New paper: Ecological opportunity from innovation, not islands, drove the anole adaptive radiation
Martha Muñoz and I recently published a new paper in Systematic Biology - Ecological opportunity from innovation, not islands, drove the anole lizard adaptive radiation. We revisit a classic mainland versus island framework, comparing rates of speciation and morphological evolution between mainland and island anoles. In addition to this base comparison, we also compare evolutionary rates between Caribbean island anoles that dispersed to their host island (dispersal-based speciation) and those that arose in situ (in situ speciation). Lastly, we compared evolutionary rates among the the four major islands (Cuba, Hispaniola, Jamaica, and Puerto Rico). As the title suggests, we comprehensive found no signal of "island effects" on the rates of speciation or morphological evolution. We show two examples in which accounting background rate variation (i.e., rate variation not attributable to the discrete character) prevented would-be false positives. The first being comparing rates of morphological evolution between the mainland and islands and the second, comparing rates morphological evolution between dispersal and in situ speciation modes (these results are detailed in the Supplemental Materials). These cases of would-be false positives points to the importance of accounting for rate heterogeneity, in particularly incorporating appropriate null models (i.e., no rate variation is generally an unrealistic null). In particular, the magnitude of these would-be false positives (3-fold rate differences) also highlights that seemingly large effects are also vulnerable to being false positives.
In light of the lack of "island effects", we conclude the paper with a simple comparison of anoles with candidate sister taxa (Polychrus and Corytophanidae) (note: the identity of the sister group is unresolved). Anoles have several putative innovations - dewlaps and adhesive toe pads. Since both candidate sister groups have dewlaps, but lack toe pads, there's a straightforward framework to tease apart their relative importance in moderating the tempo of evolution. We found that anoles have faster speciation rates than both putative outgroups and there's a clear bout of speciation associated with the origin of Anolis. Speciation rates then decline through time - a classic macroevolutionary signal of adaptive radiation (i.e., waning ecological opportunity). We interpret these results as pointing to an Anolis adaptive radiation driven by the origin of adhesive toe pads, rather than dewlaps or islands.
Citation: Burress, E.D. and M.M. Muñoz. 2021. Ecological opportunity from innovation, not islands, drove the anole lizard adaptive radiation. Systematic Biology, syab031.