Song Feature Specific Analysis of Isolate Song Reveals Interspecific Variation in Learned Components

Abstract

Studies of avian vocal development without exposure to conspecific song have been conducted in many passerine species, and the resultant isolate song is often interpreted to represent an expression of the genetic code for conspecific song. There is wide recognition that vocal learning exists in oscine songbirds, but vocal learning has only been thoroughly investigated in a few model species, resulting in a narrow view of birdsong learning. By extracting acoustic signals from published spectrograms, we have reexamined the findings of isolate studies with a universally applicable semi‐automated quantitative analysis regimen. When song features were analyzed in light of three different production aspects (respiratory, syringeal, and central programming of sequence), all three show marked interspecific variability in how close isolate song features are to normal. This implies that song learning mechanisms are more variable than is commonly recognized. Our results suggest that the interspecific variation shows no readily observable pattern reflecting phylogeny, which has implications for understanding the mechanisms behind the evolution of avian vocal communication. We emphasize that song learning in passerines provides an excellent opportunity to investigate the evolution of a complex, plastic trait from a phylogenetic perspective.

Stress Varies Along the Social Density Continuum

“…It should be recognized that effects of social isolation and social crowding have also been recorded in non-mammalian social species, including in insects (Wang et al, 2008;Lihoreau et al, 2009;Ueda and Wu, 2009;Stevenson and Rillich, 2013), fish (Halperin and Dunham, 1993;Brandão et al, 2015;Shams et al, 2015), and birds (Apfelbeck and Raess, 2008;Banerjee and Adkins-Regan, 2011). Notably, a recent study found immediate effects of social isolation in the expression of several immediate early genes in the forebrain of an avian species (George et al, 2019), a finding which has implications for the field of vocal learning, which historically relies on the isolation of animals (Love et al, 2019). It is difficult to determine at present how much of the human response to social density stressors is unique to humans; do we find similar responses among distantly-related taxa that show similarity in social systems, or does genetic relatedness play a more important role in determining how the CNS modulates behavior in response to social density?…”

Processes underlying complex patterns of song trait evolution in a Setophaga hybrid zone

“…It is this independence, which allows the two aspects of one signal to evolve separately from one another. Song rhythm is produced through song-associated respiratory patterning, which is thought to be largely innate in many species (Araki et al, 2016;Love et al, 2019;Marler & Sherman, 1983Thorpe, 1958), while syllable morphology arises through syringeal motor gesturing, which is more likely to be learned to a greater extent (Ali et al, 2013;Love et al, 2019;Marler & Sherman, 1983.…”

“…It is thought that learning increases rates of trait change through a higher copy‐error rate compared with the absence of learning, and song learning has been implicated in the rapid diversification of vocal learning songbirds (Lachlan & Servedio, 2004). However, it remains difficult to form hypotheses of precisely how vocal learning influences song evolution, because details of the learning process vary (e.g., species differences in tutor–tutee relationships, timing of the sensitive period) and substantial interspecific variation exists in which features of song must be learned (Love et al., 2019),…”

Different frequency control mechanisms and the exploitation of frequency space in passerines

“…A second and strong possibility is that the observed differences reflect the respective song development in suboscines and oscines (e.g., Gahr, 2000;Jarvis, 2004). Tyrannids develop song innately and are not vocal learners (Kroodsma, 1984(Kroodsma, , 1989Kroodsma & Konishi, 1991), whereas almost all oscines appear to rely on learning for at least some aspects of their song (e.g., Hultsch & Todt, 2008;Kroodsma, 1983;Love et al, 2019). The striking difference in frequency ranges (means differ by 3,100 Hz) of the entire song syllable repertoire (Figure 3a) between tyrannids and emberizids/passerellids may be explained by oscine vocal learning.…”