Life History Evolution Of Phrynocephalus Przewalskii

A central goal of evolutionary ecology is to explain why life history traits vary among populations and species. Reptiles have a broad diversity around the word and become an ideal model to study life history. Phrynocephalus przewalskii is a small oviparous sand lizard which is distributed widely in northern China and adjacent Mongolia. We studied the life history strategies of P. przewalskii associated with different habitat from several aspects, including habitat selection, morphology, reproduction, population ecology and molecular ecology.Parameters of selected and controlled habitat of P. przewalskii were analyzed. Habitat selection was similar between males and females, but differed among seasons or populations. Before breeding, P. przewalskii selected sites with lower cover of vegetation to achieve optimal body temperature. In order to recruit the energy used in reproduction and accumulate energy for overwinter, sites with high density and cover of grass were favored after breeding. Geographic variation mainly attributed to the balance of foraging and escaping.The diet of P. przewalskii was assessed from stomach contents. P. przewalskii is predatory carnivores that eat insects, mainly hemipterans and hymenopterans. Although the dietary overlap of males and females was almost complete, the prey composition and prey size was different. The habitat and prey selection was similar between males and females, so the diet separation may attribute to the difference of home range. Seasonal variation may rise from the seasonal variation of habitat selection and food availability. While geographic variation mainly attribute to the difference of food availability, especially the abundance of Lygaeidae and Culicidae.For juvenile P. przewalskii, no size difference was found between males and females in body characteristics. For adults, males are significantly larger than females in SVL, relative head size, relative limb length and tail length, however, relative trunk length exhibited female biased sexual size dimorphism (SSD). Neither niche separation hypothesis nor allometry can explain this SSD. Only males'tail length exhibits positive allometry which suggested that the tail length was under sexual selection. The growth rate of trunk length differs significantly between two sexes. So the SSD of P. przewalskii maight be the result of a balance of sexual selection and fecundity selection.The oldest lizard captured over the 3 years of study was 7 yr. Age distribution of all populations was standard pyramid. Sex ratio was female biased and varied among ages. The survivorship cure of P. przewalskii belongs to the typeâ…¢and the dead mainly occur during the first winter. The mortality of juveniles varied among populations while the adult mortality of different populations was similar. The different mortality of juveniles may attribute to the different rate of predation. The habitat difference especially the number of nest sites also affects the juvenile mortality. Life table analyses confirmed that all the populations, except Minqin, were in decline. This conclusion may be fallacious, because the migration was ignored in our analyses.The von bertalanffy model fitted the growth data best for all characteristics. The males and females differed in asymptotic size, but had similar specific growth rate. Age specific growth rate decreased with age for both males and females. Only the males of two years old grew faster than females of the same age. The difference of growth rate among ages and sexes may rise from the different energy allocation. Age specific growth rate also display geographic variation. The different food availability and population density may be the proximate reason for the variation.P. przewalskii have obvious breeding cycles:courtship occurs in April; ovulation occurs in mid to late spring; eggs are laid in late May to early September; Hatching occurs during early July to September. The reproductive cycle was affected by temperature and rainfall. Females laid one to six eggs per clutch, some individuals can produce two clutches per season. Female body size had positive effect on clutch size and clutch mass, but had no effect on egg mass and relative clutch mass. The negative correlation between fecundity and egg mass indicated that there was a trade off between offspring number and size. Juvenile mortality was correlated with relative egg mass, but no relationship between reproduction effort and female mortality was found.Reproductive traits varied significantly among populations: females from Alax Youqi produced relative more but smaller eggs, while females from Gantang produced little larger eggs; females from Alax Zuoqi invested more energy to per clutch, but females from Minqin invested more energy to per offspring. Our analysis indicated that females decrease investment per clutch in response to the increasing altitude or the decreasing rainfall, while increase the investment per offspring in response to the increasing density or decreasing food availabiliy.A gene tree derived from mtDNA sequence data was established. Our analyses indicate that Longshou-Heli and Helan-Yin mountain chain had significant impact on the distribution of this species. Comparition among different clades indicated that variarition of reproductive traits mainly attributed to local phenotype plasticity.