Phenotypic integration refers to the study of complex patterns of covariation among functionally related traits in a given organism. It has been investigated throughout the 20th century, but has only recently risen to the forefront of evolutionary ecological research. In this essay, I identify the reasons for this late flourishing of studies on integration, and discuss some of the major areas of current endeavour: the interplay of adaptation and constraints, the genetic and molecular bases of integration, the role of phenotypic plasticity, macroevolutionary studies of integration, and statistical and conceptual issues in the study of the evolution of complex phenotypes. I then conclude with a brief discussion of what I see as the major future directions of research on phenotypic integration and how they relate to our more general quest for the understanding of phenotypic evolution within the neo-Darwinian framework. I suggest that studying integration provides a particularly stimulating and truly interdisciplinary convergence of researchers from fields as disparate as molecular genetics, developmental biology, evolutionary ecology, palaeontology and even philosophy of science.

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Phenotypic integration: studying the ecology and evolution of complex phenotypes

The function of bird song is closely linked to sexual selection. A fundamental question regarding the evolution of sexually selected male signals is how their honesty is maintained. The neural space required for storing a large song repertoire size has traditionally been identified as a key constraint. However, it is often forgotten that bird song is a multifaceted behaviour, and that the different characters that comprise it have specific costs. Recent research has revealed the existence of new constraints, such as social aggression or learning opportunities, which limit the expression of several song characteristics. We review the existing evidence for each of these constraints, revealing some major gaps in our knowledge of this fascinating biological system.

The honesty of bird song: multiple constraints for multiple traits

Design of Playback Experiments P.K. McGregor, et al. Playback J.B. Falls. Integrating Playback C.K. Catchpole. What Studies on Learning Can Teach Us About Playback Design I.M. Pepperberg. Conducting Playback Experiments and Interpreting their Results H.C. Gerhardt. Quantifying Responses to Playback P.K. McGregor. Interactive Playback T. Dabelsteen. Playback as a Tool for Studying Contests Between Social Groups K. McComb. Song Overproduction, Song Matching, and Selective Attrition During Development D.A. Nelson. Male Quality and Playback in the Great Tit M.M. Lambrechts. Mechanisms and Function of Call-Timing in Male-Male Interactions in Frogs G.M. Klump, H.C. Gerhardt. Measuring Responses of Female Birds to Male Song W.A. Searcy. Field Experiments on the Perception of Song Types by Birds A.G. Horn. 2 additional articles. Index.

Playback and Studies of Animal Communication

Female songbirds are thought to assess males based on aspects of song, such as repertoire size or amount of singing, that could potentially provide information about male quality. A relatively unexplored aspect of song that also might serve as an assessment signal is a male’s ability to perform physically challenging songs. Trilled songs, such as those produced by swamp sparrows (Melospiza georgiana), present males with a performance challenge because trills require rapid and precise coordination of vocal tract movements, resulting in a trade-off between trill rate and frequency bandwidth. This trade-off defines a constraint on song production observed as a triangular distribution in acoustic space of trill rate by frequency bandwidth, with an upper boundary that represents a performance limit. Given this background on song production constraints, we are able to identify a priori which songs are performed with a higher degree of proficiency and, thus, which songs should be more attractive to females. We determined the performance limit for a population of swamp sparrows and measured how well individual males performed songs relative to this limit (‘‘vocal performance’’). We then compared female solicitation responses to high-performance versus lowperformance versions of the same song type produced by different males. Females displayed significantly more to highperformance songs than to low-performance songs, supporting the hypothesis that females use vocal performance to assess males. Key words: bird song, female choice, indicator mechanism, Melospiza georgiana, motor constraint, sexual selection, vocal performance. [Behav Ecol 15:163–168 (2004)]

Vocal performance influences female response to male bird song: an experimental test

http://alpha-leonis.lids.mit.edu/wordpress/wp-content/uploads/2014/04/tics-birdsong2011.pdf

