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Environmental SexDetermination
Temperature Sex Determination
• Common in many vertebrate species– Some fish
• cool males/ warm females– Some anurans and salamanders
• cool females/warm males– Many turtles
• generally cool males/warm females• Exception snapping turtle• female warm and cool/ male at moderate temperature
TSD 2• Some lizards
– cool females/warm males• All crocodilians
– cool female/warm male– Also
• cool and hot females• males at moderate temperatures
• Some birds? Not observed to date• Not observed in mammals
TSD Reptiles%
Mal
e
Mechanisms• Hypothesis
– Temperature alters estrogen production by thegonad, which influences differentiation
– Temperature-dependent aromatase actvity inEuropean Pond turtle (Emys obicularis)
• Effect only on embryo early in differentiation
Sex Differentiation in FishXX / XY / Temperature (WY,WX, XX) / (YY, XY) Social cues
Sex Differentiation in Frogs
Sex Differentiation in Alligators
TSD and Genes
• Alligators have no SRY gene• Gonadal differentiation
– DAX-1– SF-1– WT-1– SOX9– AMH– DMRT-1– P450arom– ERα β– Heat Shock
Western & Sinclair JEZ 290 (2001)
Dax1
WT1
SF1
Female Gonads (♀)
Western & Sinclair JEZ 290 (2001)
WT1Male Gonads (♂)
Sox9
AMH
AmericanAlligator
Embryos @33°C
Western & SinclairJEZ 290 (2001)
Estradiol-17β
Testosterone
P450aromatase
Quantitative Gene Expression in GAMs
Male Gonads (♂)
P450aromatase
Female Gonads (♀)
Katsu et al., unpubl. data
Sex Reversal - % FemaleSex Reversal - % Female
32.5°C : Stage 19 : N = 7-10 eggs / treatment32.5°C : Stage 19 : N = 7-10 eggs / treatment
t-Nonat-Nona DDDDDD DDD+tNDDD+tN DicofolDicofol EstradiolEstradiol00
2020
4040
6060
8080
100100 1ppt1ppt
100ppt100ppt
1ppb1ppb
100ppb100ppb
10ppm10ppm
ControlControl
Guillette et al., unpubl. dataGuillette et al., unpubl. data
Sex Reversal - % FemaleSex Reversal - % Female
32.5°C : Stage 19 : N = 7-10 eggs / treatment32.5°C : Stage 19 : N = 7-10 eggs / treatment
t-Nonat-Nona DDDDDD DDD+tNDDD+tN DicofolDicofol EstradiolEstradiol00
2020
4040
6060
8080
100100 1ppt1ppt
100ppt100ppt
1ppb1ppb
100ppb100ppb
10ppm10ppm
ControlControl
Guillette et al., unpubl. dataGuillette et al., unpubl. data
0
0.2
0.4
0.6
0.8
1
1.2
1.4
male male E2 female
0
50
100
150
200
250
300
350
400
450
500
male male E2 female
0
0.2
0.4
0.6
0.8
1
1.2
1.4
male male E2 female
ERα SF1
AMH
M M-E2 F M M-E2 F M M-E2 F
M M-E2 FM M-E2 F M M-E2 F
Aromatase
DMRT1 SOX9
Gene Expression in Neonatal Gonads Incubated at Male or Female Temperatures, or at Male Temperature Exposed to Estrogen
Katsu et al. unpubl. data