Geometric Morphometric Assessment of Toe Shape in Forest and Urban Lizards Following Hurricane Disturbances

Abstract

Evidence suggests that hurricanes can influence the evolution of organisms, with phenotypic traits involved in adhesion, such as the toepads of arboreal lizards, being particularly susceptible to natural selection during strong storms. To investigate this idea, we quantified trait variation before and after Hurricanes Irma and Maria (2017) in forest and urban populations of the Puerto Rican lizard Anolis cristatellus. We found that the hurricanes affected toe morphology differently between forest and urban sites. In particular, toepads of the forefeet were longer and narrower in forest, but wider in urban populations, compared to pre-hurricane measures. Toepads of the hindfeet were larger in area following the hurricanes. Fore and rear toes increased in length following the hurricane. There were no changes in the number of lamellae scales or lamellae spacing, but lamellae 6-11 of the forefeet shifted proximally following the hurricane. We also measured clinging performance and toe shape. We found that toepad area and toe lengths were stronger predictors of adhesive forces than toepad shape. Our results highlight an interaction between urbanization and hurricanes, demonstrating the importance to consider how urban species will respond to extreme weather events. Additionally, our different results for fore and rear feet highlight the importance of evaluating both of these traits when measuring the morphological response to hurricanes in arboreal lizards.

Early burst of parallel evolution describes the diversification of gecko toe pads

“…Toe straightness or curvature, an artifact of specimen preparation prior to collecting our images was not clearly captured by major PC axes, as it has been in previous work collecting similar data (Howell et al, 2022;Michaud et al, 2023). This is likely due to our use of a between-species groupPCA (and not a specimen-level PCA) and the variation in our dataset, which includes a wide variety of toe morphologies across families.…”

“…After assigning each species to a toe pad class, we used geometric morphometrics to capture toe silhouette and ventral scale shape of each individual specimen. We examined the fourth hind toe (often the longest toe) of each imaged foot, following the work of previous studies (Schulte et al, 2004;Howell et al, 2022;Michaud et al, 2023), placing landmarks using the TPSdig software (Rohlf, 2010). Our landmark scheme included 11 fixed landmarks and 10 curves connected to fixed landmarks at each end, with 13 semi landmarks along each curve (Figure 3).…”

“…Our observed slowing parallel evolution could have been generated by selection/adaptation, stochastic processes, or constraints (e.g., developmental or genetic), although the adaptive value of adhesive toe pads appears intuitive, allowing geckos and other pad bearing lizards to navigate their habitat in unique ways. Toe pad morphology in lizards has been linked to performance, habitat use, and selective events in a variety of contexts (Losos, 1990;Irschick et al, 2006;Winchell et al, 2018;Donihue et al, 2020;Michaud et al, 2023). However, considering adhesive toe pads as key innovations has received mixed conclusions with toe pads facilitating arboreal niches (Miller and Stroud, 2021) and the anole adaptive radiation (Burress and Muñoz, 2021) but not higher evolutionary diversification rates in Australasian diplodactyloid geckos (Garcia-Porta and Ord, 2013).…”