High dispersal ability inhibits speciation in a continental radiation of passerine birds

Abstract

Dispersal can stimulate speciation by facilitating geographical expansion across barriers or inhibit speciation by maintaining gene flow among populations. Therefore, the relationship between dispersal ability and speciation rates can be positive or negative. Furthermore, an 'intermediate dispersal' model that combines positive and negative effects predicts a unimodal relationship between dispersal and diversification. Because both dispersal ability and speciation rates are difficult to quantify, empirical evidence for the relationship between dispersal and diversification remains scarce. Using a surrogate for flight performance and a species-level DNA-based phylogeny of a large South American bird radiation (the Furnariidae), we found that lineages with higher dispersal ability experienced lower speciation rates. We propose that the degree of fragmentation or permeability of the geographical setting together with the intermediate dispersal model are crucial in reconciling previous, often contradictory findings regarding the relationship between dispersal and diversification.

How do seemingly non-vagile clades accomplish trans-marine dispersal? Trait and dispersal evolution in the landfowl (Aves: Galliformes)

“…HWI is related to wing aspect/ratio, an important metric in flight performance [26,49]. Wings with high aspect ratio/high HWI are longer, narrower and produce greater lift than wings with low aspect ratio/low HWI.…”

“…Wings with high aspect ratio/high HWI are longer, narrower and produce greater lift than wings with low aspect ratio/low HWI. HWI correlates strongly with dispersal capabilities [49][50][51]. We calculated mean HWI for phasianoids and outgroups based on measurements from traditional museum skins with the wings prepared folded on the body.…”

Dispersal has inhibited avian diversification in Australasian archipelagoes

“…Recent studies of birds have found negative, positive and unimodal relationships between dispersal and diversification. For example, in the continental radiation of the Furnariidae, a diverse family of suboscine passerines from the Neotropics, there is a predominantly negative relationship between dispersal ability, as inferred from wing shape, and speciation rates estimated using a calibrated phylogeny [12]. By contrast, a macroevolutionary analysis of all bird families recovered a positive relationship between diversification rates and an index of dispersal propensity based on ecological characteristics [14].…”

“…Alternatively, the varied findings across studies may reflect real differences in the relationship between dispersal and diversification. In particular, the degree of discontinuity of the geographical setting may determine the relationship between dispersal and speciation rate [12]. Within continents, dispersal may have a predominantly negative effect because even poor dispersers can colonize remote areas, and increased dispersal results in elevated levels of gene flow across weak or moderate barriers.…”

“…Because of the highly discontinuous geography of Australasian archipelagoes, we predict that colonization is a limiting factor controlling rates of diversification, resulting in either a positive or a unimodal relationship between dispersal ability and diversification rates [11,12].…”