Ecological opportunity from innnovation, not islands, drove the Anole lizard adaptive radiation

Islands are thought to facilitate adaptive radiation by providing release
from competition and predation. Anole lizards are considered a classic
example of this phenomenon: different ecological specialists (‘ecomorphs’)
evolved in the Caribbean Greater Antilles (Cuba, Hispaniola, Jamaica, and
Puerto Rico), resulting in convergent assemblages that are not observed in
mainland Latin America. Yet, the role of islands in facilitating adaptive
radiation is more often implied than directly tested, leaving uncertain
the role of biogeography in stimulating diversification. Here, we assess
the proposed “island effect” on anole diversification using Bayesian
phylogenetic comparative methods that explicitly incorporate rate
heterogeneity across the tree and demonstrate two cases of would-be false
positives. We discovered that rates of speciation and morphological
evolution of island and mainland anoles are equivalent, implying that
islands provide no special context for exceptionally rapid
diversification. Likewise, rates of evolution were equivalent between
island anoles that arose via in situ versus dispersal-based mechanisms,
and we found no evidence for island-specific rates of speciation or
morphological evolution. Nonetheless, the origin of Anolis is
characterized by a speciation pulse that slowed over time – a classic
signature of waning ecological opportunity. Our findings cast doubt on the
notion that islands catalyzed the anole adaptive radiation and instead
point to a key innovation, adhesive toe pads, which facilitated the
exploitation of many arboreal niches sparsely utilized by other iguanian
lizards. The selective pressures responsible for arboreal niche
diversification differ between islands and the mainland, but the tempo of
diversification driven by these discordant processes is indistinguishable.