Tiny Shrews Reveal Big Changes in the Arctic

Paying attention to the overlooked shrew is helping biologists understand the effects of climate change on other species, including humans.

The tiny shrew punches above its weight when it comes to illustrating the effects of climate change. In the National Oceanic and Atmospheric Administration's recently published 2016 Arctic Report Card, a team of researchers makes the case that studying these easily overlooked critters offers valuable insights into the complex environmental changes underway in the Arctic.

The Arctic is warming twice as fast as the rest of the globe, triggering a range of harmful impacts - from vanishing sea ice to emerging diseases - to both the wildlife and human communities that live there. To mitigate these effects, scientists need to understand the region's baseline conditions. The trouble is, the researchers write, our knowledge of existing Arctic biodiversity is "woefully incomplete."

"In general, we have not surveyed the Arctic very well across time or across space," said Joseph Cook, director of the Museum of Southwestern Biology and an author on the paper. "It's a vast region, it's very tough to get to, and when we talk about polar biology, we've spent a lot of our effort in Antarctica, and less effort in the northern latitudes."

Shrews, however, are helping fill in some of the knowledge gaps. Unlike large mammals like moose and caribou, shrews are relatively easy to sample. Collections like the Museum of Southwestern Biology and the University of Alaska Museum of the North have preserved specimens dating back to the 1800s.

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In addition to its accessibility, the world of small mammals is a microcosm of the wider ecosystem. "We use them to understand fundamental evolutionary and ecological processes that govern all species, from mites to muskox," the authors write.

Shrews are so informative because they are found in most habitats, do not migrate, host parasites that often rely on multiple hosts to complete their life cycles and eat invertebrates like worms, insects, and spiders. "By studying shrews, we can begin to make lots of connections within the surrounding communities," said Andrew Hope, a research assistant professor of biology at Kansas State University and the paper's lead author.

Using shrew specimens collected over the last 30-40 years, the researchers analyzed genetic signatures recorded in DNA to determine past population sizes and distributions. Pairing this information with climate data allowed them to understand how Arctic shrews have responded to environmental changes in the past and make projections about their future trajectories. "Each specimen in a museum holds a volume of information, such as a book in a vast library," said Hope.

For example, the study found that populations of forest-dwelling masked shrews are expanding northward in response to warmer temperatures, while barren ground shrews, which favor tundra, are losing much of their habitat. As a result of these shifting distributions, the ranges of these two species now overlap. The shared territory facilitates the exchange of parasites, diseases and even hybridization, all of which are likely to continue in the coming decades.

The troves of data housed in diminutive shrews are only a jumping off place for a complete picture of Arctic health. The paper highlights the need to catalog traditional knowledge from indigenous peoples who have inhabited the Arctic for thousands of years and improve field collections. "We need a national or global strategy to regularly build these archives," said Cook. "So that we can understand how organisms are being impacted as we move into decades of heavy change."

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