Date of Award

2021

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Biological Sciences

First Advisor

Jason J. Kolbe

Abstract

Extreme weather events have been identified as drivers of natural selection and evolutionary change across populations and species. A recent study showed that the high wind speeds generated by hurricanes caused selection favoring particular phenotypes for island lizards. Anolis lizards (or anoles) commonly live on islands and in coastal areas frequently disturbed by hurricanes. A hallmark of the Anolis radiation is the evolution of morphological variation among species as illustrated by the evolution of different ecomorphs, which have evolved varying limb and toe morphologies to occupy different parts of arboreal habitats. Differences in limb length and toepad size lead to clear functional differences in performance, including clinging ability, which is likely important during hurricanes. This study tests if morphological trait values affect clinging performance under different conditions. We evaluated three species in this study, each representing a different Anolis ecomorph (trunk-crown, trunk, and trunk-ground), which vary in limb and toepad morphology. As expected, the trunk-crown species (Anolis carolinensis) had the shortest limbs and most lamellae compared to the other two species in our study. The trunk ecomorph (A. distichus) had the longest forelimbs, intermediate hindlimb lengths, an intermediate number of forelimb lamellae, and the fewest hindlimb lamellae. Lastly, the trunk-ground species (A. sagrei) had intermediate forelimb lengths, the longest hindlimbs, the fewest forelimb lamellae, and an intermediate number of hindlimb lamellae. Based on morphology of these species, we hypothesized that the trunk-crown ecomorph would have the best clinging ability, followed by the trunk ecomorph, and, lastly, the trunk-ground ecomorph. Lizards were subjected to two types of experimental trials. First, we assessed the ability of lizards to cling to substrates varying in diameter (i.e., 12 and 33 mm) and surface roughness (i.e., smooth and rough) by measuring the force needed to pull lizards off these substrates (hereafter, clinging-force trials). Second, we measured the amount of time lizards remained perched on these same substrates while experiencing hurricane-force winds (hereafter, wind-speed trials). In the clinging-force trials, for some combinations of dowel type and species, we found aspects of morphology, including increased hindlimb length, more hindlimb lamellae and body size, were related to clinging force. Our finding that more hindlimb lamellae increased clinging ability is consistent with a previous study that detected larger toepads in anole populations after hurricanes. However, our finding that longer hindlimbs increased clinging ability is not consistent with this previous study. In the wind-speed trials, we found no significant influences of morphology on clinging. These findings are not consistent with previous studies and may be due to the added behavioral aspect that the wind-speed trials included. In the clinging-force trials, with all the substrate types pooled, the trunk-crown ecomorph A. carolinensis had the best clinging performance, the trunk-ground ecomorph A. sagrei had intermediate clinging ability, and the trunk ecomorph A. distichus had the worst clinging ability. In contrast to the clinging force trials, we found no significant differences in clinging ability among species with substrate types pooled in the wind speed trials. We did find that A. carolinensis could cling longer than the other two species on the 33-mm-rough dowel. The differences between the clinging force and wind speed trials suggest that factors other than morphological variation, such as behavior, also influence clinging performance. Together, our results increase our understanding of the mechanistic basis for how substrate type and morphology influence clinging ability. Our preliminary analysis of clinging differences among Anolis ecomorphs also provides us with more knowledge of how anole clinging performance may be a target of natural selection during extreme weather events, such as hurricanes.

Available for download on Saturday, April 23, 2022

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