The Butterfly Effect: How Caterpillars Handle Climate Change Stresses
Butterflies — the most adored member of the class Insecta. Loved for their beautiful variety, vibrant wing colors, and graceful flight patterns. With about 17,500 species populating planet earth, butterflies make up a sizable part of ecosystem biodiversity. However, with the onset of the effects of climate change — temperature change, drought, and seasonal plant failure — the future of these elegant creatures is in jeopardy.
We’ve heard it all before: climate change is melting the polar ice caps and endangering polar bears, igniting forest fires and wiping out miles of natural foliage, and even bleaching once-vivid swaths of coral reefs. But how will climate change affect butterfly species? Are butterflies at younger stages more susceptible to environmental change? How will that vary between different species? And why? Researchers Michael Klockmann and Klaus Fischer from the University of Greifswald in Germany sought to answer these questions in their study, “Effects of temperature and drought on early life stages in three species of butterflies: Mortality of early life stages as a key determinant of vulnerability to climate change?”
The species studied, Lycaena tityrus, Lycaena dispar, and Lycaena helle, have similar physiology and genetic backgrounds (they share the order Lepidoptera), but the similarities mostly end there. L. tityrus, also known as the “Sooty Copper” butterfly is aptly named. Its wings are the color of new pennies and black and orange flecks adorn the wings. L. dispar’s wings display a brilliant orange, starkly outlined with black and white. And L. helle has an orange, black, and violet pattern reminiscent of cheetah spots.
These species occupy vastly different geographic regions of Eurasia. L. tityrus prefers cool grasslands, L. dispar likes moist temperate grasslands, and L. helle roams in marshes in mountainous regions. In order to observe the butterflies all at once, researchers collected subjects in the wild and brought them to the lab. There, they were placed in a climate cabinet; a compact artificial ecosystem with temperatures and conditions parallel to their natural habitats.
The three most immediate effects of climate change that are currently hurting our ecosystems and economies around the world are temperature change, drought, and food scarcity. These researchers identified these same repercussions also as the main detriments to young butterfly survival. Once the lepidopterous participants were accustomed to their new home, they were put through a series of experiments to determine their reaction to climate change-related stresses.
Sorrel, an herbaceous plant with fibrous leaves, is the preferred egg-laying location of L.tityrus and the larvae’s first meal. One leaf is packed with nutrients essential for the newborn caterpillars’ survival success. Increasingly common drought conditions have left these plants thin-leaved and dry, robbing them of nutritional value and necessary structural robustness. The researchers took cuttings of each species’ host plant (sorrel, sorrel, and bistort), subjected the leaves to a simulated heat wave, and then placed the eggs and caterpillars among the wilted cuttings (and separately, non-wilted control leaves for comparison) to determine how they would fare.
In a separate test, the newly-hatched caterpillars were placed in an environment with high heat and low humidity (10%) to mimic drought conditions after living in elevated temperatures for two days.
In the end, it was hunger that got the best of the bugs. Plant desiccation was ultimately the biggest killer across all three species. This result reaffirmed a biological truth that we all know to be true: access to water and nutritious foods is vital for organism survival, especially on an earth in climatic fluctuation.
Just like human babies, the study found that butterflies are their most fragile in their early developmental stages. The trauma that they experience then has a more pronounced effect on their survival than it would after the creature has matured.
“Stress tolerance during early development might be a major determinant of vulnerability to climate change,” Klockmann and Fischer said.
As the researchers predicted, the butterfly eggs and larvae responded to climate stresses in a manner congruent to their calculated vulnerability scores. The species most vulnerable to environmental change, the colorful L. helle, died in greater numbers from the two experiments as compared to its cousins. The scientists pointed to this as the biggest takeaway: even if an organism belongs to the same order, family, or even genus, one cannot assume that a species will react identically to another member of a closely-related species.
The drawback to this truth is that a now whole new field of science — a Noah’s Ark approach — must now emerge to research, on an individual basis, how every species of animal on earth will react to the present and future threats of climate change.
In future iterations of this study, the researchers can improve on their methods by extending the time frame of the experiment to see how the butterflies would react to the same stresses in different seasons. Because each of the three favor very distinct topographies, variance in seasonal change would be an important factor to study. Another suggestion for improvement would be to collect a larger number of butterfly subjects to test from a wider geographic region within each species’ habitat. That way, scientists can determine inter-population differences in response to the tests.
So what is the future of these beautiful copper-and-tangerine-colored species? If we allow nature to take its course, the butterflies may be forced to pack their bags and migrate further north to avoid heat stress, and therefore have to face the challenges that come with acclimating to a new environment. Or, humans can intervene and manually move the butterflies to climate-controlled conservation centers where the species can live out their lives artificially.
Anthropogenic climate change is an inevitable force that, unless magically stymied in the next decade, will touch the lives of every living being on earth. Predicting how this change will occur and preparing the necessary procedures to help attenuate a dramatic shift or even a sixth mass extinction is an important field of work that needs our attention. Because even one plant wilting in one community can have a devastating effect on an entire population of a species. Some would call it a butterfly effect: the phenomenon whereby a minute localized change in a complex system can have large effects elsewhere.