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

Age structure and growth pattern of a high-altitude lizard population based on age determination by skeletochronology

Age determination provides crucial data regarding the life history of a species. Skeletochronology is considered to be a reliable method for age determination but is seldom applied to the genus Phrynocephalus (Agamidae) as it requires careful bone histological analysis to determine the formation of the lines of arrested growth (LAGs). We analyzed LAGs in different bones of Phrynocephalus vlangalii, a small, high-altitude lizard, and demonstrated that the phalanges are the best materials for skeletochronology in this species. We also found that the proximal half of the phalangeal diaphysis exhibits the most complete LAGs because of the unidirectional longitudinal growth of the phalange. Histologically, as the embryo bone that developed during the embryonic period was preserved even in very old individuals, no LAGs were eroded by endosteal resorption in the phalanges. The maximum age was 4 years for males and 5 years for females. It was determined that the age at maturity was 3 years for males and 2 or 3 years for females. On the basis of age determination, the age structures of both sexes were compared, and age-specific growth differences between the sexes were also analyzed. No differences in the snout-vent length were observed between sexes in any age group. However, the tail length of males aged 3 and above was significantly longer than that of females. Thus, the use of phalanges in the age determination of P. vlangalii is effective and can be widely applied to the ecological studies of this species as well as other small lizards.

Spatial patterns in the size of Chinese lizards are driven by multiple factors

BACKGROUND

For almost two centuries, ecologists have examined geographical patterns in the evolution of body size and the associated determinants. During that time, one of the most common patterns to have emerged is the increase in body size with increasing latitude (referred to as Bergmann's rule). Typically, this pattern is explained in terms of an evolutionary response that serves to minimize heat loss in colder climates, mostly in endotherms. In contrast, however, this rule rarely explains geographical patterns in the evolution of body size among ectotherms (e.g., reptiles).

LOCATION

China.

AIM

In this study, we assembled a dataset comprising the maximum sizes of 211 lizard species in China and examined the geographical patterns in body size evolution and its determinants. Specifically, we assessed the relationship between body size and climate among all lizard species and within four major groups at both assemblage and interspecific levels.

RESULTS

Although we found that the body size of Chinese lizards was larger in warmer regions, we established that at the assemblage level, size was correlated with multiple climatic factors, and that body size-climate correlations differed within the four major groups. Phylogenetic analysis at the species level revealed that no single climatic factor was associated with body size, with the exception of agamids, for which size was found to be positively correlated with temperature.

MAIN CONCLUSIONS

Geographical patterns in Chinese lizard body size are driven by multiple factors, and overall patterns are probably influenced by those of the major groups. We suggest that our analyses at two different levels may have contributed to the inconsistent results obtained in this study. Further studies investigating the effects of altitude and ecological factors are needed to gain a more comprehensive understanding of the evolution of ectotherm body size.