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. 2019 Feb 18;19(1):57.
doi: 10.1186/s12862-019-1386-3.

Sex ratios and bimaturism differ between temperature-dependent and genetic sex-determination systems in reptiles

Veronika Bókony  1 , Gregory Milne  2 , Ivett Pipoly  3 , Tamás Székely  2   4 , András Liker  3   5
Affiliations

Sex ratios and bimaturism differ between temperature-dependent and genetic sex-determination systems in reptiles

Veronika Bókony et al. BMC Evol Biol. .

Abstract

Background: Sex-determining systems may profoundly influence the ecology, behaviour and demography of animals, yet these relationships are poorly understood. Here we investigate whether species with temperature-dependent (TSD) and genetic sex determination (GSD) differ in key demographic traits, using data from 181 species representing all major phylogenetic lineages of extant reptiles.

Results: We show that species with TSD exhibit significantly higher within-species variance in sex ratios than GSD species in three major life stages: birth or hatching, juvenility and adulthood. In contrast, sex differences in adult mortality rates do not differ between GSD and TSD species. However, TSD species exhibit significantly greater sex differences in maturation ages than GSD species.

Conclusion: These results support the recent theoretical model that evolution of TSD is facilitated by sex-specific fitness benefits of developmental temperatures due to bimaturism. Our findings suggest that different sex-determination systems are associated with different demographic characteristics that may influence population viability and social evolution.

Keywords: Age of sexual maturity; Environmental sex determination; Non-avian sauropsids; Sex chromosomes; Sex ratio; Survival.

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The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
Sex ratios (a-c) and sex differences in maturation age (d) and adult mortality (e) in GSD and TSD reptiles. Sex ratios are given as the proportion of males, thus 0.5 represents an even sex ratio. For maturation age and adult mortality, positive values refer to later-maturing females and higher female mortality, respectively. In each box plot, each data point represents one population; the thick middle line, box, and whiskers show the median, interquartile range, and data range within 1.5 × interquartile range from the lower and upper quartiles, respectively. Numbers below each box denote the number of species (number of populations in brackets)
Fig. 2
Fig. 2
Estimates from Bayesian phylogenetic mixed-effects models for within-species variances (a-e), between-species variances (f-j) and means (k-o) of sex ratios and sex differences in maturation age and adult mortality in GSD and TSD reptiles. Whiskers correspond to 95% credibility intervals (CrI); asterisks indicate non-overlapping CrIs (i.e. significant differences). See Fig. 1 and Additional file 1: Table S3 for further details
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