Project Background

The work described here was done in the Derryberry Lab and driven primarily by two big, overarching questions: (1) how do animal communication systems arise and persist? and (2) can cognitive ability be sexually selected for? These two questions overlap quite nicely when studying songbirds, because their learned communication system, song, is used in mate choice. 

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First, how do animal communication systems arise and persist? 

Past research and theory on animal signaling indicates that the communication signals most likely to persist through evolutionary time are those that are costly and therefore reliable (here I will add a shameless plug for my current advisor's book, The Evolution of Animal Communication, for a more thorough explanation). Research on temperate songbirds has indicated that song is a reliable indicator of many aspects of male health and fitness, because it is costly to learn early in life and to produce later in life. 

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When we began this research, there was an interesting new hypothesis being tested, the Cognitive Capacity Hypothesis, that attempted to connect the costs of learning song with its utility as an assessment signal (something females pay attention to when selecting a mate). Research in the past few decades had established robust correlations between developmental stress, development of song-learning brain regions, and song attractiveness. This indicated that song was a valuable assessment signal of male quality, as developmentally stressed males had lower quality song and were lower quality mates in other ways as well. The "Cognitive Capacity Hypothesis" was an extension of this work, and posited that song is a valuable assessment signal because it is learned, and therefore dependent on general brain function. To relate this back to costly, reliable signals, bird song may be a useful assessment signal because it allows a female to assess a male's general brain function, which is theoretically relevant both to his quality as a "coparent" and the genes he will contribute to offspring. Perhaps over simplistically, this hypothesis assumed that cognitive ability is general in nature and that smarter is always better, two assumptions that are being increasingly questioned in birds. 

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How does this relate to the sexual selection of cognitive ability?

There has been interest in whether sexual selection can explain cognitive ability for a very long time (Darwin, for instance, speculated that humans evolved various cognitive skills to impress mates). In songbirds it takes an interesting form, particularly paired with evidence that learned song can reflect developmental conditions and therefore gross brain function. Though song may have evolved as an assessment signal because it contains relevant information about a male's brain function, could selective pressures that favor complex or varied song then inadvertently select for higher cognitive ability? Like the cognitive capacity hypothesis, this hypothesis assumes that selection on a brain for one cognitive skill (here, song learning), may end up acting on general cognitive ability.  

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Questions

Early work on this hypothesis (see Boogert et al. 2008) found correlations between male performance on a cognitive task and aspects of song that females tend to prefer. This inspired two questions for our research:

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(1) Do females prefer the songs of "smarter" males?

(2) How does female cognitive ability affect mate choice, given that females also learn to recognize, if not produce, song?

 

The first question is addressed in Howell et al. 2020. 

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The second question is addressed in Howell et al. 2019.

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