Urban environments are widespread and expanding across much of the earth, and this urbanization likely affects the flora and fauna in its path. Anoles are no exception and are frequently observed perching on anthropogenic structures. Thus, Chris Thawley, a post-doc in Jason Kolbe’s lab at the University of Rhode Island, and colleagues wondered how the abiotic and biotic changes in urban areas influence anole traits.
Thawley compared populations in urban and natural habitats of two species that we’re quite familiar with on Anole Annals – the Brown Anole (Anolis sagrei) and the Puerto Rican Crested Anole (Anolis cristatellus). Thawley found that A. sagrei prefers warmer temperatures than A. cristatellus, but that urban anoles do not differ in thermal preference than natural anoles for either species. Alternatively, urban male A. cristatellus and both sexes of urban A. sagrei were larger than their natural counterparts. As for parasites, A. sagrei had a higher parasite prevalence than A. cristatellus, but urban anoles did not differ from natural anoles in either species in parasite prevalence. However, for the A. sagrei that were parasitized, urban A. sagrei had higher parasite loads than natural A. sagrei.
These findings show that urbanization can influence anole morphology and parasite ecology. Thawley has just begun this work, and I look forward to seeing his future research on anole adaptation to urban environments!
Urbanization creates drastic changes to habitats leading to differences in microclimate, perch characteristics and distribution, and ecological communities (competitors, prey, and predators) when compared to natural (forest) habitats. Studies have found increased rates of mortality of many urban species due to generalist urban-tolerant predators such as raccoons, feral cats, and domestic animals (Ditchkoff 2006). Anolis lizards are able to voluntarily drop their tails (“autotomize”) when challenged by a predator, enabling their escape in many instances. The maimed lizards are able to regenerate their lost tails, though the replacement tail is a rod of cartilage and not the original bony vertebrae. The regenerated tail portions are often a different color and texture, and the lack of vertebrae / cartilage rod are clearly visible in X-rays.
We hypothesized that autotomy rates would be more similar between urban areas in different municipalities than to natural areas in the same municipality due to similar predator regimes in urban sites across the island. We compared the frequency and pattern (number of caudal vertebrae remaining) of caudal autotomy of A. cristatellus between urban and natural areas in Puerto Rico.
X-rays of our samples with an intact tail (A) and an autotomized tail (B).
We sampled A. cristatellus from paired natural and urban sites in four Puerto Rican municipalities: San Juan, Mayagüez, Ponce, and Arecibo. The natural sites were high quality natural forests and the urban sites were high-density residential areas. Urban sites were dominated by asphalt and other impervious surfaces, had sparse tree cover, and a large fraction of potential perches were manmade surfaces such as walls and fences. We scored 967 X-rays from these eight sites for caudal autotomy and counted the number of remaining tail vertebrae. We tested for an effect of urbanization on caudal autotomy by fitting a logistic regression model with municipality (San Juan, Mayagüez, Ponce, Arecibo) and site type (urban, natural), and their interactions, as model factors, and body size as a covariate.
Our data shows that lizards found in urban sites have a larger probability of having autotomized tails.
Interestingly, we found higher rates of autotomy in all urban populations compared to nearby natural areas. Differences in autotomy might be explained by differences in predator density and efficiency (Bateman 2011). For example, inefficient predators (those that more often than not fail to capture their prey) tend to leave behind more lizards with broken and regenerated tails (Schoener 1979). In addition, a greater abundance of predators could result in more predation attempts. Unfortunately, we did not collect data on predator abundances or community composition, so we cannot distinguish between these (non-mutually exclusive) explanations. Higher rates of autotomy in urban areas could thus reflect any of a variety of factors, including (but not restricted to) inefficient predators in urban areas, a shortage of refuges offering protection from predators, or an increase in predator density.
For lizards with autotomized tails, we found no significant difference in caudal vertebrae number between urban and natural sites.
