When I think of Puerto Rico, the first thoughts that come to mind are of sunny beaches and lush rainforests. There are, however, also lots of urban habitats in Puerto Rico. San Juan, for example, has two million human residents, and also lots and lots of anoles. Doctoral candidate Kristin Winchell has been studying adaptation in urban anoles for several years. Last year, she published1 her work showing that Anolis cristatellus in urban habitats have longer hindlimbs, bigger toe pads, and more lamellae than lizards in rural habitats.
A connection that was missing, however, was how the morphological shifts she documented related to performance differences in urban versus rural habitats. To get at this question, she conducted sprinting trials with different substrates to see how limb and toe characteristics affect sprinting capacity. Lizards in urban habitats use much smoother perches, such as fences and posts, and so the hypothesis was that the longer limbs and toe pad differences she detected improved sprinting performance on smoother substrates. She used three different substrates for sprinting trials – bark (rough surface), metal (smooth surface), and painted concrete (very smooth surface). She found that, overall, lizards sprinted more slowly on more slippery substrates. On average, lizards sprinted at 60% of their maximum capacity, indicating a strong performance hit when using slippery substrates.
Kristin confirmed that the urban anoles were better at sprinting on all substrates – including the slippery ones – than rural anoles. When she explored the results in greater detail, she found that only lamella number explained variation in sprint performance, with no appreciable effects of limb length or toe pad area. Kristin’s elegant study demonstrate how we can document evolution on recent timescales, and shows how urban environments provide strong selective pressures for the animals that live in them.
1. KM Winchell, RG Reynolds, SR Prado‐Irwin, AR Puente‐Rolón, LJ Revell. 2016. Phenotypic shifts in urban areas in the tropical lizard Anolis cristatellus. Evolution 70:1009-1022