Weak evidence for fine-scale genetic spatial structure in three sedentary Amazonian understorey birds

The ecological characteristics of a species, along with small-scale landscape features are known to affect the patterns of genetic structure within populations. Due to dispersal limitation, closely-related individuals tend to be closer spatially, leading to spatial genetic structure. Physical barriers also may prevent individuals from dispersing further, and lead individuals on one side of a barrier to be more related than individuals from different sides. We tested these hypotheses by examining patterns of fine-scale spatial genetic structure within populations of three relatively sedentary Amazonian-forest understorey birds that differ in their ecological requirements. We sampled birds in a 10,000 ha reserve, covered by largely undisturbed old-growth forests and traversed by a central ridge. We found positive spatial genetic structure at short distances only for Percnostola rufifrons, a treefall-gap specialist. Positive genetic structure occurred at 6 km for Glyphorynchus spirurus, a solitary bark-forager; no spatial genetic structure was found for Gymnopithys rufigula, an army-ant follower. Individuals of none of the three species were more related on a given side of the ridgeline than between different sides but, at greater distances, there was a tendency of individuals located on opposite sides of the ridgeline to be less related than individuals located on the same side, for all species analysed. Our study indicates that local topographic features do not prevent, but likely reduce, gene flow within populations in continuous forests, and that the development of fine-scale spatial genetic structure may depend on the dispersal propensity of a species. Thus, studies of species assemblages need to account for the different ecological characteristics of the constituent species.