Why and how some Animals Pause their Pregnancy Varies
Embryonic diapause delays childbirth for certain female animals. The reason for this is to wait until the correct physiological signs show a favorable reproductive outcome. Until then, blastocyst embryos are dormant. In order for a pregnancy to begin around the time most species enter diapause, the species must be made aware of it within the first five days after conception. Despite its rarity, many animal mothers are able to achieve this.
There are Two Primary Ways Animals do this
One strategy is to get pregnant again as quickly as possible after giving birth just in case something goes wrong with the newborn(s). Lactation-related stress and hormones halt the new pregnancy for the duration of the nursing process. After the babies leave, the pregnancy continues. This is known as facultative diapause. Second, waiting for the optimal period to conceive, which often coincides with the changing of the seasons, is often practiced. Seasonal fluctuations in the length of daylight cause obligatory diapause to begin and end at the appropriate times. There are significant variations in diapause duration despite the fact that obligate diapause exists in a wide range of species across many different groupings. This is known as obligate diapause. More than 130 animal species have proven to pause their pregnancies. Let’s dive into five of these animals below!
Polar Bears
For mammals that survive Earth’s hardest winters, there is no optimal season to produce children. Polar bear females can store fertilized eggs until they are readyto continue with the pregnancy. In polar bears, the gestation period lasts about eight months. Females find mates best in late March to early June then give birth to one to three cubs in November or December. Females give birth to their pups in their winter dens. She produces milk from her body fat until then. Polar mothers may schedule their pups’ emergence to coincide with the best weather for food, but they still face an arduous journey to sexual maturity. In the Arctic and subarctic, many large predators, such as wolves and adult male polar bears, hunt for easy prey year-round. These polar bear mothers show that there is no “perfect” time to get pregnant. However, their bodies store embryos until the ideal time to improve the rate of success.
Seals
Seals can delay pregnancy to give birth in optimal conditions. Most seal species mate within weeks of the breeding season. The bulls have established territories and many females are gathered, so the moment is perfect. However, since the gestation period is usually less than a year, delivery simply wouldn’t match with the breeding season and optimal weather for the following year. Thus, embryonic diapause helps them to delay their pregnancy so that they can give birth at the correct time. Species type, habitat, and the mother’s health determine embryonic diapause’s duration. Environmental cues control implantation timing. Most species implant depending on photoperiod, however, grey seals schedule their pregnancies based on water temperature. Delaying embryo implantation lets mothers endure tough conditions like hunger or bad weather.
Rodents
In the wild, embryos of some rodent species wait to implant until their mom’s body has sufficient reserves of food and energy. As a result of hunger or other stresses, the embryo enters a dormant period. This measure is taken to make sure they will continue to exist. Mice as well as other rodents turn to diapause or delayed implantation when life is particularly challenging. This is due to factors including lack of food, inadequate fat storage of the mother, or older siblings who have not been weaned. This can fluctuate based on the species and the surroundings. Mice that are kept as house pets or in laboratories typically have better birth outcomes because their living surroundings are more controlled. With this strategy, nature has given the mother more agency over the circumstances of the birth. The first stem cells were actually discovered by scientists in a mouse embryo during diapause when the embryo’s cell cycle was paused.
Armadillos
The nine-banded armadillo is highly adept at population regulation. Pregnant females are capable of pausing embryonic development for up to two years in response to extreme environmental stress. Embryo implantation in the uterine wall is delayed by three to four months in armadillos. This, plus the average five-month period of rapid growth throughout pregnancy, means the average time to birth is around nine months. A newly detected delay is estimated to add another 12 to 24 months onto the expected duration of pregnancy in armadillos. However, not all pregnant female armadillos have delayed births. When females are uncovered in the late autumn or winter, the customary three to four-month delay between fertilization and implantation is nearly at its end. This increases the possibility of such events. It’s possible that stress hormones can block implantation for them as well.
Marsupials
While female kangaroos and wallabies are known to utilize both uteruses during pregnancy. Marsupial pregnancy is characterized by a short duration of gestation and a prolonged period of nursing. But by forcing an embryonic diapause, a period of developmental stop, the pregnancy can be extended to 11 months. In kangaroos and wallabies, the hormones melatonin and prolactin are involved in modulating the influence of lactational and seasonal variables on diapause. During the end of pregnancy, known as parturition, marsupials seem to be fairly standard mammals, requiring the same behavioral and physiological cues as any other mammal to deliver healthy offspring.
Diapause has Taught Humans so Much
Based on years of empirical observation and evidence, scientists and academics believe all mammals, including humans, share an ancient embryonic characteristic. Until recently, it was unclear which animals employed diapause and how the pregnancy was interrupted. This mechanism fascinates scientists and helps us understand basic reproductive processes in all mammals. Understanding diapause may simplify embryo transplantation and growth. Diapause may even improve stem cells and create new cancer treatments. For example, scientists detected stem cells in mouse embryos in diapause. Stem cells also resemble diapaused embryos. Understanding molecular diapause could lead to markers for tumor stem cells, which are considered to cause cancer spread or new drugs to inhibit cell multiplication.
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