Climate change is poised to become a serial killer. With rapid temperature swings around the world, ecosystems have been thrown into flux, exacerbating problems such as habitat loss that have already pushed many plant and animal species to the brink. Some biologists argue that Earth is on the verge of another major extinction event. The big question is whether plants and animals can adapt quickly enough to outpace climate change.
We often think of evolution as something that happens slowly, but that’s not always the case. If the selection pressures are strong enough, evolution can happen over mere decades. For instance, an experiment growing brewer’s yeast in environments with deadly concentrations of salt showed that the microbe population took a hit but then bounced back thanks to rapid changes in a couple genes over just 25 generations.
Identifying genetic adaptations in response to climate change can be tricky. Long-term data sets can tell us the most about whether a species is truly evolving, but it’s hard to tell if any genetic differences were selected for climate reasons alone. What's more, not all genetic adaptations may be beneficial in the long term. And some species may not even need to evolve to survive. Physical or behavioral modifications made during an individual's lifetime may help enough members within a species thrive in a changing world.
Here are 10 species that may already be adapting to climate change—for better or worse:
Corals are highly sensitive to temperature changes in the ocean. Higher temperatures can cause bleaching, when corals spit out the colorful algae that live inside their tissues. Algae give corals nutrients in exchange for shelter, so bleaching can be a death sentence, especially for species in stressful, low-nutrient environments. A 2004 study suggested that coral populations might be shifting to favor corals with algae that are less sensitive to bleaching, but it's unclear if this involves inherited changes in corals’ genes.
However, one species shows how evolution might come to the rescue. According to an April study, table corals (Acropora hyacinthus) can adapt to resist bleaching in warmer waters. On Ofu Island in American Samoa, A. hyacinthus lives in both hot and cool pools. In the lab, researchers tested corals from both environments to see how they reacted to increased heat. They found that only 20 percent of corals from the hot pools bleached, compared to 55 percent from the cool pools. Also, corals from cooler pools that spent a year transplanted in hot pools had an advantage—only 32.5 percent of those corals bleached in the lab tests. The results suggest that the species has the genetic material necessary to adapt and survive the heat, and that heat-tolerant corals might gain a reproductive advantage over time. Some researchers advocate growing heat tolerant corals and planting them in hard hit areas, but such human-assisted evolution garners controversy.
Varieties of Mediterranean thyme (Thymus vulgaris) produce oils with different chemical compositions, and the ones with stronger smelling compounds like phenols are more effective at deterring herbivores. Producing phenols typically comes at a cost, though, as these plants are more sensitive to freezing. But in southern France’s Saint-Martin-de-Londres basin, winters are getting warmer. Since the 1970s, the basin has seen fewer freezing nights during the cold season.
Looking at 24 populations across the basin in 1974 versus 2010, one study found an increase in the proportion of plants that produce phenolic compounds. These plants are even popping up in areas where they didn’t grow in the 1970s. Since the plant’s genes determine the chemical composition of its oils, it’s likely that genetic changes are behind wild thyme’s response to warmer winters.
Environmental factors often drive migratory behavior patterns in animals. For salmon, migration is crucial to their survival as a species, because the fish swim from the ocean and up freshwater streams to spawn. The need to migrate is so strong it is even written into their genes. In Auke Creek, Alaska, one pink salmon (Oncorhynchus gorbuscha) population is migrating about two weeks earlier than it was 40 years ago. So scientists looked at both genetic and migratory data over 32 years to see if genetic changes were behind the switch.
The team found that between 1983 and 2011, the frequency of a genetic marker for late migration dropped significantly. By 2011, late migrating fish only made up about 10 percent of the population. Over that same time period, the local water temperature has increased by about one degree Celsius on average, an uptick that’s linked to climate change. The researchers argue that earlier migrating fish are better fit to handle warmer waters. Auke Creek salmon populations have held steady over the last few decades, and this adaptation may have made them more resilient.
A common nocturnal predator in the temperate forests of Europe, tawny owls (Strix aluco) come in two basic shades: brown and less brown. No matter their sex or age, an owl’s feather color depends entirely on how much of a pigment called pheomelanin ends up in its plumage, something that is dictated by a variety of genes. Though regular brown is the dominant trait, the pale brown or grayish color helps some owls blend in with snowy trees and hide from predators. More snow typically equals more gray owls.
