Acrobatic Courtship Display Coevolves with Brain Size in Manakins (Pipridae)

Abstract

Acrobatic display behaviour is sexually selected in manakins (Pipridae) and can place high demands on many neural systems. Manakin displays vary across species in terms of behavioural complexity, differing in number of unique motor elements, production of mechanical sounds, cooperation between displaying males, and construction of the display site. Historically, research emphasis has been placed on neurological specializations for vocal aspects of courtship, and less is known about the control of physical, non-vocal displays. By examining brain evolution in relation to extreme acrobatic feats such as manakin displays, we can vastly expand our knowledge of how sexual selection acts on motor behaviour. We tested the hypothesis that sexual selection for complex motor displays has selected for larger brains across the Pipridae. We found that display complexity positively predicts relative brain weight (adjusted for body size) after controlling for phylogeny in 12 manakin species and a closely related flycatcher. This evidence suggests that brain size has evolved in response to sexual selection to facilitate aspects of display such as motor, sensorimotor, perceptual, and cognitive abilities. We show, for the first time, that sexual selection for acrobatic motor behaviour can drive brain size evolution in avian species and, in particular, a family of suboscine birds.

Relative Brain Size Is Not Correlated with Display Complexity in Manakins: A Reanalysis of Lindsay et al. (2015)

“…Their analyses yielded a positive correlation between relative brain size and display complexity ( fig. 2 in Lindsay et al [2015]). However, their analyses have several potential problems, and alternative methods that correct these problems lead to different conclusions.…”

“…Lindsay et al [2015] hypothesized that a more complex acrobatic display will result in an increased demand of neural computation and, therefore, an increase in brain size. Their analyses yielded a positive correlation between relative brain size and display complexity ( fig.…”

“…In the March 2015 issue of Brain, Behavior and Evolution , Lindsay et al [2015] published a study on brain size variation in manakins (Pipridae), a family of passerine birds that exhibit remarkable variation in courtship displays, including complex, dance-like, acrobatic courtship displays in Lindsay et al [2015] failed to remove the allometric effect of body size on brain size. This is clearly illustrated in figure 1 a, which plots the relative brain size for each species (from online suppl.…”

“…This is clearly illustrated in figure 1 a, which plots the relative brain size for each species (from online suppl. table 2 in Lindsay et al [2015]) against the arithmetic mean of the absolute brain size for each species (calculated from online suppl. table 2 in Lindsay et al [2015]).…”

“…table 2 in Lindsay et al [2015]) against the arithmetic mean of the absolute brain size for each species (calculated from online suppl. table 2 in Lindsay et al [2015]). The correlation between these two variables is almost 1 (r 2 = 0.98), meaning the relative and the absolute brain values are almost identical.…”