Skeletochronology and mark–recapture assessments of growth in the North African agamid lizard (Agama impalearis)

Abstract

Patterns of growth were studied between 1993 and 1996 in a population of Bibron's agama Agama impalearis from an arid area in the central Jbilet Mountains, western Morocco. Non-linear regressions were used to model snout–vent lengths (SVL) and body masses of individuals caught during 1993–94 against skeletochronology age estimates. The overlap between male and female asymptotic SVLs (A) was negligible demonstrating sexual dimorphism, although there was no evidence of differences in characteristic growth rates (k) between sexes (males: A = 119.43 ± 2.29 mm and k = 0.849 ± 0.09 [month^-1], females: A = 108.59 ± 3.19 mm and k = 1.079 ± 0.162 [month^-1]). Asymptotic body mass differed substantially between sexes (males: 71.2 ± 3.1 g, females: 45.8 ± 4.2 g), but corresponding characteristic growth rates were similar (0.753 ± 0.339 and 0.789 ± 0.623 [month^-1], respectively). The mark–recapture method provided generally higher and more reliable asymptotic size estimates (using the logistic-by-length non-linear regression model) than the skeletochronology-based estimates. Growth parameters were also estimated on an individual year basis. Only male characteristic growth rate showed a significant year-to-year variation (0.010 ± 0.006 to 0.024 ± 0.007 [day^-1]), although this may have been due to a lack of statistical power. Annual variation in the absolute growth rate was detected only in hatchlings (0.087 ± 0.018 to 0.273 ± 0.132 mm.day^-1) and adult males (0.089 ± 0.030 to 0.206 ± 0.100 mm.day^-1).