Erm… I meant to post this yesterday. Sorry!
Anyhow… today (that should have been yesterday), I’ve a topic that has fascinated me as a biologist for many years: reproduction! Specifically, I’ll be discussing a cool reproductive mechanism occurring in some mammals. Now, should you not share my excitement about reproduction, you probably don’t want to read on. No hard feelings if you leave (and thanks for stopping by anyway)!
Still with me? Cool!
First of all, a definition: Diapause is a phenomenon in some plants and animals where a temporary halt in the growth of an embryo takes place. The most well known type of diapause is delayed implantation (DI). DI is found in mammals and much like a little alien lying in wait for the best moment to grow forth out of its host, these little wannabe babies wait for certain chemical cues to initiate growth. Over 100 species of mammals have this unique ability and include many rodents, weasels, skunks, pandas, nutrias, armadillos, badgers, bats, wild dogs, sea lions and other marine carnivores, bears, lions, and marsupials like wallabys. What happens is that instead of attaching to the uterine wall, the tiny ball of fertilized cells (called the blastocyst) free-floats. After a time, physiologic cues create one of the following scenarios: a) the blastocyst attaches and begins to grow or b) the mother’s body reabsorbs the cells because the conditions aren’t optimal for becoming pregnant.
Though we don’t know why this happens in some species and not in others similar in either form or habitat, scientists have a few theories as to why it is a good idea:
1. A female's body can allow fetus development in autumn, creating an early spring birth, which gives the newborn offspring a long summer to learn survival skills before the harsh tests of the next winter.
2. The mother can be lighter and swifter during the foraging seasons of summer and early autumn because she is carrying an embryo rather than a fetus.
3. Mating can occur in the fall when the males are in prime condition without the females becoming pregnant until it’s an optimal time for them too.
4. DI can prolong the separation time between the males and females in order to reduce the competition for food in a localized area.
Some mammals have a seasonal DI, where the fertilized cells are stored every year around the same time for about the same length of time. For example, a certain species of weasel will store the blastocyst around three months until it's time to hibernate. Storing times vary by species, but some sea lions can store the blastocysts as long as 10 months! (And here I thought Twinkies had a long shelf life.) In some species of rodents and marsupials, implanting the blastocyst doesn’t depend on the season, but rather when the female stops nursing the young already born. The female’s body cues to the cessation of suckling young and then the fertilized cells implant. This is why many rats can have multiple litters of young within a year and why kangaroos can produce a new joey almost immediately after the other jumps the pouch.
Are you fascinated yet? Glad humans don’t do this? I am on both accounts!
Other cool facts about DI:
If you, my lovely readers, have nature-related questions you’d like me to answer, feel free to email them to jackee(dot)alston(at)gmail(dot)com. I’ll post them on Wednesdays (or Thursdays if I'm a slacker) as I get them.
Have a wild Wednesday... erm... Thursday!