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Tuesday, 18 March 2014

Research article shows the importance of female song evolution in songbirds - Nature Communications

Female song is widespread and ancestral in songbirds
NATURE COMMUNICATIONS | 5:3379 | DOI: 10.1038/ncomms4379
Karan J. Odom 1
Michelle L. Hall 2
Katharina Riebel 3
Kevin E. Omland 1
Naomi E. Langmore 4
1: Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA. 
2: Department of Zoology, University of Melbourne, Melbourne, Victoria 3010, Australia. 
3: Institute of Biology (IBL), Leiden University, 2333 BE Leiden, The Netherlands. 
4: Research School of Biology, The Australian National University, Acton, ACT 0200, Australia. 
Correspondence and requests for materials should be addressed to K.J.O.

Bird song has historically been considered an almost exclusively male trait, an observation fundamental to the formulation of Darwin’s theory of sexual selection. Like other male ornaments, song is used by male songbirds to attract females and compete with rivals. Thus, bird song has become a textbook example of the power of sexual selection to lead to extreme neurological and behavioural sex differences. Here we present an extensive survey and ancestral state reconstruction of female song across songbirds showing that female song is present in 71% of surveyed species including 32 families, and that females sang in the common ancestor of modern songbirds. Our results reverse classical assumptions about the evolution of song and sex differences in birds. The challenge now is to identify whether sexual selection alone or broader processes, such as social or natural selection, best explain the evolution of elaborate traits in both sexes.

This short communication paper provides evidence to explain the author's hypothesis that evolution by sexual selection is not restricted to the male line but that female songbirds play a significant role too. This hypothesis is based on two observations: (1) the majority of songbird biodiversity exists in tropical regions, where both females and males of many species sing; (2) female song is widespread in Australasia, the region from which songbirds are thought to have originated. It is a commonly held understanding that females select a partner based on their 'fitness' and thus males would develop more elaborate song repertoires. The authors even quote from Darwin's 1859 book 'On the Origin of Species':

‘... female birds, by selecting, during thousands of generations, the most melodious or beautiful males, according to their standard of beauty, might produce a marked effect’

By way of contrast the authors aimed to provide a quantitative test of their hypothesis, by surveying the occurrence and distribution of female-specific song, and then using ancestral state reconstruction to examine the likelihood that females sang in the ancestor of all songbirds. 

The authors investigated the presence of female song in 1,141 songbird species, and were able to score 323 of these species. This represented 34 of the short-list of 44 songbird families examined from the approximate 112 total species list, after removing the Passerida. Although these are the most specious Parvorder of songbirds (3,822 of 5,023 songbirds) they were not useful in determining the ancestral lines as they were the most recent radiation.

This survey showed that female song is present in 71% of the selected species providing strong evidence that female song is globally and phylogenetically widespread.
Superimposing these data onto that of an evolutionary tree compiled from DNA sequence data (Pubmed Link), the authors then calculated that female song was most likely to have been present in the ancestral state. This challenged the view that sexual dimorphism in song production arises primarily as a result of sexual selection. 
A pictorial representation of the ancestral data is shown in Figure 1 below.

Figure 1

The tree (a) includes all species for which we could unambiguously score female song as present or absent (323/1,141 species from 34/44 songbird families). Female song was present in 229 species (32 families; red terminal nodes) and female song was absent in 94 species (19 families; blue terminal nodes). The pie chart in the centre shows that female song is reconstructed as present (red) in the common ancestor of modern songbirds (92% maximum-likelihood probability strongly supported by a likelihood decision threshold of 2.0). Pictures show females of the following species with female song from families throughout the phylogeny; (b) superb lyrebird (Menura novaehollandiae; figure reproduced with permission from V. Dunis), (c) purple-crowned fairywren (Malurus coronatus; figure reproduced with permission from M. Hall), (d) brown thornbill (Acanthiza pusilla; figure reproduced with permission from J.J. Harrison), (e) scarlet robin (Petroica boodang; figure reproduced with permission from K. Odom), (f) white-eyed vireo (Vireo griseus; figure reproduced with permission from F. Jacobsen), (g) grey butcherbird (Cracticus torquatus; figure reproduced with permission from A. Kearns), (h) tropical boubou (Laniarius aethiopicus; figure reproduced with permission from J. Friedman), (i) loggerhead shrike (Lanius ludovicianus; figure reproduced with permission from F. Jacobsen), (j) magpie-lark (Grallina cyanoleuca; figure reproduced with permission from M. Hall), (k) curl-crested manucode (Manucodia comrii; figure reproduced with permission from T. Laman).

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