(CN) — Miami, best known for fun, sun and reptiles. A cold snap there this past January proved local lizard populations may be far more resilient to lower temperatures than scientists previously believed.
Among the animals considered most vulnerable to climate change, reptiles often take the cake. Being cold-blooded, they have very little in the way of internal metabolic mechanisms to regulate their body temperature and thus rely on a stable environment to survive. Sudden cold snaps can be particularly devastating for these creatures.
Researchers from Washington University in St. Louis investigated Floridian lizards’ cold tolerance in a study published Wednesday in the journal Biology Letters. They compared their findings from the January 2020 cold snap with those of a previous study and found local lizards are growing more resilient, either through natural selection or acclimation, or perhaps both. Among the species studied, only one was native to the area.
"Prior to this, and for a different study, we had measured the lowest temperatures that six lizard species in south Florida could tolerate," said Dr. James Stroud, research associate at Washington University in St. Louis, in a statement accompanying the study. "We realized after the 2020 cold event that these data were now extremely valuable — we had the opportunity to re-measure the same lizard populations to observe if their physiological limits had changed; in other words, could these species now tolerate lower temperatures?"
Dr. Stroud and his team spent the week following the cold snap collecting surviving lizards and measuring their thermal tolerance to compare with lizards studied previously. They sought to determine if the increased cold tolerances they observed extended across species. The team also resampled the lizards’ thermal limits 10 weeks later to test whether the changes observed were a temporary stress response, or if the lizards had actually adapted.
"A major unexpected result of this study was that all species converged on the same new, lower level of thermal tolerance," Stroud said. "While there was great variation in temperature tolerance before the cold event — some, like the large-bodied brown basilisk, were very intolerant of low temperatures, while others like the Puerto Rican crested anole were more robust — we observed that all species could now tolerate, on average, the same lowest temperature.”
After resampling the lizard’s thermal limits 10 weeks later, the researchers determined the changes in their tolerance to cold were likely to persist. These results were especially surprising given the species’ vastly differing physiology, body size and ecology, while begging the question — how low can they go?
Two likely mechanisms behind the lizards’ speedy adaptation are directional selection and physiological plasticity. Directional selection is when a beneficial trait, such as cold tolerance, gets passed on more readily by virtue of fitness, growing more frequent in the gene pool. Physiological plasticity is an organism’s ability to acclimatize itself to changing conditions, such as a Navy Seal training to hold their breath underwater.
"The shifts to tolerate significantly lower temperatures that we observed were so large that we found it unclear whether natural selection was responsible," Stroud explained. "And so in our paper we discuss other alternative processes which may also have led to this pattern."
"What we now need to find out is how this was accomplished,” said Dr. Jonathan Losos, the William H. Danforth Distinguished University Professor and professor of biology at Washington University, in the statement. “Is this evidence of natural selection, with those lizards that just happened to have a lower cold tolerance surviving and others freezing to death, or was it an example of physiological adjustment — termed 'acclimation' — in which exposure to lower temperatures changes a lizard's physiology so that it is capable of withstanding lower temperatures?"
The primary way reptiles regulate their body temperature is to move in and out of sunlight and sun-warmed surfaces – it would give them a tremendous advantage if they’re able to regulate their body temperature more than previously believed.
Given that most climate scientists predict similarly unexpected whether events will become ever more frequent as climate change intensifies, these results may provide a boon for thermally vulnerable species such as lizards. This makes understanding the effects of long-term temperature increases and chaotic weather events even more vital.
"While there is no doubt that climate change represents a major threat to species and ecosystems around the world, and deserves as much research attention as possible, this study provides fascinating insight and a glimpse of hope," Stroud concluded. "Perhaps tropical and subtropical species can withstand more extreme climatic conditions."
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