Pacific Island Anoles
|Above: Seven species of anoles found on the islands in the Eastern Tropical Pacific (ETP). Top row, left to right: Dactyloa agassizi (Isla Malpelo), Dactyloa gorgonae (Isla Gorgona), Norops townsendi (Isla Cocos). Bottom row: Norops medemi, Norops parvauritus, Dactyloa princeps, Dactyloa chocorum (all Isla Gorgona).|
There are 435 species in the genus Anolis (sometimes divided into Norops and Dactyola) and while they are one of the most heavily studied lizard clades most of the work has been done on Caribbean species. However, there are seven eastern Pacific Islands species that remain poorly studied. The seven species are known from the Islas Cocos, Gorgona, and Malpelo. Anoles occupying these islands span the extreme ends of the dactyloid phylogeny and are highly variable in their ecology and natural history. In a new paper, Phillips et al. (2019) present a phylogenetic analysis of eastern Pacific island anoles considering the greater anole phylogeny and estimate the timing of divergence from mainland lineages for each species. They found two species of solitary anoles (D. agassizi and N. townsendi) diverged from mainland ancestors prior to the emergence of their respective islands. They also present population-wide morphological data that suggests that both display sexual size dimorphism, like single-island endemics in the Caribbean. All lineages on Isla Gorgona likely arose during past connections with South America, and ecologically partition their habitat. They also highlight the importance of conservation of these species and island fauna in general.
They found Dactyola agassizi and Norops townsendi are ecological generalists unlike solitary Lesser Antillean anoles. Norops townsendi appears to clearly conform to this generalization, given that is was found ubiquitously on Isla Cocos in terms of perch height, diameter, and type. Dactyloa agassizi has distinctly unique behavioral characteristics that challenge the original meaning of generalist as applied to the Lesser Antillean anoles. The food web of Isla Malpelo appears to be very tight given the lack of vegetation and scarcity of obvious food resources for all the island inhabitants. Everything seems to revolve around the birds that visit the island, particularly the Nazca Booby (Sula granti). Any food dropped by the birds, and all waste products were immediately consumed by all Dactyloa agassizi, as well as the lizard Diploglossus millepunctatus (commonly called the Malpelo Galliwasp) and crabs which congregate around these resources. The crabs and Diploglossus attempt to capture any Dactyola agassizi that venture too close, and the crabs will also consume eggs of all species. Previous observers reported that D. agassizi ate both insects and seeds, and that individuals would quickly consume potential food items revealed when rocks were turned over. All D. agassizi departed from typical anole behavior in being very curious, climbing on, and licking the observers (clearly investigating food possibilities), never displaying any defensive behaviors or territoriality. Therefore, insofar as their environment allowed them, D. agassizi appeared to be an ecological generalist. Isla Malpelo is unlike most other islands that are home to anoles, so it is not surprising that D. agassizi departs from the general patterns observed for solitary Caribbean anoles.
Phillips, J.G., Burton, S.E., Womack, M.M., Pulver, E. and Nicholson, K.E., 2019. Biogeography, Systematics, and Ecomorphology of Pacific Island Anoles. Diversity, 11(9), p.141.