TSD in Reptiles

How the physical andthe physiological conspireto defeat global warming

Arthur Georges

Applied Ecology Research GroupUniversity of Canberra

Sex versus Temperature

Established Results

Dramatic effect – usually 100% of one sex or the other

Only a small range of temperatures (threshold) produces both sexes

TSD is widespread among reptiles

European Pond Turtle (France)

NESTMEANTEMP

RANGEEXPSEX

OBSSEX

I 24.8 7.5 male female

II 23.9 6.0 male male

III 26.8 5.9 male female

IV 25.8 5.7 male female

V 25.5 5.0 male female

Threshold = 28°C

Temperatures in Natural Nests

Temperaturesrecorded atfour depthsover 24hrs

American Map Turtles

Diel Cycle

Daily Temperature

Cycle

T = R Cos (t) + M

where M is the meanand +/-R is the range

Diel Cycle

Daily Temperature

Cycle

T = R Cos (t) + M

where M is the meanand +/-R is the range

Diel Cycle

Diel Cycle

Linear CTE Model

CTE = R.Cos (t’) + M

t’ = - sin (t’) R

2 M – T0

Predicting Sex

American Map Turtles

Development Rate

Development Rate

increases linearly with time

= A(T – T0)

where T0 is thedevelopmental zero

ds

dt

Sex vs Temperature

Sex ratios versusDaily range

At a fixed mean of 26°C

Line = model prediction

Loggerhead Turtles

Loggerhead Turtles

Sex ratios versusDaily range

At a fixed mean of 26°C

Line = model prediction

Daily Thermal Regimes

Mean temperaturevaries a little –

by 0.6°C

Daily range variesby up to 3.0 °C

CTE variesby about 2.0 °C

Thermal Gradients

Development in Carettochelys

Core Temperature Trace

Core Temperature Trace

Core Temperature Trace

Linear Model

Fitting Non-linear Models

Sharpe-DeMichelle Model

Incubation Period

Sex

Sex

Conclusion

Contrary to previous reports…

Conclusion

Global warming may well NOT be the female turtle’s answer to male chauvinism!

Single Switch

Title?

Patterns of oxygen

consumption during incubation

Linear CTE Model – example

Emys orbicularis – France (Pieau, 1982)

T0 = 16.1, Mean = 24.8°C, R = 7.5 °C

t’ = 0.8980 (6 hrs 51 mins) after 14 iterations

CTE = 29.5 °C

CTE = R.Cos (t’) + M

t’ = - sin (t’) R

2 M – T0

Refinement #1

When temperatures drop below the developmental zero each day

Yet to be done…

Test the utility of the models in real field situations

Test the Linear CTE Model with Threshold in the laboratory, incorporate the Sharpe-DeMichelle Model

Simplify computation – the WEB

Explore the broader implications for hatchling phenotypes in general

Global warming

Double Switch

European Pond Turtle (France)

NESTMEANTEMP

RANGE CTEEXPSEX

OBSSEX

I 24.8 7.5 29.5 female female

II 23.9 6.0 27.4 male male

III 26.8 5.9 29.6 female female

IV 25.8 5.7 28.6 both female

V 25.5 5.0 27.8 male female

Threshold = 28°C

Sex versus Temperature