Age and annual growth rate cause spatial variation in body size in Phrynocephalus przewalskii (Agamid)

Abstract

Whether or not biogeographic rules dealing with spatial patterns of animal body sizes are valid for ectotherms is controversial. As the ectotherms grow all their lives, we explored the role of age and annual growth rate in body size variation in Phrynocephalus przewalskii in northern China. Morphological data were collected from 11 populations across a broad geographic gradient. Correlations between age, sex, climatic factors, and body size were analyzed using generalized linear model (GLM) and generalized linear mixed model (GLMM). GLM analysis indicated that the general body size of both sexes and the appendage size of females increased significantly with increasing temperature; however, the coefficient of determination was very small. GLMM analysis indicated that body size only correlated with age, whereas appendage size was affected by age, temperature, rainfall, and sunshine. Annual growth rates were positively correlated with temperature. We concluded that body size variation was mainly caused by age structure and plasticity of the growth rate in P. przewalskii and did not follow Bergmann's rule; however, females followed Allen's rule. Future studies to investigate the effect of energy restriction are needed to further understand the relationship between growth rate and body size. We also suggest that further studies on thermal advantage and sexual selection may be helpful to understand appendage size variation in P. przewalskii.

Keywords: Allen's rule; Bergmann's rule; Phrynocephalus przewalskii; age; annual growth rate; temperature.

FIGURE 1

Sampling sites ofPhrynocephalus przewalskii.SD = Shandan, SYQ = Sonid Youqi, UQQ = Urad Qianqi, EHT = Erenhot, UB = Uxin Banner, XSW = Xiangshawan, GT = Gantang, AYQ = Alxa Youqi, MQ = Minqin, AZQ = Alxa Zuoqi, QPJ = Qipanjing. The elevation gradient is represented by graduated color, from green to brown (low to high). The map was downloaded from Earth Resources Observatory and Science (EROS) Center (http://eros.usgs.gov/ #)

FIGURE 2

The correlation between general body size ofPhrynocephalus przewalskiiand temperature, for males and females, respectively. A single axis (PC_BS) used from the principal component analysis on log₁₀SVL, log₁₀BW, log₁₀HL, and log₁₀HW was general body size. The black squares and black lines represent males, while the red circles and red lines represent females. PC_BS is shown as mean ± SE

FIGURE 3

The correlation between appendage size ofPhrynocephalus przewalskiiand temperature, for males and females, respectively. A single axis (PC_AS) used from the principal component analysis on log₁₀TL, log₁₀FL, and log₁₀LL was general body size. The black squares and black lines represent males, while the red circles and red lines represent females. PC_AS is shown as mean ± SE

FIGURE 4

The geographic variation of mean age inPhrynocephalus przewalskii. The black squares and black lines represent males, while the red circles and red lines represent females. Mean age is shown as mean ± SE

FIGURE 5

The correlation between annual growth rate ofPhrynocephalus przewalskiiand temperature, for males and females, respectively. The black squares and black lines represent males, while the red circles and red lines represent females. The annual growth rate is shown as mean ± SE