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.Zachary and Bruce also gave the lizards a choice between perch diameters and branching patterns. Given the well-established relationships between perch diameter and speed in anoles, one might assume that “bigger is better.” If given a choice, the preference for a specific perch diameter is actually quite variable! For the most part, however, perch choice was associated with substantial benefits for performance. When it comes to branching, anoles appear to prefer larger perches with top pegs compared to smaller perches lacking pegs. For a given perch diameter, it does not appear that the spacing of the pegs dictates path choice.
An anole on a branch. Arboreal habitats provide a plethora of pathways for locomotion. Photo by Emily Kane.
Although it might not be as elaborate as parkour, arboreal lizards have a remarkable ability to negotiate obstacles and maneuver in their habitat. Our understanding of these behaviors is starting to expand from the recent surge of studies, and Anolis lizards are an ideal group for future work.
- The Origin of Adhesion in Geckos - October 28, 2016
- Beware Of The Branches: The Impacts Of Habitat Structure On Locomotion And Path Choice - June 5, 2012
gabriel gartner
Cool post Tim! This seems ripe for experimental manipulation in a natural setting. At what point do large-diameter branches become so obstacle-ridden as to deter animals from using them?
Timothy Higham
Absolutely. It would be really cool to do some experimental manipulation in a natural setting. The spacing between branches is positively correlated with perch diameter (from a paper by Mattingly & Jayne, 2004), so my sense is that large-diameter branches give lizards more options for avoiding obstacles.