The limits of the energetical perspective: life-history decisions in lizard growth

The study of energy allocation is essential in understanding the regulation of major life history traits. It is often assumed automatically that the limitation of an energy budget or higher allocation to a single trait affect all life history traits. This assumption was inherently included in influential models of ontogenetic growth. We aim to challenge this perspective by focusing on growth in lizards. Summarizing the results of a series of long-term manipulative experiments in the Madagascar ground gecko (Paroedura picta), we show that although growth is generally assumed to be highly plastic in reptiles and other ectothermic vertebrates, it is at least in this species largely canalized and does not seem to be affected by energy limitations under several experimental conditions. Diet restriction, resulting in lower allocation to fat storage and reproduction, and the allocation to energetically demanding traits such as reproduction in both sexes and tail regeneration had little if any effect on structural growth. We document that sexual size dimorphism does not emerge in the ontogeny of the studied species directly due to differential allocation to structural growth in males and females. Instead, sex-specific growth trajectories are driven by a signaling of ovarian hormones as the key proximate mechanism shaping sex-specific allocation decisions during ontogeny. We suggest that the large degree of canalization of the structural growth can reflect hierarchy in energy allocation with the structural growth being prioritized to investment in other traits. The prioritized allocation to structural growth can reflect selective advantage of reaching a final, optimal size for a given sex as fast as possible.