Genetic Code Holds Secret to Condors’ Survival : Scientists Struggling Against Odds to Rebuild the Population of Rare Birds

Mike Gilpin likes to say he carries the future of the California condor in his breast pocket.

Without question, the information on a 3 1/2-inch computer disc that he pulls from his coat will be a crucial element in determining whether the highly-endangered bird can be bred successfully at the San Diego and Los Angeles zoos, and reintroduced into its native habitat in central California.

Gilpin, a UC San Diego professor of population ecology, and his associate Mike Soule have just completed a computer software program designed to minimize the probability of the condor’s extinction by creating an ideal pedigree that maximizes the species’ existing gene pool.

The software--the first ever used as part of an endangered species project--will allow condor experts to see on paper the results of potential breeding combinations two or more decades into the future. The program was written specifically for the condor, but is designed for use in captive breeding any endangered animal.

Without the computer’s ability to rapidly perform the necessary complex calculations to follow generations of breeding, zoo officials would be unable to keep close track of the many offspring year after year in order to minimize deleterious in-breeding that occurs when close relatives mate with each other. With less scientific information available on the best potential pairings, the in-breeding risk to the condor population would be greater.

Behind the program’s theory is the idea that preservation of an endangered species cannot be assured simply by increasing its numbers. Rather, Gilpin and Soule say that conservationists must also plan for genetic and other uncertainties over several decades of captive breeding.

The condor program will provide one of the earliest tests, and zoo officials are anxious for all the help they can get.

“Very frankly, the whole program is a major gamble since we are working with such a small (original breeding) population,” said Bill Toone, curator of birds at the San Diego Zoo’s Wild Animal Park and the person heading up captive breeding efforts.

At the park, early breeding techniques are already under way with some of its 12 condors. There are 13 at Los Angeles for future pairings, and two in the wild still to be captured by the spring of 1987 and brought into the breeding program. The large majority of the captive population is still three to six years away from sexual maturity.

“With 27 birds total, we are down to the wire, and the wire may perhaps have even been cut already,” Toone said.

“Further, while scientists like Gilpin and Soule can give us the best abstract possibilities on whom should mate with whom, no one has ‘talked’ about this with the birds, and their concept of whom they ought to pair with could be a lot different from our concept.

“Success lies in combining the data provided by technology with the realities of the condor’s habits and behaviors.”

The genetic component looms large in the condor captive breeding program. There are only 14 birds considered “founders,” meaning that all condor offspring are or will be descendants from a small pool of genes.

Simply put, an offspring receives from its parents two copies of each genetic locus, thousands of which compose an animal’s total genetic makeup: one from the mother, one from the father. If both a mother and father have a common ancestor at some point in the past--for example, the same mother or grandmother--then they are capable of passing along identical copies of the same genetic locus to an offspring. That is called in-breeding.

And if those particular genes that are passed along happen to be harmful--such as preventing reproduction or causing serious fitness defects--the in-breeding can lead to death of the offspring and long-range extinction of the species.

“In-breeding is a problem in all small populations, which the condor group obviously is, because it is at some point inevitable,” said Oliver A. Ryder, geneticist with the research department at the San Diego Zoo.

The more that a breeding pair shares the same genetic makeup because of common ancestors, the greater the chance that its offspring will have exact copies at several genetic loci. Captive breeding programs must be designed to minimize in-breeding to prevent it from affecting the rate of growth of the population, Ryder said.

But until recently, scientists could not easily apply precise genetic science to captive breeding of small populations because of the difficulty in computing the myriad calculations in designing a pedigree.

“It’s an area that there is no book you can go to,” Ryder said. “Information is just beginning to be disseminated among zoos worldwide following (several) international conferences.”

As an example, Toone pointed to efforts to save the American peregrine falcon over the last couple of decades. While the bird has been reintroduced into the wild in many states, it suffers from reproduction problems that he said possibly stem from in-breeding during captivity.

So, as much as possible, condor planners will try to avoid similar problems.