Lastly, we did not find that lizards with autotomized tails in urban areas had lost more (or less) of their original tail to caudal autotomy. Since regenerated tails cannot be autotomized past the original break point (i.e. cartilage cannot autotomize), this suggests that lizards in urban areas are no more likely to be subject to multiple unsuccessful predation attempts (resulting in caudal autotomy) than lizards in natural forest. Future investigation quantifying predation attempts or predator community composition in urban and forest habitats could help us better understand the source of this intriguing pattern.
BATEMAN, P. W., AND P. A. FLEMING. 2011. Frequency of tail loss reflects variation in predation levels, predator efficiency, and the behaviour of three populations of brown anoles. Biological Journal of the Linnean Society 103:648–656.
DITCHKOFF, S. T. 2006. Animal behavior in urban ecosystems: modifica- tions due to human-induced stress. Urban Ecosystems 9:5–12.
SCHOENER, T. W. 1979. Inferring the properties of predation and other injury-producing agents from injury frequencies. Ecology 60:1110–1115.
Anolis cristatellus on a smooth, vertical substrate in Puerto Rico (photo by K. Winchell)
In urban areas, the number of natural substrates (e.g. trees) is reduced. In their place are novel manmade substrates (e.g. walls, metal gates). These surfaces undoubtedly have different properties relevant to anole locomotion: they are smoother, harder, and (in the case of walls) much broader and flatter compared to natural surfaces in a forest. In urban areas lizards still use these substrates at high frequency, but do they do so effectively? Kolbe and co-authors began to dive into this complex topic in their recent publication, “City slickers: poor performance does not deter Anolis lizards from using artificial substrates in human-modified habitats” (Kolbe et al. 2015).
The relationship between habitat use, morphology, and performance for anoles has been extensively studied in natural environments (reviewed in Losos 2009). Urban environments add new dimensions to this area of research. Resource distribution and abundances differ drastically compared to natural areas. For example, the distribution of available perches and what they are made of in urban habitats is very different from a forest. Moreover, the properties of these resources differ drastically as well: urban substrates are smoother, broader, and have different thermal properties, to start. Understanding these differences in habitat use and how they influence performance and, ultimately, adaptive responses in anoles is the topic of ongoing collaborative research that I (K. Winchell) and the Kolbe lab have been conducting.
Evolution 2015 is officially over and we have all sadly left beautiful Guarujá, Brazil. There were a lot of great talks and posters and a great representation of South American students and researchers. For coverage on the conference as a whole, check out #evol2015 on twitter! The herps were few and far between (I only saw 2 in my 16 days in Brazil!) but the posters and talks on herps were numerous. Unfortunately, anoles were poorly represented at Evolution this year with only three anole talks and a couple of others that briefly highlighted anoles. If you weren’t able to make it to Brazil, I’ve got the recap for you here.
A glimpse at the variation in gecko toepads
Starting off in one of the first sessions was a talk by Travis Hagey titled “Independent Origins, Tempo, and Mode of Adhesive Performance Evolution Across Padded Lizards.” Although his talk was mostly about geckos, he did shine the spotlight on anoles for a few minutes. He focused on the phylogenetic pattern of toepad adhesion in pad-bearing lizards: geckos, skinks, and anoles. Specifically he looked at how clinging ability (measured as angular detachment – check out one of his videos showing this) varied within and among clades. Unsurprisingly, he found that anoles don’t cling nearly as well as geckos. He also demonstrated that gecko toepad diversification best followed a Brownian motion model with weak OU and anole toepad diversification was best fit by a strong Ornstein–Uhlenbeck process. In other words, gecko toepads diversified slowly over a very long period while anoles were quickly drawn towards an optimum over a short time-period. Travis concluded that these patterns explain why there is a large amount of diversity in gecko toepads but not in anole toepads.
Urbanization poses a major challenge for many species, altering natural environments in ways that few animals can tolerate. Despite this, some species persist and even thrive in urban areas. In my research in the Revell lab at UMass Boston, I’ve been studying adaptation in response to urbanization in Anolis cristatellus, the Puerto Rican crested anole. However, among anoles urban tolerance is by no means restricted to A. cristatellus. We suspect that readers of this blog have probably observed many different anole species occupying and thriving in urban areas. Consequently, we would like to ask for your help in gathering some information on this topic.