Anne - Temp-dependant Sex Determination

Question 1

What are the 3 hypothesis of adaptive significance of TSD?

Answer 1

• Ancestral condition that is adaptively neutral
• The Charnov-Bull model (1977)
  Sex-specific fitness effects
  e.g.: at warm temp, females hatch earlier, more time to get bigger before breeding
• Divergent selection due to different climate

Question 2

Describe MF TSD and provide and example

Answer 2

Females produced at warm temps and Males at cold.
Turtles

Question 3

Describe FM TSD and provide an example

Answer 3

Males produced at warm temps and Females at cold.
Tuatara

Question 4

Describe FMF TSD and provide an example

Answer 4

Females are warm and cold temps, intermediate temps are male.
Crocodilia

Question 5

What is Tpiv?

Answer 5

Pivotal Temperature - the temperature at which males and females are produced evenly 50/50

Question 6

What is TSP and the mechanisms for TSP?

Answer 6

Thermo Sensitive Period - this is when sex is determined, usually middle third of incubation, it is because germ cells are localised during TSP and undifferentiated and after the are differentiated.

Question 7

What is an experiment to determine TSP?

Answer 7

Egg shift experiment - Shift the temperature at different times and observe the % of the gender hatched.

Question 8

What is happening during the thermosensitive period? Use MF to explain.

Answer 8

in undifferentiated gonad there is low aromatase activity. In the thermosensitive period at high temps there is high aromatase activity which means ovaries will be produced due to aromatase being the enzyme that converts T to oestrogen. At low temps there is low aromatase activity and therefore testes are produced due to the T levels.

Question 9

What are 2 disadvantages of TSD?

Answer 9

• TSD species are sensitive to climate change (e.g.: turtles, tuatara)
• TSD can be ‘overridden ’ by exposure of the embryo to sex steroid hormone or endocrine disruptive compounds (PCBs, BPA, pesticides like atrazine, nitrates…) during thermo-sensitive period

Question 10

Why are TSD and GSD not mutually exclusive?

Answer 10

TSD does occur primarily in species without sex chromosomes BUT In some species with sex chromosomes, extreme temperatures can override the influence of sex chromosomes