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The genetic sex-determination system predicts adult sex ratios in tetrapods



The adult sex ratio (ASR) has critical effects on behaviour, ecology and population dynamics1,2, but the causes of variation in ASRs are unclear3,4. Here we assess whether the type of genetic sex determination influences the ASR using data from 344 species in 117 families of tetrapods. We show that taxa with female heterogamety have a significantly more male-biased ASR (proportion of males: 0.55 ± 0.01 (mean ± s.e.m.)) than taxa with male heterogamety (0.43 ± 0.01). The genetic sex-determination system explains 24% of interspecific variation in ASRs in amphibians and 36% in reptiles. We consider several genetic factors that could contribute to this pattern, including meiotic drive and sex-linked deleterious mutations, but further work is needed to quantify their effects. Regardless of the mechanism, the effects of the genetic sex-determination system on the adult sex ratio are likely to have profound effects on the demography and social behaviour of tetrapods.

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Figure 1: Phylogenetic distribution of the ASR and genetic sex-determination systems across tetrapods.
Figure 2: Variation in the ASR as a function of the sex-determination system in amphibians, reptiles, mammals and birds, and across tetrapods (all four clades combined).


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M. Pennell and G. Imreh helped construct the phylogeny figure. We thank T. H. Clutton-Brock, S. P. Otto, D. Bachtrog and K. Reinhold for suggestions, and R. P. Freckleton for advice on analyses. We were supported by the European Union (TÁMOP-4.2.2.B-15/1/KONV-2015-0004), and by the US National Science Foundation (DEB-0819901 to M.K.). T.S. was supported by a Humboldt Award and MTA-DE ‘Lendület’ grant in projects that lead to the current work. A.L. was supported by the Hungarian Scientific Research Fund (OTKA K112838) and a Marie Curie Intra-European Fellowship.

Author information

Authors and Affiliations



T.S. and A.L. conceived the study. T.S., A.L. and V.B. designed the analyses. I.P., V.B., P.F.D. and A.L. collected the reptile, amphibian, mammalian and bird data, respectively. I.P., V.B. and A.L. conducted the analyses. M.K. developed the population genetic models. All authors wrote the paper.

Corresponding author

Correspondence to András Liker.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Phylogenetically corrected mean and s.e.m. of ASR in clades with different sex-determination systems.

Parameter estimates for the mean and associated s.e.m. were calculated by PGLS models18 presented in Extended Data Table 2 (with branch lengths estimated by Nee’s method54).

Extended Data Table 1 Detailed analyses of the effect of sex-determination system on the ASR.
Extended Data Table 2 Phylogenetically controlled analyses of the relationship between ASR and genetic sex-determination system using different branch length assumptions.

Supplementary information

Supplementary Information

This file contains Supplementary Information Parts 1 and 2 and Supplementary References. (PDF 587 kb)

Supplementary Data

This file contains the full dataset and references used in the phylogenetic analyses. (XLSX 63 kb)

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Pipoly, I., Bókony, V., Kirkpatrick, M. et al. The genetic sex-determination system predicts adult sex ratios in tetrapods. Nature 527, 91–94 (2015).

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