Lighter-colored and smaller-winged tropical butterflies are at greater climate change risk

Interesting new research from a team of ecologists at the University of Cambridge has highlighted how the physical characteristics of tropical butterflies directly affect their resilience to rising temperatures. Namely, their wing length and color are direct indicators of their risk from climate change.

With climate change presenting an increasing threat to survival for many species, the findings could prove pivotal in identifying those most at risk.

In a world where temperature is steadily increasing due to global warming, certain butterflies find themselves at a disadvantage. The research discovered that butterflies possessing smaller or lighter-colored wings could be the unfortunate ‘losers’ in the climate change game.

One example is the Lycaenidae family. This beautiful sect of butterflies consists of over 6,000 species primarily living in the tropics.

On the other hand, the study found that butterflies with larger or darker-colored wings are likely to withstand the rising heat better. Albeit, within limits.

Even these butterflies could still face substantial declines if they were to encounter sudden heatwaves. They could also be impacted if cool microclimates, which they heavily rely on, disappeared due to deforestation.

How scientists studied tropical butterflies

To reach these conclusions, published in the Journal of Animal Ecology, the research team carried out extensive fieldwork. They joined forces with the Smithsonian Tropical Research Institute (STRI) to examine the thermal buffering and thermal tolerance strategies of tropical butterflies across various habitats in Panama.

Thermal buffering refers to a butterfly’s ability to maintain a stable body temperature amidst fluctuating air temperatures, often through adaptive behaviors like seeking shade or angling wings away from the sun.

On the other hand, thermal tolerance is a physiological mechanism, involving the production of heat shock proteins, allowing butterflies to endure extreme heat when adaptive behaviors aren’t sufficient. Butterflies need both these strategies to cope with climate change.

Recording the temperatures of 1000 tropical butterflies

Armed with handheld nets and a small thermometer-like probe, the team recorded the temperatures of over 1,000 butterflies. They compared this to the temperature of the surrounding air or the vegetation the butterfly was resting on, measuring the thermal buffering capacity of each butterfly.

Next, at STRI’s Gamboa facilities, the researchers tested the butterflies’ thermal tolerance. They captured a subset of butterflies, placing them in glass jars within a water bath and gradually increased the temperature. The temperature at which the butterflies could no longer function provided an assessment of their thermal tolerance.

What the data revealed about heat extremes

The data suggested that butterflies with larger wings tend to have better thermal buffering abilities, but lesser thermal tolerance, compared to their smaller counterparts. Further reinforcing this, another study conducted by the same research team found that butterflies with larger, longer, and narrower wings were superior at thermal buffering.

Interestingly, the study found a trade-off in these cooling strategies. Butterflies that were good at thermal buffering were not as proficient in thermal tolerance and vice versa.

Researchers believe this suggests that over the course of evolution, butterflies have developed to handle temperature changes using one strategy over the other. This is likely due to selective pressures.

Lead author Esme Ashe-Jepson, a PhD student at Cambridge’s Department of Zoology, explains, “Butterflies with physical characteristics that may help them to avoid the sun’s heat, like having large wings that enable them to fly quickly into shade, rarely experience high temperatures, and so have not evolved to cope with them. On the other hand, species which can cope with higher temperatures physiologically have experienced less selective pressure to evolve heat-avoiding behaviors.”

Adaptation will be very difficult for tropical butterflies

As Ashe-Jepson warns, with rising temperatures and escalating deforestation, butterflies relying on their surroundings to evade high temperatures might not be able to traverse between dwindling forest fragments or cope with increasingly frequent heatwaves.

The study also suggests that species with large dark wings, adept at thermal buffering, may initially remain unaffected by warming temperatures. They can continue to thermoregulate effectively using behavior and microclimates.

However, their survival could be at risk if sudden heatwaves occur. This could also happen if cool vegetation retreats.

“Butterflies, and all insects globally, are likely to be impacted by climate change,” Ashe-Jepson points out. “Adaptation to climate change is complex and can be impacted by other factors such as habitat destruction. We need to address these two global challenges together.”

Research team calls for more research

Further research is needed to explore how warming climates might affect other life stages of butterflies. For instance, how will it impact them at different life stages, such as caterpillars and eggs. Also, how will it impact other insect groups?

Senior author Greg Lamarre is from the Czech Academy of Science and Research Associate at STRI. He added, “Worldwide, most entomologists are observing drastic declines in insect biodiversity. Understanding the causes and consequences of insect decline has become an important goal in ecology, particularly in the tropics, where most of terrestrial diversity occurs.”

This research was supported by the GACR Czech Science Foundation, an ERC Starting Grant, a Smithsonian Tropical Research Institute short-term fellowship, and the Sistema Nacional de Investigación (SENACYT), Panama.

More about impact of climate change on butterflies

Climate change, characterized by global warming, erratic weather patterns, and changes in precipitation, has a profound impact on various species, including butterflies. Here are some ways in which climate change affects these delicate insects:

Shift in geographic range

As temperatures rise, butterflies that prefer cooler climates may start moving poleward or to higher altitudes to find suitable habitats. Conversely, species that thrive in warmer climates may expand their range.

This change in distribution can result in new interactions with other species (like predators, prey, or competitors). It may also influence ecosystem dynamics.

Altered lifecycles of tropical butterflies

Butterflies are ectothermic organisms. This means that their body temperature and metabolic processes are influenced by external temperatures.

Warmer conditions could speed up developmental rates, leading to earlier emergence of adults. This shift might not align with the availability of resources like food plants. It would impact their survival and reproduction.

Mismatch with food resources

Many butterflies have evolved to synchronize their lifecycle with specific host plants. If climate change causes the timing of leaf-out or flowering in these plants to shift, it could result in a phenological mismatch. This is where butterflies emerge at times when their food resources are scarce.

Increased mortality due to extreme weather events

Extreme weather events such as storms, heavy rainfall, or heatwaves, which are projected to increase due to climate change, can directly cause butterfly mortality.

Drought conditions can also reduce the availability of nectar. This is a primary food source for many adult butterflies.

Impacts on overwintering populations

Some butterfly species, like the Monarch, migrate long distances to overwinter in a more favorable climate. Changes in temperature and precipitation can influence the survival of these overwintering populations. For instance, warmer winters may cause butterflies to emerge from their overwintering state too early.

Reduced genetic diversity

As suitable habitats for butterflies shrink or become fragmented due to climate change, some populations may become isolated. This can result in inbreeding and a reduction in genetic diversity.

The outcome would make these populations more vulnerable to other threats. It would also reduce their capacity to adapt to future changes.

Thermal stress and physiology

Butterflies require certain temperatures for activities like feeding, mating, and flying. As temperatures rise beyond their optimal range, they can experience thermal stress. This can impact their physiology and behavior.

For instance, increased temperature can cause heat shock proteins to be produced. This might help them survive in the short term but could have negative impacts in the long run.

Predation and parasitism in smaller-winged butterflies

Changes in climate can also impact the relationship between butterflies and their predators or parasites. If warming conditions are more favorable for these predators or parasites, it could lead to increased rates of predation or parasitism.

Scientists are working hard to understand the complex interactions between butterflies and changing climates. They are using various tools such as ecological models, long-term monitoring, and experiments.

This research will help in developing effective conservation strategies to protect these beautiful and ecologically important creatures.