Reproductive Life-history Traits And Phenotypic Responses Of Offspring To Gestation Temperature

The brown forest skink (Sphenomorphus indicus) is a viviparous sincid lizard that is widely distributed in the southern part of China, India (Darjeeling and Sikkim), Indochina and Malay Peninsula. In the present study, I investigate sexual dimorphism in body size and head size and variation in female reproductive characteristics and offspring phenotypes induced by thermal environments experienced pregnant females. Newly ovulated females were maintained under seven thermal conditions for the whole gestation period to assess the effects of gestation temperature on female reproduction and offspring phenotypes (including size, morphology, gender, early growth, and locomotor performance). In five of the seven treatments females were maintained in five different constant temperature rooms, where they could maintain mean body (cloacal) temperatures at23,24,26,28and29℃, respectively. In the sixth treatment females were exposed to naturally fluctuating temperatures, at which they could regulate body temperature through behavioral mechanisms. In the last treatment females were provided the chance to regulate body temperature in the laboratory thermal gradients ranging from18to60℃created by heating lights on a cycle of14light:10dark.The skink is a sexually dimorphic species, with adult females being larger than adult males in body size, but smaller than adult males in head size. for both juveniles and adults, males have larger heads (head length and head width) than do females of the same size. Parturition occurred between late June and early August, with females at higher temperatures giving birth to young earlier than did those at lower temperatures. The smallest reproductive female was67.4mm SVL, and all sexually mature female could produce a single litter per breeding season, with a litter size of3-11young. Litter size, litter mass and neonate mass varied from3to11(mean=5.8) offspring,0.47to5.34(mean=2.42) g and0.24to0.60(mean=0.43) g, respectively. Litter size determined by counting the number of yolked follicles and oviductal eggs outnumbered that determined by counting the number of neonates produced by0.6offspring. Litter size and litter mass were both positively correlated with maternal SVL. Litter size did not differ among treatments, whereas postpartum body mass, neonate mass and, thus, litter mass differed significantly among treatments, with females in the treatments of23and29°C producing smaller offspring. The trade-off between size and number of offspring was evident in all treatments, thus signifying that females with a relatively high fecundity tended to produce relatively small offspring. A principal component analysis resolved two components (eigenvalues>1) based on four size (SVL)-adjusted female reproductive traits, accounting for74.4%of variation in the original data. The first component (46.2%of variance explained) had high positive loading for SVL-free values of neonate size and litter mass, and the second component (2cS.2%of variance explained) had high positive loading for litter size. females under different thermal regimes differed significantly in their scores on the first and second axes.Offspring produced in different treatments differed in SVL, tail length, body wet mass, body dry mass, head length, head width, fore-limb length and hind-limb length. Offspring produce at23℃and29℃were smaller not only in SVL but also in fore-and hind-limb length than those offspring produced in the other treatments. A principal component analysis resolved two components (eigenvalues>1) from size-adjusted offspring traits, accounting for56.1%of variation in the original data. The first component (35.9%) of variance explained had high positive loading for offspring wet mass, and the second component (20.2%of variance explained) had high positive loading for fore-limb length and hind-limb length. Offspring under different thermal regimes differed significantly in their scores on the first and second axes. Gestation temperature significantly affected locomotor performance of offspring, with those from29℃exhibiting the worst performance in any examined trait (burst speed, the maximal length, and the number of stops in a single running trial).Females in all treatments produced a mix of sexes that didn’t differ from equality with one exception at24℃. The sex steroid concentration of blood presumably plays an important role in sex determination. Among litter comparison reveals a correlation of mean body mass between sons and daughters; that is, mothers producing larger sons also produced large daughters. This observation suggests that mothers can modify offspring phenotypes by selecting specific thermal regimes during pregnancy but exert no differential effects on sons versus daughters in this way. Gestation temperature did not affect the sexual phenotype of offspring but changes in mass and locomotor performance in the first45postpartum. When comparing locomotor performance of45-day offspring produced from the treatments of24℃,28℃and Ft, offspring from28℃exhibited the worst performance in any examined locomotor trait (burst speed, the maximal length, and the number of stops in a single running trial). Repeated measures ANOVA on0-day and45-day offspring revealed significant effects of gestation temperature on mass changes, with offspring from28℃and29℃growing more slowly than did those from the other treatments. Again, we did not detect differences in locomotor performance and early growth between sons and daughters.