Why I have not been posting much.

[Shark Bait]

I know it does not sound like science but it is, here is my research for ecology that I am giving a talk on today, if this goes well I will present at the florida bio symposium in the spring and may get this stuff published before senior year. Please for the love of god dont coppy this work yet because it has not formally been submited anywhere but within the school. and sadly i cant post the pictues, graphs and tables but you get the idea i think..


Sticky Fingers: Effect of Perch Diameter on Toepad Morphology


Authors: Rusell Davis and Allison Sang


Abstract

Toepad morphology in Anolis lizards is very significant in determining the species clinging ability to their arboreal microhabitat. Anolis sagrei toepads should vary as the available perch diameter changes from location to location. Lizards were collected from three different sites and toepad morphometric data and microhabitat measurements were tabulated for each lizard. Statistical results showed that there was a significant different between lizards exposed to different perches. Therefore, the environment has an effect on a lizard’s morphology which must change to survive in new habitats.


Abbreviations ANOVA – Analysis of Variance; LF – lamellae front; LR – lamellae rear; MANOVA – Multivariate Analysis of Variance; SVL – snout-vent-length; TPF – toepad width front; TPR – toepad width rear


Introduction

Lizards from the Anolis genus are known to easily adapt when encountering a new habitat (Irschick et al. 2005). There have been many experiments conducted on the variation of limb length of Anolis sagrei lizards, particularly between different species (Losos et al. 2000). However, variation has also been shown between members of the same species, which correlates to the mean diameter of their perching locations. Several different mechanisms for this variation have been proposed including both micro-evolution (Losos et al. 1997) and phenotypic plasticity (Losos et al. 2000). A correlation has also been demonstrated between perch height and diameter versus toepad area showing a positive association between the two (Macrini et al. 2003). Yet overall size of the toepads and limb length on lizards may not be the only factor influenced by perch diameter.
The toepads of Anolis lizards have modified scales on their undersides known as lamellae which aid in clinging to a surface through Van der Waals forces. This structure allows the lizard to produce a traction force that acts against the force of gravity (Zani 2000). From previous studies it was discovered that the clinging ability of anoles greatly decreases if one of their toes are clipped (Bloch and Irschick 2004). Consequently, the toepad structure of an anole determines its perching location within a tree (Elstrott and Irschick 2003). It is expected that lizards that perch high in the canopy will have much larger toepads than those that perch at lower parts of the tree (Irschick et al. 2006). The effect of snout to vent length (SVL), as a substitute for body size, has been shown to correlate to toepad structure, where a positive association becomes quite clear (Irshick et al. 1996). The possibility that the number of lamellae as well as the toe pad dimensions change in response to perch diameter certainly warrants investigation.
There exists a possibility that there is a correlation not only between width of toepads, but also to the number of lamellae that the lizards have, and the average perching diameter. Additionally, there is the question of whether or not these changes in the lizard’s toepad morphology are an expression of micro-evolution or simply phenotypic plasticity. It would be great if there were somehow a way to study lizards that have lived in areas with mostly wide or small diameter perches available; lucky for us there was. In 1994, two dredge spoil islands, P1 and P2, in east-central Florida were inoculated with brown anoles from Pahokee, Florida as part of a study on introduced species (Campbell and Echternacht 2003). As a fortunate coincidence these sites also showed a good difference in average of perching diameter (Campbell and Echternacht 2003). Therefore, because these populations of brown anoles have been isolated for such a short period of time it would be thought that this would demonstrate phenotypic plasticity similar to that described in Losos 1997.
In conclusion, our hypothesis is that toepad width and lamellae count will differ, due to phenotypic plasticity, as the diameter of available perches vary by location. Consequently, our null hypothesis is that the toepad morphology of the lizards does not change as perching diameter varies. To test our hypothesis, we measured the toepad widths and counted the lamellae of Anolis sagrei lizards obtained from the introduced species study by Campbell and Echternacht 2003. In total, lizards from three sites, Pahokee, P1, and P2, were analyzed. The morphometric characters of the lizards were compared by location. The available perches in each site differed greatly in perch diameter with Pahokee having the widest perches, followed by P2 and then P1 (Campbell and Echternacht 2003). Therefore, the effect of perch diameter on toepad morphology was determined by studying the difference between lizards obtained from different sites.

