Monday, 1 March 2010

Repost: Beavers and monogamy.

Things are busybusybusy. I'm going to phone it in today. How about a blast from the past: Beaver monogamy!



About two years ago, I decided I would destroy monogamy. That's right, I'm one of those people who are out to wreck family values that the `Focus on the Family` bunch warn us all about. Except I deal mostly with animals, so I suppose I'm who `Focus on the Family Castor Chapter` warned us all about.

See, I, in 2005-06, I first began wondering about beavers - no, not that sort. Perverts. Though, I suppose I could write off a lot of things as business expenditures if I was researching them. (I'm done with the bawdy jokes now, honestly). See, the issue with beavers is that they're stereotyped as good old, monogamous, happy family critter. And it's been my experience that when we think that's so, it simply ain't so bob.

For example, for the longest, we assumed a number of species were monogamous. Take Swift Foxes. Swift Foxes are socially monogamous, and mate for life. However, a study showed 52% of offspring were not sired by the apparent mate of the mother (Kitchen et. al 2006). Among Tree Swallows, 50% of broods studied were extra pair young (Lifjeld et. al 1992). Far from being unique, many other species of birds are apparently monogamous, but only insofar as we tend to not catch them cheating on each-other.

Mr. Beaver Began to suspect his wife was less than faithful when
he read papers in the journal
Animal Behaviour describing
the rarity of monogamy in actual breeding systems.
Also, that she was cooking someone else's log for dinner was a bit of a hint.

In 2007, a book came out called Rodent Societies – An Ecological and Evolutionary Perspective, by Jerry O. Wolff(ed) and Paul W. Sherman(ed). It has a chapter written by Peter Busher on Social Organization in the Beaver. In it, he discusses facets of the beaver's social ecology, synthesizing a large amount of work for what would a grand paper. Would be, except for a single line, where he makes a parenthetical statement:
"[...] (although in most cases, this [genetic monogamy] has yet to be confirmed by DNA analysis) [...]" (p.281).
Put another way, it says that the remainder of his chapter is based off of a massive, un-validated assumption.

I was flabbergasted that people had poured so much work into a subject, when it was built on such a shaky premise. Sure enough, when I dug through the literature, I found no one had actually done the genetics (and published them) to show that beavers don't cheat on each other behind their flat little tails (I'm not fond of beaver tail, but I recently found it shouldn't be acridic tasting). This astounded me, and I resolve to study it right away.

Hah. Yeah Right.

Well, I never got resources together to look into the issue, but a group from EIU were wrapping up asking the same questions right around the time I decided `honestly! Really! Any day now!` Crawford et. al (2008) decided to sample colonies from south central and south east Illinois between from 2005-2007 using Conibear traps. The sexed them, weighed them, and then aged them. The took just a tiny bit of skin from each one. For a segment of the beavers, they sampled using live-trapping snares. In the end, they got samples from about 127 beavers, which is far more than I'd have been able to wing (I was looking at ~1/2 that, which would make for a less convincing paper.)

After this, they went home and extracted DNA from the skin samples, and then did parent-typing. This is done by looking at small junk regions we call `microsatellites` that are littered liberally throughout the genome. These microsats are of variable size, and so you can use a technique called PCR to make lots of copies of them, and then analyse them in a jell-o like substance and see which copies of the microsats the individual has. As you get one from mom and one from dad, you can then compare what mom and punative-dad had to see if they match. By doing lots of these microsats (Crawford et al did 7 different ones), you can assign a probability that a random individual could be the pup's mother or father. And if the pup has a form of the microsat that the punative father doesn't have at all, it's indicative of that male not being the actual father.

Actual parent typing is a tad more complex than that, but that's actually a good portion of the broad strokes. It's really, actually, quite simple in totality.

And then comes the figure the everyone's looking for. 56% of litters had more than one father. Zadgooks! This is not what they showed us in the Chronicles of Narnia at all! If that movie was to be biologically accurate, Mrs. Beaver would be spending a whole lot of time down at the gym, or showing the plumber where exactly that pipe's broken in the basement for the 3rd time that week.

And that's how it goes for Monogamy, by-and-large. There really aren't that many species that are strictly so, no matter what romantic notions we saddle them with. And why should they? Humans are scarcely monogamous - Jerry Springer's continued existence is testament to this fact, if nothing else! In most situations, it's in a critter's biological interest to mate with as many other males/females as they can get away with. It's sometimes not in their social interest, however, as Mr. Beaver might try to scratch Joe Beaver's eyes out for playing around with his wife. Humans, in the same vein, have firearms.

Joe Beaver suffers a mysterious log-related accident

after visiting Mrs. Beaver one fine afternoon. Mr. Beaver denied
wrongdoing, but in great detail, and before he'd been accused.

Crawford, J.C., Liu, Z., Nelson, T.A., Nielsen., C.K. and Bloomquist, C.K. (2008). Microsatellite analysis of mating and kinship in beavers (Castor canadensis). Journal of Mammalogy, 89(3), pp. 575-581.
Kitchen, A.M., Gese, E.M., Waits, L.P., Karki, S.M., and Schauster, E.R. (2006). Multiple breeding strategies in the swift fox, Vulpes velox. Animal Behaviour, 71(5), pp. 1029-1038.
Lifjeld, J.T., Dunn, P.O., Robertson, R.J., and Boag, P.T. (1992). Extra-pair paternity in monogamous tree swallows. Animal Behaviour, 45(2), pp. 213-229.

1 comment:

Arvay said...

Have fun storming the castle!