Skip to main content

Evolution of sexual dimorphisms: all about losing not choosing?

Periodic Reporting for period 1 - YnotSing (Evolution of sexual dimorphisms: all about losing not choosing?)

Reporting period: 2016-09-01 to 2018-08-31

Animals exhibit a diverse array of elaborate communication traits, like flashy colors and song. Such elaborate traits were long thought to have evolved primarily in males through sexual selection. However, females of many animals are ornamented, too. Specifically, research we published in 2014 showed, that female song is surprisingly common and most likely was ancestral in songbirds. Thus, the diversity of bird song we see today must be due, in part, to female song becoming reduced or lost in some lineages. In order to understand how complex bird song evolved in males and females, in this project supported by a MSCA-IF fellowship, our goals were to (1) document and quantify similarities and differences in female and male songs, (2) examine how female and male songs have changed through evolutionary time, and (3) to identify what factors have led to elaborate song in both sexes in some lineages, but losses of female song in others.

To quantify the world’s diversity of bird song requires recordings and documentation of female bird song from many different species of songbirds. Female bird song is underrepresented in biological collections, however. To address this, we worked with Xeno-canto, the largest online database of bird songs, sponsored by Naturalis Biodiversity Center, and Cornell’s Macaulay Library of Natural Sounds to create a citizen science project (www.femalebirdsong.org). This project directly addresses citizen scientists, birders, and wildlife recordists encouraging them to submit observations and recordings of female bird song to biological collections and to raise the research community’s awareness of the deficit of female bird song in collections so that they can also work to right this imbalance.

The great diversity in singing styles has led to species specific methods to describe individual and sex-specific variation in song. While this has allowed us to zoom in on individual differences within a species, it has hampered comparative work which requires metrics that are standardized across species. To address this we worked with researchers form Queen Mary University of London to devise methods for quantifying female and male song to be compared on a phylogenetic tree of species relationships. Altogether, our research will help us understand how female as well as male songbirds evolved their range of complex songs. Documenting the evolutionary processes responsible for these kinds of diversity are key to understanding how life has been shaped on our planet.
The fellowship was terminated early due to an excellent career opportunity for the fellow at Cornell University in the US that will both advance the fellow’s personal career and allow us to continue our collaborations while the fellow is at a prominent sound collection. During the 7.6 months until the termination of this project, we made progress on several important components of our research:

1. We created a website and set up social media outlets for a citizen scientist project: The Female Bird Song Project – www.femalebirdsong.org. It provides tools and information to encourage birders, wildlife recordists, and the general public to contribute female bird songs to collections, and provides background for those unfamiliar with this topic. We also set up a Facebook page (https://www.facebook.com/femalebirdsong/) and a twitter account (@femalebirdsong).

2. The fellow co-authored a popular article about the website and the citizen science project which appeared in Birding Magazine, a top magazine for birders: Benedict, L. and Odom, K. J. 2017. Listening to Nature's Divas. Birding Magazine 49: 34-43. The article aims to raise awareness within the birding community that female songbirds sing and provides tools and knowledge for citizen scientists interested to participate.

3. The fellow also wrote a perspectives paper to inform researchers about the deficit of female bird song documentation. This paper provides researchers with tools and knowledge so that they can also aid in documenting female bird song, with citizen scientists and young researchers. Intended submission June 2017: Odom, K. J. and Benedict, L. A call to document female bird songs.

4. The fellow completed the planned secondment at Queen Mary University in London, where she learned bioacoustic techniques for multi-species comparison using Luscinia software from Rob Lachlan.

5. The knowledge gained from this secondment was implemented in a methods paper establishing methods useful for quantifying differences in song structure among diverse species. Intended submission to a field-specific journal: Varkevisser, J.M. Odom, K.J. Lachlan, R.F. Brunton, D.H. Cain, K.E. Dowling, J.L. Greig, E.I. Hall, M.L. Igic, B. and Riebel, K. Methods for comparing female and male bird song among diverse species. Intended submission Summer 2017.

6. The fellow served as a daily supervisor for a masters student. He conducted a broad meta-analysis of factors correlated to female bird song and a phylogenetic comparison. His preliminary analyses suggest the need for more refined comparisons of male and female song structure than traditional presence/absence studies. These findings will be published in Antonis Kalimeris’ masters thesis.


7. Dissemination to scientific community: the fellow gave research presentations at the following universities:
Queen Mary University of London, October 2016.
Leiden University, Institute of Biology, October 2016. ‘Spotlight’ departmental seminar.
Leiden University, Animal Cluster, October 2016. Lightning talk.
Leiden University, Behavioral Biology group, October 2016.
Dutch Behavior Meeting, December 2016, The Netherlands.
Evolution of Sex Roles workshop, April 2017, Tihany, Hungary.
One important aim was to raise awareness in the general public that female bird song is common in nature but underrepresented in biological collections. One month after launch, our Facebook post launching our website has reached 4,664 people and 170 followers. The citizen science website has had 700 visits and citizen scientists have already uploaded 13 female song recordings of 11 different species (more than we could have collected in the field during this time) to Xeno-canto. This response within the first month exceeds our expectations and shows an immediate, positive response by the general public to this research. This in turn reflects the great impact this effort will have on increasing awareness of female bird song and documentation for collections.

Our research also impacts gendered issues in science in two ways: 1) it urges the inclusion of data on females in ornament evolution (raising awareness in the scientific community and the general public), 2) it emphasizes the need for women and people from a diversity of backgrounds in science.

Lastly, this research has launched an international collaborative project involving researchers from Leiden University and Naturalis Biodiversity center (NL), Queen Mary University of London (GB), the Australian National University and Melbourne University (AU), and Cornell University and Northern Colorado University (USA), that the fellow will maintain from the new position. Therefore, this project created and strengthened ties among an international network of researchers that will advance techniques and research questions to address the evolution of complex behaviors, such as bird song.
This project created a website to help document female bird song for biological collections.
Female bird song is common, even in temperate songbirds, like this wren species.