Warming Arctic could change animal mating schedule

a squirrel
A hibernating Arctic ground squirrel (Lesa Hollen/UAF)

Rapid changes in Arctic temperatures are influencing animal reproductive behavior. A University of Alaska Fairbanks scientist published a study in the current edition of Science magazine, building on 25 years of measurements.

Dr. Brian Barnes has studied a lot of Arctic and sub-Arctic animals since he came to UAF. But, he’s primarily known as the “squirrel guy.” That’s because Barnes and his colleagues rocked the scientific world in the late 1980s with the discovery of a mammal that can lower its body temperature below freezing, and survive: the Arctic ground squirrel.

“We call them ‘Sik siks,’ which is onomatopoeic for their warning call, which is, ‘chirp/chirp’ and similar to the Inupiaq name for Arctic ground squirrels, which is Siksrik,” Barnes said.

That discovery is still influencing cryogenic research and stroke medicine.

Over the years, researchers affiliated with the university have collected data on 199 living squirrels, sometimes in the lab or outdoor enclosures behind the science buildings on campus, but mostly at Toolik Lake research station where the squirrels are in their natural Arctic habitat.

”It wasn’t until recent years that we’ve been able to look back, and while there have been no significant changes in annual air temperature, the soil temperatures in the winter have become warmer. And what’s important for this paper, we’ve detected a response by the animals to it,” Barnes said.

Barnes authored this latest study along with former UAF students who are now researchers and professors. Cory Williams at Colorado State University is the lead on this research. Lore Buck from Northern Arizona University began work with Barnes in the 1990s to learn how Arctic ground squirrels survive such long, cold, dark, winters and just how cold their hibernation spots were. Helen Chmura started the analysis while a postdoctoral fellow at the University of Alaska Fairbanks in 2018. In addition, Cassandra Duncan and Grace Burrell assisted with the research while they were UAF students.

There’s something more you need to know about this animal besides the spectacular low hibernation temperature. And that is the males turn on and off their reproductive homones, because mating takes up a lot of fuel, which is scarce in the short Arctic summer.

After coming out of hibernation in March, it takes about a month for the male squirrels to turn on the cascade of hormones that makes them fertile by the time the females emerge from their individual burrows. And that time on the calendar seems to be hard-wired in the males. It has not changed over the 25 years of the study.

But the scientists have tracked an entirely different calendar for the females.

“And it’s that, that we have seen shifting over the 25 years of our study: that the average date that these females are electing to come above ground and start off their active season, is now occurring 10 days earlier than it was when we first began to record all of this in the early ’90s,” Barnes said.

That’s the biggest finding from analyzing the data. The males are still on their annual calendar, but the females are ready to mate 10 days earlier.

“But the fact that these females are coming up earlier and earlier, but the males aren’t because they have this hardwired clock that says, don’t come up until the right time, is leading to gender mismatch,” Barnes said.

That could mean the squirrels miss the opportunity to mate.

Barnes says temperatures measured in the soil layer above the permafrost, freezes later in the fall, doesn’t get as cold in the middle of winter, and thaws slightly earlier in the spring. The scientists suspect the females are influenced by the warmer soils.

 ”A 10-day difference in coming early is a big piece of that,” he said. ”So we’re wondering what’s gonna happen. If females continue in this way and come up earlier and earlier and males don’t respond, females are just gonna be hanging out with no mates available and, and that’s where this could go wrong for the Arctic ground squirrel.”

And if they hang around too long, they have a greater risk of being eaten.

“’Cause they would be more subject to predation by the golden eagles and the foxes and the wolves that are very much looking for that first squirrel that’s coming up,” Barnes said.

Barnes and his colleagues’ latest research is published in the current edition of Science magazine.

UAF hosts the one-of-a-kind Center for Transformative Research in Metabolism, which studies hibernating animals to benefit biomedicine for humans. UAF will be hosting an international Hibernation Science Conference and Workshop in August.

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