The Advantages Of Lizards' Fertility In The Warm Climate Area

Squamate reptiles (snakes, lizards and amphisbaenians) represent extremely promising animals for studies of viviparity. Viviparity has originated among squamates on over100separate occasions, more often than in all other vertebrates combined. The evolution of viviparty is regarded to be classical topic in the study of reptiles, and squamate reptiles are the ideal model animal. The selective advantages of viviparity includes:accelerated rates of embryonic development, reduced embryonic mortality, optimized offspring phenotype (and hence increased offspring fitness), freeing females from having to find suitable egg-laying sites and, in species with temperature-dependent sex determination, providing females the opportunity to select the sex of their offspring. Costs associated with viviparity include:increased maternal mortality, reduced locomotion performance, increased metabolic rates, and reduced fecundity and/or reproductive output. There are several hypotheses for the evolution of viviparity, of which three are coted most frequently:cold-climate hypothesis, predictability hypothesis, and maternal manipulation hypothesis. Most studies in this field have been conducted outside China, and a few in China.Female reptiles with viviparous reproduction should leave space for their eggs that reach the maximum mass and volume in the oviducts, so is the evolution of viviparity accompanied by a relative increase in maternal abdomen size, thus allowing viviparous females to increase the amount of space for eggs? To answer this question, we compared morphology and reproductive output between oviparous and viviparous species using three pairs of lizards of which each included two congeneric species with different reproductive modes. The two lizards in each pair differed morphologically, but were similar in the patterns of sexual dimorphism in abdomen and head sizes and the rates at which reproductive output increased with maternal body and abdomen sizes. Postpartum females were more heavy-bodied in viviparous species, suggesting that the strategy adopted by females to allocate energy towards competing demands differs between oviparous and viviparous species. Reproductive output was increased in one viviparous species, but was reduced in other two viviparous species, as compared with congeneric oviparous species. The space requirement for eggs did not differ between oviparous and viviparous females in one species pair, but was greater in viviparous females in other two pairs with greater values of relative clutch or litter mass. However, in no viviparous species did females increase reproductive output by increasing the relative size of the abdomen."We therefore conclude that the evolution of viviparity is not accompanied by a relative increase in maternal abdomen size in lizards.Fitness of an offspring is highly associated with its phenotype, which is affected by many external and internal factors. We compare offspring fitness between two congeneric lizards, Eutropis multifasciata and Eutropis longicaudata, from an area where they coexist. The two lizards differ morphologically in head size, a trait determining an individual’s foraging ability, with head size being larger the viviparous species than in the oviparous species. The two lizards did not differ locomotor performance, nor in the heart rate. Overall, in the area where the two lizards coexist, fitness of offspring is higher in the viviparous species than in the oviparous species.Maternal effects and environmental conditions embryos encounter during development have important toles in influencing an organism’s phenotype and can affect fitness in reptiles. Temperature is one of the most important factors inducing phenotypic variation and, as such, pregnant females often shift the setpoint of thermoregulation to level optimal for embryonic development. We assigned female Eutropis multifasciata to three different rooms with temperature set at22℃,25℃and28℃, observed daily activity of lizards, recorded surface temperatures of lizards with an infrared thermometers, and collected reproductive data. The results show that:(1) the activity level of a lizard is affected by background temperature to which it is exposed, with the activity level being negatively correlated with background temperature;(2) females are more active than males at the background temperature; and (3) offspring produced by females at25℃seem to be better that those produced by females at the other two lower or higher temperatures.We studied male and female reproductive cycles and reproductive output of a tropical viviparous skink, Eutropis multifasciata, from China. Females produced2-9offspring per litter. Parturition never occurred in the driest season (January and February), nor in the wettest season (September and October). Litter size, neonate mass and litter mass were all positively related to female body size, and year-to-year variation in these three variables was not significant. Testicular mass and volume, seminiferous tubule diameter and epithelial height in males, ovary mass and largest follicular volume in females, and plasma hormones (testosterone and17P-estradiol) in both sexes varied seasonally. Peak spermiogenesis was nearly in synchrony with maximal vitellogenic activity, but reproductive synchronicity among females was relatively low. The relationship between testicular size and rainfall was significant, whereas the relationship between testicular size and temperature was not. The relationship between vitellogenic activity and temperature was significant, so was the relationship between vitellogenic activity and rainfall. Rainfall explained a greater proportion of variation in vitellogenic activity than temperature. As for the climatic correlates of seasonal variation in plasma steroid hormones, we found only in males that the level of testosterone was negatively correlated with rainfall. Our data show that male and female reproductive activities are more tightly correlated with rainfall in E. multifasciata.There is an association between reproductive stage and plasma steroid hormone level in many species of lizards. Estrogens, such as17β-estradiol (E2), stimulate reproductive behaviors and vitellogenesis in females of some reptile species, and are expected to be elevated during these events. Androgens, such as testosterone (T), stimulate reproductive behaviors and spermatogenesis in male reptiles. We studied the relationship between temperature and steroid hormone in plasma and yolk. Female E. multifasciata were assigned to three rooms with temperature set at26,30,33℃, respectively. We collected blood and yolk samples. Though there is no different in plasma E2and T level among temperature treatments, the level of yolk steroid is influenced by temperature, with the steroid hormone level being lower in females assigned to the highest temperature. This result suggests that steroid hormone may be accumulated in the yolk, and plays a role in affecting embryonic development, and that females may have the potential to adjust yolk steroid hormone level by changing their body temperature.Viviparity has evolved in squamate reptiles in the relatively recent past and at low taxonomic levels, allowing us an opportunity to reconstruct the evolutionary transition towards this reproductive mode. It is important to study congeneric species with different reproductive modes to show the ecological and evolutionary significances of the evolution of reptilian viviparity. Here, I studied two congeneric lizards, E. multifasciata and E. longicaudata, from, an area where they coexist, with the aim to show morphological, life-history and physiological adjustments accompanied by the evolution of viviparity, and to offer empirical evidence for the selective advantages accruing from viviparity and mechanisms adopted by females to compensate for costs associated with this reproduce mode.