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

Patterns of growth were studied between 1993 and 1996 in a population of Bi bron's agama Agama impalearis from an arid area in the central Jbilet Mount ains, 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 asymp totic SVLs(A) was negligible demonstrating sexual dimorphism, although ther e 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)], fem ales: 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-recaptur e method provided generally higher and more reliable asymptotic size estima tes (using the logistic-by-length nonlinear regression model) than the skel etochronology-based estimates. Growth parameters were also estimated on an individual year basis. Only male characteristic growth rate showed a signif icant year-to-year variation (0.010+/-0.006 to 0.024+/-0.007 [day(-1)]), al though this may have been due to a lack of statistical power. Annual variat ion 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 mnn.day(-1)).