Abstract
Population sex ratios naturally fluctuate around equality. It is argued that the production of an equal number of male and female offspring by individual parents should be favoured by selection, if all costs and benefits are equal. Theoretically, an even sex ratio should yield the highest probability for a fetus to be adjacent to a fetus of the opposite sex in utero. This may cause developmental costs or benefits that have been overlooked. We examined the physiological and developmental parameters associated with in utero sex ratios in the nutria (Myocastor coypus), an invasive wildlife species with a strong reproductive output. Using hair testing, we found that litters with even sex ratios had the highest average cortisol levels. Fetuses neighbouring the opposite sex exhibited longer trunks than those neighbouring the same sex, which might imply better lung development. Our results are the first, to our knowledge, to link intra-utero sex ratios and fetal cortisol and suggest that fetal cortisol might be a mechanism by which even sex ratios are maintained via developmental advantages.
| Original language | English |
|---|---|
| Article number | 171636 |
| Journal | Royal Society Open Science |
| Volume | 5 |
| Issue number | 9 |
| DOIs | |
| State | Published - 1 Sep 2018 |
Bibliographical note
Publisher Copyright:© 2018 The Authors.
Funding
Ethics. Permits are not needed for collecting nutria carcasses because they are an invasive species, not protected by Israeli laws. Moreover, we took advantage of regional culling efforts, and did not initiate culling. Data accessibility. Data available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.f1j384s [67]. Authors’ contribution. U.S. and Y.V. initiated the nutria system. L.K. designed the study. R.F. and Y.V. collected nutrias in the field. R.F. dissected, collected samples and ran the steroid analysis. L.K., Y.V. and R.F. analysed and interpreted the data. R.F. drafted the manuscript and all the authors commented on it. Competing interests. The authors declare no competing interests. Funding. Funding support was from Bar Ilan University’s start-up seed fund to L.K. Acknowledgements. We are grateful to Dr Devorah Matas for her devoted support. We thank Itai Dolev, Sharon Dolev and Liran Tal for collecting nutrias, and the KKL-JNF for permission to work in the Agamon Hula Park. We also wish to thank our many undergraduate student assistants, particularly Ari Timokhin, Elina Tsirulnikov, Nataly Navon and Dor Nehoray, and our field assistant Linor Aviram. We are obliged to Profs. Eli Geffen, Ally Harari and Mathieu Douhard, and three anonymous reviewers for their comments, and to Sharon Victor for English editing. The authors have no conflict of interests to declare.
| Funders | Funder number |
|---|---|
| Bar Ilan University |
Keywords
- glucocorticoids
- hair testing
- intrauterine position
- sex ratio