Reproductive Output And Effects Of Incubation Thermal Environments On Hatchling Phenotypes Of Three Species Of Oviparous Snakes

The reproductive output and effects of incubation thermal environments on hatchling phenotypes of three species of oviparous snakes(Ptyas korros, Elaphe bimaculata and Dinodon rufozonatum) were reported.We collected gravid gray rat snakes P. korros from three geographically distinct populations in China, Chenzhou (CZ), Jiangshan (JS) and Dinghai (DH), to study geographical variation in female reproductive traits. Egg-laying dates differed among the three populations such that at the most northern latitude egg-laying was latest, and earliest at the most southern latitutde. Clutch size, clutch mass, egg mass, egg shape, within clutch variability in egg sizes and relative clutch mass differed among the three populations, whereas post-oviposition body mass did not. Except for egg-laying date, none of the traits examined varied in a geographically continuous trend. CZ and DH females, although separated by a distance of approximately1100km as the crow flies, were similar in nearly all traits examined. JS females were distinguished from CZ and DH females by their higher fecundity (clutch size), greater reproductive output (clutch mass) and more rounded eggs. Our data do not validate the prediction that larger offspring should be produced in colder localities. The absence of an egg size-number trade-off in each of the three populations presumably suggests that P. korros is among species where eggs are well optimized for size within a population.The Chinese cornsnakes (E. bimaculata) were collected from Siyang, Jiangsu, to study the reproductive output and the impact of constant incubation temperature on hatchling phenotypic traits. The ovipisition date was from late July to middle August. Clutch size was independent from maternal body length, while clutch mass and egg mass" were positively correlated with maternal body length. The range of embryo stage was from26to27. Eggs were incubated under three constant temperatures (24,27and30℃), with mean incubation period being44.0,40.0and31.3days respectively. There were no significant difference in hatching success, wet mass and head width among the three temperature treatments. The snout-vent length, tail length and head length of hatchlings from24and27℃were larger than those from30℃treatment, processing of all larval morphological characteristics were not significant differences. All of the examined traits of hatchlings from24and27℃did not differ from each other. There was no significant difference in swimming speed among all the three temperatures.We incubated the eggs of E. bimaculata at three constant temperatures (24,27and30℃) to study the effect of incubation temperature on hatchlings'metabolism and behavior. All hatchlings were used to evaluate the response to chemical cues, respiration metabolism and sex determination. Because physiological and behavioral performances are highly sensitive to variation in body temperature in reptiles, we conducted all trials at the body temperature of28℃. This was achieved by placing hatchlings in an incubator at the test temperature for approximately1h prior to the test. We presented a cotton-tipped applicator soaked with cologne water to the lip of hatchlings and recorded tongue flicks for1min. Tongue flicking was measured because many reptiles flick their tongues frequently to detect both predators and prey and to gather information about other members of their own species. This behavioral character is therefore a potentially important indicator of fitness. Selected body temperature was examined in a100x60x60cm terrarium covered with sand, sward and pieces of clay tiles. The terrarium was placed in constant temperature rooms where the temperature was set at24℃. One light bulb (200W) suspended above one end created a thermal gradient ranging from room temperature to50℃for12h daily, and lights were switched on at0700h. Snakes were moved from the cool side into the terrarium at1000h and,24h later, they were measured for body temperature (cloacal temperature, Tb) at1300h using a UT-325electronic thermometer (made in Taiwan) individually, which had an external thermal probe and was previously calibrated with a standard thermometer. Great care was taken to avoid heat transfer occurring between hands and the measuring snake. Hereafter, we continuously measured the temperature of hatchling snakes for three days. Our results reveal that there were no significant differences in the effects of incubation temperature (24-30℃) on hatchlings'tongue flicks, selected body temperature, respiration metabolism and the initial feeding in E. bimaculata. The amount of carbon dioxide was decreased with the increase of age from nativity to residual yolk, and the amount of carbon dioxide decreased to minimum value when the hatchlings'residual yolk was absolutely exhausted. The amount of carbon dioxide breathed out by hatchlings incubated at24,27and30℃was10.58,12.06and10.88μL/min respectively. Influences. of incubation temperatures on hatchling initial feeding was negligible; the weight of preys were4.92,4.34and3.60g and the proportion of predation was46.2%,56.3%and40%by hatchlings incubated at24,27and30℃respectively. Our results reveal that the effects of incubation temperature (24-30℃) on hatchlings behavior and feeding are not significant in E. bimaculata. E. bimaculata fit to live in this temperature range.The red-banded snakes (D. rufozonatum) were collected from Xiaoshan, Zhejiang to study their reproductive output and effect of fluctuating incubation temperatures on hatchling phenotype. The ovipisition date was from middle July to late August. Clutch size and clutch mass were positively correlated with maternal snout-vent length, while egg mass was not. The range of embryo stage of new born egg was from25to27. Eggs of the D. rufozonatum were incubated at one of the four temperature regimes (27,27±3and27±5℃). Eggs were incubated under three constant temperatures (24,27and30℃), with an interval of3h of fluctuated incubation temperature to detect the effect of variance and interval of fluctuated incubation temperature on hatchling phenotypic traits. Results from the present study showed that the interval of fluctuated incubation temperature did not influence the examined traits. Therefore, data from the same variance treatments were blocked. The incubation period differed significantly among the three thermal treatments, with longest incubation period in27±5℃treatment, shortest in constant temperature, with27±3℃treatment in between. The snout-vent length and tail length of hatchlings from27±5℃treatment were smaller than those from other two thermal treatments.