A major outstanding question in urban evolution (and evolutionary biology in general) is whether adaptation occurs in similar ways in different populations and across species boundaries. In other words, can the common selective pressures of urban environments lead to convergent adaptation? In my doctoral research, I found that the Puerto Rican crested anole, Anolis cristatellus, adapted repeatedly to urban environments across its native range. In each pair of populations (urban and forest) across the island, I have found urban lizards to be different from nearby forest lizards in the same ways: urban lizards have relatively longer limbs and larger toepads, traits that are especially important in combination when climbing smooth vertical surfaces like buildings and fences. In my post-doctoral research, I’ve set out to understand if these same adaptations are occurring in other species of anoles around the Caribbean.
We know from our (forthcoming) analysis of patterns of urban tolerance in anoles that there is strong phylogenetic signal within the clade (i.e., related species are likely to share similar tolerance of urbanization). Anoles can be grouped into several distinct “ecomorphs” that share similar ecologies and morphologies, yet there does not appear to be a correlation between ecomorphology and urban tolerance. Nevertheless, several species found in urban environments in the Greater Antilles belong to the trunk-ground ecomorph, providing an interesting natural experimental setup: if distantly related species come from the same ecological and morphological starting point, will they adapt to urbanization in the same way? And similarly, if species belong to different ecomorphs, will they adapt differently?
At Evolution 2019 I presented the preliminary results from this study, including results from my trip to Jamaica and the Dominican Republic which I returned from only last week! With the expectation that species would adapt to urbanization in the same way, especially within ecomorphs, I have so far sampled 4 additional species of anoles in urban environments in the Greater Antilles: Anolis lineatopus and Anolis grahami from Jamaica, Anolis cybotes from Hispaniola, and Anolis sagrei from the Bahamas.
I have only begun to dig into the morphological and habitat analysis, but I was surprised to find that my preliminary data suggests something a little more complicated than simple convergence. Two of the species, A. grahami and A. cybotes, both appear to be adapting to urbanization in a similar way as A. cristatellus: urban lizards have relatively longer limbs. This is somewhat surprising as they are from two different ecomorphs (A. grahami is a trunk-crown specialist while A. cybotes is a trunk-ground specialist). The other two species appear to be doing something differently: A. sagrei and A. lineatopus both have relatively shorter limbs in urban habitats. Intriguingly, despite this non-convergence at first glance, both of these species have absolutely longer limbs as well as substantially larger body sizes.
Is this a case of convergence in function and not morphology? perhaps. Longer limbs, whether a small-bodied or large-bodied animal, should lead to faster sprinting across the ground. Alternatively, these preliminary results could be attributable to variation in urban environments and habitat use among the five species. As I dig into these data and collect from additional populations and species, hopefully the picture will become clearer as to how convergent urban adaptations are and what ecological and evolutionary factors influence them. Stay tuned!
- New Lit Alert: Urban environment determines population genetics in the green toad, Bufotes viridis - September 11, 2023
- Contribute to the New York Canid Project! - July 21, 2023
- Parallel Urban Adaptation from Phenotype to Genotype in Anolis Lizards - January 19, 2023