Materials and Methods

Study Sites

In 1994, Anolis sagrei lizards were introduced to two dredge-spoil islands, P1 and P2, in Mosquito Lagoon, Volusia County, Florida. The two islands were far apart and differed in available microhabitats for the brown anoles. P1 is a 0.048 ha in area above mean high water, consisting of a 0.020 ha area that is vegetated. The island is made up of coral rocks, has negligible soil and there is a thin layer of leaf litter in the shrub zone. Among the available perches for the lizards, there are 6 isolated cabbage palm trees (Sabal palmetto) and a patch of Brazilian pepper (Schinus teribinthifolius), 1-3 m high. Island P2 is 0.150 ha in area above mean high water. It contains 0.030 ha of forested area and it is flanked by a 0.120 ha salt marsh. The palm forest is made up of 69 cabbage palms, 4-7 m in height. The soil in the forest is sandy and there is a deep leaf litter due to dead palm fronds. Meanwhile, the salt march is dominated by Borrichia frutescens and bordered by narrow spoil sand beaches and by a regularly submerged Batis zone. (Campbell and Echternacht 2003)

Methods and Data Analyses

The lizards introduced to P1 and P2 were captured from the southeastern shoreline of Lake Okeechobee at Everglades Marina and Campground which is south of the Pahokee State Recreation Area in Pahokee, Palm Beach County, Florida. The captured lizards, 25 females and 12 males, were obtained from a long-established and dense population of Anolis sagrei. In total, 18 lizards were introduced to P1 and 19 to P2. During the summers of 1995-1997 capture-mark-recapture techniques were done to follow the progress of adult brown anoles in the two sites. Afterwards, lizards from each site, 60 from Pahokee, 61 from P1, and 58 from P2 were captured and SVL and other morphometric data were obtained for each lizard. In addition, the perch height and diameter for lizards at each site was measured. The lizards were then preserved in a formaldehyde solution. (Campbell and Echternacht 2003)
In 2006, the preserved lizards were transferred from the formaldehyde solution into an 80% ethanol solution. The SVL was re-measured to determine how much the brown anoles had shrunk. The toepad width and lamellae count for the front middle toe and the fourth rear toe, of the left limbs, were measured (Table 1). All the morphometric measurements for toepad morphology were done with the aid of a dissecting scope. The toepad widths of the front toe (TPF) and of the rear toe (TPR) were measured with a caliper to within .01mm. The lamellae were individually counted for the front toe (LF) and for the rear toe (LR). The lamellae were counted from the end of the toepad up to the first knuckle crease. The toepad morphometric data was measured twice, and then averaged.
The data was then entered into an Excel spreadsheet and the toepad width and original SVL measurements were log transformed since the data was not normally distributed. The lamellae count was not log transformed because it was a quantitative value. The data was then imported to JMP software for statistical analysis. To analyze the difference in toepad morphology between sites, residuals needed to be calculate to standardize the data since the lizards from different sites varied in size (SVL). To obtain residuals a log-log regression was done for toepad width values and only a log regression for lamellae count values was done. After residuals were calculated, a MANOVA was used to compare all four morphometric parameters; LF, LR, TPF, and TPR. Afterwards, one-way ANOVA’s of the original SVL by sex were calculated for the three sites. Using the residuals values, one-way ANOVA’s were plotted for LF, LF, TPF, and TPR by site.

Results

As expected the SVL of males were much greater than that for females at all three sites (Figure1), but it was not due to chance (Prob>f = <.0001). It was also discovered that the specimen had shrunk significantly. These results, however, do not affect the study, because it still accounts for a change in overall toepad morphology. After the calculation of residuals for toe pad dimensions by the log SVL, the values were entered into an ANOVA to compare the residuals by site. The ANOVA showed a significant difference between the sites for the LF (Table 2), LR (Table 3), and TPF (Table 4); however, the TPR (Table 5) was not shown to have a significant difference. The number of lamellae, both front and rear, was shown to be the least at the Pahokee site where the average perch diameter was the largest, while it was shown to be greatest at site P2 where the diameter of available perches was between Pahokee and P1 (Figures 2, 3). Lastly, the number of lamellae for individuals collected from P1 was higher than those of the Pahokee site but less than the individuals from P2 (Figures 2, 3).
Meanwhile, the width of the rear toepads was shown to have no significant difference, yet the front toepad width showed a clear difference between the three sites. However, in this instance the P2 site showed the smallest width, while P1 showed the largest, and the Pahokee site was in the middle (Figure 4). This caused some confusion even thought the values had been adjusted for size of the animal (SVL), so values were put into a MANOVA. Location and sex were found to be significant, while location*sex was not. The MANOVA results for location (Pillai’s trace 8.1277 = F, <.0001= Prob.>F, shown in Table 7), sex (F-test 4.5864=F, 0.0041=Prob>F, shown in Table 8) and Location*sex (Pillai’s trace 0.9435=F, 0.4638=Prob>F shown in Table 6).

