Science Club: Jonathan Ballou

DCist: In situations when zoos are not managed, population size responds to popular demand?

JB: When I was first working in the early 80s, half of [the National Zoo's] Elephant House was filled with pygmy hippos, and pygmy hippos were extremely popular. Now there are only a handful in North America.

I'm not sure anyone's really done an analysis of why that's the case. Maybe there are animal fads. But it's not so much driven by the public as it is by curators and directors of zoos -- more by zoo management than by public interest.

That's one size of population management, to maintain animals for exhibit. The other side is: In order for a captive population to help preserve a species, that requires a healthy population. Zoos need someone who's looking at the big picture across many zoos.

DCist: Decreases to a natural animal population's size will have negative effects on that population's genetic pool.

JB: Generally true, yep.

DCist: At what point does that begin to happen?

JB: It's not a break-off point. It's a gradual line. What determines the effects is both population size and time. You can have a small population and it will accumulate inbreeding quickly and a larger one will accumulate inbreeding more slowly, but it will also get there in time.

So you have a population and you're breeding animals and they become more and more related. The more rapidly they become related, the more inbreeding problems you'll have.

DCist: Is there any kind of rate to this acceleration?

JB: Yes. There are formulas that tell us how rapidly that happens. Inbreeding is predicted by an equation, one over two times the population's effective size. The effective size is different than the real size: It has to do with how many different members of the population are doing the breeding and the male-to-female ratio.

If you have a situation where one male is breeding with lots of different females, that's not great. We know what the breeding strategies are to maximize the breeding population. When you see from one generation to the next, you want to provide all the animals of the parental generation with the opportunity to pass on their genes to the next generation.

DCist: That's the rule for maintaining animals in the wild, but it's not natural selection.

JB: We don't want natural selection in zoos. If we were to do that, we'd end up with animals adapted to zoos. We're trying to do the opposite. Imagine that animals go into a pipeline. They're in this pipe for an uncertain amount of time. We want to take the genes that go into the pipe and change them as little as possible from the moment they go into the pipe to the time they come out of the pipe.

That means maintaining as much of the genetic diversity in the population that goes into the population. We want to freeze that genetic diversity that goes into the pipe so that at the end of the pipe it's the best representation of animals in the wild that we can get.

That's the core of our genetic breeding program: We don't want them to adapt to zoos.

DCist: Is there any species that's more difficult to maintain in this way?

JB: There's been a bunch of people who have tried to figure out which species is more problematic than the others. It's very unpredictable. There are two issues. It doesn't matter what species you're talking about -- plants, animals, fungi, whatever -- you're trying to change this species as little as possible as it's going through this pipe we're talking about. Suppose this pipeline is 100 years long. One of the goals is to maintain the diversity for 100 years. Genetic diversity is the function of the generation length of the animals. So elephants have a much longer generation length than a mouse, say. With every generation, you lose a few genes. So elephants have a much greater advantage: That 100 years is only 2 or 3 generations for them, whereas with that mouse it's maybe 200 generations.

Elephants and animals who live longer have much more of an advantage in this sense than those who live shorter lives.

That other issue: During that time period, animals are going to become inbred. So a lot of conservationists have been interested in the question, "Can you predict which species will have a bigger problem with inbreeding?" The answer is no. Inbreeding is caused because all animals have mutations in their genetics and inbreeding exposes those mutations. It doesn't matter what species you are, you're going to have those inbreeding problems.

Those are the two main concerns in that pipe: maintaining genetic diversity and surviving genetic problems.

DCist: Are there any factors that mitigate the inbreeding concern?

JB: The only one we can think of is that species that inbreed in the wild -- okay, so, the inbreeding problems come from these harmful genes that live in all of us. Humans have six genes that, if they were exposed by inbreeding, our children would be dead. Other species have fewer than these. The answer is yes and in one case in particular: Plants that normally inbreed in the wild are less susceptible to inbreeding problems.

DCist: Why is it so difficult for pandas to mate?

JB: It's not. It's more got to do with humans figuring out what the right conditions are for them to date. We see that in the data. There are a couple of breeding centers in China, Wolong and Chengdu, and they're just breeding gangbusters.

Now, the females are only in heat one or two days of the year, so you have to have the male ready. At these larger panda breeding centers, where you have many males and many females, you're more likely to have them together at the right time. The fact that they exist in the wild tells me they know what they're doing.

But when zoos outside China have only one male and one female, it becomes difficult to synchronize the animals.

DCist: What is the significance of having mapped the panda genome on supporting the panda population size?

JB: Nothing yet, but in the long term? Every animal has genetic diseases. It will be useful to know which animals have what diseases and how we breed animals based on that. Imagine it's 100 years from now. You have 300 pandas living in zoos. We've identified a rare genetic disease that will cause 100-percent mortality in the baby cub. If we can identify animals that are carrying that gene, we won't exclude that animal from breeding --

DCist: So this isn't panda eugenics.

JB: -- but we will try to prevent two animals from coming together. We're doing this exactly with California condors. [They have a] a genetic disease, it causes 100-percent mortality in the chicks. [Dr. Ballou is the genetic adviser for the California condors.] So when we make breeding arrangements, we don't exclude them, we just avoid pairing them with another bird that has a high probability for carrying that gene.

DCist: Do you usually know or do you usually have a probability for this information?

JB: With condors, we know that some birds have those genes. We see their offspring have that trait. So we trace it back to the pedigree and model the probabilities to see who's got that gene.

DCist: You're doing your Punnett squares backwards.

JB: Yeah. Then we do it forward again. For every bird in the population we do the modeling and say, "Given what we know about where these genes occurred, this bird over here has a 5-percent chance of having this gene."

DCist: How do population management programs operate?

JB: Most of the captive breeding programs are probably regional. The American Zoo Association coordinates zoos within North America. That's a good population. The same thing exists within Europe, Japan, China, Australia, Africa. There are different regions organized under those areas to maximize population management.

There are a few species done at a global scale. Even the ones done at the regional level will periodically check in with other regions for gene flow -- for example, the European program for gorillas will check in with the U.S. program for gorillas and exchange animals to keep up gene flow.

[Dr. Ballou is the global coordinator for golden lion tamarins.] We're one of the few programs that does the global program. Daily we'll get email from some zoo, saying London Zoo, saying, "We have a pair of our golden lion tamarins. We had an old male, he's died, we need a new male to pair with our female." So we'll go to our database and find a genetic match, maybe in, who knows, Taipei or Mexico City. Then we'll coordinate with them to ship the female to the London Zoo.

DCist: You're running a golden lion tamarin dating service.

JB: Exactly. You sign on to the web service. All we need to know is your age and who your parents were.

DCist: Happy customers?

JB: I'm really lucky. If you put a male and a female together, the chances are about 90 percent that they'll breed. They don't care.

Panda with pipe photo by Kevin H..