Ectotherms and climate change: temperature-dependent sex determination
Why in news: A Science Advances study of 2 September 2026 found heat-driven sex reversal could push Hungary's agile frog populations towards extinction sooner.
Ectotherms, cold-blooded animals such as fish, amphibians, reptiles and insects, take their body temperature from their surroundings. In many reptiles, nest temperature decides an embryo's sex, and in some frogs heat can override chromosomes to cause sex reversal. A Science Advances study of Hungary's agile frogs, published on 2 September 2026, links heat-driven sex reversal to extinction risk.
Syllabus: Prelims · Environment & Ecology; Prelims · Science & Technology; GS3 · Environment & Conservation
Why this matters for UPSC
GS3 environment and Prelims general science: Prelims can ask how temperature-dependent sex determination works, which animals show it and which animals are ectotherms; Mains, how climate change threatens species such as the olive ridley.
In short
Ectotherms are cold-blooded animals whose body temperature follows their surroundings; where early-life heat also fixes sex, warming can tilt sex ratios and threaten survival.
Where heat decides sex, warming can empty a population even when its habitat survives; cutting emissions and keeping nests and ponds cool must go together.
Why it matters
A turtle egg cannot leave a hot nest, and a tadpole cannot escape a warm pond. When heat tilts the sex ratio, adults run short of mates, populations shrink and lose genetic diversity, and small populations can vanish. In India, olive ridley turtles nest in mass arrivals on the Odisha coast, where nest temperature decides the sex of the young. Earlier research also found young ectotherms barely raise their heat tolerance as temperatures climb. The larger issue is that climate-impact estimates built on adult animals may understate the damage, so shaded nesting sites and cool refuges become part of conservation.
Prelims pointers
- Ectotherms (cold-blooded animals) take body heat from their surroundings; fish, reptiles, amphibians and insects, together more than 99% of animals.
- Temperature-dependent sex determination: the egg's incubation temperature fixes sex; seen in sea turtles and other reptiles, including alligators and crocodiles.
- Sea turtles: warmer nests produce more females, cooler nests more males.
- Genetic sex determination: mammals XX female, XY male; birds ZZ male, ZW female, so the female bird carries two different sex chromosomes.
- Olive ridley turtle: Schedule I of the Wild Life (Protection) Act, 1972; mass nesting (arribada) at Gahirmatha and Rushikulya in Odisha.
- Acclimatisation is a change within an individual's lifetime; adaptation is a change across generations through evolution.
- Ranavirus: a group of viruses that can cause high mortality in amphibians; in the agile frog experiment, all infected froglets died within 12 days.
- Paris Agreement (UN Climate Change Conference, COP21, Paris, 12 December 2015): hold warming well below 2 °C and pursue 1.5 °C above pre-industrial levels.
Practise a UPSC-style question
With reference to ectotherms, consider the following statements:
1. Ectotherms produce most of their body heat through their own internal metabolism.
2. Fish, amphibians, reptiles and insects are ectotherms.
3. Ectotherms account for more than 99% of the animal species on Earth.
Which of the statements given above is/are correct?
- (a) 1 and 2 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Show the answer
Answer: (b) 2 and 3 only
1 is incorrect: an ectotherm's body temperature reflects the temperature outside; it takes its heat from its surroundings, not mainly from its own metabolism. 2 is correct: fish, reptiles, amphibians and insects are ectotherms. 3 is correct: ectotherms make up more than 99% of animals on Earth.
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