Sex reversal triggers the rapid transition from genetic to temperature-dependent sex

Journal name:
Nature
Volume:
523,
Pages:
79–82
Date published:
DOI:
doi:10.1038/nature14574
Received
Accepted
Published online

Sex determination in animals is amazingly plastic. Vertebrates display contrasting strategies ranging from complete genetic control of sex (genotypic sex determination) to environmentally determined sex (for example, temperature-dependent sex determination)1. Phylogenetic analyses suggest frequent evolutionary transitions between genotypic and temperature-dependent sex determination in environmentally sensitive lineages, including reptiles2. These transitions are thought to involve a genotypic system becoming sensitive to temperature, with sex determined by gene–environment interactions3. Most mechanistic models of transitions invoke a role for sex reversal3, 4, 5. Sex reversal has not yet been demonstrated in nature for any amniote, although it occurs in fish6 and rarely in amphibians7, 8. Here we make the first report of reptile sex reversal in the wild, in the Australian bearded dragon (Pogona vitticeps), and use sex-reversed animals to experimentally induce a rapid transition from genotypic to temperature-dependent sex determination. Controlled mating of normal males to sex-reversed females produces viable and fertile offspring whose phenotypic sex is determined solely by temperature (temperature-dependent sex determination). The W sex chromosome is eliminated from this lineage in the first generation. The instantaneous creation of a lineage of ZZ temperature-sensitive animals reveals a novel, climate-induced pathway for the rapid transition between genetic and temperature-dependent sex determination, and adds to concern about adaptation to rapid global climate change.

At a glance

Figures

  1. Geographical distribution of sex reversal in wild populations of P. vitticeps.
    Figure 1: Geographical distribution of sex reversal in wild populations of P. vitticeps.

    Location of sex-reversed ZZ females (ZZf) across years is indicated by red circles (N = 11), normal ZW females (ZWf) by black circles (N = 72) and normal ZZ males (ZZm) by grey circles (N = 48). Pie charts indicate the relative proportions of ZZf and ZWf in years where sample size exceeded 15 phenotypically female individuals. The temporal trend is suggestive, but not significant (χ2 = 1.65, d.f. = 2, P = 0.44).

  2. Offspring sex ratio as a function of egg incubation temperature in P. vitticeps.
    Figure 2: Offspring sex ratio as a function of egg incubation temperature in P. vitticeps.

    a, GSD system of sex determination with a high-temperature override. Data are from ref. 12 (open circles) and this study (filled circles). Proportion of phenotypically female offspring from control ZZm × ZWf crosses is a function of constant incubation temperature T, given by . b, Functional TSD by sex reversal. Proportion of phenotypically female offspring from ZZm × ZZf crosses is given by . Dashed lines, extrapolation of the fitted curve beyond the data. Shaded regions, 95% confidence limits. The number of individuals in each treatment is shown.

  3. Rate of sex reversal as a function of egg incubation temperature in P. vitticeps.
    Figure 3: Rate of sex reversal as a function of egg incubation temperature in P. vitticeps.

    Offspring of sex-reversed mothers (ZZf shown in red) are reversed more frequently and at a lower temperature than the offspring of control mothers (ZWf shown in black), implying that temperature sensitivity is variable in the population and heritable. Vertical bars, standard error of the observed proportion. Dashed lines, extrapolation of the fitted curve beyond the data (see Methods for equations). Dotted lines, the pivotal temperature at which half of ZZ offspring are reversed. Sample size (numbers) is the total number of ZZ individuals.

  4. C-banded P. vitticeps chromosomes.
    Extended Data Fig. 1: C-banded P. vitticeps chromosomes.

    a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a W chromosome identified by dense black staining of a single microchromosome. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. Scale bar, 10 μm.

  5. Comparative genomic hybridization in P. vitticeps.
    Extended Data Fig. 2: Comparative genomic hybridization in P. vitticeps.

    Genomic DNA was labelled by nick translation incorporating SpectrumGreen-dUTP for males and SpectrumOrange-dUTP for females. a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a single W microchromosome identified by the enriched orange fluorescence of female specific genomic DNA labelled with SpectrumOrange-dUTP. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. df, DAPI staining of the same metaphases, control ZW female, sex-reversed ZZ female and control ZZ male, respectively. Scale bar, 10 μm.

