Anole Annals

Lauren Davis presenting her work on invasion success in lizards.

As our planet becomes increasingly connected and humans facilitate novel species interactions, we must ask why some introduced species are destructive and others relatively harmless. Lauren Davis, a senior in Dr. Michele Johnson’s lab at Trinity University, conducted a study on behaviors, and their neural correlates, that may influence the invasiveness of non-native lizards. She compared the invasive Anolis sagrei to the native Anolis carolinensis, the invasive House Gecko (Hemidactylus turcicus), and the native Texas Banded Gecko (Coleonux brevis). They hypothesized that highly invasive species display more ‘bold’ behaviors (in this case, the number of enclosure boundaries crossed during an experimental period) and have larger and/or denser neurons in associated brain regions than less invasive species. While there are many documented behavioral trials with boldness in Anolis, geckos have received little attention in this regard. Lauren and her fellow researchers found that A. sagrei is indeed bolder than A. carolinensis, but that the two gecko species do not differ in traits associated with the boldness syndrome (Fig. 1).

Figure 1: Invasive Brown Anoles are bolder than native Green Anoles

The researchers also found that neuron size in brain regions known to influence boldness and aggression were opposite than expected values, so the team plans to analyze neuron density in these regions to help explain the observed behaviors. This is one of the first studies comparing behavior and brain morphology to invasion success, and it paves an exciting path towards our understanding of species interactions in our changing world.

Lauren is graduating in May, and hopes to work in conservation or public health before continuing her education in graduate school.

Anolis sagrei mating. Taken from the Cox lab website.

On the first day of SICB 2015 Robert Cox gave an interesting talk about reproductive investment and sexual selection in lizards. At the center of his talk was the striking notion that males and females are different biologically, yet should still be integrated into cohesive theories of sexual selection. According to Dr. Cox, past theory has generated mutually exclusive ideas about the costs of reproduction for each sex. Whereas theories about females have focused on life history and investment in the egg and offspring, theories about males have focused on mating investment. Cox stressed that this is overly simplified and doesn’t reflect biological reality,  as males and females also share many of the same costs of reproduction as well. Issues like growth, survivorship, energy storage, and parasite load are shared between the sexes. Dr. Cox is now trying to test how sex-specific reproductive mechanisms affect these shared reproductive constraints by surgically removing the gonads of each sex. Preliminary analyses show that parasite load appears to be a shared effect among the sexes regardless of the underlying mechanism (testosterone derived from testes versus estrogen derived from the ovaries). Studies directly comparing the underlying mechanisms of sexual dimorphic anatomy, physiology, and behavior are critical for the further development of sexual selection theory and for improving our understanding of anoles. Studies like Dr. Cox’s are an important step in that direction.

Anolis cristatellus in Miami, Florida. Picture by Jason Kolbe.

Humans and wildlife are sharing the same spaces more and more frequently, but there’s still much that we do not know about how animal behavior is altered in urban environments. To address these questions, graduate student Kevin Avilés-Rodriguez (pictured below) and Dr. Jason Kolbe of the University of Rhode Island studied the responses of Anolis cristatellus to simulated predators in urban and natural environments in Puerto Rico. They found that lizards in an urban habitat had shorter flight initiation distances (the distance a simulated predator – in this case, Kevin – could approach before the lizard fled) than in a natural, forested site.  In addition, lizards’ predator-escape behaviors generally corresponded to the sizes of their perches and to their proximity to vegetation, but perch types differed between the urban and natural sites.  Whereas lizards in natural habitats tended to jump into nearby plants to escape, urban lizards tended to avoid capture by squirreling on larger, more isolated perches.  Kevin also reported that lizards perching on cement walls had adjusted their predator responses dramatically, as they generally did not jump or squirrel. In sum, this study suggests that habituation to humans and/or human-shaped habitats have altered the responses of these lizards to potential predators in important ways.

Kevin Aviles, stalking lizards in the field. Photo from Kolbe lab website.

How do lizards move in nature? Note the added emphasis on “in nature.” For many years people have studied the mechanics and patterns of of lizard movement and anoles have played an important role in this research. But today Jerry Husak of the University of St. Thomas in St. Paul reminded us that most of this research has focused on characterizing maximum performance ability, despite the fact that  animals rarely achieve this level of activity in nature. For example, most of the time many lizards are merely scurrying about on the ground and not sprinting at their full ability. Hence, although measuring maximal spring speed in the lab is a common theme, this measurement may not actually reflect what animals do in nature. Dr. Husak also stressed to the audience that animal locomotion is context dependent. Specifically, a lizard’s speed depends on whether it is moving in grass or over rocks, and whether it is foraging or fleeing from a predator. During his enlightening discussion, which included a description of him trying to sprint on a frozen Minnesota sidewalk, Dr. Husak described a series of biotic and abiotic factors that should be incorporated into models of terrestrial lizard movement.  Finally, he concluded by challenging our obsession with maximum sprint speed once again by asking whether running at top speed can lead animals to make to costly mistakes. Based on a set of foraging data, he showed that this may be the case.  Dr. Husak’s talk highlighted the importance of understanding the natural habits of lizard behavior and performance. 

When I was a kid, the first week of January used to be such a bummer for me because it meant that the holidays were over. But now the first week of each year means that the annual meeting of the Society for Integrative and Comparative Biology (SICB) is underway! The meetings run from January 3rd until January 7th, and there are 30 talks/posters this year about anoles! I won’t be attending this year, as I’m currently based out of Australia (AKA land of no anoles), so I’ll be looking forward to the posts on this blog to hear what’s new and exciting in Anolis research. Stay tuned!