Meadow brown butterflies are losing their spots as temperatures rise

Meadow brown butterflies may lose their spots as a result of climate change, according to a study from the University of Exeter. The researchers found that females, in particular, experience a decrease in the number of spots on their wings when they develop in warmer temperatures.

“For butterflies, the critical period for determining the development of wing pattern formation is during late larval development or early pupation,” wrote the study authors. “However, most studies of butterfly eyespot variation to date come from temperature-controlled laboratory experiments and not from the field.”

Female development is evolving 

The research, conducted by scientists at the University of Exeter’s Centre for Ecology and Conservation, specifically found that female meadow browns developed differently based on the temperature of their environment. 

“Females that developed at 11°C had six spots on average, while those developing at 15°C had just three,” wrote the researchers. This correlation between temperature and spot formation suggests that as the climate warms, these butterflies could become less spotty.

Significance of the eyespots 

Professor Richard ffrench-Constant, from the Penryn Campus in Cornwall, explained the significance of these spots. 

“Meadow browns always have large ‘eyespots’ on their forewings, probably for startling predators. They also have smaller spots on their hindwings, probably useful for camouflage when the butterfly is at rest.”

“Our findings show that fewer of these hindwing spots appear when females experience higher temperatures during their pupal stage (in a chrysalis before emerging as a butterfly).”

“This suggests the butterflies adapt their camouflage based on the conditions. For example, with fewer spots they may be harder to spot on dry, brown grass that would be more common in hot weather.”

“We did not observe such a strong effect in males, possibly because their spots are important for sexual selection (attracting females),” noted Professor ffrench-Constant.

Thermal plasticity 

For years, the variation in eyespot number on the meadow brown butterfly has been a classic example of “genetic polymorphism,” as noted in the works of biologist EB Ford. 

However, this new research indicates that eyespot variation is actually due to thermal plasticity, meaning the butterflies’ ability to react to changing temperatures, rather than purely genetic factors.

Consequences of climate change

“This is a family story for me, as my father collected butterflies for EB Ford here in Cornwall,” said Professor ffrench-Constant.

“In the new study, we looked at current Cornish populations – collecting males and females from the same field every day throughout the flight season – and historical collections from Eton and Buckingham.”

Meadow browns spend about 28 days in the pupal stage, usually emerging in late spring. The researchers predict that their spots will decrease year after year as our climate warms.

Professor ffrench-Constant added: “This is an unexpected consequence of climate change. We tend to think about species moving north, rather than changing appearance.”

More about meadow brown butterflies 

The meadow brown butterfly, known scientifically as Maniola jurtina, is a common and widespread species especially prominent across Europe and extending into Asia and North Africa. This butterfly is characterized by its predominantly brown coloration. 

Habitat

In terms of habitat, meadow browns are quite adaptable and are often found in a variety of environments including meadows, woodland clearings, and grassy paths. Their versatility in habitat choice has contributed to their widespread presence across their range.

Life cycle

Their life cycle follows the typical butterfly pattern of complete metamorphosis. This includes a transformation from egg to larva (caterpillar), then to pupa (chrysalis), and finally to the adult butterfly. The larvae primarily feed on a range of grasses, which aligns with their preference for grassland habitats.

Behavior 

As adults, meadow brown butterflies feed on nectar and are commonly seen visiting various wildflowers. A notable behavior of this species is their ability to fly in less sunny and duller weather conditions, unlike many other butterfly species that are more dependent on sunshine.

Reproduction

The reproductive cycle of meadow browns involves females laying eggs individually on or near host plants. The species generally has a single generation per year, with adults typically emerging in late spring or early summer, depending on the climate of their habitat. The adult lifespan of meadow browns, like many butterflies, is relatively short, emphasizing the importance of each life stage in their overall life cycle and survival.

The study is published in the journal Ecology and Evolution.

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