About the Blog Author: Dr. Oliver Ryder (@frozenzoo) is the Kleberg Endowed Director of Conservation Genetics at Beckman Center for Conservation Research, part of the San Diego Zoo Wildlife Alliance. He has been a leader in the recovery of the condors through captive breeding since the 1980s, and created the genetic database for all California condors.
The excitement of the moment of realization that a dataset with confounding results actually provided proof, clear proof, of parthenogenesis in California condors is vividly in my memory. It still brings goosebumps.
My longtime colleague Leona Chemnick had suggested that we complete parentage analysis on the entire set of condor genetic samples we have, dating back to the earliest days of the California condor Recovery Program, using the twenty-two microsatellite loci developed by other researchers and collaborators. (Later we reduced the number to twenty-one loci, omitting a diagnostically difficult locus.) There were good reasons to confirm parentage in the small but growing reintroduced population, and we were able to confirm extra-pair matings. The reasons for confirming parentage in the captive population were less obvious, but it was valuable for confirming identity of individuals, and in fact facilitated the discovery of switched identity for two of the condors.
There is an elegance in having samples from the entire population of a species and its ancestors back to the founding of their management under human care, and from these be able to produce a complete and accurate pedigree. More than being just an elegant dataset though, it gives a record of the transmission of the genetic heritage of a species, its diversity and genealogy, providing a powerful tool for population management for sustainability.
Certainly, the complete dataset was a remarkable accomplishment, but Leona came to me one afternoon as I was leaving the office to tell me about puzzling findings for two condor chicks, studbook numbers 260 (SB260) and SB517. I asked her to walk with me to my car because I was in a hurry. Along the way, she told me that the males housed with the females that laid the eggs did not qualify to be sires of the chicks. They had been excluded at multiple loci. The results had been confirmed and other males were evaluated as potential sires, but none qualified. In fact, no male qualified to be the father of the chicks. And, curiously, the chicks were all homozygous for all microsatellite loci, inherited from their separate dams.
Leona had my attention at this point. I asked if both chicks were males and when she replied that they were, I said she had discovered parthenogenesis in California condors. And it came with goosebumps.
This finding, published recently in Journal of Heredity (Ryder et al. 2021) certainly raises questions for the impact and potential importance of parthenogenesis in California condors but, more broadly, for all avian species. Previously, parthenogenesis in birds was recognized because females who had no access to males laid eggs that initiated or even completed development, and in the case of domestic turkeys, could be fertile. Our recognition of parthenogenesis in condors came only because we had the complete dataset of DNA variation profiles for over 900 condors. And, it occurred in females who were continuously paired and had reproduced with males, so was facultative. How often might this be occurring in other species and is yet undetected? That will be interesting to learn more about.
For more on this story, see San Diego Zoo Wildlife Alliance Conservation Scientists Report First Confirmed Hatchings of Two California Condor Chicks from Unfertilized Eggs