With milder winters in Finland, one population of tawny owls showed a significant uptick in brown-plumed owls over the last 28 years, according to a 2011 Nature Communications study. The researchers also saw a nationwide increase in brown owls over the last 48 years. It makes sense that natural selection might favor brown coloration: With less snow, brown owls are better at blending in with the surrounding forest, giving those birds a better chance to survive and reproduce.
Pitcher Plant Mosquitoes
In the bogs of eastern North America, the larvae of pitcher plant mosquitoes (Wyeomyia smithii) hibernate in winter and blossom into fully grown adults come spring, when they thrive on the nectar inside their namesake plants. As the days grow shorter, the mosquitoes are genetically programmed to hibernate. Mosquitos at the southern end of the species’ range had already adapted to delay hibernation based on the longer growing season. But now northern populations are also hibernating later as global temperatures rise.
A 2001 study in PNAS showed that the genetic changes responsible for the shift can manifest in as little as five years, according to lab tests. In areas where the selection pressures are stronger, the change in hibernation behavior can happen even faster. Other studies hint that the Asian tiger mosquito, a carrier of West Nile virus, and the water strider are experiencing similar shifts in hibernation periods based on seasonal impacts of climate change.
For banded snails (Cepaea nemoralis), shell coloration is determined not only by genes, but also by body temperature: Snails with light shells tend to be cooler customers. Scientists suspect that warmer temperatures in Europe might make the lighter coloration become more prevalent. One study published in Global Change Biology found that banded snail populations sampled at 16 sites in the Netherlands in 1967 and again in 2010 had an increasing proportion of yellow shells compared to brown ones. Over 43 years, the area has also seen a 1.5° to 2°F increase in annual temperature. The trend even held for shaded areas, where one might expect darker shells to provide better camouflage.
But the verdict may still be out on whether climate change is causing the snails to evolve. Another study, published in PLOS ONE in 2011, found no difference in the prevalence of light-colored shells across the board. The researchers hypothesize that individual snails are instead changing how they regulate their body temperature to cope with the changing climate.
In the Columbia River, sockeye salmon (Oncorhynchus nerka) are migrating earlier every year in the spring and early summer to spawn. A 2011 study in American Naturalist examined this migration trend over 60 years to see if warmer river temperatures might be to blame. Luckily, sockeye salmon migration counts go back decades, so the researchers were able to factor daily migration data into statistical modeling of historic environmental pressures. Evolution in response to higher water temperatures proved the most likely explanation for about two-thirds of the shift, while individual adaptation to river flow changes could explain the rest.
The southwest Yukon has seen increasingly warm springs and a drier environment, encouraging white spruce trees to produce more cones—and giving North American red squirrels (Tamiasciurus hudsonicus) more to eat. In red squirrels, the more cones females eat in the fall, the earlier they give birth. Looking at an individual population of red squirrels near Kluane Lake, Canada, researchers did see a shift to earlier birthing times of almost 2 days per year over the last 10 years. Birthing time can vary a bit, but the team argues that the data can only be explained if at least some of the shift is attributed to genetic changes inherited over generations.
Species can vary a lot based on their geography. In the case of the common fruit fly (Drosophila melanogaster), genetic variants correspond to populations living at different latitudes, and specific enzyme mutations can serve as biomarkers. So researchers examined the prevalence of three protein forms in fruit flies along the east coast of Australia between 1979 to 1982 and 2002 to 2004. Southern Australia is more temperate and tropical, while northern Australia is dry and hot. The team found that many fruit flies living in Southern Australia now have the genetic mutations common in more northern populations—as if they’d moved nearly 4 degrees in latitude. Scientists suggest that these changes are linked to coping with a warmer and drier climate, and researchers have found similar trends in Europe and North America.
Sometimes organisms are slow to adapt. In Holland’s Hoge Veluwe Park, caterpillars are maturing earlier each year as spring comes earlier. But their predators, great tits (Parus major), aren’t always changing their schedule to hatch when the caterpillars are at their peak, and bird numbers are dropping. As with the hibernating mosquitoes, great tits have a genetic trigger that spurs them to lay eggs when spring arrives. But there’s some variation in how much an individual bird can tweak its egg-laying date in response to an earlier spring. A study of 833 great tits in Hoge Veluwe over 32 years did find greater genetic selection for birds that could vary their egg-laying time to match the caterpillars' arrival. If this trend continues, it could save them from decline, but it remains unclear whether they can change fast enough to beat rising temperatures.