Plumage convergence resulting from social mimicry in birds? A tetrachromatic view

Abstract

35Social mimicry may lead to convergent evolution when interactions with conspecific and 36 heterospecific individuals drive evolution towards similar phenotypes in different species. Several 37 hypotheses accounting for convergence in communication signals based on mechanisms of social 38 mimicry exist, but evaluations of how similar species are given the visual system of receptors of 39 such signals have been ostensibly missing from tests of such hypotheses. We used plumage 40 reflectance measurements and models of avian color discrimination to evaluate the efficacy of 41 visual deception and therefore the plausibility of mimicry hypotheses accounting for plumage 42 convergence among six species of passerine birds in the flycatcher family (Tyrannidae) with 43 strikingly similar plumage. We rejected interspecific social mimicry hypotheses as an explanation 44 for the similarity between one putative model species and putative mimics because deception seems 45 unlikely given the visual system of passerines. However, plumage similarity was consistent with a 46 role for selective pressures exerted by predators because dorsal coloration of putative model and 47 mimic species was indistinguishable by visually oriented raptors. Experiments and behavioral 48 observations are necessary to better characterize social interactions and to test predictions of 49 alternative mimicry hypotheses proposed to account for convergence. 50 51 Keywords: Convergence, coloration, visual models, social mimicry, interspecific social dominance 52 mimicry, predation. 53 54 55 56Convergent evolution, the process through which two or more distinct lineages independently 57 acquire similar traits, reveals that the paths of evolution are not infinite, but may instead be rather 58 restricted. Convergence may happen rapidly or over the course of millions of years by random drift 59[1] or, more likely, because a given phenotypic trait is repeatedly favored by natural selection in a 60 particular environment [2,3]. Likewise, convergence may also occur via biases in the production of 61 phenotypic variation, such as shared developmental constraints [3][4][5]. One well-studied form of 62 convergent evolution is mimicry, in which one species (the mimic) evolves to resemble another 63 species (the model), often to deceive a third species (the receptor; [6]). 65There are numerous examples of phenotypic convergence among birds [7][8][9][10][11][12][13][14][15], and several authors 66 have proposed hypotheses to explain this phenomenon in the context of mimicry [7,13,[16][17][18][19][20][21][22]. 67Among leading ideas suggested to account for phenotypic convergence in birds, the social mimicry 68 hypothesis [18] posits that convergent similarity in traits like coloration and plumage patterns may 69 evolve to promote efficient communication maintaining cohesion both among conspecifics and 70 heterospecifics in mixed-species flocks. A variant of this hypothesis suggests that rather than 71 maintaining cohesion of mixed flocks, social mimicry serves mainl...