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

Abstract

Diversifications often proceed along highly conserved, evolutionary trajectories. These patterns of covariation arise in ontogeny, which raises the possibility that adaptive morphologies are biased towards trait covariations that resemble growth trajectories. Here, we test this prediction in the diverse clade of Anolis lizards by investigating 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 Anolis species. Our results demonstrate that species differences in relative limb length are established already at hatching, and are resulting from both differential growth and differential sizes of cartilaginous anlagen. Multivariate analysis revealed that Antillean Anolis share a common ontogenetic allometry 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 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 to be the result of modifications that manifest at the earliest stages of limb development.

Diversification of the Ruminant Skull Along an Evolutionary Line of Least Resistance

“…This study builds on a growing body of literature showcasing the profound macroevolutionary implications that ontogenetic allometric patterns may have (e.g., Watanabe 2018, Feiner et al 2021, Navalón et al 2021, Fabbri et al 2021, Chatterji et al 2022, Pavón-Vázquez et al 2022). The findings presented here suggest that morphological diversification of the ruminant skull proceeded along an evolutionary line of least resistance defined by allometry (CREA), and that the eccentricity of population-level variation acted as a facilitator to morphological diversification in that direction because this direction of variation confers adaptive value.…”

Detecting (non)parallel evolution in multidimensional spaces: angles, correlations and eigenanalysis

“…A variety of toolkit exists for analysing evolutionary or developmental trajectories in multidimensional spaces. One useful concept is the allometric space [12][13][14][15][16], where variation among multivariate allometric axes (typically principal component (PC) vectors; [17][18][19][20][21]) can be visualized and analysed in various ways by treating empirical allometric axes as observations [22][23][24][25][26][27][28][29]. Another broadly employed tool is the phenotypic trajectory analysis [3,[30][31][32], which primarily concerns quantification and statistical testing of inter-population differences in the magnitude, direction and shape of phenotypic trajectories.…”

Beyond facial width-to-height ratios: bizygomatic width is highly sexually dimorphic when adjusting for allometry

“…Facial morphology is defined by complex interactions among suites of correlated traits [4]. This scaling relationship between the size of a morphological feature and overall body size is termed allometry, routinely captured using principal components analyses (PCAs) [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The resultant components of major morphological variation represent allometry, often simply termed size [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and recent research has recommended that these size measurements should be modelled as covariates to adjust for allometry rather than using a ratio method [26].…”

“…This scaling relationship between the size of a morphological feature and overall body size is termed allometry, routinely captured using principal components analyses (PCAs) [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The resultant components of major morphological variation represent allometry, often simply termed size [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and recent research has recommended that these size measurements should be modelled as covariates to adjust for allometry rather than using a ratio method [26]. It is important to account for allometric effects in facial morphology research because it otherwise remains unknown whether the morphological feature is merely a by-product of an overarching developmental system responsible for the combined growth of all morphological features [9].…”