Saturday, March 10, 2018

[Ornithology • 2018] Macroevolutionary Patterning of Woodpecker Drums reveals How Sexual Selection Elaborates Signals Under Constraint

in Miles, Schuppe, Ligon & Fuxjager, 2018.

Sexual selection drives elaboration in animal displays used for competition and courtship, but this process is opposed by morphological constraints on signal design. How do interactions between selection and constraint shape display evolution? One possibility is that sexual selection continues exaggeration under constraint by operating differentially on each signal component in complex, modular displays. This is seldom studied on a phylogenetic scale, but we address the issue herein by studying macroevolutionary patterning of woodpecker drum displays. These territorial displays are produced when an individual rapidly hits its bill on a hard surface, and drums vary across species in the number of beats included (length) and the rate of drumbeat production (speed). We report that species body size limits drum speed, but not drum length. As a result of this biomechanical constraint, there is less standing variation in speed than length. We also uncover a positive relationship between sexual size dimorphism and the unconstrained trait (length), but with no effect on speed. This suggests that when morphology limits the exaggeration of one component, sexual selection instead exaggerates the unconstrained trait. Modular displays therefore provide the basis for selection to find novel routes to phenotypic elaboration after previous ones are closed.

KEYWORDS: sexual selection, animal behaviour, signal design, constraint 

Figure 1. Cladogram of the woodpeckers (family: Picidae) from Dufort et al. [2016]. At the tips, longer bars indicate species with longer drums. Bars are coloured by drum speed (beats s–1), with warm colours (green to red) indicating progressively faster drums than cool colours (blue-green to blue). Edge colors indicate the evolution of drumming determined from ER Mk1 ancestral state reconstruction (black, drum; orange, drum-like signal; blue, no drum or drum-like signal). Silhouettes are aligned near their corresponding tips, and drawn to-scale based on phylogenetic PCA of body size.

Meredith C. Miles, Eric R. Schuppe, R. Miller Ligon IV and Matthew J. Fuxjager. 2018. Macroevolutionary Patterning of Woodpecker Drums reveals How Sexual Selection Elaborates Signals Under Constraint. Proc. R. Soc. B. 285; 20172628. DOI:  10.1098/rspb.2017.2628
M. J. Dufort. 2016. An augmented supermatrix phylogeny of the avian family Picidae reveals uncertainty deep in the family tree. Mol. Phylogenet. Evol. 94, 313–326.   DOI:  10.1016/j.ympev.2015.08.025

The evolution of woodpecker drums @meredithcmiles @fuxjagerlab  #openaccess #ProcB  

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