Endangered rat study shares the seal of non-contact

Photo: A salt marsh harvesting mouse walks through a sedge in the Grizzly Island Wildlife Area in San Francisco.
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Credit: Cody Aylward/UC Davis

From badger species to moles, shrews and mice, many of the world’s endangered mammals are tiny. Genetic sampling is important for understanding how populations are maintained and protected. But finding effective, non-invasive ways to collect genetic samples from young animals can be challenging.

A study from the University of California, Davis, describes a new, non-invasive genetic scanning technique for the endangered salt marsh harvester mouse, which lives only within the tidal marshes of the San Francisco Bay Estuary.

In large mammals, scientists often collect stool samples, but the poop of young animals can be too small to detect in the wild.

New technology published in Mammalology Journal, uses a combination of bait stations and genetics to sample and identify salt marsh harvest mice, or “salt” as the researchers affectionately call them. This species has lost more than 90% of its habitat due to development and is also threatened by sea level rise. That is why it is necessary to accurately and efficiently identify the remaining populations, the authors note.

Eat and rush

The technique is simple: bait boxes for scientists with a snack of seeds, millet and oats, and lay out cotton bedding. Mice are free to come and go. The researcher returns a week later to collect stool pellets for genetic sampling in the laboratory. There, a unique species identification test distinguishes the samples of salt marsh harvest mice from those of other rodents that may have used the bait box.

Compare this process with the most common and intensive live trap method: a team of three to five researchers examine the traps at sunrise and sunset for several days in a row. To prevent animal drowning, these traps should be placed above the tide line, excluding several areas of tidal swamp habitat. But with this new, non-invasive technology, mice can leave at any time, allowing researchers to monitor more swamps and more mice safely and efficiently.

Lead author Cody Aylward, a recent graduate and former PhD student at Mammal Conservation and Environment Unit at the University of California, Davis College of Veterinary Medicine. “I I hope someone studying a small endangered animal somewhere will read this study and say, “This is something I can do.”

little wonder

Little is known about the salt marsh harvesting rat, so the effects of their potential loss are also unclear. Scientists know the species is unusual in many ways. For example, saltpeters are strong swimmers, can drink sea water and have a unique genetic lineage, Aylward explains:

He said, “Genetic data indicate that there is a difference of 3.5 million years between them and their closest relatives.” “So if we lose them, that would be 3.5 million years of lost evolutionary history.”

Co-authors are principal investigator Mark Statham, Robert Grahn and Benjamin Sachs from the University of California, Davis School of Veterinary Medicine. Douglas Kilt of the Department of Wildlife, Fish and Conservation Biology at the University of California, Davis; and Lauren Barthman-Thompson of the California Department of Fish and Wildlife.

The research was funded by the California Department of Water Resources and the USDA’s National Institute of Food and Agriculture.

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