How Hurricanes Are Pushing Lizards To Evolve
Climatic disasters such as droughts and hurricanes can play a role in shifting natural selection, introducing strong selective pressures very different from those various animals experience in normal conditions. However, we do not yet know if the evolutionary effects of such rare but intense events diminish quickly or endure for longer to shape biodiversity patterns. Do the effects persist widely, both geographically and across animal groups? As hurricanes become more frequent due to climate change, they may be an overlooked driver of ecological and evolutionary change.
A large group of researchers from many scientific institutions worldwide led a joined research effort to try to answer these questions. The group gathered data on how the feet of anoles, a type of tree-dwelling lizard, looked like historically, in 2017 — prior to and right after the islands of Turks and Caicos in the Caribbean were hit by two hurricanes — and in 2019. A good grip is crucial for the survival of these animals when strong winds sway the trees they live in. The researchers hypothesized that the lizards who had survived the hurricanes would have larger toepad (think finger pads and soles) surface areas and, potentially, could have passed their ‘bigfoot’ genes along.
The research showed that hurricanes may indeed have enduring evolutionary impacts on the morphology of anoles as post-hurricane populations, on average, had larger toepads. Furthermore, forelimb and hindlimb toepad surface areas in populations measured in 2019 (the new generation of lizards) were nearly identical to those of the hurricane survivors, and generally much larger than those in pre-hurricane populations. To test for whether this is just a geographically limited and new anomaly, the team surveyed historical populations of brown anoles across 12 islands. The results were clear and consistent – the number of hurricanes throughout the last 70 years was a good predictor for anole toepad surface areas.
The same could not be said for other potential compounding factors, though. Apparently, variables such as local maximum tree heights, air temperature, or precipitation did not correlate with toepad surface area, although one might think that bigger feet could help hold on at greater heights, when it’s cold or wet. It is, however, at this point still impossible to tell which hurricane attributes, such storm duration, wind direction, or accompanying rainfall, are most impactful in terms of pro-large toepad selection in anoles.
Although it is great news that animals are capable of adapting to such adverse weather conditions rapidly and improving their chances of survival, extreme climate events are on the rise. Whether via more intense or more frequent extreme conditions, many environments and ecosystems are changing, pressuring animals to act quickly or perish. Animal advocates will surely ask how such overlooked drivers of selectivity impact overall populations of wild animals, their behavioral repertoires, and, most importantly, the well-being of individuals that are forced to fight for survival on ever more fronts.