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Z and W sex chromosomes in the cane toad (Bufo marinus)

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Abstract

The cane toad (Bufo marinus) is one of the most notorious animal pests encountered in Australia. Members of the genus Bufo historically have been regarded as having genotypic sex determination with male homogamety/female heterogamety. Nevertheless, as with many toads, karyotypic analyses of the cane toad have so far failed to identify heteromorphics sex chromosomes. In this study, we used comparative genomic hybridization, reverse fluorescence staining, C-banding, and morphometric analyses of chromosomes to characterize sex chromosome dimorphism in B. marinus. We found that females consistently had a length dimorphism associated with a nucleolus organizer region (NOR) on one of the chromosome 7 pair. A strong signal over the longer NOR in females, and the absence of a signal in males indicated sex-specific DNA sequences. All females were heterozygous and all males homozygous, indicating a ZZ/ZW sex chromosomal system. Our study confirms the existence of sex chromosomes in this species. The ability to reliably identify genotypic sex of cane toads will be of value in monitoring and control efforts in Australia and abroad.

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Abbreviations

DAPI:

4′,6-diamidino-2-phenylindole

NOR:

Nucleolus organizer region

GSD:

Genotypic sex determination

CGH:

Comparative genomic hybridization

SSC:

Standard saline citrate

CMA3:

Chromomycin A3

dDNA:

Genomic deoxyribonucleic acid

rDNA:

Ribosomal deoxyribonucleic acid

dUTP:

2′-Deoxyuridine 5′-Triphosphate

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Acknowledgments

We thank Chris Hardy from CSIRO Entomology for cane toad tissue and blood samples, Cate Browne for assistance with blood culture techniques, Ikuo Miura for discussion of preliminary results, and members of the Koopman and Graves laboratories for insightful discussions on technical aspects of the research. Finally we thank the two anonymous reviewers for their valuable comments on this manuscript. This work was funded by the Invasive Animals Cooperative Research Center, the Queensland State Government, and the Australian Research Council. Peter Koopman is a Federation Fellow of the ARC.

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Authors and Affiliations

  1. Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia

    John Abramyan & Peter Koopman

  2. Comparative Genomics Group, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia

    Tariq Ezaz & Jennifer A. Marshall Graves

  3. Institute for Applied Ecology, University of Canberra, Bruce, ACT 2616, Australia

    Tariq Ezaz

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  1. John Abramyan
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  2. Tariq Ezaz
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  3. Jennifer A. Marshall Graves
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  4. Peter Koopman
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Correspondence to Peter Koopman.

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Responsible Editor: Herbert Macgregor

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Abramyan, J., Ezaz, T., Graves, J.A.M. et al. Z and W sex chromosomes in the cane toad (Bufo marinus). Chromosome Res 17, 1015–1024 (2009). https://doi.org/10.1007/s10577-009-9095-1

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