Reproductive Ecology Of Chinese Softshell Turtle(Pelodiscus Sinensis)

Chinese soft-shelled turtle(Pelodiscus sinensis)is widely distributed in East Asia,from the Amur and Ussuri Rivers in the far East of Russia through Korea,Japan,and eastern,central,and southern China to southern Vietnam.The research on this species mainly focused on morphological classification,cytology,physiology and breeding.However,the reproduction of this species in the field has not been reported.In recent decades,overfishing,habitat loss and pollution have resulted in drastic reductions in the wild population of this species.Reproduction plays an important role in the life history.The study of reproduction helps to understand the life-history strategies of species and"trade-offs"and is of great significance to species developmental biology,evolutionary biology and conservation biology.The research on the reproductive ecology of the wild population of P.sinensis will fill in the blank of this species which has the widest distribution and the largest population in China and provide the basic data for its wild resource protection.This study,carried out between April 2017 and September 2018,investigated the reproductive ecology of P.sinensis in the natural habitats of the Yellow River at Dali County,Shaanxi Province,northwestern China.The nest site selection,nesting behavior,hatching and nest,egg and hatching characteristics of this species were revealed and the main results were as follows:Nesting season and nesting behaviors:18 gravid female turtles were tracked from April2017 to September 2018(10 in 2017,8 in 2018)and 11 nest sites were located.P.sinensis nested during the day from May to August.However,none of individuals showed during the time duration of 02:00-08:00 and 12:00-18:00 of a day.The whole nesting spent 29.2min(n=7)including 16.9min of chamber excavation(n=7),6.4min of egg laying(n=11),5.9min of filling and covering(n=11).Nest site selection and nest characteristics:P.sinensis nested on the wetland along the Yellow River and fish ponds along the tributaries in the study area.The nest sites on wetlands and fish ponds were all located on upslope,close to water(wetlands with 6.70±2.49m,n=8;fish ponds with 3.03±1.99m,n=3),high above water(wetlands with 1.05±0.19m,n=8;fish ponds with 1.00±0.10m,n=3),low vegetation coverage(wetlands with 3.13±4.58%,n=8;fish ponds with 6.67±11.55%,n=3)and height(wetlands with 10.63±3.96cm,n=8;fish ponds with 8.33±7.64cm,n=3).However,there was significant difference in vegetation density(P=0.017)between two areas.When nested on the wetland,females preferred more vegetation density P.sinensis(wetlands with 50.00±16.04 plants/m~2,n=8;fish pond with18.33±16.07 plants/m~2,n=3).It was difficult to distinguish where the nests of P.sinensis from their surroundings.The shape of the nests'entrance was irregular.The internal space was spacious and roughly elliptical with an inclination angle of about 30°.The inclination direction was consistent with the head direction of the females when nesting.The mean measurements of nests were as follows:longitudinal depth,10.45±1.72cm;oblique depth,13.40±2.53cm;width,5.75±0.53cm(n=6).Egg,incubation and hatching characteristics:The eggs were pure white and spherical.The mean clutch size was 17.8±6.0 ranged from 10 to 31(n=11).The mean measurements of eggs were as follows:fertilization,92.89%;egg mass,4.38±0.81g;egg length,19.53±1.22mm;egg width,19.50±1.26mm(n=196).Turtle body size showed significant positive correlation with egg mass,egg length and egg width,while no correlation with clutch size was found.The incubation period was 54.8±7.8d with the mean temperature during incubation was 28.5?and hatching rate of 66.38%(n=8).Hatchlings all emerged at night.Bodies of the newly born hatchlings were bent to the same degree as that of the round eggs with folded carapaces.Their bodies would slowly straighten out after 24 hours.Hatchlings'carapaces were light yellow or dark black with tubercles widely distributed on them.Plastrons were oval yellow with large black patches,and the bottom of plastron was connected with yolk.There were two vertical black stripes across the eyes and connected between the eyes by a horizontal stripe.White speckles in the shape of dots and stripes were distributed under jaw and both sides of the neck.If felt danger in the water searching process,they would drill into the soil to protect themselves.The mean measurements of straightened hatchlings were as follows:body mass,7.2±0.4g;carapace length,25.48±1.79mm;carapace width,24.42±1.95mm and body height,8.63±0.94mm(n=32).