Geographical Patterns Of Variation In Life-history Traits And Genetic Structure Of The Northern Grass Lizard, Takydromus Septentrionalis

The northern grass lizard (Takydromus septentrionalis) is an oviparous lacertid lizard that is endemic to China and widely distributed in southeastern part of the country. Lizards collected in April of 2005-2006 from ten geographically separated populations were used to study (1) geographic patterns of variation in life-history traits, (2) the potential causes for geographic variation in female reproduction, and (3) the effects of incubation thermal conditions on egg incubation and resultant hatchlings.Females were allowed to lay eggs in laboratory enclosures of which each held individuals from the same population, without constraints from food availability on reproduction. Oviposition occurred between late April and late August, with females from the high latitudinal (and thus, cool) populations laying eggs earlier than did those from the low latitudinal (and thus, warm) populations. The embryonic stage [Stage 21-27, in the Dufaure and Hubert's (1961) developmental series] at oviposition differed significantly among populations. Eggs were incubated under three temperature regimes [one constant (28℃) and two variable with different sequence of temperatures: first cold (24℃) and then hot (32℃), and vice versa] to assess the effects of incubation temperature on hatching success, incubation length and morphological phenotypes of hatchlings.Takydromus septentrinalis is among lizard species where adults of both sexes are monomorphic in body size but sexually dimorphic in head size and abdomen length, with males being larger in head size and females being larger in abdomen length in all sampled populations. Body mass, body size (SVL, snout-vent length) and head size (head length and head width) differ significantly among populations, but no clear-cut geographic patterns of variation in these morphological traits can be detected in this species. Egg size (clutch mean egg mass), clutch size and clutch mass were positively correlated with female SVL in all sampled populations. Geographic variation in these three life-history variables was very pronounced, with females from the low latitudinal populations laying more but smaller eggs and investing a relatively small amount of resources in single reproductive events than did those from the high latitudinal populations. Geographic variation in egg size, clutch size and clutch mass was evident even when removing the influence of variation in female size, thus signifying that differences in the involved traits are at least partly determined genetically.Eggs incubated under different thermal conditions differed considerably in incubation length, with the mean vaule being shortest in the CT treatment and longest in the CF treatment. Incubation length differed significantly among populations, with eggs from the Liuan and Chuzhou populations hatching earlier than did those from the Guiyang and Xiushan populations. Hatching success was higher in the CT treatment and lower in the CF treatment, with one exception of eggs from the Chenzhou population.Hatchlings differed among populations in size and morphology. Hatchlings from higher latitudinal populations (Qinling, Liuan and Chuzhou) were larger than those from low latitudinal populations, primarily because of their larger egg sizes. Among population differences in hatchling morphology were evident even when removing the influence of variation in hatchling size. The three incuation thermal conditions involved in this study exerted nearly no differential effects on morphological phenotypes of hatchlings, partly because the three treatments did not differ in mean temperature.A total of 329 lizards from the 24 mainlan and island (Zhoushan Islands) populations were used to study intra-specific genetic variation. Of the 1143 bps of the mitochondrial Cyt b gene full length sequenced, 194 variation loci and 74 mitotypes were identified. Within the distributional range of the lizard, the phylogeographic structure is more evident in the central and western populations than in the others. What can be inferred from the phylogenetic relationship and separation history of Zhoushan Islands is that the foundation of T. septentrionalis in Zhoushan Islands presumably occured 20000-10000 years ago, with at least two genetically distinct source populations.