FIU Graduate Student Researches On Lizard Climate Tolerance

James Stroud examining a lizard at the Fairchild Site photo credit: Day's Edge Productions

Neeraj Konathan /Staff Writer

Florida has gone through cold seasons in the past, significantly impacting the population of lizards in South Florida.

This year, lizards are becoming more resistant to the cold, according to a recent study published in Biology Letters.

James Stroud, FIU alum, and a former graduate student from the Department of Biological Sciences conducted a study showing no evidence indicating Florida’s invasive lizards are evolving to adapt to the cold and are adapting to the cold.

In January lizards, specifically, iguanas were falling from trees as a result of temperatures plunging below 40 degrees Fahrenheit in South Florida.

The research concentrated on how climate differences could result in community-wide patterns of trait shift.

For experimental purposes, Stroud conducted the experiments with the lizards from Fairchild Tropical Botanical Garden, then brought them back to the laboratory, where they were gradually cooled until they could no longer move.

Stroud’s study focused on the cold thermal tolerance of six species of lizards including the Cuban brown anole, Puerto Rican crested anole, Hispaniolan bark anole, American green anole, Brown basilisk, and the African house gecko.

While most lizards were unharmed by the lower temperatures, some could only tolerate average temperatures, which in the experiment varied depending on species.

This temperature limit was different for each species, with small temperature variances in the Crested anole of 1.09 degrees Celsius to huge differences in the Brown basilisk of 4.04 degrees Celsius.

After testing them 10 weeks later these different levels of temperature tolerance remained unchanged.

Stroud told PantherNOW there are two explanations for this. The first is that they have a physiological change in their body that allows them to survive cold weather. The second is natural selection, where one individual within a species could tolerate the cold and another species could face extinction. The species which tolerated the cold would have a higher chance of survival through many generations.

Iguanas are invasive species, as they disrupt the ecological balance of Florida’s wildlife. Invasive species are non-native to a particular area which can cause significant environmental and economic harm.

They have been known to cause damage to infrastructure, where they burrow themselves into the ground and in the roofs of buildings, compromising their structural integrity according to the National Wildlife Research Center.

This change causes other species’ populations to decline or increase drastically, causing the ecological scale to favor a few species similar to the overpopulation of the Burmese python.

In an effort to regulate their population, the state of Florida allows for the killing of iguanas on private property, with permission from landowners.

Stroud did not use iguanas in his study.

“We didn’t do [the study] on iguanas [specifically] because iguanas were too big, physically, [for] the equipment that we [used] to test the cold tolerance,” said Stroud.

He found, most of the lizards in the experiment reacted differently to the change in temperature.

“We record for each individual lizard the temperature, the lowest temperature that they can tolerate and still move, and then as soon as they can’t move we record that temperature,” said Stroud.

Florida’s warm climate is favorable for these creatures, as they enjoy the state’s sunny, humid weather where highs reach an average of 72 to 82 degrees Fahrenheit.

Typically they will spend time in the sun to regulate their body temperature, this is because lizards are cold-blooded animals and rely on the environment to maintain warmth.

“It seems as though the tolerance levels towards colder temperatures have increased and they have become more resilient,” said Stroud.

As lizards adapt, he wonders if global warming may cause colder temperatures to be less of a concern in the future.

Stroud told PantherNOW, “Not only is the background temperature slowly getting warmer, by one or two degrees per century, but… the hottest days [of] summer and the coldest days of winter are getting more extreme.”

Competitors and predators also come into play when adjusting to these evolving conditions. These conditions are called biotic and abiotic factors. Biotic factors are referred to any living component which affects another organism and abiotic are the nonliving factors influencing an organism.

With Stroud’s preliminary research on lizards, he suggests more testing is needed in order to understand why lizards are becoming more tolerant to the cold.

“We don’t have those long term data [results] yet to understand exactly what mechanism [is true],” he said.

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