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