Anole Annals

The green anole, A. carolinensis, is the only native anole in North America. Over the years, the question of whether it is distinct from the Cuban A. porcatus has been debated–morphological differences are pretty minor, other than the Cubans generally being a bit larger.

Now, in an open access paper published last year in Ecology and Evolution, Johanna Wegener and colleagues have driven the final nail in the coffin of the idea that North American carolinensis is a distinct species.

For some time, we have known that carolinensis is nested phylogenetically in the western clade of porcatus, rending porcatus paraphyletic. This phylogeny indicates that North American populations are the result of a colonization event from western Cuba, perhaps 6-12 million years ago (see references in Wegener et al. paper).

From Wegener et al. (2019). Florida populations are usually referred to as “ carolinensis,” Cuban populations as “porcatus“

The novel contribution of the Wegener et al. paper is to look for evidence of hybridization between recently introduced “porcatus” from Cuba and native “carolinensis.” And she found it in spades! The abstract, pasted at the bottom of this post, provides some more details and, of course, you can read the paper itself.

So, Florida populations of the green anole are derived from Cuban populations, and the two readily interbreed when given a chance. Given these facts, there is no justification for treating North American populations as a distinct species. The morphological differences that do exist–quite minor–are the result of geographic variation. Paraphyly plus no reproductive isolation = one species!

But now here’s where it gets interesting. By the rules of zoological nomenclature, the older name has precedence, and so this single species takes the name Anolis carolinensis. That’s right: A. carolinensis is the correct name for Cuban green anoles! I’m sure that won’t go over so well in some quarters.

But it gets more interesting! Cuban Anolis porcatus as currently recognized is not a monophyletic entity, as shown in the attached figure, based on Glor et al. (2005). As the figure shows, eastern populations of porcatus are more closely related to A. allisoni (remember, North American populations are nested in the western clade). Given that the species-level distinctness of allisoni has not been question, most systematists would recognize the two clades of porcatus as different species. Thus, the eastern clade retains the name porcatus.

Bottom line: both A. carolinensis and A. porcatus occur in Cuba!

Abstract

In allopatric species, reproductive isolation evolves through the accumulation of genetic incompatibilities. The degree of divergence required for complete reproductive isolation is highly variable across taxa, which makes the outcome of secondary contact between allopatric species unpredictable. Since before the Pliocene, two species of Anolis lizards, Anolis carolinensis and Anolis porcatus, have been allopatric, yet thisvperiod of independent evolution has not led to substantial species‐specific morphologicalvdifferentiation, and therefore, they might not be reproductively isolated. Invthis study, we determined the genetic consequences of localized, secondary contactvbetween the native green anole, A. carolinensis, and the introduced Cuban green anole, A. porcatus, in South Miami. Using 18 microsatellite markers, we found that the South Miami population formed a genetic cluster distinct from both parental species. Mitochondrial DNA revealed maternal A. porcatus ancestry for 35% of the individuals sampled from this population, indicating a high degree of cytonuclear discordance. Thus, hybridization with A. porcatus, not just population structure within A. carolinensis, may be responsible for the genetic distinctiveness of this population. Using treebased maximum‐likelihood analysis, we found support for a more recent, secondary introduction of A. porcatus to Florida. Evidence that ~33% of the nuclear DNA resulted from a secondary introduction supports the hybrid origin of the green anole population in South Miami. We used multiple lines of evidence and multiple genetic markers to reconstruct otherwise cryptic patterns of species introduction and hybridization. Genetic evidence for a lack of reproductive isolation, as well as morphological similarities between the two species, supports revising the taxonomy of A. carolinensis to include A. porcatus from western Cuba. Future studies should target the current geographic extent of introgression originating from the past injection of genetic material from Cuban green anoles and determine the consequences for the evolutionary trajectory of green anole populations in southern Florida.

A few more photos. 1-3 are from Cienaga de Zapata area and 4 is from a cave near Havana (Parque Escaleras de Jaruco).

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Rachana applying fluorescent powder to a wild brown anole

If you’ve ever tried to note how often lizards mate, you’ve likely found yourself staring at an individual for hours at a time, sometimes with little to no movement at all, let alone observing copulations! Further, if you’re unable to catch the animal after your behavioral observations, you may not be able to draw any conclusions about traits that influence how successful an individual is at mating with another.

Rachana Bhave, a fourth year PhD candidate in Bob Cox’s lab at University of Virginia, studies pre- and post-copulatory sexual selection in brown anoles (Anolis sagrei). One of her interests includes estimating mating rates in the wild and, in particular, testing if traits such as body size directly influence these rates. Given the power required to detect selection statistically, using simple behavioral observations can be inefficient. Further, because selection is a measure of covariance between phenotype and fitness, one needs phenotypic values for each individual within her analyses. Thankfully, Rachana was able to come up with a robust technique to estimate mating rates using an island population of brown anoles in Florida: fluorescent powders!

To understand how size affects mating rate in the brown anole, Rachana and colleagues caught 153 adult male lizards in May and 128 adult male lizards in July, weighed them, and then assigned them to one of four fluorescent powder treatments. Each mass quartile was painted with a unique color of fluorescent powder on their cloaca and released to their initial capture location. After two days, all females on the island were captured and their cloaca were examined under UV light to look for the presence and color of fluorescent powder, which would suggest that she mated with a painted male. Using this technique, Rachana found that within two days, 24% of the captured females had mated in May and 48% had mated in July. These rates were shockingly high for such a short time frame!

A) Powdering an adult male brown anole; B) copulating brown anoles; C) powder visible on the cloaca of a female brown anole, evidence of copulation
Images from Rachana’s poster

Further, she found that both larger males and larger females mated significantly more than smaller males and females across the two sampling periods. Interestingly, 2% of females had multiple colors on their cloacas, which suggests they mated multiple times with males from different size classes in the two-day span. Because multiple matings within the same size class would be undetectable, this is likely an underestimation of multiple matings in the wild.

Next, Rachana plans to quantify male reproductive success using genetic parentage analysis to begin to tease apart how pre- and post-copulatory selection influences selection. We are all looking forward to her results next year! Meanwhile, you can take a look at her poster to find out more on her website.