Life History Evolution Of Phrynocephalus(Agamidae)Along Altitudinal Gradients On Tibetan Plateau

Being ectothermic species, reptile (especially the lizards and snakes) life history traits are highly dependent on habitat conditions, thus exhibiting many life history variations induced by environmental factor. Therefore, they are favored by ecologjsts. Reptile life history traits often exhibit both interspecific and intraspecific variations, and elevation and related environmental factors contribute largely to the geographical variation. The geographical environment on Tibetan Plateau is unique, and there have great elevation drop and various habitat environments, which have contributions to current particular species distribution and diversity. Thus, it provided an ideal place for evolutionary biology studies. In this study, we chose seven populations belonging to four species of Phynocephalus (P. putjatia, P. vlangalii, P. guinanensis and P. erythrurus), which distributed in different altitudes, as object to study the life history traits variation and evolution in different altitudes from several aspects, including morphology, population ecology, reproductive ecology and molecular ecology. We intended to explore the life history variations of lizards from different altitudes and verify whether these variation trends conform to the known rules of biogeography, and to identify the sources of variation in life history.There are many differences in morphological traits were found between male and female in the four species. For adults, females have larger SVL and abdomen length than males, while males have larger tail length, relative head size and limb length in all the four Phrynocephalus. Relative head sizes are different in female between juveniles and adults, and adult female have smaller relative head size than juveniles, indicating that the development of female head is slow down after sexual maturity. The sexual size dimorphism (SSD) of these four Phynocephalus may be the result of a balance of sexual selection and fecundity selection, and also may be caused by the trade-off of energy allocation in vivo of lizards.Body size decreased with the increasing of altitude among species, which follows the converse to Bergmann’s rule. The species at higher altitude with smaller body size is adaptive evolution on the environment and controled by the phylogeny. Under the condition of low temperature and hypoxia, the temperature maintenance and energy metabolism of lizard are under restrictions and energy for growth may relatively less, which make lizards evolve into smaller size. However, the higher altitude species had relative smaller tail length and head size which match the Allen’s rule. Smaller appendages have smaller superficial area that would be conducive for lizard to make full use of the environment temperature and reduce energy consumption to keep the relatively constant temperature of body. The difference in male and female size among species allows rejection of Rensch’s rule.Within P. putjatia and P. vlangalii, lizards from high altitude have larger body size than those from low altitude, which follows Bergmann’s rule and may be the results of the differences in newborn body size and sexual maturely size among populations. The intraspecific difference may be under the influence of environment. Lizards from high altitude population have smaller tail length, head size and limb length, which follows Allen’s rule. There is no difference in the relative abdomen length of male among altitudes. However, females from high altitude have larger relative abdomen length in P. vlangalii, but have smaller relative abdomen length in P. putjatia, than those from low altitude. The difference in abdomen length among populations may affect offspring size.The caudal vertebra number of Phrynocephalus has no difference between the genders, and has no significant correlation with body size, which indicated that the caudal vertebra number of Phrynocephalus is fixed after birth, and would not change with the increasing of body size. So this phenomenon could not be explained by the Jordan’s rule. The variation of caudal vertebra number may be affected by genetic and phylogenetic factors, as well as temperature.Skeletochronology analysis showed that the oldest age of reproductive individual in the four Phrynocephalus was6yr (experience six hibernation). Body size was almost the same between the genders before2yr; however, the difference arisen at3yr. Females grew faster than males from2yr to3yr (before sexual maturity), and the other age stages have the same growth rate between the genders. The growth rate also differed among populations/species. The variation of growth rate may caused by the difference of energy allocation in the process of growth and reproduction. Within P. vlangalii and P. putjatia, the age at sexual maturity of lizards from low altitude was2yr and younger than that from high altitude (3yr). And the age at sexual maturity of P. guinanensis and P. erythrurus were3yr.3yr and4yr were the predominant age of females participated in reproduction.3yr females dominate at low altitude and4yr females dominate at high altitude. These differences may be related to the variation of environmental temperature at different altitudes.Females gave birth between29June and7September, and the birth dates of females from lower elevation were earlier than those from higher elevation. Within species, females from the higher elevation had larger SVL at sexual maturity and mean SVL. Female size and age have positive effect on litter size, litter mass and offspring size in three Phrynocephalus except for P. erythrurus. Newly born offspring have no gender-bending, and the sex ratios have no difference among years.Reproductive traits varied significantly among populations and species. Reproductive traits were correlated with elevation. Females from the higher elevation localities had a lower RLM than those from the lower elevations. In P. vlangalii, females from the high elevation produced fewer and larger offspring. However, in P. putjatia, females from the high elevation produced fewer and smaller offspring. Trade-offs between offspring size and number were detected in P. putjatia, P. vlangalii and P. guinanensis, but not in P. erythrurus.The genetic diversity varied among populations and species. MtDNA (ND2) genetic diversity was higher than nuclear DNA (RAG1). The genetic diversity of Phrynocephalus may be affected by environmental factors and the migration of population. ND2and RAG1data were used to establish cladogram tree. ND2tree revealed three clades, and the haplotypes from GN and DTH were in the clade of P. putjatia. The genetic distance among GN, DTH and other P. putjatia populations were smaller than that between species, which indicated that lizards from DTH and GN are P. putjatia, and P. guinanensis is not a species. The pattern of RAG1tree is not clear. A haplotype from DTH and some haplotypes from DLH mixed in a clade, indicating that the ancestors of P. putjatia and P. vlangalii might have hybridization. Hence, it is make sense that lizards from DTH have similar life history traits with P. vlangalii.Life history phylogenetic comparative analysis suggested that phylogeny had large effect on the interspecific variation of morphological characteristics and offspring size, and had little effect on total reproductive investment (litter size, litter mass and RLM), which may also affected by environmental factors. Phylogeny had little effect on the intraspecific variation of life history, indicating that the intraspecific variation of life history may mainly affected by environmental factors.In summary, the variation of environmental factors along elevation, which caused by the uplift of the Tibetan Plateau, may be the main force behind the variation and evolution of life history.