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

ABSTRACT: 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. This study explores the validity of Bergmann's rule and Allen's rule in Phrynocephalus przewalskii, a small sand lizard prevalent in the deserts of northern China. Analysis of correlations between climatic factors and body size enabled us to conclude that body size trends were mainly caused by plasticity of growth rates, whereas appendage size trends were due to heat balance in females. We believe that our study makes a significant contribution to literature because we have shown that age should be considered, along with general body size, when testing biogeographic rules; we also recommend the use of temperature instead of latitude or altitude in such studies.

SUBMITTER: Zhao W 

PROVIDER: S-EPMC7771167 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature