Estimating asymptotic body size and testing geographic variation in Agama impalearis

Methods for estimating 'typical' asymptotic body size in populations of the North African agamid Agama impalearis is using individuals of undetermined age were investigated, and the pattern of geographic variation in this cha racteristic described and tested against simple models based on putative ca uses. Resampling of a large single-site data set indicated that use of the sample mean led to substantial underestimation of asymptotic size while use of the largest animal per sample led to overestimation, on average. The 80 th percentile provided the most accurate estimate of asymptotic size and, c ompared with the largest individual per sample, had low variance, showed lo w dependence on sample size and was amenable to bootstrap estimation of con fidence intervals. A clear pattern of geographic variation in asymptotic si ze was evident across Morocco: animals were smallest in the north and east and largest in the southwest. This pattern was discordant with previously-d escribed patterns of variation in scalation and size-free body dimensions a nd, unlike these characteristics, could not be explained by a model based o n secondary contact of previously vicariant populations. Among-site differe ntiation was strongly associated with a model based on a proxy of current p otential gene flow between sites, supporting an alternative in situ differe ntiation hypothesis based on the combined effects of isolation-by-distance and the dispersal barrier provided by the higher parts of the Atlas mountai n range. Possible reasons for the discordance between the pattern of variat ion in body size and other morphological characteristics are discussed.