Survival of the Fittest

Survival of the Fittest

Researchers study how animals are adapting or struggling in the midst of climate change.
By Glenn Cook

John Wingfield, PhD, has spent several decades examining how animals cope with the changing environment. Like most physiologists, his job has become increasingly complex as the world struggles to deal with global warming and climate change.

“That used to be just seasonality. Now it includes climate change resulting in changing seasonality as well as unpredictable extreme weather events. We now have to look at our research in different ways,” says Wingfield, distinguished professor emeritus at the University of California at Davis.

Brought on by global warming that is largely the result of burning of oil, gas and coal, climate change has resulted in increased heat, drought, wildfires, floods and insect outbreaks around the world. Since the Industrial Age, the Earth has warmed an average of 1.9 degrees Fahrenheit; once this number reaches 2.7 degrees Fahrenheit, scientists say the planet will tip into an “irreversible future” that also includes food scarcity and mass migration.

As scientists warn of these devastating effects, physiologists are studying how organisms are responding to change and how that will impact human and animal populations. In the process, they are moving away from tried-and-true research models on environmental changes.

Hollie Putnam, PhD, associate professor at the University of Rhode Island who studies the ecophysiology of marine invertebrates, says coral reef ecosystems are at high risk due to climate change. The reefs have an annual value “on the order of hundreds of billions of dollars” because of their impact on coastal protection, fisheries, tourism and the production of pharmaceuticals, she says. 

“Currently, the rate of environmental change is pushing corals to the brink of collapse, which threatens food security, the coastal habitat and cultural connections,” Putnam says. “Passing a tipping point can represent catastrophic consequences for the system, as well as the humans that depend on them.” 

Warren Burggren, PhD, FAPS, distinguished research professor of developmental physiology at the University of North Texas, studies how animals adapt to different environments. He says past and current research on climate change has “an Achilles heel” because it focuses on long-term projections and doesn’t take into account “the huge weather variations we’re seeing.”

“A lot of the predictions on climate’s effects on speciation, population dynamics and the survival of populations are based on what is projected to happen to temperature over 100 years or 500 years,” Burggren says. “I love the quote by Mark Twain: ‘Climate is what we expect. Weather is what we get.’ And the weather is affecting animal populations in dramatic ways.”

CHALLENGES OR ANIMALS

Researchers are witnessing a race to see whether animal populations “can, through natural selection, modify at a rate quickly enough to catch up or to maintain their survival in changing environments,” Burggren says. Most can’t, but some “very rapid rates of evolution” will allow others to survive.

“The problem is that when you look at things like temperature or water availability, you’re looking at not just coloration or a little change in body size, but some pretty fundamental physiological changes that are induced by either water availability or temperature. That fundamental physiological retooling is not really able to occur at the rate that many environments are changing,” Burggren says. 

Wingfield, who combines field studies with laboratory experiments to see how birds and other animals respond to changes in their physical and social environments, says researchers are “not always clear” in distinguishing between the predictable environmental changes over the seasons they have traditionally studied and the effects of climate change. The unpredictable nature of the latter, he says, has resulted in “acute and sometimes chronic stress,” leaving some populations as “refugees from their normal habitat.” 

“How an animal responds to something it can predict, such as seasons, is very different from actually responding facultatively to what’s going on in the immediate present,” Wingfield says. “The unpredictable component is a real problem.”

Jonathon Stillman, PhD, professor of biology at San Francisco State University and the University of California at Berkeley, has focused his research on how climate change and human activities affect marine and aquatic organisms. His lab has studied these problems in an array of organisms, including crabs, sea hares, coccolithophores, clams, freshwater crustaceans and insects.

In the laboratory’s study of intertidal zone porcelain crabs, Stillman has seen how populations move away from long-term habitats as they are affected by warmer average temperatures and more frequent and severe heat waves in the winter and summer. This affects both the population density as well as “inter-individual interactions,” which can lead to greater aggression, fighting, injury and ultimately decreased fitness.

 “Stressed humans are in a different physiological state than relaxed humans, and the same is true for animals,” Stillman says. “If climate change causes species distributions to shift, that can change the way that organisms interact with others from the same or from different species.”

THE CHANGES WE SEE

Wingfield’s research, which involves the study of birds for more than three decades in Arctic Alaska, shows that climate change is affecting migration and breeding.

“Some species are moving further north, and growth of shrubs and small trees like willows are increasing on the tundra,” Wingfield says. “Before they were only 10, 15, maybe 20 centimeters tall; now some are two meters plus. As a result, these birds are retreating further north where tundra is still mostly short. Other species from the south are moving onto areas with expanded growth of shrubs where the higher arctic birds used to be.”

What was once a four-week Arctic summer has become eight weeks in just the past two decades. “Some birds had just four weeks or so in which to raise young, so that would limit them to one brood. If they lost a brood early enough to a predator, maybe they could renest, but mostly it’s just one brood,” he says.  “Now we’re seeing evidence that these birds are raising two. That’s quite a change for the Arctic. It is phenomenal.”

Wingfield says physiologists are “really just beginning to understand” how major storms, which are coming with greater intensity, duration and frequency, affect animals and humans. He says the most important data involve integration of field work and in-lab research.