Songs to syntax: the linguistics of birdsong

Female canaries are sexually responsive to special song phrases

Two-note syllables in canary songs elicit high levels of sexual display☆

We studied the mechanism of song production in the outbred common or domestic canary (Serinus canaria). The contribution that each side of the syrinx makes to song was investigated by observing the effect of unilaterally occluding the left or right primary bronchus, followed by section of the ipsilateral branch of the tracheosyringeal nerve. In other birds with a bilaterally intact vocal system we monitored airflow through each side of the syrinx, together with subsyringeal pressure, during spontaneous song. Song production by domestic canaries is not strongly lateralized as it is in the conspecific song-bred waterslager strain. Some syllables are produced entirely on the left or right side of the syrinx, whereas others contain sequential contributions from each side. Low fundamental frequencies are produced with the left syrinx and high frequencies by the right syrinx, increasing the frequency range of domestic canary song compared to that of the waterslager strain. Midrange frequencies can be generated by either side. Syllables at repetition rates below about 25 s−1 were accompanied by minibreaths, which were usually bilateral. Unilateral minibreaths were typically on the left side. At higher syllable repetition rates, minibreaths were replaced by a respiratory pattern of pulsatile expiration. Our data show that strong unilateral dominance in song production, present in the waterslager strain, is not a trait of the species as a whole and that the pattern of song lateralization can be altered by selective breeding for particular song characteristics. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 381–393, 2004

Bilateral song production in domestic canaries.

The song of male canaries (Serinus canaria) differs greatly from one strain to another (wild and different domesticated breeds) depending on breeders' attempt during selective breedings. Female canaries (common canary strain) previously treated with estradiol were tested for their sexual copulation solicitation display in response to heterospecific and conspecific song stimuli. Heterospecific songs, winter wren (Troglodytes troglodytes) and greenfinch (Chloris chloris), elicited significantly weak reactions from females, but most of the females did react to these heterospecific songs. Two conspecific songs, the females' own strain song and a Border song, elicited significantly strong reactions compared to Harzer roller. A wild canary song has an intermediate song potential between Border and Harzer roller. As a whole these results support the ideas that artificial selection may have relaxed the strength of reproductive isolation and sexual selection.

Differences in the Responses of Captive Female Canaries To Variation in Conspecific and Heterospecific Songs

The preference of female songbirds for particular traits in the songs of courting males has received considerable attention, but the relationship of preferred traits to male quality is poorly understood. Female domestic canaries (Serinus canaria, Linnaeus) preferentially solicit copulation with males that sing special high repetition rate, wide-band, multi-note syllables, called 'sexy' or A-syllables. Syllables are separated by minibreaths but each note is produced by pulsatile expiration, allowing high repetition rates and long duration phrases. The wide bandwidth is achieved by including two notes produced sequentially on opposite sides of the syrinx, in which the left and right sides are specialized for low or high frequencies, respectively. The emphasis of low frequencies is facilitated by a positive relationship between syllable repetition rate and the bandwidth of the fundamental frequency of notes sung by the left syrinx, such that bandwidth increases with increasing syllable repetition rate. The temporal offset between notes prevents cheating by unilaterally singing a note on the left side with a low fundamental frequency and prominent higher harmonics. The syringeal and respiratory motor patterns by which sexy syllables are produced support the hypothesis that these syllables provide a sensitive vocal-auditory indicator of a male's performance limit for the rapid, precisely coordinated interhemispheric switching, which is essential for many sensory and motor processes involving specialized contributions from each cerebral hemisphere.

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Eric Vallet

Papers

Female canaries are sexually responsive to special song phrases

Two-note syllables in canary songs elicit high levels of sexual display☆

Bilateral song production in domestic canaries.

Differences in the Responses of Captive Female Canaries To Variation in Conspecific and Heterospecific Songs

Bilateral coordination and the motor basis of female preference for sexual signals in canary song