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AP BIOLOGY. Essential Knowledge 2.A.1: All living systems require constant input of free energy. Life-history strategy.

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ap biology


Essential Knowledge 2.A.1:

All living systems require constant input of free energy.

life history strategy
Life-history strategy
  • 2.A.1.d.2: Reproduction and rearing of offspring require free energy beyond that used for maintenance and growth. Different organisms use various reproductive strategies in response to energy availability.

Reproductive diapause


Did you know that the female European roe deer (Capreoluscapreolus) uses embryonic diapause to control when her fawn will be born? From the late-summer mating through the end of December, the embryo remains at about the 30-cell stage in a state of diapause. This delays implantation of the fertilized egg until a more ideal time for birth.

SO! What is reproductive diapause?


Diapause is a genetic switch that results in suspended animation in which embryonic cell growth and development are reversibly stopped or slowed.

Diapause occurs in a diverse range of vertebrates and invertebrates that includes insects, copepods (crustaceans), fish, birds, rodents, and marsupials (animals with pouches, such as the kangaroo) and other mammals, including deer.


Temperature-dependent diapause

Inchicken eggs, development stops whenever the hen gets off the egg and the eggs cool down and starts back again when the hen returns to her nest. Environmentally triggered diapauseDiapause differs dramatically from hibernation and aestivation in that during diapause, every cell ceases growth, achieving dormancy. In hibernation and aestivation, metabolism only slows as a survival reaction to harsh conditions. Diapause, on the other hand, begins before these severe conditions occur and is brought about by environmental triggers. During diapause, cell growth and development are reversibly stopped or slowed. Annual killifish eggs in diapause can survive for months or even years! Recent findings suggest that the female killifish, in response to environmental cues, relays a message to the egg to stop growing for a fixed amount of time. Essentially, the biological clock stops. These “sleeping” embryos can remain alive for periods two times longer than their normal life expectancy! When diapause is broken and the embryo “wakes up,” it continues to develop and hatch – as if time had stood still until then!


Read about some examples!



What about cicadas? Do they experience diapause?