‘Curiously isolated’ butterfly found in Canada's Rocky Mountains

In the rugged landscapes of Canada’s Rocky Mountains, researchers have identified a previously unknown butterfly species hiding in plain sight. 

Long mistaken for the Half-moon Hairstreak (Satyrium semiluna), the butterflies found in the Blakiston Fan region have now been named Satyrium curiosolus, or the Curiously Isolated Hairstreak.

This discovery reveals the species’ unique evolutionary path, suggesting it has remained cut off from its closest relatives for tens of thousands of years – potentially as long as 40,000 years – slowly evolving into a distinct population both genetically and ecologically.

A completely isolated butterfly population

Zac MacDonald, co-first author of the study, is a postdoctoral researcher at UCLA’s Institute of the Environment and Sustainability. 

“Our whole-genome sequencing of S. curiosolus revealed strikingly low genetic diversity and exceptionally high levels of historical inbreeding compared to the geographically nearest S. semiluna populations in British Columbia and Montana, more than 400 km distant,” said MacDonald.

Despite its small size, the species appears to have persisted independently for millennia. “Like the Channel Island Fox, S. curiosolus may have purged some of its harmful recessive genetic variation through a long, gradual history of inbreeding, allowing it to persist as a small and completely isolated population today,” MacDonald added.

The butterfly is not only genetically distinct, but also occupies a unique prairie-grassland habitat, unlike its relatives, which typically reside in sagebrush steppe ecosystems. It has adapted to a different set of environmental conditions, relying exclusively on the silvery lupine (Lupinus argenteus) as its host plant – a species not used by S. semiluna populations in British Columbia.

A rare mutualistic partnership

In another unexpected twist, the study uncovered a mutualistic bond between S. curiosolus larvae and a specific ant species. 

“Furthermore, we recently discovered that S. curiosolus larvae have mutualistic relationships with a particular species of ant (Lasius ponderosae), which has not been observed in other S. semiluna populations,” said co-author James Glasier, an ecologist at the Wilder Institute/Calgary Zoo.

The caterpillars secrete a sugary substance known as honeydew, which the ants consume. In exchange, the ants protect the larvae from predators and parasites.

Caterpillars even retreat into ant nests when disturbed or during extreme temperatures, while adult females strategically lay eggs near the entrances of ant colonies beneath silvery lupines.

Protecting Canada’s isolated butterfly

Formally recognizing S. curiosolus as a distinct species has critical implications for conservation. Its long isolation has led to very low genetic variability, which can make adaptation to environmental shifts more difficult. 

Genetic rescue – introducing individuals from closely related populations to increase genetic diversity – is often proposed in such cases. But for S. curiosolus, this approach may not be feasible.

Due to the high degree of differentiation from S. semiluna, the risk of outbreeding depression – where introduced genes reduce fitness – is high. In fact, the species may not even be reproductively compatible with its closest relatives.

Alternative conservation strategies, such as establishing new populations in safe habitats, may be necessary to preserve this butterfly’s future.

Genomic tools advance biodiversity studies

Co-first author Julian Dupuis, an assistant professor at the University of Kentucky, noted that the discovery of S. curiosolus is a powerful demonstration of how genomics is revolutionizing taxonomy and conservation.

“While traditional taxonomic methods often rely on morphology alone, our study underscores the importance of integrating genomic and ecological data to uncover hidden diversity,” said Dupuis.

“With the rise of genomic tools, previously unrecognized species like S. curiosolus are being discovered, highlighting the need for conservation strategies that account for cryptic biodiversity.”

Tackling complex conservation challenges

This kind of research would not be possible without strong partnerships. Academic institutions, national parks, and conservation groups worked together to make the discovery possible.

“Our studies on S. curiosolus and S. semiluna highlight the importance of collaboration between academic scientists, nonprofit organizations, and conservation managers,” MacDonald said. “All of this work was made possible through partnerships between academic researchers, Parks Canada, and the Wilder Institute/Calgary Zoo.” 

“By combining expertise in genomics, field ecology, and conservation management, we were able to produce findings that not only reshape our understanding of biodiversity but also provide actionable insights for species protection.” 

MacDonald noted that moving forward, these interdisciplinary collaborations will be critical for tackling complex conservation challenges and ensuring the long-term survival of species like S. curiosolus.

Significance of the isolated butterfly

Now that the isolated butterfly Satyrium curiosolus has been officially recognized, the researchers emphasize that further study is needed. Investigating its evolutionary relationships, interactions with host plants and ant species, and responses to climate change will be essential. 

Long-term monitoring led by Parks Canada and the Wilder Institute/Calgary Zoo will help determine how the butterfly copes with ongoing environmental shifts.

“This is a wonderful example of how such monitoring can connect diverse approaches and impactful answers to a simple question like ‘that’s odd – why is it there?’” said senior author Felix Sperling, a professor at the University of Alberta and curator of the Strickland Museum of Entomology.

For now, the Curiously Isolated Hairstreak serves as a reminder of how even the smallest, most overlooked creatures can play a vital role in our understanding of biodiversity – and in shaping how we protect it for future generations.

The study is published in the journal ZooKeys.

Image Credit: MacDonald et al.

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