Embryonic diapause

Embryonic diapause (from late 19th century English: dia- ‘through’ + pause- 'delay') (aka delayed implantation) is a reproductive strategy used by approximately 100 different mammals in seven or eight different orders. In embryonic diapause, the embryonic blastocyst does not immediately implant in the uterus after sexual reproduction has created the zygote, but rather remains 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 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, armadillos, mustelids (e.g. weasels and 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]


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]


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 suckling 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]


  1. ^ Desmarais, J.A.; V. Bordignon; F.L. Lopes; L.C. Smith; 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. 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. Retrieved 2008-04-05.
  4. ^ "Implantation". University of Wyoming. Retrieved 2008-04-05.
  5. ^ a b Daniel, J.C., Jr. (Apr 1970). "Dormant embryos of mammals". BioScience. 20 (7): 411–415. doi:10.2307/1295231. JSTOR 1295231.
  6. ^ Lopes, Flavia L; Joëlle A Desmarais; Bruce D Murphy (2004). "Embryonic diapause and its regulation". Reproduction. 128 (3): 669–678. doi:10.1530/rep.1.00444. PMID 15579584. 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. doi:10.1554/02-619. PMID 14503635.

Aestivation or æstivation (from Latin: aestas, summer, but also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions. It takes place during times of heat and dryness, the hot dry season, which are often the summer months.

Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo aestivation. The fossil record suggests that aestivation may have evolved several hundred million years ago.

Organisms that aestivate appear to be in a fairly "light" state of dormancy, as their physiological state can be rapidly reversed, and the organism can quickly return to a normal state. A study done on Otala lactea, a snail native to parts of Europe and Northern Africa, shows that they can wake from their dormant state within ten minutes of being introduced to a wetter environment.

The primary physiological and biochemical concerns for an aestivating animal are to conserve energy, retain water in the body, ration the use of stored energy, handle the nitrogenous end products, and stabilize bodily organs, cells, and macromolecules. This can be quite a task as hot temperatures and arid conditions may last for months. The depression of metabolic rate during aestivation causes a reduction in macromolecule synthesis and degradation. To stabilize the macromolecules, aestivators will enhance antioxidant defenses and elevate chaperone proteins. This is a widely used strategy across all forms of hypometabolism. These physiological and biochemical concerns appear to be the core elements of hypometabolism throughout the animal kingdom. In other words, animals who aestivate appear to go through nearly the same physiological processes as animals that hibernate.

Agile wallaby

The agile wallaby (Macropus agilis) also known as the sandy wallaby, is a species of wallaby found in northern Australia and New Guinea. It is the most common wallaby in Australia's north. The agile wallaby is a sandy colour becoming paler below. It is sometimes solitary and at other times sociable and grazes on grasses and other plants. The agile wallaby is not considered threatened.

Black-flanked rock-wallaby

The black-flanked rock-wallaby (Petrogale lateralis), also known as the black-footed rock-wallaby or warru, is a kind of wallaby, one of several rock-wallabies in the genus Petrogale.

Bluntnose stingray

The bluntnose stingray or Say's stingray (Dasyatis say, often misspelled sayi) is a species of stingray in the family Dasyatidae, native to the coastal waters of the western Atlantic Ocean from the U.S. state of Massachusetts to Venezuela. It is a bottom-dwelling species that prefers sandy or muddy habitats 1–10 m (3.3–32.8 ft) deep, and is migratory in the northern portion of its range. Typically growing to 78 cm (31 in) across, the bluntnose stingray is characterized by a rhomboid pectoral fin disc with broadly rounded outer corners and an obtuse-angled snout. It has a whip-like tail with both an upper keel and a lower fin fold, and a line of small tubercles along the middle of its back.

More active at night than during the day when it is usually buried in sediment, the bluntnose stingray is a predator of small benthic invertebrates and bony fishes. This species is aplacental viviparous, in which the unborn young are nourished initially by yolk, and later histotroph ("uterine milk") produced by their mother. Females give birth to 1–6 pups every May after a gestation period of 11–12 months, most of which consists of a period of arrested embryonic development. The venomous tail spine of the bluntnose stingray is potentially dangerous to unwary beachgoers. The International Union for Conservation of Nature (IUCN) has listed this species under Least Concern, as it is widely distributed, common, and minimally threatened by commercial fisheries.

Common wallaroo

The common wallaroo (Macropus robustus) or wallaroo, also known as euro or hill wallaroo is a species of macropod. The word euro is particularly applied to one subspecies (M. r. erubescens).The eastern wallaroo is mostly nocturnal and solitary, and is one of the more common macropods. It makes a loud hissing noise and some subspecies are sexually dimorphic, like most wallaroos.

Critical thermal maximum

Critical thermal maximum, in zoology, is the temperature for a given species above which most individuals respond with unorganized locomotion, subjecting the animal to likely death. This concept is particularly relevant in periods of aestivation or quiescence, in which circumstances an organism experiences limited mobility and lacks the ability to seek a microhabitat of reduced thermal stress.


