Dueling Anole Adaptive Radiations on the Macroevolutionary Stage

In a new study published in the Proceedings of the National Academy of Sciences, Patton et al. (2021) examine island and mainland radiations of Anolis lizards in an effort to understand what occurs when “adaptive radiations collide.” Discussion of mainland anoles merits featuring one of the oddest mainland species, the Ecuadorian Anolis proboscis (female and male pictured here; credit Santiago Ron [Wikimedia Commons]).

New literature alert!

Upon hearing “anole lizards,” those in the evolution and ecology community familiar with the outstanding diversity of Anolis lizards may immediately reflect on the replicative adaptive radiations that have occurred in the Greater Antilles, painting a portrait of adaptation, convergence, and ecological character displacement that has served as the basis of research among Caribbean biologists for decades. But, perhaps, what is less generally appreciated is that the vast bulk of Anolis lizard diversity (currently sitting at 436 species, per the ReptileDatabase) actually occurs on mainland Central and South America! Indeed, if we were to zoom out on the Anolis Tree of Life, we could pick out three major clades that represent independent adaptive radiations– one in the Greater and Lesser Antilles, and then two on the Mainland. Hence, as has been appreciated by many Anolis biologists before (most recently, Huie et al. 2021), the multiple radiations of these lizards provides the substrate to examine not only convergence, but, additionally, what happens when these clades come into contact? What happens when adaptive radiations collide?

This question forms the basis (and title) for a recently published study by Patton et al. (2021), who attempt to untangle themes of adaptation, historical biogeography, convergence and divergence in ecology and morphology, and the diversification dynamics of the three major Anolis radiations.

When adaptive radiations collide: Different evolutionary trajectories between and within island and mainland lizard clades

In PNAS

Patton, Harmon, Castañeda, Frank, Donihue, Herrel, and Losos

Abstract:

Oceanic islands are known as test tubes of evolution. Isolated and colonized by relatively few species, islands are home to many of nature’s most renowned radiations from the finches of the Galápagos to the silverswords of the Hawaiian Islands. Despite the evolutionary exuberance of insular life, island occupation has long been thought to be irreversible. In particular, the presumed much tougher competitive and predatory milieu in continental settings prevents colonization, much less evolutionary diversification, from islands back to mainlands. To test these predictions, we examined the ecological and morphological diversity of neotropical Anolis lizards, which originated in South America, colonized and radiated on various islands in the Caribbean, and then returned and diversified on the mainland. We focus in particular on what happens when mainland and island evolutionary radiations collide. We show that extensive continental radiations can result from island ancestors and that the incumbent and invading mainland clades achieve their ecological and morphological disparity in very different ways. Moreover, we show that when a mainland radiation derived from island ancestors comes into contact with an incumbent mainland radiation the ensuing interactions favor the island-derived clade.