  6. Physical mapping of a W-chromosome-linked microsatellite motif in P. vitticeps.
    Extended Data Fig. 3: Physical mapping of a W-chromosome-linked microsatellite motif in P. vitticeps.

    a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a W chromosome identified by a strong hybridization of (AAGG)8-Cy3 florescence (orange) on a single microchromosome. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. df, DAPI staining of the same metaphases, control ZW female, sex-reversed ZZ female and control ZZ male, respectively. Scale bar, 10 μm.

  7. Modelling the decline of the ZW genotype resulting from frequency-dependent selection.
    Extended Data Fig. 4: Modelling the decline of the ZW genotype resulting from frequency-dependent selection.

    Frequency of the ZW genotype declines precipitously with increasing incubation temperature. Our wild population (shown in red, 14.3% sex reversal) resides on the precipice between GSD and TSD and requires only a small change in environmental temperature to precipitate loss of the W chromosome.

Accession codes

Primary accessions

GenBank/EMBL/DDBJ

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Author information

  1. Present addresses: Research Center for Aquatic Genomics, National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan (K.M.); John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2601, Australia (B.A.).

    • Kazumi Matsubara &
    • Bhumika Azad

Affiliations

  1. Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia

    • Clare E. Holleley,
    • Denis O'Meally,
    • Stephen D. Sarre,
    • Jennifer A. Marshall Graves,
    • Tariq Ezaz,
    • Kazumi Matsubara,
    • Bhumika Azad,
    • Xiuwen Zhang &
    • Arthur Georges
  2. School of Life Science, La Trobe University, Melbourne, Victoria 3086, Australia

    • Jennifer A. Marshall Graves

Contributions

C.E.H. and A.G. designed the study. C.E.H. conducted breeding experiments, egg incubations, parentage SNP analysis and prepared figures. D.O'M. collected the animals from the field. C.E.H. and X.Z. conducted the molecular sex testing. B.A. and K.M. undertook the cytogenetic analysis and prepared extended data figures, under the supervision of T.E. A.G. and C.E.H. undertook the statistical analyses and A.G. conducted the modelling of ZW genotype frequency with temperature. All authors contributed to writing the manuscript.

Competing financial interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to:

The W chromosome sequence has been deposited in GenBank under accession number KM508988.

Author details

Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: C-banded P. vitticeps chromosomes. (163 KB)

    a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a W chromosome identified by dense black staining of a single microchromosome. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. Scale bar, 10 μm.

  2. Extended Data Figure 2: Comparative genomic hybridization in P. vitticeps. (193 KB)

    Genomic DNA was labelled by nick translation incorporating SpectrumGreen-dUTP for males and SpectrumOrange-dUTP for females. a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a single W microchromosome identified by the enriched orange fluorescence of female specific genomic DNA labelled with SpectrumOrange-dUTP. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. df, DAPI staining of the same metaphases, control ZW female, sex-reversed ZZ female and control ZZ male, respectively. Scale bar, 10 μm.

  3. Extended Data Figure 3: Physical mapping of a W-chromosome-linked microsatellite motif in P. vitticeps. (196 KB)

    a, Mitotic metaphase chromosomes of a ZW control female individual. Arrowhead indicates the presence of a W chromosome identified by a strong hybridization of (AAGG)8-Cy3 florescence (orange) on a single microchromosome. b, Mitotic metaphase chromosomes of a female putative ZZ sex-reversed individual. No evidence of a W chromosome was detected. c, Mitotic metaphase chromosomes of a control ZZ male individual. No evidence of a W chromosome was detected. df, DAPI staining of the same metaphases, control ZW female, sex-reversed ZZ female and control ZZ male, respectively. Scale bar, 10 μm.

  4. Extended Data Figure 4: Modelling the decline of the ZW genotype resulting from frequency-dependent selection. (74 KB)

    Frequency of the ZW genotype declines precipitously with increasing incubation temperature. Our wild population (shown in red, 14.3% sex reversal) resides on the precipice between GSD and TSD and requires only a small change in environmental temperature to precipitate loss of the W chromosome.

Supplementary information

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  1. Supplementary Information (169 KB)

    This file contains Supplementary Tables 1-4.

Excel files

  1. Supplementary data (1 MB)

    This file contains the source data used to make Supplementary Table 1.

Additional data