Discussion

Based on this study, there were significant variations in toepad morphology between lizards from different locations that were exposed to perch diameters that greatly varied in size. Variations in TPF, LF, and LR by location were significant; although it was not significant for TPR. This means that lizards have different requirements for perching on different surfaces. There appears to be a balance point between perch diameter and required toepad structure. The Pahokee site, which had the widest perches, contained the least number of lamellae and the middle value for TPF, which implies that toe pad structure is less significant when wide diameter perches are available. This may be the result of distribution of mass across the reach of the animal, so required static friction at individual points is less (Zani 2000). Inversely, the conditions of P2 favored a thinner and longer toepad with more lamellae. Meanwhile, P1 conditions favored a wider toepad with a moderate number of lamellae, which provides balance to lizards on extremely small perch diameters (Elstrott and Irschick 2004).
It was mentioned in the laboratory that the Anolis lizards often use the claws on their rear toes to literally hang from a surface facing downward. Additionally, if the number of lamellae is used as a substitute for length of toepad we see that, overall, the rear toe is much longer but the width does not increase significantly. This perhaps means that the difference in perching behavior of lizards, when oriented facing up or down, has an effect on the morphology of the rear toe, which perhaps is independent of perch diameter. Previous studies only concluded that lizard claws do not aid a lizard in exerting a force when clinging to a surface, but it did not study whether the structure of a toepad could be altered when the claw was used by lizards to hang downward (Bloch and Irschick 2004). This could warrant a further laboratory study on the length of the rear claw in reference to a difference in available perching surfaces.
In conclusion, to solidify the results obtained in this study and prove that phenotypic plasticity is at work, not micro-evolution, it would be necessary to run a study in the laboratory were lizards are raised under controlled conditions (Losos et al. 2000). In a laboratory study it would be possible to control to which perches the lizards are solely exposed to. Although the three sites used in this study varied in available perch diameter, it is impossible to know all the perches each lizard collected used. A simpler lab experiment would be to test the toepad morphology of lizards exposed to perches with wide perch diameters versus small perch diameter because it is easier to see the changes when only analyzing two extreme possibilities rather than three. Therefore, further studies on toepad structure will provide additional knowledge on how lizards are able to change their morphology to survive and reproduce in new surroundings.
Acknowledgements

We would first and foremost like to thank Dr. Campbell for providing us with a project that allowed us to work in the lab. We also want to thank him for his continuous input and guidance throughout our study and data analysis.


Literature Cited


Bloch N., D. J. Irschick. 2005. Toe-clipping dramatically reduces clinging performance in a pad-bearing lizard (Anolis carolinensis). Journal of Herpetology 39:288-293.

Campbell T. S., A. C. Echternacht. 2003. Introduced species as moving targets: changes in body sizes of introduced lizards following experimental introductions and historical invasions. Biological Invasions 5:193-212.

Elstrott, J., D. J. Irschick. 2004. Evolutionary Correlations Among Morphology, Habitat Use, and Clinging Performance in Caribbean Anolis lizards. Biological Journal of the Linnean Society 83:389-398.

Irschick D. J., C. C. Austin, K. Petren, R. N. Fisher, J.B. Losos, O. Ellers. 1996. A comparative analysis of clinging ability among pad-bearing lizards. Biological Journal of the Linnean Society 59:21-35.

Irschick, D. J., E. Carlisle, J. Elstrott, M. Ramos, C. Buckley, B. Vanhooydonck, J. Meyers, A. Herrel. 2005. A Comparison of Habitat Use, Morphology, Clinging Performance and Escape Behavior Among Two Divergent Green Anole lizard (Anolis carolinensis) Populations. Biological Journal of the Linnean Society 85:223-234.

Irschick D. J., A. Herrel, B. Vanhooydonck. 2006. Whole-organism studies of adhesion in pad- bearing lizards. Journal of Comparative Physiology A 192:1169-1177.

Losos, J. B., K. I. Warhelt, T. W. Schoener. 1997. Adaptive Differentiation Following Experimental Island Colonization in Anolis Lizards. Nature 387:70-73.

Losos, J. B., D. A. Creer, D. Glossip, R. Goellner, A. Hampton, G. Roberts, N. Haskell, P. Taylor, J. Etling. 2000. Evolutionary Implications of Phenotypic Plasticity in the Hindlimb of the Lizard Anolis sagrei. Evolution 54:301-305.

Macrini, T. E., D. J. Irschick, J. B. Losos. 2003. Ecomorphological Differences in Toepad Characteristics Between Mainland and Island Anoles. Journal of Herpetology 37:52-58.

Zani, P. A. 2000. The comparative evolution of lizard claw and toe morphology and clinging performance. Journal of Evolutionary Biology 13:316-325.

[Comrade Tortoise]

Very, very nice work. I am however insanely jealous that you will publish in my field before I do...

[Shark Bait]

I actually have a stack of possible papers in ecology of anoles and such just need to talk to DR Campbell.

[Mayabird]

Wow, awesome! Congrats, man.

If I may ask, where are you hoping to publish it?

[Shark Bait]

probably one of the herp journals I'm working pritty closely with Dr. Campbell he's kinda advising me and much of my research is intertwined with his. I might have to turn over some of my data to him in which case i'll be listed as a co author with him and Dr. Lossos in which case the paper would probably be published in Evolution as part of a study on phenotypic plasticity. I've got another paper on the effects of preservation on spinal compression in lizards that is a spin off of this (extra data was collected but not used for this on how SVL had shrunk) that will probably be published in (i think its called) Herp. Review. In any event i'm going to be here all summer continuing some research so it should be rather interesting to see what happens.

[Graey]

This madness is making my major look like Special Ed.

[Shark Bait]

Is it bad this research makes more sense to me than the classes i have to take so i can go do this research professionally?

[Comrade Tortoise]

No. Not at all.