Diapause, when referencing animal dormancy, is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions. Diapause is a mechanism used as a means to survive predictable, unfavorable environmental conditions, such as temperature extremes, drought, or reduced food availability. Diapause is most often observed in all the life stages of arthropods, especially insects. Embryonic diapause, a somewhat similar phenomenon, occurs in over 130 species of mammals, possibly even in humans, and in the embryos of many of the oviparous species of fish in the order Cyprinodontiformes.Activity levels of diapausing stages can vary considerably among species. Diapause may occur in a completely immobile stage, such as the pupae and eggs, or it may occur in very active stages that undergo extensive migrations, such as the adult monarch butterfly, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.


Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions. Organisms can synchronize entry to a dormant phase with their environment through predictive or consequential means. Predictive dormancy occurs when an organism enters a dormant phase before the onset of adverse conditions. For example, photoperiod and decreasing temperature are used by many plants to predict the onset of winter. Consequential dormancy occurs when organisms enter a dormant phase after adverse conditions have arisen. This is commonly found in areas with an unpredictable climate. While very sudden changes in conditions may lead to a high mortality rate among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer and are therefore able to make greater use of available resources.


Hemolin is an immunoglobulin-like protein exclusively found in Lepidoptera (moths and butterflies). It was first discovered in immune-challenged pupae of Hyalophora cecropia and Manduca sexta.Hemolin has a horseshoe crystal structure with four domains and resembles the developmental protein neuroglian.

Hemolin increases 18-fold up to 7 mg/ml following injection of bacteria in H. cecropia. Induction of Hemolin in moths after bacterial injection have been shown in several species including Antheraea pernyi, Bombyx mori, Helicoverpa zea, Heliothis virescens, Hyphantria cunea, and Samia cynthia.Hemolin has also been suggested to participate in the immune response to virus infection and shown to bind to virus particles. It is expressed in response to dsRNA in a dose-dependent manner. Galleria melonella responds to caffeine intake by increased Hemolin protein expression.Hemolin is thought to be a gene duplication of the developmental protein neuroglian, but has lost two of the protein domains that neuroglian contains. In the potential function as a developmental protein, Hemolin has been shown to increase close to pupation in Manduca sexta, and is induced during diapause and by 20-Hydroxyecdysone in Lymantria dispar. RNAi of Hemolin causes malformation in H. cecropia.

Hoary bat

The hoary bat (Aeorestes cinereus) is a species of bat in the vesper bat family, Vespertilionidae. It lives throughout most of North America and much of South America, with disjunct populations in the Galápagos Islands and Hawaii.

Implantation (human embryo)

In humans, implantation is the stage of pregnancy at which the embryo adheres to the wall of the uterus. At this stage of prenatal development, the conceptus is called a blastocyst. It is by this adhesion that the embryo receives oxygen and nutrients from the mother to be able to grow.

In humans, implantation of a fertilized ovum is most likely to occur around 9 days after ovulation, however this can range between 6 and 12 days.

Instant Fish

Instant Fish was an idea conceived by the Wham-O toy company in the early 1960s.


Laimosemion is a genus of fish in the family Aplocheilidae from the Amazon basin and basins in the Guiana Shield in tropical South America. They mostly inhabit small streams, creeks, swamps and pools in lowlands, but locally occur to an altitude of 1,300 m (4,300 ft).Like their relatives, the adult Laimosemion often inhabit very small isolated waters, but they are not annual species like some other killifish. The adults can move some distance over land to find another water source. They do this by repeatedly flipping their body. They commonly complete their life cycle in the water, often laying their eggs among plant material. However, their eggs can survive several days of drought, only hatching when again covered by water.The largest are up to 8.5 cm (3.3 in) in total length, but most Laimosemion species only reach around half that size.


The Mustelidae (; from Latin mustela, weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, mink, and wolverines, among others. Mustelids () are a diverse group and form the largest family in the order Carnivora, suborder Caniformia. Mustelidae comprises about 56–60 species across eight subfamilies.

Rebecca Spindler

Rebecca Spindler (born in Melbourne) is the Head of Science and Conservation at non profit conservation organisation Bush Heritage Australia. She previously was the Manager of Research and Conservation at Taronga Conservation Society Australia, in the New South Wales Office of Environment and Heritage (OEH).

Robert Hermes

Robert Hermes, DVM, Ph.D.(born November 15, 1969 in Celle, Germany) is a veterinarian researcher at The Leibniz-Institute of Zoo and Wildlife Research in Berlin. He studied veterinary medicine at the Freie Universität Berlin. He completed a Ph.D. in reproductive management.

Siberian roe deer

The Siberian roe deer or eastern roe deer (Capreolus pygargus) is a species of roe deer found in northeastern Asia. In addition to Siberia and Mongolia, it is found in Kazakhstan, the Tian Shan Mountains of Kyrgyzstan, eastern Tibet, the Korean Peninsula, and northeastern China (Manchuria).

Its specific name pygargus, literally "white-rumped", is shared by the pygarg, an antelope known in the antiquity. The name was chosen by the German biologist Peter Simon Pallas in the late 18th century.

The roe deer has long antlers.

Veiled chameleon

The veiled chameleon (Chamaeleo calyptratus) is a species of chameleon native to the Arabian Peninsula in Yemen and Saudi Arabia. Other common names include cone-head chameleon and Yemen chameleon.

Winter rest

Winter rest (from the German term Winterruhe) is a state of reduced activity of plants and warm-blooded animals living in extratropical regions of the world during the more hostile environmental conditions of winter. In this state, they save energy during cold weather while they have limited access to food sources.

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