Contingency and determinism in the evolution of bird song sound frequency

Abstract

Sexual signals are archetypes of contingent evolution: hyper-diverse across species, often evolving fast and in unpredictable directions. It is unclear to which extent their evolutionary unpredictability weakens deterministic evolution, or takes place bounded by deterministic patterns of trait evolution. We compared the evolution of sound frequency in sexual signals (advertisement songs) and non-sexual social signals (calls) across > 500 genera of the crown songbird families. Contrary to the acoustic adaptation hypothesis, we found no evidence that forest species used lower sound frequencies in songs or calls. Consistent with contingent evolution in song, we found lower phylogenetic signal for the sound frequency of songs than calls, which suggests faster and less predictable evolution, and found unpredictable direction of evolution in lineages with longer songs, which presumably experience stronger sexual selection on song. Nonetheless, the most important deterministic pattern of sound frequency evolution—its negative association with body size—was stronger in songs than calls. This can be explained by songs being longer-range signals than most calls, and thus using sound frequencies that animals of a given size produce best at high amplitude. Results indicate that sexual selection can increase aspects of evolutionary contingency while strengthening, rather than weakening, deterministic patterns of evolution.

Body size and sexual selection shaped the evolution of parrot calls

“…Sound attenuation and degradation differ between closed and open habitats, and the AAH thus predicts that, to maximize sound transmission, closed‐habitat species should evolve lower‐frequency vocalizations and narrower frequency bandwidths and use longer notes (Blumenrath & Dabelsteen, 2004; Graham et al, 2017; Hansen, 1979; Morton, 1975; Wiley & Richards, 1978). However, similarly to previous results for neotropical parrots (Medina‐García et al, 2015) and to recent comparative work across passerine birds (Friis, Dabelsteen, et al, 2021; Mikula et al, 2020), we found no evidence that parrot species living mostly in closed habitats differ from those living mostly in open habitats neither on sound frequency, frequency bandwidth nor call duration. Parrots are very mobile, and many species, although having a preferred habitat, can move between closed and open habitats, or forest species may fly and vocalize at different heights in or above the canopy (Gilardi & Munn, 1998), which contributes to make our test of the AAH conservative.…”

Ostrich (Struthio camelus) syrinx morphology and vocal repertoire across postnatal ontogeny and sex: Implications for understanding vocal evolution in birds

“…However, adult ostriches have a wider vocal repertoire than is often discussed, with our study identifying at least 5 distinct adult tonal call types (not including hisses) (Figure 6). The fundamental frequencies of adults were significantly lower than juveniles, as would be expected in a bird that goes through an extreme change in body size through ontogeny even among other paleognaths, reaching an average adult body mass of 111 kg (Bradbury & Vehrencamp, 2011;Dunning, 2008;Fletcher, 2004;Friis et al, 2021;Marcolin et al, 2022). One hypothesis that has been lightly discussed in ostriches and other paleognaths is that a biomechanical or energetic constraint on the ostrich syrinx such as higher driving pressures required to vibrate increasingly large labia prevents adults from vocalizing as frequently or for as long as juveniles.…”

Assessment of the acoustic adaptation hypothesis in frogs using large‐scale citizen science data

“…While this prediction has been corroborated in many studies of birds (e.g. Lijtmaer & Tubaro, 2007; Nicholls & Goldizen, 2006; Tobias et al., 2010; but see Friis et al., 2021; Mikula et al., 2021; Wiley, 1991), pivotal studies in frogs have observed no relationship (e.g. Kime et al., 2000; Penna & Solís, 1998; Röhr et al., 2020).…”

“…Recent decades have seen a rise in the quantity of citizen science projects, and an increasing recognition of the potential value such projects offer professional scientific studies (see review in McKinley et al., 2017), including in bioacoustic studies (e.g. Diblíková et al., 2019; Friis et al., 2021; Mikula et al., 2021; Searfoss et al., 2020).…”