Understanding the mechanisms of adaptation to climate change: a real challenge
Growing urbanization, intensive agriculture, overexploitation of resources, the introduction of non-native species, and climate change: all these environmental changes combine to form a dangerous mix for biodiversity.
Céline Teplitsky, University of Montpellier; Anne Charmantier, National Center for Scientific Research (CNRS) and Suzanne Bonamour, Sorbonne University
In light of these changes, certain questions keep coming up: Will wildlife be able to adapt to changes that are so rapid and far-reaching? Will the adaptations we’ve observed help preserve some of the world’s biodiversity?
Over the past few decades, our understanding of how living organisms adapt to their environment has changed dramatically.
For a long time, it was believed that species evolved over very long periods of time, before it was realized that evolution could occur very rapidly, as evidenced, for example, by the development of antibiotic resistance in bacteria that cause disease in humans, or by the change in coloration in a common moth, the peppered moth, following the darkening of tree bark due to heavy air pollution in England in the 19th century.
Vincent Guili, CC BY-NC-SA
Evolution and Plasticity
Living organisms adapt to changes in their environment (such as decreased precipitation or the arrival of a new predator) through two major processes: genetic evolution and/or phenotypic plasticity.
Adaptation through genetic evolution occurs through changes in the genetic composition of a population across generations, driven by natural selection. For example, mosquitoes carrying a new mutation that emerged in the 1980s have a much higher survival rate against insecticides than other individuals that do not carry this genetic innovation. As a result, this mutation and the insecticide resistance it confers have spread throughout natural mosquito populations in about two decades.
This process of adaptation through changes in genetic composition requires that the selected traits (such as resistance) be at least partially “heritable”—that is, transmissible across generations, from parents to offspring—and genetically variable. It is important to note that since genetic changes occur across generations, genetic evolution is all the faster when the species’ generation time is short: thus, the mosquito can adapt to a new environment more quickly than the whale.
A second adaptive mechanism is "phenotypic plasticity."
While genetic evolution is a process that leads to changes across generations within a given population, phenotypic plasticity is an adaptive process that can lead to changes within each individual in the population.
For example, in many mammals, the amount of adipose tissue an individual possesses can vary depending on several environmental factors, particularly cold temperatures. Similarly, many species increase their vigilance when the risk of predation is high.
Plasticity thus manifests itself within a single generation, enabling adaptations to occur more rapidly than through genetic evolution. In particular, it allows the organism to readjust in response to changing environmental conditions throughout an individual’s lifetime.
Organisms often need time to adapt to new environmental conditions: if the adaptive response involves developing a defense against predators, this defense must be established well before the organism encounters the predator. Organisms therefore use cues present in the environment to develop the appropriate response at the right time. This is the case with tadpoles, which develop different morphologies depending on whether or not a predator’s scent is present.
In the current context, the existence of a mechanism such as phenotypic plasticity—which is widespread throughout the living world and enables rapid adaptation to environmental changes—is of major importance for understanding and anticipating the consequences of human-induced disruptions on biodiversity.
Laying eggs at the right time
The blue tit (Cyanistes caeruleus), a small passerine bird, is widely studied in the field of ecology and is the subject of numerous research studies based on observations of natural populations.
Research on this species has contributed to a better understanding of the importance of phenotypic plasticity for organisms’ adaptation to climate change.
Field studies, some of which have been ongoing for several decades, have given us a better understanding of the ecology of the blue tit. In this species, as in most other insectivorous passerines living in temperate forests, chicks are fed mainly on caterpillars by both parents—about 1,800 caterpillars to feed a single chick from hatching to fledging.
Lumiks Lumiks/Flickr, CC BY-NC-SA
Thus, the synchronization between the chicks’ food needs and the period when caterpillars are abundant has a major impact on the chicks’ survival. To ensure the chicks hatch at the right time—that is, when the parents can find a large quantity of caterpillars to bring back to the nest—the female chickadee must lay her eggs about 30 days before the peak of caterpillar abundance in the forest.
But how do you lay eggs at the right time?
The timing of egg-laying in chickadees, as in many birds, depends in part on the environment and, in particular, on temperature: in warm years, chickadees lay their eggs earlier than in cold years, perfectly illustrating the concept of phenotypic plasticity.
The period during which chickadees are most sensitive to temperature—that is, the time when the birds pick up on signs of a warmer or earlier spring—can vary between one and three months before breeding. Depending on the population, this period of temperature sensitivity begins in the spring or at the end of winter. The reliability of temperature as a predictor of the period of food abundance (caterpillars) is crucial for breeding success.
Temperature-induced plasticity is common. As a result of global warming, many animal and plant species are reproducing earlier and earlier in the year, just as trees are budding earlier. These changes in life cycles, which stem from organisms’ responses to temperature shifts, are already evident in our gardens and forests.
Plasticity therefore largely explains what is known as increasingly early springs. Phenological plasticity—that is, the timing of events throughout the year, such as the egg-laying date of chickadees—is in fact one of the primary ways in which wild species respond to climate change.
However, little is known about how global changes might affect this response and test the limits of adaptation. Is it possible for species to adapt quickly to these unprecedented and stressful environments? A recent study suggests that phenological plasticity may already be insufficient to ensure the survival of populations.
See also:
Climate Change and the Biodiversity Crisis: A Dangerous Alliance
New and stressful disruptions
When it comes to how animals adapt to climate change, many scientific questions remain unanswered.
What happens when environments become too different from those historically experienced by organisms? In particular, how does adaptation to gradual climate change enable organisms to cope with extreme weather events such as heat waves? How will differences in responses among species affect their interactions (for example, between prey and predators or among cooperating species)?
Caterpillars are developing earlier and earlier in response to climate change, but is there a limit for chickadees—a date before which it is physiologically impossible for them to begin breeding, preventing synchronization with their prey? How do global changes affect the reliability of the information organisms need to respond to their environment?
For example, when they hatch, sea turtle hatchlings often head toward cities rather than the sea, since urban lights are brighter than the moonlight. Could this kind of misinterpretation limit or even negate the benefits of plasticity?
Finally, will organisms be able to cope with multiple environmental changes thanks to phenotypic plasticity? In addition to climate change (changes in temperature and precipitation), organisms are indeed facing a wide range of disturbances—new pathogens and predators, the presence of pesticides, urban expansion, and so on.
Our research project, “Mommy Knows Best,” aims to assess whether the limits of plasticity are already detectable in natural populations, using the blue tit as our study model. We will test the effect of various environmental factors on the plasticity of the breeding date in chickadees (such as the effects of urbanization or agricultural practices, for example) and model the effects of plasticity on chickadee population dynamics, in order to understand the extent to which changes in plasticity can affect the risk of population extinction.
The findings of this project may also provide conceptual insights into the process of phenotypic plasticity in the context of climate change and be applied to other wild species.
Understanding the limits of adaptation in the face of global changes will give us a better grasp of the scale of the challenge currently facing biodiversity… But there’s no need to wait to fight against its ongoing destruction!
The “Mommy Knows Best” research project, of which this publication is a part, received support from the BNP Paribas Foundation as part of the Climate and Biodiversity Initiative.
Céline Teplitsky, Researcher in evolutionary ecology, CNRS, University of Montpellier; Anne Charmantier, Research Director in Evolutionary Ecology, National Center for Scientific Research (CNRS) and Suzanne Bonamour, Postdoctoral Researcher, National Museum of Natural History, Sorbonne University
This article is republished from The Conversation under a Creative Commons license. Readthe original article.