversity of light conditions that reptile embryos face during development, studies on the response of reptile embryos to light may offer a unique opportunity to understand the mechanisms of embryonic light sensitivity in animals.

Food restriction affects maternal investment but not neonate phenotypes in a viviparous lizard

Food availability significantly affects an animals energy metabolism, and thus its phenotype, survival, and reproduction. Maternal and offspring responses to food conditions are critical for understanding population dynamics and life-history evolution of a species. In this study, we conducted food manipulation experiments in field enclosures to identify the effect of food restriction on female reproductive traits and postpartum body condition, as well as on hatchling phenotypes, in a lacertid viviparous lizard from the Inner Mongolian desert steppe of China. Females under low-food availability treatment (LFT) had poorer immune function and body condition compared with those under high-food availability treatment (HFT). The food availability treatments significantly affected the litter size and litter mass of the females, but not their gestation period in captivity or brood success, or the body size, sprint speed, and sex ratio of the neonates. Females from the LFT group had smaller litter sizes and, therefore, lower litter mass than those from the HFT group. These results suggest that female racerunners facing food restriction lay fewer offspring with unchanged body size and locomotor performance, and incur a cost in the form of poor postpartum body condition and immune function. The flexibility of maternal responses to variable food availability represents an important life strategy that could enhance the resistance of lizards to unpredictable environmental change.

The vulnerability of developing embryos to simulated climate warming differs between sympatric desert lizards

The vulnerability of species to climate warming varies along latitudinal and elevational clines, but how sympatric species vary in vulnerability to climate warming remains largely unknown. We experimentally simulated nest temperatures of two sympatric lizards with divergent microhabitat preferences (Phrynocephalus przewalskii and Eremias argus), under climate warming senarios, to determine the response of embryos to increased mean temperatures and heat waves. Our study demonstrated that simulated climate warming reduced hatching success and hatchling size and growth in E. argus (that prefers closed microhabitats), but had less effect in P. przewalskii (that occupies open microhabitats). The reduced growth rate of E. argus hatchlings was associated with a decrease in metabolic rate, which was more evident in hatchling E. argus than in P. przewalskii. Our results suggest lizards that prefer closed microhabitats may be more vulnerable to climate warming than those that prefer open microhabitats; further studies are needed to test this hypothesis. More generally, the divergent responses of sympatric species to climate warming highlights the importance of distinguishing the thermal sensitivity of behavior and physiology for each species of a community, in order to make predictions about the impacts of climate warming at regional scales.

A simulated heat wave shortens the telomere length and lifespan of a desert lizard

Understanding how organisms respond to warming contributes important information to the conservation of biodiversity that is threatened by climate warming. Here, we conducted experiments on a desert agama (Phrynocephalus przewalskii) to test the hypothesis that climate warming (an increase in both mean temperature and heat waves) would induce oxidative stress, shortening telomere length, and thereby decreasing survival. Our results demonstrated that one week of exposure to a simulated heat wave significantly shortened telomere length, and decreased the overwinter survival of lizards, but mean temperature increase did not affect the survival of lizards. However, the antioxidant capacity (anti-oxidative enzyme) was not affected by the warming treatments. Therefore, heat waves might have negative impacts on the desert agama, with shortened telomeres likely causing the lifespan of lizards to decrease under climate warming.

Why do female desert lizards construct burrows to lay eggs

Many oviparous animals construct well-designed nests to provide relatively favourable conditions for their eggs and hatchlings, but the direct evidence that nest structure can determine their reproductive success is insufficient. In the present study, we explored the structure of nests and its effect on nest environments and reproductive success in the toad-headed agama (Phrynocephalus przewalskii). We observed that female P. przewalskii constructed burrow nest consisting of an inclined tunnel and an expanded chamber. We constructed artificial nests with or without the burrow to determine how burrows influence nest environments, egg survival and successful emergence of hatchlings. Our results indicated that burrow nests had higher and more stable humidity than non-burrow nests. More importantly, egg survival and the emergence success of hatchlings were significantly higher for burrow nests than for non-burrow nests. Therefore, our manipulation experiments provide direct evidence that maternal nest construction behaviour could determine parental reproductive success in reptile.