Pacific Science Center Life Sciences: evolution

Pacific Science Center’s Dinosaur exhibit is many things. It’s iconic. It’s beloved. To many kids, it’s real. It’s also a bit static, and very much considered a place for kids to go and play make-believe. For a space that introduces animals that once occupied the earth, lived, changed, and eventually became extinct, the exhibit cries out for an infusion of liveliness. With those criteria in mind, the Animal Care team decided to try a small experiment with live animals in the Dino exhibit space.

At PSC we exhibit snakes, a turtle and an iguana. Because scientists once assumed that dinosaurs resembled modern reptiles, it was a reasonable idea to feature one of our animals in the Dino exhibit.

However, recent fossil discoveries in hearts, bones, skeletons, and even feathers from dinosaurs have blurred the line between these extinct creatures and modern birds. This doesn’t mean dinosaurs were not reptiles. The research suggests that birds are part of that group as well.

Currently, PSC does not exhibit any birds and so Animal Care decided to start with a bird that is rugged, that everyone knows, and could be observed hatching. We chose a bird that lots of Seattleites keep in their yards, and know how to care for.

We present the humble but amazing chicken!

In early February, we started incubating two-dozen eggs in an eye-pleasing variety of colors and sizes, projecting footage of the eggs onto a big screen so guests could observe them hatch. A lot of kids expressed the hope that velociraptors would hatch out of them! Instead, on Feb. 22, baby chicks hatched out.

In case our eggs didn’t do well, we planned accordingly. But we had a great success and more eggs hatched than we have room for in our display. Seattle Farm Coop has offered to accept the extra chicks. They also helped us with early care for our new hatchlings and got them off to a healthy start.

If you are planning a visit to Pacific Science Center before March 15, we encourage you to come by the Dinosaur area and say “Hi” to our chicks or watch their antics on our web cam. After that, the brood heads to their permanent home with a devoted Seattle chicken keeper.

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Over the course of the night on Tuesday, February 9th, Elphaba- one of our two “queen” naked mole-rats, gave birth to a surprisingly large litter of pups. When we came in on Wednesday morning, we found 22 brand new babies in the colony.

The size of the litter surprised those of us on the Animal Care team because it was more than twice the size of her largest previous litter. She also just didn’t look like she had that many pups inside her when she was pregnant. In fact, she looked relatively trim. Whereas Galinda (the other “queen”) often looks like she’s swallowed a couple of golf balls by the end of her pregnancies, Elphaba has generally remained smaller, and this pregnancy was no exception. It may go without saying that all of the babies born in this litter were very undersized.

The pups were born into a completely sterile environment, as we had just completed day 14 of our “superclean” the previous day. The older colony members seemed to do very well with the babies, taking care of them when necessary and not being too rough with them as they ran around the enclosure. Still, none of this was enough for these pups. By the end of day on Saturday, they had all passed away. None of them made it to that crucial day 5.

So why didn’t they make it? It seems there’s always something, with our naked mole-rats. This time we believe it was the sheer size of the litter. There were simply too many pups, and they were all too small for any of them to have a fighting chance.

As I explain the problems with this litter to visitors and staff, I can’t help but be reminded of one of the basic theories of animal ecology and reproductive strategy. Famously, ecologists Robert MacArthur and E.O. Wilson developed the theory of r/K selection based on their studies of island ecosystems. According to this theory, the processes of evolution push all animal species towards two main reproductive strategies, K-selection or r-selection. K-selected species have relatively few offspring, into which they invest a lot of time and energy, so that most of those offspring are likely to survive. Conversely, r-selected species have many offspring (think millions), into which they invest little time or energy, so that few of their offspring are likely to survive. There is a trade-off, essentially: Quality versus quantity. Do you want to spend more energy making babies or raising babies?

How naked mole-rats fit into this theory is a little confusing, but that’s to be expected from this eccentric species. As mammals, they and their ancestors have been pushed towards K-selection for millennia. That’s why mammals give live birth and nurse our young. For mammals, it is evolutionarily risky to have too many offspring, simply because most mammalian biological systems are not designed for many babies. At some point mammals can no longer provide the care that the offspring need to survive.

Naked mole-rats have the largest litter size of any mammal — up to 28 pups in a litter. But when litters are this large, usually few or none survive. And unlike real r-selected species, naked mole-rats don’t reproduce quickly enough to make up for this low survival rate. Their gestation period is still at about three months. In these instances they are behaving like neither r-selected nor K-selected species. They are in an evolutionary no-man’s land, which is not positive for the growth of our own mini-mole-rat population. So why have such large litters? What is the evolutionary benefit here?

For most animals, reproducing is about more than just spreading your genes around, at least in the short term. When an animal is able to produce successful and healthy offspring, they are also making a statement to their peers. They are proving their fitness, attracting better mates, and in some species, actually improving their social standing. In a naked mole-rat colony, especially one where two queens are competing for dominance of the colony, a female that gives birth to 22 babies may prove herself to be more “queen-like” than one who only produces 10.

And so the saga continues. Although it’s sad and frustrating that another litter was lost, this may just be a blip in a truly epic battle. Elphaba has proven that she can have just as many babies as Galinda (two more, even!). The gauntlet has been thrown. What will happen next? What can happen next? We will know more in just a few more weeks. Galinda is pregnant, and predicted to give birth in the mid-March. We will, of course, keep you posted.