The anole species examined by Davis and Johnson

The anole species examined by Davis and Johnson

The annual meeting for the Society for Integrative and Comparative Biology (SICB) has kicked off and anoles are off to a roaring start. At the first poster session of the conference this afternoon, Lauren Davis, an undergraduate student working with Dr. Michele Johnson at Trinity University, will present her work on the behavioral and neural correlates of invasive ability in anoles (poster 1.19). Davis wanted to know whether invasive anoles can be identified by specific behavioral syndromes, or suite of behaviors that are expressed across different contexts. Specifically, she wanted to know whether invasive lizards are ‘bolder’ than native lizards and, in turn, invasive lizards have larger or denser neurons in neural regions associated with boldness (i.e., the amygdala, hippocampus, and hypothalamus).

To address these questions Lauren focused on three species of anole that vary in ‘invasiveness.’ These were Anolis carolinensis, a native species, A. distichus, a ‘semi-invasive’ species, and A. sagrei, a highly invasive species. She hypothesized that more invasive anoles should be ‘bolder’, meaning that they exhibit a propensity to explore novel environments, exhibit more aggressive behavior, possess higher overall activity levels, and have more behavioral flexibility (defined below) than native range lizards.

She caught all three species within their native ranges (the bark anole, A. distichus, and the brown anole, A. sagrei, from Bimini, Bahamas and the green anole, A. carolinensis, from Bexar County, Texas) and sampled an additional population of A. sagrei from its invasive range in Florida. After a period of laboratory acclimation, she measured “boldness” by (i) timing the latency period for the focal lizard to catch a cricket; (ii) counting aggressive displays to a conspecific by a focal lizard in arena trials in which lizards competed for a single perch; (iii) overall activity as the total number of moves during a 15 minute open arena trial; and (iv) the latency period for a lizard to cross a novel divider to reach the opposite end of an arena (i.e., ‘behavioral flexibility’).

Results showing how aggression and activity levels differed among species.

Results showing how aggression and activity levels differed among species.

The overall results indicate that invasive lizards are bolder than native-range lizards, but the results varied somewhat between tests and species. All species showed similar levels of aggression towards prey (i). Green and invasive brown anoles showed similar amounts of aggressive displays towards conspecifics (ii), although A. sagrei was more active (iii) and crossed the divider faster (iv) than A. carolinensis.

Results showing how behavioral flexibility and brain-to-body-mass ratios differ among species.

Results showing how behavioral flexibility and brain-to-body-mass ratios differ among species.

Contrary to their expectations, they found that the bark anole, A. distichus, dewlapped at conspecifics more than A. sagrei (ii). Furthermore, they found that A. distichus was significantly more active that A. sagrei during the 15 minute open arena trials (iii), but these species did not differ in latency to crossing a novel divider (iv). Together, their results suggest that invasive lizards tend to be bolder than native-range lizards, but the results from Bimini suggest that there may be population-level variation that complicates this pattern.

Although the neurological assays are currently underway, Lauren did find that, contrary to their predictions, A. carolinensis has a larger brain-to-body-mass ratio than A. sagrei. These ratios did not differ between A. distichus and A. sagrei from Bimini. These results suggest that brain volume, which is generally associated with interspecific differences in behavioral flexibility in other taxa, may not correlate with invasive ability among anoles.

Studies examining the behavioral and neurological underpinnings of invasion success are extraordinarily rare. The early results from Lauren’s study are promising, and hopefully the results from her neurological assays will provide new insights into what determines lizard invasion success.

Martha Muñoz
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