A Study On The Energy Metabolism Of Eremias Multiocellata And Reproductive Biology Of Three Phrynocephalus Lizards

The maintenance costs of pregnancy (MCP) and energy metabolism of lizard Eremias multiocellata as well as sexual size dimorphism (SSD), reproductive strategies and the effects of incubuting condition on the hatching success, morphological features and locomotor performance of offsprings in three lizards Phrynocephalus przewalskii, P. versicolor and P. axillaris were studied. The mechanisms of their physiological and ecological adaptations to the environment were also discussed in this paper. The concrete results are as follows:The body temperature (Tb) and resting metabolic rate (RMR) of female Eremias multiocellata, a viviparous lizard, were measured at25,30and35℃during pregnancy and after parturition to assess energy requirement of reproduction. The results showed that female lizards’Tbs were slightly higher than actual ambient temperature in25and30℃groups, while they were slightly lower than ambient temperature in35℃group. Ambient temperature significantly affected RMR and gestation period of females. Energy requirement was constant in non-pregnant females, while it increased in pregnant females. The maximal estimates of MCP accounted for19.40%,14.15%and12.32%of the total metabolic rate in25,30and35℃group, respectively. The results indicated the MCP was an important component of total energy cost for the lizard E. multiocellata. It is suggested that pregnant females could guarantee the pregnancy at low temperature by increasing the portion of MCP in total energy cost.The relationships between temperature and the activities of lactate dehydrogenase (LDH) and hexokinase (HK) and mitochondrial respiration were studied in cardiac muscle, liver and gastrocnemius muscle in two populations of E. multiocellata. The enzymatic activity and mitochondrial respiration were very sensitive to temperature. The Tianzhu population of lizard E. multiocellata which were from colder regions exhibited a relative higher resting metabolic rate and mitochondrial respiration rate than Minqin population in three kinds of tissues. LDH and HK activity of cardiac muscle and LDH activity of gastrocnemius muscle in Tianzhu population were also higher than that of Minqin population. The results indicate that Tianzhu population of E. multiocellata could response to cold acclimation not only by increasing the aerobic enzymatic activity of cardiac and gastrocnemius muscle, but also by increasing maximal oxidative capacities of tissue mitochondria. The metabolic adaptation to cold stress may accelerate development and increase survival capacity of the population.The morphological features and female reproductive characteristics were studied in three species of toad-headed lizards, P. przewalskii, P. versicolor and P. axillaris. The results showed that males were the larger sex in P. przewalskii and P. axillaris, whereas female and male adults of P. versicolor did not differ in mean SVL. In P. przewalskii and P. versicolor, females were larger in abdomen length but females of P. axillaris were smaller in abdomen length. Females of three species laid a single clutch of1-6eggs per breeding season. The trade-off between size and number of eggs was evident in all species. The female reproductive traits, clutch size, egg mass and relative clutch mass were differed among species, with females of P. przewalskii laying fewer but larger eggs than did females of P. versicolor in the same SVL. P. axillaris had the smallest body size, and laid relative fewer and smaller eggs, which may related to its cool climate and less precipitation. Our result indicated that climate, habitat and population competition may be the proximate factors affecting the reproductive parameters of three lizards.Flexible-shelled eggs of lizard P. przewalskii, P. versicolor and P. versicolor were incubated in different thermal and hydric environments to elicit the effects of incubation environment on hatching success, incubation duration and hatchling phenotypes. The embryogenesis of two species were not sensitive to the hydric environment except P. przewalskii incubated in30℃group. Hatching success was much higher at26and30℃than34℃. Hatchling incubated at26and30℃had longer snout-vent lengths, larger body masses, and better locomotor performance than hatchlings incubated at higher temperature. Compared to P. przewalskii, P. versicolor incubated longer, and had smaller hatchlings, which would benefit more to the species survival living at drier wildlife habitat. We conclude that an incubation temperature of30℃would provide the best balance between developmental rate, hatching success, and posthatch performances, and we suspect the upper egg developmental thresholds for P. versicolor egg incubation may near and slightly higher than34℃. Because of the lower hatching success, egg incubation in P. versicolor should be of more concern in the further.