Investigating the structure and function of mimetic song in female superb lyrebirds (Menura novaehollandiae)
Female song is ancestral and phylogenetically widespread in oscine passerines (Odom et al. 2014), but we have a relatively limited understanding of its function and how it differs from song produced by males (Hall et al. 2015; Langmore 1998; Riebel et al. 2005). Following the recent discovery that female song was already present in the ancestors of oscine passerines (Odom et al. 2014), there has been a surge in research in this field (Hall & Langmore, 2016) However, this research has focused on species-specific songs despite evidence that up to 40% of oscine passerines imitate other sound sources in their environment (Dalziell et al. 2015). At present, little is known about female song in basal oscine passerines (Odom et al. 2014), but research on such early diverging species is vital for our understanding of the evolution of both female and male vocalizations in song birds (Dalziell & Welbergen 2016; Odom et al. 2014).
Superb lyrebirds (Menura novaehollandiae) are a basal oscine passerine with an exceptionally slow life history. Male superb lyrebirds are well known for their spectacular mimetic abilities (http://www.hbw.com) (opens in a new window), however the displays of females have largely been ignored and their vocalisations interpreted as by-products of sexual selection (http://www.hbw.com) (opens in a new window). Recently, however, female superb lyrebirds have been shown to have both complex and diverse vocalisations that are used in female-specific behaviours such as nest defence (Dalziell & Welbergen 2016). Females also appear to consistently mimic sounds different to those mimicked by males, but there is considerable variation among females in their propensity to mimic (Dalziell & Welbergen 2016). These exciting but preliminary observations raise many questions about the evolution and function of mimetic vocalisations in female superb lyrebirds specifically, and the evolution of complex vocalisations in oscines passerines more generally.
Current research gaps
That female superb lyrebirds, like males, are capable of learning complex sounds in their environment raises the question of what accounts for sexual differences in vocalisations in this species. Dalziell and Welbergen (2016) suggest that sexual difference may be determined more by what is learned than the ability to learn (Riebel 2003), but this has yet to be formally quantified. Indeed, the mechanisms of learning complex mimetic song in female lyrebirds have never been investigated. Additionally, it is not yet known why females do not share the same mimetic repertoire as males, or why there is more variation in mimetic vocalizations among females than among males (Dalziell & Welbergen 2016).The different structures of mimetic vocalisations between males and females of this species also indicate different selective pressures for complex vocalisations (Dalziell & Welbergen 2016; Price 2015). However, the functions of female and male lyrebird vocalizations are not presently understood.
The study of female song function in a basal oscine passerine will provide important information about the evolution of complex learned vocalisations in general. Thus, the presence of female-specific song and behaviours in this species provides a valuable opportunity to address current gaps in research.
Dr Justin Welbergen, Professor James Cook, A/Professor Naomi Langmore (ANU), Dr Anastasia Dalziell
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