Embryonic diapause

Delayed Implantation or Embryonic Diapause is a reproductive strategy used by approximately 100 different mammals in seven or eight different orders. In embryonic diapause, the embryo (blastocyst) does not immediately implant in the uterus, but is maintained in a state of dormancy. Little to no development takes place while the embryo remains unattached to the uterine wall. As a result, the normal gestation period is extended for a species-specific period of time.^[1][2] While much of the molecular regulation involved in activating dormant blastocysts has been characterized, little is still known about entry into diapause, and the conditions which enable a blastocyst to remain dormant.

Some mammals that undergo embryonic diapause include rodents, bears, mustelids (e.g. badgers), and marsupials, (e.g. kangaroos). Some groups only have one species that undergoes embryonic diapause, such as the roe deer in the order Artiodactyla.^[2]

Purpose

Mammals may undergo diapause to avoid the risk to their own lives during unfavourable and/or environmental conditions. Mammals use embryonic diapause to time the birth of their offspring for favorable metabolic and/or environmental conditions. Reproduction has a large energy cost and it is beneficial to have ideal conditions (e.g. available food, mild weather, previous offspring weaned) to ensure the offspring survives before giving birth.^[3][4]

Types

Two types of mammalian embryonic diapause have been identified.

Facultative diapause

Facultative diapause is also known as lactational delayed implantation due to its regulation via lactation. If a female copulates while still lactating for a previous litter, the sucking stimulus will cause the embryos to enter into diapause. This is known to occur in some rodents, insectivores and marsupials.^[5]

Obligate diapause

Obligate diapause is also known as seasonal delayed implantation and is a mechanism that allows mammals to time the birth of their offspring for favorable environmental conditions. This mechanism occurs as a regular part of the reproductive cycle in mammals such as armadillos, all species of pinniped, many mustelids, all ursids, one species of fruit bat, and the roe deer.^[5][6][7]

Remarks

The term Diapause is also used to refer to the temporary, partial, or complete metabolic suspension in various life stages of insects and plants. This can cause problems in terminology. Delayed implantation or embryonic diapause is a specific type of diapause which developed independently of other instances of the phenomenon. A uterus is required for implantation; therefore, the terms "delayed implantation" and "embryonic diapause" may only be used in describing the phenomenon in mammals.

References

1. ^ Desmarais, J.A.; V. Bordignon, F.L. Lopes, L.C. Smith and B.D. Murph (2004). "The escape of the mink embryo from obligate diapause". Biology of Reproduction 70 (3): 662–670. doi:10.1095/biolreprod.103.023572. PMID 14585805. http://www.biolreprod.org/cgi/content/full/70/3/662. Retrieved 2008-04-05. 
2. ^ ^{a b} Renfree, M.B.; B. Shaw (2000). "Diapause". Annual Review of Physiology 62: 353–375. doi:10.1146/annurev.physiol.62.1.353. PMID 10845095. 
3. ^ "Class Mammalia". University of Michigan Museum of Zoology: Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Mammalia.html. Retrieved 2008-04-05. 
4. ^ "Implantation". University of Wyoming. http://www.uwyo.edu/wjm/Repro/implant.htm. Retrieved 2008-04-05. 
5. ^ ^{a b} Daniel, J.C., Jr. (Apr. 1970). "Dormant embryos of mammals". BioScience (BioScience, Vol. 20, No. 7) 20 (7): 411–415. doi:10.2307/1295231. JSTOR 1295231. 
6. ^ Lopes,, Flavia L; Joëlle A Desmarais and Bruce D Murphy (2004). "Embryonic diapause and its regulation". Reproduction 128 (3): 669–678. doi:10.1530/rep.1.00444. PMID 15579584. http://www.biolreprod.org/cgi/content/full/70/3/662. Retrieved 2008-04-05. 
7. ^ Lindenfors, P; Dalen, L., Angerbjorn, A. (2003). "The monophyletic origin of delayed implantation in carnivores and its implications". Evolution 57 (8): 1952–1956. PMID 14503635. 

• "Roe Deer Research Group". http://www.roedeer.com. Retrieved 2008-04-05.