“The rate at which we’re accumulating data is not as rapid as we would like,” Wingfield says. “Because lab work does not always apply to what is happening in the field, we stay out there during storms and actually follow what the animals are doing, but not everybody likes to do that. We take those novel field observations into the lab and do controlled experiments that allow us to get at some of the mechanisms.”

HOW ANIMALS AND ORGANISMS ADAPT

Stillman says some organisms affected by climate change have been shown to adjust their physiology and behavior better than others. His research has shown that organisms with the greatest tolerance to high temperatures have a “zero thermal safety margin,” meaning they can’t adapt to environmental changes or differences. In that instance, he says, the increased intensity of heat waves “is likely to cause a reduction in population size,” while others can survive the climate shifts.

“Rather than ask, ‘What happens if we take a freshwater fish from 20 degrees to 25 degrees over a number of years?’ how about, ‘What happens if we take it from 20 degrees to an average of 25 degrees, but fluctuating on a daily basis?’ I think in the long run that information will be much more revealing.”

Warren Burggren, PhD, FAPS

“For terrestrial animals, another major environmental driver is availability of water to prevent dehydration and for evaporative cooling,” Stillman says. “As climate warms and droughts intensify, many organisms may not overheat, but rather dehydrate, as has been evidenced in mass mortality of birds and mammals in Australia.”

Rising temperatures and the increasing intensity and frequency of marine heat waves have a negative effect on corals, Putnam says. This increase in temperature results in coral bleaching, a breakdown of the interaction between the coral and their symbiotic algae.  Bleaching can result in coral starvation and mass mortality.

An adult coral can be 10 to hundreds of years old, she says, and once it settles on the ocean floor it is “in that position for life.” Because of climate change, Putnam says much of her research is focused on “the legacy of the environment throughout connected life stages.” 

“Given this fairly long generation time, the changes that are now taking place in the environment are happening very rapidly,” she says. “It is critical not only to examine any single life stage, but how conditions such as marine heat waves impact all the life stages and may generate carryover effects or environmental legacies that may benefit the coral through thermal priming, or negatively impact them through compounded or accumulating stress.”

Corals typically follow one of two reproductive modes, Putnam says. In the first, corals send their gametes into the ocean in a synchronized manner on a lunar schedule, with larval development taking place while exposed to the ocean conditions. In the second, they fertilize and brood larvae internally for a period of one to several months, after which the larvae are released to settle and attach quickly to the ocean floor.

“It is essential to study a variety of aspects of coral reproduction each year to generate data that can be used to understand when and how climate change is impacting the various life stages,” Putnam says. “Even more important, it is essential mechanistically to understand life-stage specific sensitivities or carryover of the stress response from one stage to another.”

Wingfield points to instances in recent decades in which birds arrived in Europe ready to breed but found their food supply had already peaked. The “mismatch” means these birds missed their best opportunity to raise their young. Nonetheless, there are signs that some have been “more flexible and are able to adjust and arrive earlier to initiate breeding at the right time,” he says.

“When you look at animal populations and plants, there’s no clear trend for a slow change or a dramatic one or a rapid one. There’re always some species that are much more adaptable and flexible and respond with greater rapidity than other species,” Wingfield says. The next question is “why are some populations and individuals more flexible than others?”

Even though Putnam is worried about the long-term effects of climate change, she notes many corals have proven they can acclimate. “What doesn’t kill corals can make them stronger, even across a generation,” she says.

WHAT LIES AHEAD

What are the next steps that physiologists should pursue to get a better handle on how climate change is affecting animals and, ultimately, humans?

Burggren says physiologists should “reconsider our experimental paradigm” by focusing on stochasticity—the random variables that are taking on increased importance in climate change. “There’s a whole underlying undercurrent of stochastically driven biology that we haven’t really plumbed as physiologists,” he says. “Our training is to hold everything constant, except the one variable we’re interested in, and then we manipulate that to a new level. 

“Rather than ask, ‘What happens if we take a freshwater fish from 20 degrees to 25 degrees over a number of years?’ how about, ‘What happens if we take it from 20 degrees to an average of 25 degrees, but fluctuating on a daily basis?’ I think in the long run that information will be much more revealing.”

Physiologists who work at the cell and molecular levels will need to collaborate with ecologists, as well as behavioral and evolution biologists,  before they can “get some handle of the answers” about the effects of climate change, Wingfield says.

“In the recent past, we’ve taught our students to be specialists. They tend to focus on very narrow topics out of necessity to apply all the cutting-edge techniques to a very clear, but focused, question,” Wingfield says. “Out there in the field we see animals responding to a suite of information. We’ve got to find some way to integrate field and lab investigations. Understanding the future of environmental change and how plants and humans are responding to climate change requires us to collaborate as each brings expertise needed to address the problems.”

Stillman agrees: “Comparative physiology is ever more important as human activities are changing Earth’s environment on a global scale,” he says. “Most of what we know about physiology comes from a rather small group of organisms. Though all life shares fundamental biochemical and cellular architecture, the great biodiversity of nature is reflected at the physiological level, too.”

This article was originally published in the July 2022 issue of The Physiologist Magazine.