In the Funding section, the name of the first funder is incorrect. The correct name is: Medical Research Scotland. The correct funding information is: This work was supported by Medical Research Scotland [grant 354FRG to AJC] and the Medical Research Council [grant G1100357 to RAA]. J.H. is supported by a University of Edinburgh Darwin Scholarship and K.S. is the recipient of a Society for Reproduction and Fertility Summer Vacation Scholarship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.