Uncovering the Impacts of Population Decline on Disease Immunity in Channel Island Foxes by Nicole Adams

(Thank you to our guest blogger University of Southern California graduate student Nicole Adams)

Besides being adorable, why should we care about the island fox?

You probably know the story of the island foxes–that they suffered great population declines in the last two and a half decades. Over three years the northern islands’ fox populations declined 96-99% due to hyperpredation by goldeneagles. (In other words, unusually large numbers of island foxes were killed for food by golden eagles.) At the same time, on the eastern end of Santa Catalina Island there was a 90% population decrease in one year due to a canine distemper virus outbreak.

Fortunately, rigorous captive breeding programs were swiftly and effectively put in place to save the foxes from sure extinction on some of the islands. Island fox estimates as of 2014 show substantial population recovery. A conservation success story! This is great news for the stability of the Channel Island ecosystem, but should we declare victory and stop worrying about the foxes?

photo courtesy of Kevin Schaffer

I don’t think so. The number of foxes has increased, but such severe population declines can have lasting effects on the genetics of a population. Important questions remain. How much genetic diversity was lost due to these crashes? What type of genetic diversity was lost? Which genes were changed as a result? These questions are crucial to answer because genetic diversity allows the foxes to adapt to their ever-changing environment.

Foxes are continually facing health threats such as those caused by introduced species. Known health concerns in the island fox populations include a number of viruses, bacteria, and fungi that cause diseases. On Catalina, earmites in the foxes often lead to ear tumors. And a new pathogen, a spiny worm, is currently causing fox fatalities on San Miguel.

It is difficult to know when another outbreak like the one on Santa Catalina Island will occur, what the next pathogen will be, or how much genetic diversity will be lost. So it’s important that the fox populations are monitored for the presence of known pathogens and the emergence of new ones. Monitoring for pathogens can be easily done by non-invasive sampling, which allows useful animal material to be collected while causing the least amount of stress on the animal. Therefore, I am monitoring pathogens in fox populations by collecting scat samples, a smelly but non-invasive sampling technique.

Catalina Island fox sitting next to its deposited specimen at USC's Wrigley Institute of Environmental Studies; Photo courtesy of Nicole Adams

I received scat samples from all of the six inhabited islands as well as from captive foxes in zoos. I extracted all available DNA out of the scat samples including that from the fox, bacteria, fungi, and fox prey. Then I sequenced 16S rRNA, a common gene that can differentiate among species. I am currently processing the sequences from the scat samples and comparing them to known pathogen sequences in order to identify putative or possible pathogens.

USC undergraduate assistant, Lauren Stoneburner, weighing out island fox scat for DNA extraction. Photo courtesy of Nicole Adams

I will then compare the genetic diversity of a gene family associated with the immune system (major histocompatibility complex II) to the diversity of organisms found in the scat to better understand the current diversity of the immunity genes in the Channel Island fox and how this affects the health of individuals.

The complex population history, combined with ongoing health issues, contribute to the need for conservation of the island foxes. I look forward to sharing my results and conclusions and potentially informing the management practice of these curious critters.

Nicole Adams is a Graduate Student at the University of Southern California in Los Angeles, CA.

More Research Regarding Island Foxes:

Origins of the Island Fox

New Findings on Island Fox Diet

Epidemic Disease Threats to the Island Fox

More 

The Origins of the Island Fox by Courtney Hofman

(Thank you to our guest blogger, researcher Courtney Hofman) 

photo courtesy of Kevin Schafer

People have long wondered how the island fox first arrived on the Channel Islands. Did they swim? Were they swept out to sea on a piece of debris? Did Island Chumash and Gabrieliño people or their ancestors introduce them? Researchers have proposed a number of possible hypotheses of how the fox arrived but to test each hypotheses we must first examine the data on when foxes arrived on the islands.

For a long time scientists thought that island foxes had been on the islands for at least 16,000 years and some argued they had been there as early as 40,000 years ago (Aguilar et al. 2004). This is well before people arrived on the islands some 13,000 years ago. These early date estimates were based on island fox bones recovered from paleontological sites. However, direct radiocarbon dating of these same fox bones indicate that they are less than 7000 years old (Rick et al. 2009). Additional radiocarbon dates on island fox bones recovered from archaeological sites indicate that island foxes may have arrived on the islands approximately 7100 years ago, well after people.

When combined with radiocarbon dates, genetic data can also be used to test hypotheses about the origins of the island fox. Mitochondrial DNA is inherited from a fox’s mother and can tell us a lot about the history of the island fox. In my recent study, mitochondrial DNA was sequenced from 185 island and mainland gray foxes to explore how these different populations are related to each other (Hofman et al. 2015).

Median-Joining Network of Island and Mainland Mitochondrial DNA

By comparing these DNA sequences, we know that northern island (Santa Cruz, Santa Rosa, and San Miguel) foxes are closely related to each other while the southern island populations are more distinct (Santa Catalina, San Clemente and San Nicolas). Together with radiocarbon dates, mitochondrial DNA suggest that island foxes arrived on the northern islands between 9200 and 7100 years ago and were likely quickly moved by humans to the other islands. We cannot yet say how the foxes first arrived on the islands. More genomic and archaeological data are needed to distinguish between a human or natural introduction. 

Read the full paper at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118240

• Aguilar, A., Roemer, G., Debenham, S., Binns, M., Garcelon, D. and Wayne, R. K. (2004). High MHC diversity maintained by balancing selection in an otherwise genetically monomorphic mammal. Proc. Natl. Acad. Sci. U. S. A. 101: 3490–3494.
• Hofman, C. A., Rick, T. C., Hawkins, M. T. R., Funk, W. C., Ralls, K., Boser, C. L., Collins, P. W., Coonan, T., King, J. L., Morrison, S. A., Newsome, S. D., Sillett, T. S., Fleischer, R. C. and Maldonado, J. E. (2015). Mitochondrial Genomes Suggest Rapid Evolution of Dwarf CaliforniaChannel Islands Foxes (Urocyon littoralis). PLoS ONE 10:e0118240.
• Rick, T. C., Erlandson, J. M., Vellanoweth, R., Braje, T. J., Guthrie, D. A. and Stafford Jr., T. W. (2009). Origins and Antiquity of the Island Fox (Urocyon littoralis) on California’s Channel Islands. Quat. Res. 71: 93–98.