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Red squirrels that gamble at the game of reproduction outperform their counterparts, even if it costs them in the short term, research finds.

Imagine overhearing the Powerball lottery winning numbers, but you didn’t know when those numbers would be called—just that at some point in the next 10 years or so, they would be. Despite the financial cost of playing those numbers daily for that period, the payoff is big enough to make it worthwhile.

Animals that live in highly variable environments play a similar lottery when it comes to their Darwinian fitness, or how well they are able to pass on their genes.

Natural selection favors female squirrels that have large litters in years when food is abundant because they contribute lots of babies to the gene pool, says Lauren Petrullo, lead author of the study and a postdoctoral research fellow in biopsychology at the University of Michigan.

“We were surprised to find that some females have large litters in years when there won’t be enough food for their babies to survive the winter,” she says. “Because it’s biologically expensive to produce offspring, we wanted to know why these females make what appears to be an error in their reproductive strategy.”

The red squirrels studied live in the Canadian Yukon and experience a “mast year,” or boom in their main food source—seeds from the cones of white spruce trees—once every four to seven years. Squirrels forecast the large mast crop of food before it occurs and increase litter sizes in the months prior, ensuring better future survival for their babies and better fitness for themselves.

“There is a constant tug-of-war between the trees and the squirrels at our study site,” Petrullo says, “with each player trying to deceive the other for its own fitness gain.”

Petrullo and Ben Dantzer, associate professor of psychology and of ecology and evolutionary biology, used data collected by the Kluane Red Squirrel Project, a collaborative, 34-year-old field study involving the University of Michigan, the University of Colorado, the University of Alberta, and the University of Saskatchewan.

“This is exciting because it suggests that squirrels are eavesdropping on the trees.”

“Each year, we collect data on how many babies squirrels produce and how many spruce cones the squirrels eat,” Dantzer says.

The scientists quantified the reproduction of female squirrels during both food booms and busts, discovering differences in their fitness whether they gambled with their reproductive strategy or not. While some squirrels played it safe by keeping litter sizes small each year, those that took a “pie in the sky” approach by having large litters even when food was scarce enjoyed greater lifetime fitness if they got to experience a mast year, the research showed.

Unlike the Powerball example, though, squirrels aren’t guaranteed to eventually win.

“In some ways, this strategy of gambling with litter sizes is like playing with fire,” Petrullo says. “Because the average squirrel lifespan is 3.5 years and masts only happen every four to seven, a female could potentially be sabotaging her fitness by having too many babies in low-food years, hoping for a mast when she may die before she ever gets to experience a mast at all. This could be pretty costly.”

Alternatively, for squirrels, the cost of not gambling at all in the game of reproduction can be insurmountable if they end up missing their shot at the jackpot.

“It’s essentially impossible for a female to recuperate the fitness costs of not ramping up reproduction in a mast year, so the stakes are extremely high,” Petrullo says.

Females that increased litter sizes in low-food years did take a short-term hit to their fitness. But they were more likely to increase litter sizes if and when they experienced a mast, taking home the ultimate prize of greater lifetime reproductive success, she says.

The squirrels’ best bet, according to the researchers, is to take their chances and suffer short-term fitness costs in order to avoid the unmatched cost of missing the fitness jackpot completely.

“Determining the relative costs of different types of errors is key to understanding why animals make what look to us like mistakes,” Petrullo says.

Scientists are still unsure exactly how the squirrels are able to forecast future food production. The animals may be eating parts of the spruce trees that affect their physiology and alter the number of babies they produce, Dantzer says.

“This is exciting because it suggests that squirrels are eavesdropping on the trees, but we still have much more to do to solve this puzzle,” he says.

Because many animals use cues about things like food in their environment to make reproductive decisions, and the reliability of these cues is declining due to global climate change, scientists also wonder how the costs of these types of errors will alter what is the best reproductive strategy.

“If the predictability of a food boom is reduced and squirrels can no longer forecast the future, this could impact the number of squirrels out there in the Boreal forest,” Dantzer says. “This could be problematic given that squirrels are prey for many predators.”

The research, which appears in Science, had partial funding from the National Science Foundation and the Natural Sciences and Engineering Research Council of Canada.

Source: University of Michigan

Warming waters and heat waves have contributed to the loss of an economically and culturally important fishery, the production of bay scallops, according to a new study.

As climate change intensifies, heat waves are becoming more and more common across the globe. In the face of such repeated events, animals will acclimate, migrate, or perish.

Since 2019, consecutive summer mass die-offs of bay scallops in the Peconic Estuary on Long Island, New York, have led to the collapse of the bay scallop fishery in New York and the declaration of a federal fishery disaster, with landings down more than 99%.

The findings in Global Change Biology reveal that extreme summer temperatures, becoming more frequent under climate change, exacerbate the vulnerability of bay scallops to environmental stress and has played a role in the recurrent population crashes.

The study reports the mass die-off of all scallops at a New York site in 2020, when an eight-day summer heat wave event coincided with repeated episodes of low oxygen. Yet, scallops at locales with higher oxygen or lower temperatures survived. Further investigation that year confirmed that the combination of high temperatures and low oxygen reduced feeding and energy reserves, causing mortality in ecosystem and laboratory scenarios.

“Global warming is happening at an uneven pace in space and time. It just so happens that summer water temperatures in the Northeast are increasing at a rate more than three times the global average, leaving organisms adapted to cooler temperatures endangered,” says senior author Christopher Gobler, chair of coastal ecology and conservation at Stony Brook University.

By using a combination of satellite temperature and long-term environmental records, field and laboratory experiments, and measurements of scallop heartbeat rates in an ecosystem setting because scallops heartbeat rates vary with water temperatures, the researchers demonstrated that coastal waters from New York to Massachusetts—home to the nation’s northern bay scallop fisheries—are rapidly warming and that bay scallops have become increasingly susceptible to the combination of high temperatures and impaired water quality.

The bay scallop fishery was formerly one of the largest shellfisheries on the East Coast and has progressively vanished from regions south of New York. With the New York fishery collapsed, the only remaining commercial US fishery is in Massachusetts.

The study also reveals that although Massachusetts waters are still in the safe range for bay scallops, they have warmed at a rate even faster than New York waters and could be threatened in the future.

Stephen Tomasetti, a graduate of Stony Brook’s School of Marine and Atmospheric Sciences and currently a visiting assistant professor of environmental studies at Hamilton College, points to other examples of heat-induced mass mortality on the East Coast, like the loss of lobsters in Long Island Sound and blue mussels in coastal bays south of Delaware.

“Commercial shellfisheries are a vital part of our blue economy, and shellfish habitats are changing rapidly,” he says. “Mitigating further warming by transitioning to clean energy is critical. But while these global efforts are underway, committing to practices that will improve our local water quality like reducing nutrient pollution is also important.”

Warmer waters physically hold less oxygen, so increasing the baseline oxygen levels in the estuary by improving water quality will help offset future oxygen loss from increased temperature.

The authors warn that warming in the Northeast US is projected to continue at a faster pace than the global average. The populations of mobile species like fish can respond by moving to waters with more tolerable temperatures.

But for populations of bay scallops and other economically important shellfish species, movement is limited by their ability to disperse through spawning and the availability of suitable habitat. Populations forced to cope with temperature extremes may be more vulnerable to mass mortality events.

Source: Stony Brook University