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TSD in Reptiles

TSD in Reptiles. Modes, mechanisms and evolution. Arthur Georges Applied Ecology Research Group. Sex determination in lizards. Pough et al: Herpetology 1998. Fundamentally Different?. Genetic sex determination (GSD): Sex determined by genetic factors independent of environment

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TSD in Reptiles

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  1. TSD in Reptiles Modes, mechanisms andevolution. Arthur Georges Applied Ecology Research Group

  2. Sex determination in lizards Pough et al: Herpetology 1998

  3. Fundamentally Different? • Genetic sex determination (GSD): Sex determined by genetic factors independent of environment • Environmental sex determination (ESD/TSD): Sex determined after fertilisation by environmental factors

  4. Outline • Overview of modes of action of TSD in reptiles • Dichotomy or Continuum? • Predisposition for TSD? • Overview our work, linking to the more specific talk by Tariq Ezaz

  5. 1.0C Pig-nosed Turtle Young Georges Doody Canadian J. Zool, in press

  6. 4.5C Loggerhead Georges Stoutjesdijk Limpus J. Experimental Zool. 1994

  7. Water Dragon Harlow 2001, unpubl. thesis

  8. One Pattern? After Pieau, 1996

  9. Middle Third of Incubation is Influential Young Georges Doody Canadian J. Zool. in press

  10. Mean 26C (Male) Both Magnitude and variability are important Georges Stoutjesdijk Limpus J. Experimental Zool. 1994

  11. Fundamentally Different? ~ • Remarkable conservatism of vertebrate sexual differentiation genes, including reptiles with TSD. • Taxonomic distribution of TSD and GSD species suggests both modes have evolved independently multiple times. Evolutionary transitions between the two mechanisms may be relatively simple, perhaps involving one or only a few genes Sarre Georges Quinn Bioessays 2004

  12. Top Sex Determining Gene or Gene Complex - WNT4 (?) + DAX1 (?) - WT1 SF1 + + - AMH SOX9 DMRT1 Aromatasegene Aromatase Androstenedione Testosterone Estrone Estradiol 17B Receptors Sarre Georges Quinn Bioessays 2004

  13. Dichotomy or Continuum? A. Mutually exclusive mechanisms of sex determination A B B. Intermediate forms with varying degrees of interaction

  14. H-Y antigen expression(25-26C) Zaborski et al. 1988 Differentiation

  15. H-Y antigen expression(30-30.5C) Zaborski et al. 1988 Differentiation

  16. H-Y antigen expression(at the Pivotal Temp) Zaborski et al. 1988 Differentiation

  17. H-Y antigen expression(in the field) Girondot Zaborski et al. 1994 Genetical Research

  18. Proportion MALE Bassianaduperreyi Temperature (deg C) Shine Elphick Donnellan 2002 Ecology Letters

  19. Bearded Dragon Present study

  20. Dichotomy or Continuum? • Extraordinary conservatism in the genes involved in sexual differentiation across vertebrates • Abundant examples in fish of co-existence of genetic and environmental influences • Evidence of co-occurrence of genetic and environmental influences in at least some reptiles • Relative ease by which species appear to have moved from one mode to the other in evolutionary history

  21. Sister Taxa A.muricatus A.norrisi

  22. Coincidence? Homeotherms Ectotherms Poikilotherms TSD Common Strictly GSD TSD Rare

  23. Top Sex Determining Gene or Gene Complex SexDifferentiationGenes Range of temperatures experienced up to 23C (22 – 45C) Hormonal Environment

  24. Top Sex Determining Gene or Gene Complex Network of genes and gene products Thermal Compensation Consistent signal SexDifferentiationGenes Hormonal Environment TSD

  25. Challenging Opportunities for the Future Reptiles provide tractable opportunities for studying vertebrate sex determination through the provision of eggs for study before sex is determined, and provision of numerous examples of GSD/TSD models for study. Viewing GSD and TSD as discrete and fundamentally different processes is overly myopic and distracts us from the possibility that genotypic and environmental influences may interact in determining sexual phenotypes.

  26. Challenging Opportunities for the Future Comparative approaches, where closely related species with differing modes of sex determination are selected, show great promise. Reptiles may well be predisposed to TSD. We aught to be looking for evidence of temperature compensation in the expression of sex genes in GSD species to provide insight into where to look for changes accompanying the move to and from TSD.

  27. Contributors Funding ARC Discovery Grants 1996, 2003, 2004-6 UC Research Grant 2002 CRC for Freshwater Ecology Collaborators Hofstra University, USA Dr Russell Burke University of Sydney Prof. Rick Shine The Team Applied Ecology Research Group Dr Stephen Sarre Alex Quinn Brett Lidbury Sean Doody Enzo Guarino Comparative Genomics Group Australian National University Prof Jenny Graves Dr Frank Gruetzner Dr Ann Gaeth Dr Tariq Ezaz

  28. Differential Advantage When environmental conditions favour fitness of one sex over the other, and when information on which sex is to be favoured is not available at the time of nesting, the decision on sex is deferred. • Temperature during incubation confers differential advantage, directly or indirectly. • TSD defers the decision until information on the direction of that advantage is available.

  29. Crews: Evolution and Development 2003

  30. Top Sex Determining Gene or Gene Complex SexDifferentiationGenes Temperature Hormonal Environment • Networks not “linear” sequences of gene action • Redundancy in function • Complex system of thermal compensation

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