New Tools for Genetic Rescue
A nagging concern occurs for endangered species that are the subject of recovery efforts, but that have experienced population bottlenecks (severe population declines). Is the amount of genetic diversity that passes through the bottleneck sufficient for sustainability, which requires resilience to disease and adaptability to changing environmental conditions?
Even as offspring are produced and the population grows, we worry if it can survive over the long term, even if the factors leading to endangerment can be addressed. We can keep our fingers crossed, for it may take generations of animals to know the real answer.
However, new approaches in advanced genetic and reproductive technologies may offer hope for intervention. For some species, sperm samples may be frozen so that males can contribute offspring generations after they have died. Also, the collection of frozen cell cultures in the Frozen Zoo® might also be called upon to provide a form of genetic rescue for endangered species suffering from the consequences of small population size. For some species this might make the difference between survival and extinction.
Stem cells, or more explicitly, pluripotent stem cells – meaning cells that can make any cell in the body – may contribute to genetic rescue, especially if they are derived from individuals whose potential genetic contributions would otherwise be lost. If animals die without reproducing, or if their descendants are few or do not survive, their cells may contain a slice of the gene pool pie that would be of value to population sustainability.
These possibilities offer hope to increase the probability of survival of species with a critically small population size – providing appropriate samples were saved – if the scientific and technical hurdles can be overcome.
We are working to address these challenges so that the prospects for using advanced genetic and reproductive technologies can be realistically assessed, not just be the subject of speculation.
With our collaborators at The Scripps Research Institute, we are continuing to explore the production of pluripotent stem cells from endangered species that have experienced population declines and for which cells of genetically valuable animals have been saved. This exciting collaboration has been extended beyond our original landmark study published in 2011.
Skin cells from additional species banked in the Frozen Zoo® have been induced to become stem cells.
One is the Somali wild ass, which faces an extremely high risk of extinction in the wild, though a small captive population exists. With the prospect slim that additional animals might come from the wild to bolster the captive population, banked cells from genetically valuable individuals may offer a means to conserve genetic diversity in the captive population.
Cells from other endangered species, such as the Javan banteng and Arabian oryx are targeted for efforts to establish pluripotent stem cells. Pluripotent stem cells from these species would allow the next steps – to produce eggs, sperm and embryos from stem cells – to be explored, as has been successfully accomplished in the mouse. While we are aware of the challenges that face these research efforts, we are confident that retaining genetic diversity in small populations can contribute to their sustainability; it is this hope that drives us on.
Oliver Ryder, Ph.D., Director of Genetics and Kleberg Chair