Effects Of Thermal Environment, Hormones And Food On Life History Characteristics And Larval Phenotype Of Lizards

Viviparity (live-bearing) is a reproductive mode that evolves from oviparity through gradual increasing in the length of egg retention and intrauterine development. This reproductive mode can be offering pervasive benefited by lowering embryonic mortality, accelerating embryonic development, optimizing offspring phenotype and obviating the need for females to find suitable egg-laying sites with this reproductive mode. I collected skinks (Sphenomorphus indicus, Scincella reevesii and Scincella modesta) from several localities in Zhejiang, Jiangsu and Guangdong provinces to examine the influence of thermal environment, dietary quality and hormones on maternal life-history traits and offspring phenotype of skink species.Body size and shape are among the most important determinants of reproductive output in diverse animal taxa. We compared morphology and reproductive output between two Scincella lizards (Scincidae), S. modesta (oviparous) and S. reevesii (viviparous), to examine whether viviparous females compensate for their lower reproductive output by modifying maternal body size and/or shape. As predicted, reproductive output was lower in S. reevesii than in S. modesta when corrected for body size. The two lizards differed morphologically, but were similar in three aspects: females were the larger sex, the relative head size was greater in adult males, and the relative abdomen size was greater in adult females. Sexual dimorphism in abdomen length (AL) was more evident in S. reevesii than in S. modesta, but this difference was attributable to a smaller sexual difference in AL in S. modesta, rather than to the greater relative maternal AL in S. reevesii. Female S. reevesii on average were larger than female S. modesta in snout-vent length (SVL), but this increase in overall body size cannot be viewed as a way of allowing female S. reevesii to compensate for lower reproductive output, as the linear slope of reproductive output against maternal SVL did not differ between the two species. Our data show that selection for increased maternal body-volume does not differ between the two Scincella lizards with different reproductive modes. To measure the possible influence of gestation temperature (body temperature during pregnancy) on reproduction and offspring phenotype, pregnant females of S. indicus were maintained under four thermal conditions (thermal treatments) for the whole gestation period. Females of S. indicus in three of the four treatments were maintained in three controlled temperature rooms, where they could maintain their body temperatures constant at24,26and28(±0.3)℃respectively. Females of S. indicus in the fourth treatment (the TR treatment) were maintained in a room where they could regulate body temperature within their voluntary range during the light phase. Females of S. reevesii were maintained in three controlled temperature rooms of22,25,28(±0.3)℃and a TR treatment.Females at higher gestation temperatures gave birth to young earlier than did females at lower gestation temperatures in both Scincella lizards. All female reproductive traits (litter size, neonate mass and litter mass and postpartum mass) examined in S. indicus except for postpartum mass did not differ among the four thermal treatments. Neonates differed among thermal treatments in SVL, tail length, head length, and fore-limb length. A principal component analysis resolved two components (eigenvalues≥1) from five size-adjusted offspring traits, accounting for50.7%of variation in the original data. The first component (27.7%of variance explained) had high positive loading for hind-limb, and the second component (23.0%of variance explained) had high positive loading for tail length. Offsprings under different thermal regimes differed significantly in their scores on the first axes. Gestation temperature affected locomotor performance of neonates, with those from28℃exhibiting the worst performance in the examined traits (sprint speed and the maximal length).Thermal environments encountered by gravid females of S. reevesii affected timing of parturition but not the traits (litter size, neonate mass and litter mass) determining reproductive output. Postpartum body mass differed significantly among treatments. Neonates differed among thermal treatments in SVL, head width and fore-limb length. A principal component analysis resolved two components (eigenvalues≥1) from seven size-adjusted offspring traits, accounting for78.6%of variation in the original data. The first component (34.2%of total variance explained) had high positive loading for head width, fore-limb and hind-limb. Offspring under different thermal regimes differed significantly in their scores on the first and second axes. Locomotor performance of neonates differed significantly among treatments.We used S. reevesii as the model system to test the possible impacts of climate warming on reptiles by3background temperatures (22,25and28℃). One-way ANOVA revealed that:lizards at lower background temperatures thermoregulated more actively than did those at higher background temperatures. Lizards in the22℃treatment selected higher body temperatures than did those in the25℃treatment, and lizards in the25℃treatment selected higher body temperatures than did lizards in the22℃treatment. SVL of females and neonate mass did not differ under the three thermal regimes, whereas postpartum body mass, litter mass and litter size differed significantly among treatments. Background temperature affected SVL, abdomen length, head size, fore-and hind-limb of neonate, and also in birth date. Female S. reevesii gave birth earliest in the28℃treatment and latest in the20℃treatment. Effects of background temperature on locomotor performance did not differ under different thermal regimes.The plasma and yolk of reptiles contain detectable levels of several steroid hormones, and experimental application of such steroids can reverse genetically determined sex of the offspring. However, any causal influence of maternally derive yolk steroids on sex determination in reptiles remains controversial. Sphenomorphus indicus is a TSD lizard and its gestation temperature could affect sexual phenotype of neonatal. I measured plasma and yolk hormones (17β-estradiol and testosterone) of the scincid lizard S. indicus under different thermal regimes (24,26and28℃). I found that females of S. indicus at different reproductive conditions and thermal treatments did not differ from each other in the levels of E2and T in both plasma and yolk. Thus, plasma and yolk steroid hormones did not appear to play a critical role in sex determination for S. indicus.Maternal hormones during gestation acted as a bridge between the environments experienced by the mother and her offspring. We used an experimental design allowing us to increase plasma corticosterone concentration (vs. control) in gravid female Reeves’ smooth skinks (S. reevesii) to examine whether such a manipulation could indirectly influence the hormonal environment experienced by developing embryos. The result revealed that high concentrations of maternal corticosterone had significant effects on birth date, locomotor performance (sprint speed and the maximal length), reproductive success and body temperatures selected by the monthers. Female S. reevesii undergoing the corticosterone manipulation gave birth later, performed less well in the racetrack, showed lower reproductive success, and selected higher body temperatures than did controls not undergoing such a manipulation. Of the offspring characteristics compared, only abdomen length and tail length were affected by high concentrations of corticosterone. Corticosterone affected locomotor performance of neonates, with those from the corticosterone treatment exhibiting worse locomotor performance.Life-history traits such as offspring size, number and sex ratio are affected by maternal feeding rates in wide range of animal taxa, but the consequences of variation in maternal dietary quality (rather than food quantity) are poorly understood. We manipulated dietary quality in reproducing female lizards Scincella reevesii (viviparous), to examine strategies of reproductive allocation. Females fed with mealworm produced fewer offspring and thus ligther litters than did females taken cricket. Dietary quality had significant effects on birth date, with females fed with cricket giving birth earlier than did those taking mealworm. Thermal preference (i.e., body temperature preferred or selected by a lizard) did not differ between females taking mealworm foand cricket. Offspring produced by females taking cricket were longer in total length (SVL and tail length) and performed better in the racetrack than did offspring produced by female taking maealworm.