We investigated whether a
relationship exists between the number of lamellae and the height and diameter
of perches utilized by a diverse set of anoline lizards. Although
the number of lamellae on both the fore- and hindfoot is related to both
ecological variables, these results are confounded by body size.
When the effect of size is removed, the number of lamellae is related to
perch height, but not perch diameter. When the data are analyzed
in a phylogenetic framework, results are similar, but only the number of
lamellae on the forefoot is related to perch height. Consequently,
although inter- and intraspecific correlations exist among the number of
lamellae on different toes of the fore- and hindfeet, examining the number
of lamellae on a single toe may be insufficient for ecomorphological analyses.
Anolis lizards are famous for their expanded subdigital toepads that allow them to cling to smooth surfaces, such as leaves and hotel walls. These toe pads are composed of a set of enlarged scales, termed lamellae. Many of the lamellae are covered with millions of microscopic, hairlike projections termed setae. Recent studies indicate that the adhesive capabilities of these pads are a result of bonds formed between electrons on these setae and electrons on the surface of the substrate. Similar structures have evolved convergently in two others types of lizards, geckos and prasinohaemid skinks.
Anoles vary widely in the number of lamellae on their toe pads. Workers have long assumed that this variation was adaptive and related to habitat use, but the evidence underlying this belief was not substantial. One confounding problem is that a general relationship between body size and number of lamellae exists. Hence, it is possible that correlations between lamellae number and habitat use might be artifactual if body size and habitat use are related. In addition, previous studies had not incorporated information on evolutionary relationships, thus suggesting the possibility that results were confounded by phylogeny.
To address these questions, we measured the number of lamellae on four toes (two from the forefoot and two from the hindfoot) of 545 adult male lizards of 62 species of Caribbean Anolis lizards, plus the South American Phenacosaurus heterodermus (which is, phylogenetically, an anole). We also counted the number of lamellae on eight toes of 66 specimens--both male and female--of A. carolinensis from Louisiana.
We found that number of lamellae is related to perch height, perch diameter, and body size. When the effect of body size is statistically removed, number of lamellae is still related to perch height, but not to perch diameter. When these analyses are conducted with methods that take account of phylogenetic relationships, only the number of lamellae on the forefeet were still related to perch height. Hence, our results do reveal a statistically robust relationship between number of lamellae and habitat use, but they also reveal that some of the apparent correlations are artifacts of correlations with a third variable, body size, and of the pitfalls of analyzing data without regard to the evolutionary relationships of the species involved.
Anoles are also famous for the convergent evolution of habitat specialists on different islands of the Greater Antilles (Cuba, Hispaniola, Jamaica, and Puerto Rico). These habitat specialists--termed ecomorphs--occupy different microhabitats and exhibit morphological differences. Our analyses indicate that the ecomorph classes exhibit differences in number of lamellae on both the fore- and hindfeet, even when body size and phylogenetic relationships are considered.
Our analyses of variation
with A. carolinensis indicate that males have more lamellae on all
toes than females and that, within a sex, the number of lamellae on a given
toe was strongly related to number of lamellae on other toes. Within
a sex, number of lamellae is not correlated with body size; hence, these
correlations are not artifacts.