Embryos Go Into Dormancy

photograph of female kangaroo carrying joey in pouch

Biological Strategy

Red kangaroo

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Regulate Reproduction or Growth

Reproduction and growth are two physiological processes that occur in all living systems. There are situations when conditions are right for both, and other situations when continuing either harms the living system because both have a very high energy cost. Reproduction and growth are unique in that both can stop until conditions improve, although stopping either for an extended time can cause problems. An example of regulating reproduction is a process called delayed implantation or embryonic diapause found in some mammals, such as otters. An otter’s embryos sometimes temporarily cease developing and won’t develop further until the female senses that conditions are suitable.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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The reproductive system of female red kangaroos holds embryos in developmental dormancy via hormones.

“One to three days after giving birth, a female kangaroo often mates again and another fertilized egg settles into her uterus…The fate of the egg…depends on what happens to [the first] baby. If the recently born baby has reached the pouch and latched onto a teat, the newly fertilized egg develops only to the blastocyst stage (about seventy to one hundred cells) and then stays in developmental dormancy until it receives the signal to continue to development. The blastocyst can remain dormant in the uterus for several months. If the newborn baby hasn’t made it to the pouch or if it dies while in the pouch, the female’s body releases a pulse of the progesterone. This signals the blastocyst to continue to develop, and about thirty-three days later the ‘replacement baby’ will be born. The same happens once a mature joey is about to leave the pouch permanently and is nursing less: the mother’s hormones kick in and the fertilized egg begins to develop.” (Crump 2005:56)

Crump, M. 2005. Headless Males Make Great Lovers & Other Unusual Natural Histories. University of Chicago Press, Chicago, IL. 199 pp.

Last Updated August 18, 2016

References

Book

Headless Males Make Great Lovers: And Other Unusual Natural Histories

University of Chicago Press | 01/05/2007 | Marty Crump

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