tsd in reptiles
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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
• Environmental sex determination (ESD/TSD): Sex determined after fertilisation by environmental factors
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
TSD
TSD G SD
G SD
Young Georges Doody Canadian J. Zool, in press
Pig-nosed Turtle
1.0C
Georges Stoutjesdijk Limpus J. Experimental Zool. 1994
4.5C
Loggerhead
Water Dragon Harlow 2001, unpubl. thesis
One Pattern?
After Pieau, 1996
Middle Third of Incubation is
InfluentialYoung Georges Doody Canadian J. Zool. in press
Both Magnitude and variability are important
Mean 26C(Male)
Georges Stoutjesdijk Limpus J. Experimental Zool. 1994
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
Top Sex Determining Gene
or Gene Complex
WNT4 (?)
DAX1 (?)
WT1 SF1
Aromatasegene
AMH
SOX9
DMRT1
AromataseAndrostenedione
Testosterone
Estrone
Estradiol 17B Receptors
-
-
-
+
++
Sarre Georges Quinn Bioessays 2004
A. Mutually exclusive mechanisms of sex determination
B. Intermediate forms with varying degrees of interaction
A BTSD
TSD G SD
G SD
Dichotomy or Continuum?
Zaborski et al. 1988 Differentiation
Gonad Blood
HY+ HY- HY+ HY-
MALE 100% 50% 50%
H-Y antigen expression(25-26C)
Gonad Blood
HY+ HY- HY+ HY-
FEMALE 100% 50% 50%
H-Y antigen expression(30-30.5C)
Zaborski et al. 1988 Differentiation
Blood
HY+ HY-
MALE 0 22
FEMALE 42 6
H-Y antigen expression(at the Pivotal Temp)
Zaborski et al. 1988 Differentiation
Girondot Zaborski et al. 1994 Genetical Research
Blood
HY+ HY-
MALE 3 24
FEMALE 106 7
H-Y antigen expression(in the field)
Temperature (deg C)
ProportionMALE
Bassianaduperreyi
Shine Elphick Donnellan 2002 Ecology Letters
Temperature Males Females
34 17 47
32 14 14
30 15 15
28 30 26
26 13 17
24 14 10
22 20 15
Bearded Dragon
Present study
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
Sister TaxaA.muricatus
A.norrisi
Coincidence?
Homeotherms Ectotherms Poikilotherms
Strictly
GSD
TSD
Common
TSD
Rare
Top Sex Determining Gene
or Gene Complex
SexDifferentiation
Genes
Hormonal
Environment
Range of temperatures experienced up to 23C
(22 – 45C)
Top Sex Determining Gene
or Gene Complex
SexDifferentiation
Genes
Hormonal
Environment
Network of genes and gene products
Thermal Compensation
Consistent signal
TSD
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.
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.
The Team
Applied Ecology Research Group Dr Stephen SarreAlex QuinnBrett LidburySean DoodyEnzo Guarino
Comparative Genomics Group
Australian National University
Prof Jenny Graves
Dr Frank Gruetzner
Dr Ann Gaeth
Dr Tariq Ezaz
Funding
ARC Discovery Grants 1996, 2003, 2004-6UC Research Grant 2002CRC for Freshwater Ecology
Collaborators
Hofstra University, USA
Dr Russell Burke
University of Sydney
Prof. Rick Shine
Contributors
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.
Crews: Evolution and Development 2003
Top Sex Determining Gene
or Gene Complex
SexDifferentiation
Genes
Hormonal
Environment
• Networks not “linear” sequences of gene action
• Redundancy in function• Complex system of thermal compensation
Temperature