Monday, 9 March 2009

Muskox in Alaska

I want to write a little bit about muskoxen in Alaska. Most of this comes from my infinitely fallible memory, and a paper called `Status of Muskoxen in Alaska` by T.E. Smith in 1984. We're getting ready to do some work on Muskox in the Seward Peninsula, so this is a great way to collect my thoughts on the subject.

Muskox are a large terrestrial grazing ungulate that are a) smaller than most people imagine and b) larger than most muskox handlers would like. It's interesting to note that muskox are actually closest related to a group of species called `Serows;` evolutionarily, muskox are a sort of goat-antelope. Don't see it? It's weird, but apparently true!

They're sort of like the blue-bloods of ungulates, having about as much diversity as a 1920s golf course (and the intelligence of one to boot) - for example, at the MHC DRB locus, a region of DNA responsible for disease resistance, the species has one allele. Even moose have 11, and Cattle? 68, which is more the norm in the rest of vertabrates. There's a dumb science joke that if you've tested one muskox, you've tested every muskox.

Muskox are endemic to alaska, but have had a checkered history, in the 1800s, due to a myriad of reasons, hunting being one of them. They are thought to have been totally expatriated (locally extinct) from Alaska by the late 1800s. In 1930s, spurred by concerns of global muskox numbers, the US feds funded the capture of 34 east greenland muskox, and they were transported to Fairbanks for a 5 year quarintine. In 1935, they relocated four animals (two m two f) to Nunivak Island, choosing the island on the basis that it was an enclosed space with apparently rich forage and no native predators. In 1936, they transplanted the remaining surviving animals, and some offspring that had been subsequently born, totaling 16 males 11 females.

After 32 years, mannagers selected Nelson Island as the next reintroduct for Alaska. Though Nelson Island isn't far from Nunivak, they're seperated by a patch of ocean, and Nelson Island varies considerably in its topography and browse - how, exactly, I'm not sure, but I'm told the veg is different, and I trust the folks who told me. The first introduction was 8 in 1967 (5m 3f), followed by six males and 9 females in 1968. Nelson Island is really just an island in name, and there isn't as much barrier to dispersal (beyond habitat) for the Mox.

Future introductions were ANWR (1969-1970; 65 animals), Cape Thompson (1970 and 1977; 70 animals) and Seward Peninsula (1970 and 1981; 72 animals). There's been a number of other events, where they took animals into captivity for either the LARS herd, the Unalakleet herd, or zoo animals, but those really don't factor into my world (well, except the LARS animals). Currently, I don't know if there's been any moving animals around since 84.

You can see my lovely pen-addations to the Mox-map off to the left. I-are-an-arteest, yes, but that should give you the idea what happened. Nunivak came from a small founder population, and all other populations in the state are serial dilutions of the Nunivak Island population. This is of special note, because of the effects it would have on the over-all diversity of the animals. As I mentioned before, diversity was extremely low to begin with, but every time you go throug a `bottleneck` (a period where a few animals are responsible for all the resulting offspring) you experiance a large loss in diversity. This, by the by, is why humans are roughly 28th cousins with every other human. We love talking about how different we are, but thanks to a pre-history bottleneck, we've got scant diversity to talk about. If dolphins were studying us, I bet they'd treat us like a bunch of inbred yokels. :)

If you'll forgive a bit of math, in a randomly breeding population with non-overlapping generations (two huge assumptions!), the probability of losing any given allele (or form of a gene) is
(1-p)^2N
Where p=the frequency of the allele before the bottleneck and N is the size of the bottleneck. Let's pretend we had an allele that made up 10% of all the copies of the gene. That gives us
(1-.1)^(2*31)=0.001455
in the case of the Nunivak introduction, or .145% chance of it being lost. That assumes all 31 animals who were introduced into Nunivak had reproductive success. For the cows, that seems fairly probable, but given males engage in Harem defence, it seems improbable that all 18 males had success. Assuming only a third of the males had any success in their lifetime, we get,
(1-.1)^(2*19)=0.01824
Or about 2%. This may not seem like much, but taken across the whole genome, these effects are steadily accumulative.

However! While some is lost, as they say,`all is not lost.` If you run the numbers, a founder size of 10 is still enough to preserve 95% of the heterozygosity (the number of individuals with two different copies of the same gene). Using Van Coeverden De Groot and Boag's 2004 estimate of heterozygosity for perfect alleles, 95% of 0.504, while low, is dangerously low. However, if you use the previous H estimate of 0.018, 95% of that is a very small number.

Where does that leave us? Alaskan muskox are a currently mixed story. While some populations have shown success, others appear to be floundering markedly. As the state would like to see the muskox fully restored to its entire endemic range (as would many sport and subsistence hunters), we need to sort out what's going on demographically, and tease apart the factors involved in the success of some populations, and the detriment of others. We need to know how much nutrition is a factor in the troubles some are facing, and how much the high degree of relatedness has impacted this nascent population.

Mox picture brazenly stolen from LARS.

No comments: