How hurricanes shape lizard evolution

Anoles cling to leaves, bark and walls with toepads: pads of enlarged scales on the undersides of their fingers and toes, each scale covered in millions of microscopic hair-like structures. Bigger pads grip better. In a hurricane, grip can decide who survives.

In 2017 Hurricanes Irma and Maria swept across the Caribbean, including two small islands in the Turks and Caicos, Pine Cay (350 hectares) and Water Cay (250 hectares), where Colin Donihue and colleagues had measured the local anole, Anolis scriptus, before the storms. Measuring the survivors afterward, they found that the lizards still on the islands had larger toepads than the population before the hurricanes.

Does it last?

A shift in the survivors is one thing. Would it carry into the next generation, or be erased by whatever selection came next? Returning in 2019, the team, which included James Stroud, focused on young lizards that had most likely hatched after the storms, the offspring of hurricane survivors. Their toepads were just as large, relative to body size, as their parents' had been, and still larger than those of the lizards measured before the storms.

From two islands to 188 species

If hurricanes favor bigger toepads every time they hit, then places hit more often should have lizards with bigger toepads. Combining 70 years of historical hurricane tracks with toepad measurements, the team tested exactly that at two scales: across 12 island populations of the brown anole, and across 188 anole species throughout the Neotropics. In both, lizards from places struck by more hurricanes tended to have proportionately larger toepads, linking a few violent days in a single population to patterns spread across an entire group of species.

Hurricanes are expected to grow more severe as the climate warms. Our results suggest that extreme events like these may shape the evolution of the communities they hit far more than has been appreciated, acting as brief, intense bursts of natural selection rather than simply as disasters to be recovered from.

The study, led by Colin Donihue with James Stroud among the co-authors, was published in PNAS in 2020.

Read the research

• Hurricane effects on Neotropical lizards span geographic and phylogenetic scales. Proceedings of the National Academy of Sciences (2020)