Can convergence in mixed-species flocks lead to evolutionary divergence? Evidence for and methods to test this hypothesis

Abstract

One of the most fundamental goals of modern biology is to achieve a deep understanding of the origin and maintenance of biodiversity. It has been observed that in some mixed-species animal societies, there appears to be a drive towards some degree of phenotypic trait matching, such as similar coloration or patterning. Here we build on these observations and hypothesize that selection in mixed-species animal societies, such as mixed-species bird flocks, may drive diversification, potentially leading to speciation. We review evidence for possible convergent evolution and even outright mimicry in flocks from southwestern China, where we have observed several cases in which species and subspecies differ from their closest relatives in traits that match particular flock types. However, understanding whether this is phenotypic matching driven by convergence, and whether this divergence has promoted biodiversity, requires testing multiple facets of this hypothesis. We propose a series of steps that can be used to tease apart alternative hypotheses to build our understanding of the potential role of convergence in diversification in participants of mixed-species societies. Even if our social convergence/divergence hypothesis is not supported, the testing at each step should help highlight alternative processes that may affect mixed-species flocks, trait evolution and possible convergence. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Investigating flock-associated mimicry: examining the evidence for, and drivers of, plumage mimicry in the greater and lesser necklaced laughingthrush

“…From the empirical perspective, there have been many instances where birds that participate in MSFs have been hypothesized to look similar to each other; a previous study showed that for the majority of these cases, the birds do look more similar to each other than closely related species or others in the same habitat, at least to human eyes [ 26 ]. A recent article [ 27 ] has also hypothesized that plumage convergences in MSFs could even lead to speciation, if there are flock types in different areas that have distinct plumage colours (such as ‘yellow belly’ or ‘rufous-white’ flocks [ 28 ]) and then different populations of the same species come to resemble these different flock types. Nonetheless, it remains unclear whether flock-associated mimicry is a separate phenomenon from ISDM, or is closely connected to it.…”