Age-determination in the tropical agamid garden lizard, Calotes versicolor (Daudin), based on bone histology

Abstract

Male garden lizards showed excellent positive correlations between body weight and S-V length; body weight and tail girth; and body weight and gonad weight, suggesting the utility of these parameters as indirect markers of chronological age. However, the reliability of such morphometric data needed rapport from a more accurate method of bone histology based on the techniques of ‘skeletochronology’. Cross-sections of diaphyses of the humerus and femur of bones lizards of a complete age series revealed that while in young, immature and sexually mature lizards who have not yet completed a year in the wild there are no distinct annulations, the representative of fully mature and old lizards exhibited an alternation of thinner and thicker annulations arranged concentrically. Cross-sections of phalanges of old lizards also showed agreement with the annulations in diaphysis. The thinner annulations (LAC), corresponding with the period of slow growth, as in temperate species of lizards, were haemotoxylinophilic (chromophilic) and showed yearly growth patterns, their number representing the age of the lizards in years. Transverse sections of humeral epiphysis of old lizards exhibited, in contrast to the cartilaginous nature of young immature lizards, an almost complete calcification and bony union, suggesting a limitation of further growth. Thus, based on the recurrence of growth lines (LAC) in the diaphysis of long bones and in the phalanges, it is possible as in temperate species of lizards and turtles, to determine accurately the age of individuals belonging to a wild population of tropical lizards.