Human Scrambled Wildlife Populations

Last week I was at a conference on the genomics of admixed populations. What is admixture? Admixture is a within species process that occurs when two (or more) populations that previously diverged come back into contact and mate. Thus the offspring have genetic signatures from the original populations.

A particularly engaging session at the meeting was on the ethics of admixture. During the panel, the human geneticists discussed issues of consent, providing raw or analyzed data to study participants, and how knowing ones admixture proportion may impact cultural identities of individuals and/or communities within admixed human populations. Wow; those human geneticists may have better data than me, but I’m glad those issues don’t weigh on my mind! So what ethical issues do wildlife conservationists think about related to admixture? Two main issues: creating admixed populations through active management, and protecting admixed or hybrid populations.

Anthropogenic Admixture
Let’s consider the following scenario: a population declines to a small size and becomes isolated from other populations making it hard for new individuals to join the population (ie- there’s no gene flow). If wildlife managers want to increase population size, one way is to introduce new adult individuals into the population and hope that they first, settle in nicely, but then, reproduce. Over several generations, the population should grow, especially if the managers can remove the threats that shrunk the population size in the first place.

There are several examples of this reintroduction strategy, particularly when animals from a different and distant part of the range are the ones captured and transported to the population of interest. When animals live in distant parts of the range, they will have different population genetic signatures which can be due to the neutral process of genetic drift or from local adaptation. Thus the offspring following translocation will have a signature of admixture. Population geneticists measure this using neutral loci not expected to affect fitness; however, many worry that when humans create admixed populations than the target population will suffer because any genes under selection (due to local adaptation) will get washed out when individuals from another population are introduced. This concern for outbreeding depression may be overblown. Additionally, several successful cases such as black panthers and black bears in the USA, reveal admixture in the genetics but with hindsight we see how important translocations were for decreasing inbreeding depression and increasing population size.

Thus, some ethical questions to consider when thinking about creating an admixed population include:
• Should we introduce individuals from a large source population to a declining population to increase population size?
• Is the answer to the above question dependent on understanding the genetics? What if we have no money for a new genetics study?
• Does the answer to the first question depend on if the populations are locally adapted?
• Should local adaptation be a consideration in population management if we do not have information and/or cannot assess what selective pressures the population is adapting to and the direction of selection?
• Should we minimize inbreeding or outbreeding depression?
• Is creating admixed populations only acceptable for common/least concern species, or also threatened and endangered species?

Protecting Hybrids
Hybrid populations are similar to admixed populations, except that there was more divergence between the populations that came together to form the hybrids; usually so much divergence that biologists may call the parental populations separate species or subspecies. Hybrids can form in nature, and may form a new species with sufficient time. However, human changes to the landscape may remove barriers that were previously keeping species apart. When hybrid populations are produced anthropogenically, biologists and policy makers question if they should be protected if one of the parental populations is threatened or endangered.

Some questions to think about hybrids specifically include:
• Should natural hybrids be protected under threatened and endangered species laws?
• Some taxa, such as plants, hybridize more readily than other taxa. Thus, should protection of hybrid populations and/or species be taxa specific?
• Should anthropogenic hybrids be protected under threatened and endangered species laws?
• Should anthropogenic hybrids, whether of common or threatened species, be culled to protect gene pools of the parental species?
• Does the age of the hybridization event (recent or ancient) change our perception on the protection of hybrid populations?

These are some truly tough issues to think about, especially in a world where anthropogenic hybrids may become more common. Beyond these ethical considerations, there are practical ones as well, including do we have the data on hand to make some of these decisions? If not, can we obtain data given constraints of money/resources for studies and within acceptable time frames for decision making? Studying admixed populations is A LOT of fun, and brings up important questions relevant to conservation debates.