Thursday, September 16, 2010

Wild Wednesday: Mammalian Reproduction (Delayed Implantation)

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:

I. Conservation: Species with delayed implantation may be more vulnerable to the effects of pollution through endocrine (hormone) disruption. For example, female polar bears are food deprived during pregnancy and their pollution loads increase because they use their fat stores, where pollutants are stored, for energy. Since the cubs are first grown in fetus during that time then nursed on fat-rich milk as well, the cubs are exposed to very high pollution loads from their mother.
II. Human Medical Research: If shutting off growth to a wannabe baby is possible, then it might be possible to shut off growth in other cells, such as cancer. Cancer cells are characterized by rapid growth as is fetus growth, so understanding the mechanisms that cease or retard cell division in DI could shed light on how to do the same with carcinomas. Something my mother and I would thank God for every day more we have together.

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!


  1. OMG, if humans did this there would be a ton of women who had NO clue who the father was....over and above the ton of women who already suffer from this problem. Imagine how awful to discover your pregnant from some yahoo you (ahem, figurative you, not specific you) broke up with six months ago? Good luck explaining that to your current boy toy....

  2. Oh no! Not the polar bears! Global warming, delayed embryo growth, seems like the world is really out to get them polar bears :(

  3. I had never heard of this. My husband must have since he's done cancer research. Finding a cancer-growth blocker is promising. I hope it happens soon, for people just like your mom.

    Wonderful post.

  4. How amazing!! Thank you so much for such an informative and very intriguing insight into DI! I am constantly in awe at mother nature - how she really gives each creature on this planet the best it can have to survive - only if all things are as they should be.

    Take care

  5. Wow. Talk about learning something new every day. I hope you and your mother have many many more days together.

  6. Fascinating! (Um. Vicki saw something quite disturbing...)
    I'm so sorry for those polar bear cubs.
    And hugs to you and your mom.

  7. Wow, I had never even heard of DI. Those poor polar bears.

    I love the picture of you and your mom. I'm glad she is here. =)

  8. That's absolutely fascinating. To fertilize the egg, but have it start growing only when the time is right for it- what will Mother Nature think of next.
    And you are right, the moment we figure it out, it can be applied to cancer cells.
    Wishing you and your Mum, many more years together.

  9. Wow! I'm always amazed that I can still learn something new!

    Thanks for stopping over at my blog.

  10. I remember learning about this in college, and I thought it was just as cool then as I do now. :o)

    How about those desert animals and plants with condensed life cycles that can wait years for optimal conditions (rain)?

    Nature is amazing.

  11. This is fascinating stuff! I love when scientific people can explain things in terms I understand. Thank you :)

  12. A fellow writer friend of mine works at one of the major companies on cancer research. (a team of 12, their goal is to cure cancer). we can only hope. Anyways, thanks for making me a bit smarter today! And I hope your mom is doing well!

  13. I'm impressed by all of the nature-ly things you know. If I ever have a question (probably a silly one, but oh well), I'll know who to come to. :)

  14. This is absolutely fascinating! I read it over twice. It's amazing what our improved knowledge of science has revealed to us. Scary, but amazing!

  15. OMG! Oh the things we learn with blogging. Thanks for the fun information!

  16. Very interesting, Jackee, and well-written too. I had heard that about kangaroos, but I didn't know other animals could do that also.

  17. My thoughts and prayers are with you and your Mom for many many more years together...

    Hugs from the midwest. :)

  18. I didn't know any of this, and you wrote it so perfectly, in language I understand.

    I hope more DI research is underway. And may you enjoy more time with your mom.

  19. I've always thought reproduction was fun (for purely intellectual reasons) but you've just made me realise it's even more fascinating that I'd thought.