DOI: 10.5061/dryad.w0vt4b8zd
title: Data from: Sperm as a speciation phenotype in promiscuous songbirds

description: The paper compares 20 population pairs of Passerida songbirds and shows
 that their rate of divergence in sperm length was positively associated
 with the level of female promiscuity (expressed by the proportion of
 offspring sired by extrapair males). The effect was largely caused by a
 reduced population variance in sperm length in more promiscuous species.
 The paper suggests that rapid sperm length divergence can promote
 postcopulatory prezygotic isolation and hence rapid speciation in
 promiscuous songbirds.
description: Population pairs had estimates of total sperm length from minimum
 six males in each population, a published estimate of their divergence
 time using a molecular clock model, and an estimate of the proportion of
 extrapair young (EPY) for the actual populations or a population in the
 species complex. The two populations were either of the same taxonomic
 subspecies, different subspecies of the same species, or congeneric
 species with a known hybrid zone. Maximum divergence time was 2.41 million
 years since last common ancestor. For three population pairs, EPY was
 estimated from relative testes mass (no paternity studies
 known).  Sperm length data were extracted from raw data
 in published studies or from the database of the Avian Sperm Collection at
 the Natural History Museum, University of Oslo (Lifjeld 2019). In some
 cases, data from published studies were extended with additional
 unpublished data from the same study populations available in the museum’s
 database. As a standard, ten or more sperm cells were measured by light
 microscopy from formalin-fixed ejaculates to calculate the mean sperm
 length for each male (Grønstøl et al. 2023). Each mean value was
 log-transformed. From these log-means we calculated mean sperm length and
 the standard deviation for each population. Sperm length divergence was
 expressed in Hedges' g (Hedges 1981). We also calculated an overlap
 index for the sperm length distributions. <strong>References:</strong>
 Grønstøl, G., Danielsen, M., Cramer, E. R. A., Johannessen, L.
 E., Johnsen, A., Whittington, E., & Lifjeld, J. T. (2023). Effects
 of fixatives and storage duration on avian sperm morphology.
 <em>Journal of Ornithology, </em>164(1), 171-181.
 doi:10.1007/s10336-022-02015-x Hedges, L. V. (1981).
 Distribution theory for Glass's estimator of effect size and related
 estimators. <em>Journal of Educational Statistics, </em>6(2),
 107-128. doi:10.3102/10769986006002107 Jetz, W.,
 Thomas, G. H., Joy, J. B., Hartmann, K., & Mooers, A. O. (2012).
 The global diversity of birds in space and time. <em>Nature,
 </em>491(7424), 444-448. doi:10.1038/nature11631
 Lifjeld, J. T. (2019). The avian sperm collection in the Natural
 History Museum, University of Oslo. <em>Alauda, </em>87(3),
 93–101.
description: # Data from: Sperm as a speciation phenotype in promiscuous songbirds The
 data files and the associated .R script were used in the statistical tests
 and result presentations in the paper "Sperm as a speciation
 phenotype in promiscuous songbirds" and its Supplementary Material
 (Table S1 and Table S2). **Data files** RawData20pairs.xlsx: Raw data for
 each population with source information of the sperm length measurements,
 and the calculation of Hedges' g for each population pair.
 20pairs.nex: Time-calibrated phylogeny for the 20 species pairs used in
 PGLS analyses. Can be visualized with the FigTree software
 ([http://github.com/rambaut/figtree/](http://github.com/rambaut/figtree/)). 40populations.nex: Time-calibrated phylogeny for the 40 populations with their within-pair divergence time. The phylogeny was visualized in Figure 2 (left panel) in the paper, using the FigTree software ([http://github.com/rambaut/figtree/](http://github.com/rambaut/figtree/)). Passerinetree_Jetz.tre: Consensus tree of passerine birds derived from BirdTree.org (Jetz et al. 2012). Data20pairs.txt: data used for the main analyses in the paper SpermmeansSD.txt: data used to calculate the overlap coefficient for sperm length distributions of each population pair. RelTestisSize_data.txt: data used to calculate the PGLS regression between testes mass and body mass for 160 passerine species. RelTestisSize_EPY_66species.txt: data used to calculate a predicted EPY rate from relative testes mass for 3 species. **Analytical code** SpermDivergence.R: the R script used for data processing, statistical analyses and figure construction. The script has undergone a slight revision regarding the code for the construction of the horizontal boxplot in Figure 2. The change was purely cosmetic and did not affect any data or analytical results.