A highly conserved ontogenetic limb allometry and its evolutionary significance in the adaptive radiation of Anolis lizards

A key characteristic of adaptive radiations is the diversification into ecologically specialized morphologies. However, comparative morphology indicates that diversifications often proceed along narrow, and phylogenetically highly conserved, evolutionary trajectories. These patterns of covariation between characters arise in ontogeny, raising the possibility that adaptive morphologies might be biased towards trait covariation that resemble growth trajectories. Anolis lizards are an excellent system to test this prediction since they have repeatedly evolved highly specialized locomotor morphologies. Here, we investigate the covariation of embryonic growth of 13 fore- and hindlimb bones in 15 species, and compare these to the evolutionary covariation of these limb bones across 267 species of the entire Anolis clade. Our results demonstrate that species differences in relative limb length are established already at the time of hatching, and are the result of differential growth as well as differential sizes of cartilaginous anlagen. Multivariate analysis of limb bones revealed that Antillean Anolis share a common allometric pattern that is characterized by positive allometric growth of the long bones relative to metapodial and phalangeal bones. This major axis of ontogenetic allometry in limb bones deviated from the major axis of evolutionary allometry of the Antillean Anolis, and was equally disparate to the evolutionary allometries of the two clades of mainland Anolis lizards. These results demonstrate that the remarkable diversification of locomotor specialists in Anolis lizards are accessible through changes that are largely independent from ontogenetic growth trajectories, and therefore likely the result of genetic modifications that manifest at the earliest stages of limb development.Funding provided by: John Templeton FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000925Award Number: 60501Funding provided by: Royal Physiographic Society*Crossref Funder Registry ID: Award Number: NAFunding provided by: Wenner-Gren StiftelsernaCrossref Funder Registry ID: http://dx.doi.org/10.13039/100014437Award Number: NAFunding provided by: Royal Physiographic SocietyCrossref Funder Registry ID:See details in manuscript