The quickest way initially to preserve the condor gene pool is to breed as many babies as fast as possible because the number of breeding pairs are as yet so few, Toone said.

“The total numbers are so low now that any baby is desirable and important at this point,” Ryder said, “in order to preserve as wide a sample as possible of the genetic material of a set of parents.” Officials assume that the 14 founders are not related, even though there is no way of knowing for sure because pedigree records do not exist for the birds captured in the wild.

Already, Toone and others have paired up the mature condors in captivity for possible mating, with one pair in San Diego and a second in Los Angeles. While a fertilized egg is possible with the San Diego pair this spring, he said, the first condor ever conceived in captivity is more likely to occur in 1988, when the birds are more accustomed to their caged environment. Gestation takes up to six months.

Normally, a condor pair--which mates for life--produces one chick every other year. Given the 50% chance of survival in the wild, that means an average of one chick every four years.

But in captivity, officials can realize an increase up to 12 times the rate in nature through multiple clutching. When a pair lays its first egg, keepers will remove it and incubate it artificially, expecting that the pair will then lay a second and perhaps even a third egg in a single season.

If all the eggs survive, the process can lead to three chicks a year, every year, for each mating pair. Biologists successfully tried the procedure several years ago with condors in the wild. The zoos’ ability to manipulate pedigrees as well as assure better nutrition and lower mortality are the major ways to produce much greater numbers of offspring than possible in the wild, Toone said.

Once several pairs of condors have successfully borne offspring, then officials will manipulate pairings of subsequent generations according to the computer program to arrange matings among condors most distant genetically. If some in-breeding eventually occurs, officials hope it will not be fatal to the species because enough genetic diversity will then have been established.

In genetics, scientists assume that a mother and father each pass on 50% of their genes to the first chick. For the second chick, they assume that 25% of its genes are different from its sibling, meaning that 75% of the parents’ total genes are represented in the two chicks. In each succeeding offspring, the additional percentage of parental genes represented is cut by half: so total parental representation is 87.5% in the third, 93% in the fourth, and so on, never actually reaching 100%.

After the fifth offspring, more than 96% of the parental genes will be represented in their offspring. Soule said that the eventual goal of the program is to keep at least 90% of the genes of each breeding pair passed along to subsequent generations for a period of 200 years.

Officials also want to equalize the number of offspring among breeding pairs as much as possible in order to prevent one pair from being overrepresented genetically.

But validation of the program will take decades, said Gilpin, “10 years or more to see what kind of genetic problems could come out of all of this. But we hope to minimize potential difficulties through the (computer) program.”

Those connected with the breeding admit that the ideal computer pairings will not always work at the “condorminiums” at Los Angeles and San Diego.

“The real unknown is what happens when two birds we think should be mated may not want to do it together,” Toone said. “It will be up to us to determine whether we should perhaps wait two or three years--and risk missing two or three years of productivity--to see whether a particular pair will get along because we think their genetic mating is (important) to have in offspring.”

Added Ryder: “It’s very hard to get animals to behave as ideal creatures.” For that reason, the computer’s ability to recalculate annually the best pairings, based on condor behavior, is a godsend, Toone said.

A sticky question for breeders is in deciding which birds to release back into the wild. The official condor recovery team set up by the U.S. Fish and Wildlife Service has recommended that only the offspring of the birds presently in captivity be eligible for release. Further, the team recommended releases only of offspring whose parents have 96% of their genes already represented in the captive population; i.e., the release of one of the chicks would take place only after the fifth chick of a breeding pair is born.

And before any releases are authorized, there must be at least three pairs breeding in captivity, the team has recommended.

“So if we have a particular pair that is breeding a lot of chicks, their offspring could probably be the ones released first,” Toone said.

Ryder said, “If you have a choice of which animals to release, and put in situations they have never encountered before, you might as well choose those you can identify as somewhat less important for the long-range survival, in that their genetic makeup is more likely to already be represented with other (brothers or sisters in captivity.)”