Abstract
Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world’s largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs) and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species.
Highlights
Somatic growth patterns represent a major component of an organism’s life-history [1,2,3]
Males and 122 individuals of unknown sex predominantly spanning the post-arboreal phase from,28–157 cm snout-ventlength (SVL), with $54% of dragons recaptured during multiple annual sampling periods
The use of mixed-effects models incorporating individual ID as a random variable allowed for repeated measures so all recapture events greater than six months were used in the analysis
Summary
Somatic growth patterns represent a major component of an organism’s life-history [1,2,3]. Age-specific body size and growth rates represent complex organismal trade-offs reflecting energy allocation partitioned among growth, maintenance, storage and reproduction, so as to maximise fitness [4,5,6]. Perhaps the most vital implication of growth is its effect on maximal body size, which influences competitive ability [10], survival [11,12], and fecundity [13]. Sex-specific growth variation must occur to result in sexual size dimorphism (SSD), reflecting different tactics and requirements for energy acquisition and investment between maximum female and male body size [14,15]. For size-dimorphic species in which males are larger, female growth rate must asymptote at a smaller size than males due to selection prioritizing reproductive investment at the expense of further growth [14]
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