Friday Weird Science: Of Mice and...Seals?

Nov 21 2008 Published by under Friday Weird Science

This SHOULD be the time when I'm working crazy hard on InAdWriMo, trying to get those paper drafts up and running (ideally they should be ready on MONDAY). Perhaps I should have been doing that rather than writing a 3,000 word post on posters (Really! Count!). So it goes. But here I am, and instead of writing what I need to write, we are BACK with Friday Weird Science!
Sent to me by a friend (who just got his PhD!!! w00t! Can we get a shout-out for Dr. John!), this is one that grabbed me with the title, and it's not so much weird science as...well, weird. de Bruyn, et al. "Mass Mortality of Adult Male Subantarctic Fur Seals: Are Alien Mice the Culprits?" PLoS ONE, 2008.

Ok, so this weird science is sad, because it involves dead seals. And they are awfully cute seals.
Die-offs of large marine mammals are actually relatively common, and it's not just because people are clubbing them. Marine mammals are apparently pretty sensitive to infectious agents, particularly bacteria and viruses, and are also susceptible to poisoning. However, most of the time these mortalities don't pay much attention to age or sex. This time, however, was different.
In January of 2007, researchers started finding dead seals around Marion Island, a big fur seal breeding ground. The difference? These were just male seals. Adult males. No female, no pups. And it was just after the pupping season, when males had been up on the beach for weeks, grabbing and defending territory. The die-off ended up being as high as 300 seals in 14 days!
Immediately, researchers began coming up with theories. Pollution and toxins in the ocean and their food can be stored in seal fat, and the release of the toxins from the fat could cause deaths, but not 300 in two weeks. Also, if it had been a toxin, male and female seals would have been dying at equal rates. High temperatures on the island could case deaths, but temperatures had been no higher than normal. The rookery (where seals breed) had remained roughly the same size, no population pressure. So population is the same, the food is the same, the ocean is the same, what is different?
It turns out that the seals had a mouse problem. ALIEN MICE!

Ok, the mice weren't really aliens (heh, little green mice with antenna, that would be SO cute). But they were alien invaders to the ecosystem. The common house mouse (Mus musculus domesticus) was introduced to the Marion Island ecosystem by seal hunters in the 1800's. It probably was aboard their ships, as mice like following people around, they usually carry food and make mouse lives very easy indeed. But once the mice had been introduced to a new ecosystem, they began to spread out. And it turns out that seal beaches are GREAT places for mice to reside. I guess maybe it's the rocks and the copious amounts of seal poop? And all those warm seal bodies would keep you pretty warm at night.
It turns out that wild mice aren't the healthiest of things. They are constantly contracting various bacterial infections (I suppose it's the amazing reproduction rate that keeps the little guys going). They also aren't very clean, I mean, the nasty things eat their own poop ALL the time. Not good for keeping a healthy mind and healthy body. So the researchers here decided to look at the MICE to see why the SEALS were dying. The theory is that if you've got enough mice around, you've got a lot of mouse poop. Mouse poop (and mouse pee) can get a lot of bacteria in it, and is small enough to be accidentally ingested.
And sure enough, when they looked, they found that the mice on Marion Island had an awfully high infection rate (30%!) with Streptococcus, a subtype of bacteria which not only causes strep throat, but can also cause pneumonia, meningitis, and flesh eating bacterial infections. Charming. Unfortunately they don't have samples from the deals that died (apparently no one takes autopsies of seals, and given that the males get up to 460 lbs, I wouldn't want to do an autopsy on one, either.
So why only the MALES? Why weren't the females and pups dying at the same rate? Well, remember, in the life cycle of the seal, the males come up onto the beach for up to three weeks before the female, grabbing and defending territory for their harems. The females are relatively free to go, and spend much more time in the water during this period. So it was only the males that were continuously exposed to the mouse infections, and only the males that died.
Of course this is still a hypothesis, and there is no definitive link. The next step would be to test the blood of the surviving seals and see they have signs of former infection from the mice. But next time you have a mouse in your house, men, screw your harems and get back in the water! It's not worth it.
P. J. Nico de Bruyn, Armanda D. S. Bastos, Candice Eadie, Cheryl A. Tosh, Marthán N. Bester (2008). Mass Mortality of Adult Male Subantarctic Fur Seals: Are Alien Mice the Culprits? PLoS ONE, 3 (11) DOI: 10.1371/journal.pone.0003757

5 responses so far

  • chezjake says:

    screw your harems
    This may not have been the best choice of phrasing under the circumstances. 😉

  • Dr. John says:

    I stand by my original assessment. These are sub-Antarctic seals here, people. Isn't it obvious that the NINJA PENGUINS are to blame?

  • Tasha says:

    Dr. John, you've got a point. A friend of mine has a theory that all black and white animals are inherently dangerous killers. Panda bears, zebras, killer whales. What more proof do you need?

  • Luna_the_cat says:

    Mice. Should have known. Furry little bastards.
    Seriously, I started out thinking that mice were cute, and having serious qualms about doing anything that hurt them. After having observed mouse behavior, and life in the wild, I came to a rather different conclusion: our ancestors were right. Mice are icky.*
    *"Icky" is a technical term, yes.

  • Ed Yong says:

    "A friend of mine has a theory that all black and white animals are inherently dangerous killers. Panda bears, zebras, killer whales."
    Nonsense. Black and white animals are paradigms of racial harmony: 😉