How do species respond as the climate warms? Although most research on Arctic animals focuses on economically important or charismatic species like caribou or polar bears, small mammals, such as shrews, and their parasites can serve as indicators of environmental change.
Hope and his colleagues chose shrews for a number of reasons. They live in the Arctic year-round, rather than migrating seasonally like many other species. Additionally, shrews consume considerable quantities of invertebrates and act as intermediate carriers of many parasites, making them a key link in Arctic ecosystems.
The researchers collected shrews from a broad geographic area, gathering as much information from each specimen as possible. They performed genetic analyses and tested for viruses and other pathogens. They collected all the external parasites on each shrew, such as fleas and ticks, as well as the parasites inside the animals’ bodies, such as roundworms and flukes. The shrews’ skins and skeletons were preserved for future use.
Hope and his colleagues also combed through natural history museums to collect the same data from decades-old preserved shrews. Advances in genomics technology allowed the researchers to use the shrews’ DNA to understand past distributions, population sizes, and responses to environmental change. They also recreated the preserved shrews’ diets and parasite communities for comparison with those of modern shrews.
“Little did the scientists from back then know how we would be using the specimens they collected,” says Hope. “The methods we use weren’t possible back then. We’re beginning to ask questions and use methods that were not on the radar decades ago.
“It’s a valuable lesson for us collecting specimens now, because who knows what questions scientists will be asking ten or twenty years down the road. Preserved specimens are enormous resources available in many museums throughout the world.”
Small Animals, Big Changes
Hope and his colleagues found that the forest-dwelling masked shrew (Sorex cinereus) is expanding its range, while its neighbor to the north, the tundra-dwelling barren ground shrew (Sorex ugyunak), is experiencing constriction and fragmentation of its habitat.
The encroachment of the masked shrew into the barren ground shrew’s territory also brings parasites and pathogens that can spread among shrews and possibly to other animals.
Based on climate data and the genetic data collected from all the shrew specimens, Hope and his colleagues predict the masked shrew will continue to expand northward, while the barren ground shrew’s range will become more fragmented.
“All over, but particularly at higher latitudes, species are rapidly shifting around the landscape,” says Hope. “The ranges of many species are changing as environmental conditions change, and the result is a sudden increase in overlap in these communities.”
When environmental conditions change, species may adapt to the new conditions, shift their distributions to follow their preferred conditions, or die out. But Hope says that what usually occurs is a more complicated combination of these options.
“Species can compete with each other, potentially interbreed, and spread parasites and diseases between communities that haven’t always shared such close interactions,” he says.
This is not the first time the climate has warmed and the barren ground shrew’s range has decreased – but the current rate of climate change is unprecedented.
Species such as these shrews have been responding to changes in climate through numerous climate cycles over hundreds of thousands of years. The issue is that the change going on now is different than the ones they have experienced in the past.
“The carbon dioxide levels in the atmosphere are higher than they have ever been in the experience of these species, and the accompanying climate change is much more rapid,” says Hope. “That translates to conditions that no one has really experienced before, and we’re not sure exactly how animals and ecosystems are going to respond.”
Hope’s work demonstrates that small mammals, such as shrews, and their parasites can serve as key indicators, reflecting the evolutionary and ecological changes in many species dealing with climate change. Studies such as this are needed to anticipate the effects that accelerating climate change will have on northern animals.