Twitchy Lizards

Fire ants are unpleasant, to say the least: their venomous bites are more than a minor annoyance for humans, and according to National Geographic News, they can strip animals as large as calves down to the bone. For the small fence lizard, the stings of just a dozen fire ants can mean death in a single minute.

Populations living alongside fire ants, infant lizards are more likely to have longer limbs.

Penn State University biologist Tracy Langkilde has been studying the various responses fence lizards have to the fire ants. Langkilde selected adults from four lizard populations and determined that longer legs and “skittish” behavior—both of which protect the lizards from the ants—are “more common at sites where lizards and fire ants had co-existed longer.” According to Langkilde, the findings are evidence of “a rapid evolutionary response to the fire ants.”

Specifically, the lizards’ skittish twitching removes the fire ants before they can sting the lizards’ soft underbelly, while the long legs are thought to help the lizards fling the ants off and then flee more quickly. Lizards from populations where fire ants are not common sat still when under attack, as if hoping the fire ants would eventually go away.

But is the twitch-and-flee response just something the lizards had learned after being exposed to the fire ants? To answer this question, Langkilde exposed baby lizards from various populations to the fire ants. Surprisingly, all of the lizards responded skittishly, whether from a population that lives near fire ants or not.

According to Langkilde, most of the lizards seem to lose their skittish response once they develop adult scales. But in populations exposed to fire ants, losing the skittishness proves deadly, and thus, the lizards whose genes keep them skittish are more likely to survive and pass on those genes. “It seems like it’s this baby-response behavior that’s been retained in populations because of the risk the fires ants pose,” Langkilde explains. Langkilde also discovered that, among the populations living alongside fire ants, infant lizards are more likely to have longer limbs.

National Geographic News quotes both University of Massachusetts–Amherst biologist Duncan Irschick and University of California–Davis ecologist Sharon Strauss as claiming the research provides “solid evidence” for evolution.

Yet Strauss adds, in the words of reporter John Roach, that “A genetic trait for twitching in adulthood is likely to have existed within the lizard population prior to the fire ant invasion.” The fence lizard populations have “evolved” only in the sense that the frequencies of different characteristics in the population have changed—not in the sense that there is any new genetic information in the population. If fire ants spread and, one day, all short-legged, non-twitching fence lizards are extinct, there will have been a reduction in the genetic information of the fence lizard species, exactly the opposite of what molecules-to-man evolution would require.

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