California Condor Genetic Studies: Sex Determination, Identification of Clan Structure and Coping with a Genetic Disease

The critically endangered California condor Gymnogyps californianus has been the focus of intensive conservation efforts for several decades. The population decline reached a crisis state in the mid-1970s; eventually in 1987, the entire surviving population was held in captivity. Intensive intervention in support of California condors began in the mid-1970s with the development of a recovery plan directed by the California Condor Recovery Team that included monitoring by radio collaring and captive breeding. By late 1985 there was broad recognition that the situation was grave and the decision was made to take all the remaining California condors into captivity. The last California condor living in the wild was captured in 1987. This individual was released back into the wild in 2001 after having fathered 16 chicks and with 40 descendants. Now, there are more than 270 California condors, with over 120 living in the wild.

Genetic studies at the San Diego Zoo's CRES have played an integral part in the efforts to recover the California condor. These efforts began in 1981 with the development of cytogenetic sexing of all birds. A definitive method, independent of age of the bird or season of sampling, was needed for identification of the sex of individuals. Subsequently, DNA probe hybridization and then polymerase chain reaction (PCR) amplification for identification of sex-specific DNA fragments have been utilized for sex determination using blood samples taken opportunistically and eggshell membrane material collected non-invasively (Chemnick, et al., 2000).

The entire surviving population was founded by 14 individuals. Data obtained from DNA fingerprinting and mitochondrial DNA restriction fragment length polymorphism (RFLP) analysis have provided insights into the relatedness of the founder birds and the amount of genetic diversity in the extant California condor population. Three genetically distinct groups (referred to as clans) were identified within the founder population using a statistical model to analyze data from multilocus DNA fingerprints (Geyer, et al., 1993).

The California condor is among the first endangered species under captive management for which a genetic disease has been demonstrated. Adoption of any of the alternative scenarios for management (including no management) of the trait could have fundamental consequences for population demography and recovery (Ralls, et al., 2000). An advantage of delaying selection against the putative allele is that this strategy would allow for the development of a diagnostic method to distinguish carriers from non-carriers, an activity that is being conducted at CRES with support from the Seaver Institute. A carrier test would provide the most informed method for management of the potential impacts of chondrodystrophy on both the captive and wild subcomponents of the condor population.

Knowledge of the genetic makeup of individuals in small populations will provide a crucial tool for management of small populations for survival. Thus, efforts undertaken now to better understand the genetic makeup of California condors will serve as a model for other species.

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California Condor Recovery Program
Milestones in California Condor Conservation
California Condor Mortality Challenges
Social Development and Reintroduction of California Condors
Studies of Courtship and Parental Care in Reintroduced California Condors in the U.S. and Mexico
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