Anole Annals

The elegant skink, Plestiodon elegans, in Taiwan. Photo by Gerrut Norval

Most community ecology studies involving anoles focus on interactions between anole species. This is not surprising, because in the Caribbean, anoles are extraordinarily abundant and most of their ecological interactions are, indeed, with other anoles. Less studied are interactions with other taxa, the exception being predator-prey interactions, such as those with curly-tailed lizards (discussed many times in these pages, most recently here).

One widespread group of lizards are skinks, the most species rich family of lizards. There are few reports of anole-skink interactions, probably in large part due to the fact that skink diversity in the Caribbean is relatively low, and many species have been extirpated by human agents. However, anoles have been introduced to places around the world where skinks are more abundant, and some reports of interactions have been made. For example, in the Ogasawara Islands of Japan, A. carolinensis has reached high population densities and has been implicated in the decline of the native skink.

Gerrut Norval has been studying the introduced populations of A. sagrei in Taiwan. He now reports an observation of a somewhat odd interaction between a brown anole and a skink in which the anole fell to the ground from a utility pole and then was quickly chased back up the pole by an elegant skink, Plesiodon elegans. Given the relative size of the two lizards, attempted predation was probably not the cause. Gerrut speculates that this is an example of interspecific territoriality, transcending lizard family lines.

In Taiwan, A. sagrei reaches high population densities (as it does just about everywhere it occurs)–possibly cause for alarm for the native herpetofauna. Norval also mentions some intriguing preliminary observations: A. sagrei seems to attain smaller sizes at sites where it co-occurs with other lizard species. Interesting! Hopefully, we’ll hear more from Gerrut soon on this provocative possibility.

Imagine running quickly among a network of obstacles while attempting to maximize performance. It’s not an easy task, but one that arboreal lizards perform every day. In addition to variable inclines and perch diameters, arboreal lizards often encounter obstacles in the form of branches. The size of these branches, and their spacing, could have a significant impact on locomotor performance, such as sprint speed. Using a clever experimental design, Zachary Jones and Bruce Jayne (University of Cincinnati) recently determined how these important characteristics impact running performance in Anolis sagrei, A. carolinensis, and A. angusticeps (Click here to read paper from the Journal of Experimental Biology).

(A) Dorsal view silhouettes of the three Anolis study species compared against the diameter of the running surfaces. The lizards and cross-sectional areas of the running surfaces are all shown to the same scale. All running surfaces were cylindrical, but only one-half of the largest diameter is shown. (B) Schematic diagram of the peg treatments (not to same scale as the lizards). Pegs along the top center were placed at 10 cm (TC10) or 20 cm (TC20), horizontal pairs of pegs (HP) were placed every 10 cm, and alternating pairs of pegs (AP) oriented vertically or horizontally were placed every 10 cm along the length of the primary running surface (gray). The cylinder with no pegs (NP) is not shown.

Similar to previous studies, increases in perch diameter resulted in increased sprinting speed. With pegs added to the perch, things changed. When pegs were placed at 10cm intervals, and sticking directly up from the top of a 3cm-diameter perch, running performance of A. sagrei was sliced in half compared to running on a peg-free perch or a perch with pegs sticking out from the sides. Especially for the smaller perch diameter treatments, the number of pauses increased with increased branching, and this was greatest when the pegs came out from the top of the perch. This increase in pausing results in a decrease in overall speed (increased transit time) as they move through their habitat.  This is also a result found by Higham et al. (2001), where turning angles in the locomotor path resulted in increased pausing in Anolis lizards.  The take home message is that branching can have a negative impact on locomotion, forcing lizards to take longer getting from point A to point B.  This could make them vulnerable to predation or reduce their ability to effectively capture prey.
Luckily, the array of pathways in an arboreal habitat provides an opportunity for Anolis lizards to select what works best for them.

Read More

Another week brings another nice batch of anole publications from a few previously held meetings. This batch comes from a combined special issue of General and Comparative Endocrinology that features articles from The Inaugural Meeting of the North American Society for Comparative Endocrinology (NASCE) and the 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology (ISAREN) held last July.  The papers from this meeting are now available at the journal’s page at Elsevier ScienceDirect.

Wade (2012) provides a nice review of structure and function of three sexually dimorphic anole features in green anoles (Anolis carolinensis): the forebrain, the dewlap neuromuscular system, and the copulatory neuromuscular system.  She also reviews comparative studies across anole species of the dewlap system and provides a detailed discussion of endocrine regulation in green anoles.  Cohen & Wade (2012) investigated “Aromatase and 5 alpha-reductase type 2 mRNA in the green anole forebrain: An investigation of the effects of sex, season and testosterone manipulation.”  Finally, in a non-anole paper about other iguanid lizards Hews et al. (2012) investigate “neuroendocrine correlates of aggression differences in adults of two Sceloporus lizard species.”