Ontogenetic changes in head scale symmetry in the pygmy bluetongue lizard

Abstract

ABSTRACTFluctuating asymmetry (FA, small and random deviations from perfect symmetry in otherwise bilaterally symmetrical traits) has been used as a monitoring tool for species at risk. Differences in the levels of FA in a trait are attributed to the different levels of environmental or genetic stressors during the developmental phase of an organism. In this study, we used a symmetry index (SI) in the head scales of the endangered pygmy bluetongue lizard, Tiliqua adelaidensis, to investigate the relationship between the SI and jaw width (JW) (as an indirect measure of fitness) among lizards from different age classes (neonate, subadult and adult) to shed light on the ontogeny of symmetry. Also, we explored changes in the levels of symmetry among different age classes to determine possible selection processes. Our findings showed that there was a positive relationship between the SI and JW in neonates (individuals with larger jaws were more symmetric) whereas the trend was reversed in adults (individuals with larger jaws were less symmetric). The relationship was not significant in subadults. This confirms that a transition happened during the growth of lizards. We suggest this resulted from adults allocating more resources to the growth rather than symmetry of head scales. We found no significant differences in the mean SI between adults and neonates, although subadults showed significantly higher values of the SI. This study has revealed some valuable insights into ontogenetic changes in symmetry of head scales in pygmy bluetongue lizards, but it did not provide any evidence that survival from neonate to adult is influenced by head scale symmetry.