# Novel genetic association with migratory diapause in Australian monarch butterflies

## TL;DR

Australian monarch butterflies have regained migration after centuries of non-migration, and a specific gene is linked to this trait.

## Contribution

Identifies a genetic association with migratory diapause in Australian monarch butterflies, involving the Karst protein.

## Key findings

- Reproductive diapause in Australian monarchs is strongly associated with variation in the spectrin beta chain protein Karst.
- Migratory SNPs linked to diapause are present at low frequency in North American populations.
- The Australian population likely used existing genetic variation to reacquire migration after bottlenecks.

## Abstract

Monarch butterflies (Danaus plexippus) are a charismatic and culturally important North American butterfly species famous for their unique, dramatic migratory life history. While non-migratory populations of the species are widespread and apparently stable, migratory populations in North America have recently seen declines, prompting concern that the migratory phenomenon in North America may be at risk of disappearing. In contrast, a relatively recently-established monarch population in Australia has rapidly re-acquired a migratory life history following hundreds of generations of residency and successive bottlenecks as the species island-hopped across the Pacific during the late 1800s and early 1900s. The process by which migration re-emerged in Australian monarchs is not currently known.

We raised and sequenced individuals from Queensland, Australia under environmental conditions associated with migration initiation and found strong variance in reproductive diapause, a key migratory trait, between families which was associated with variation at the spectrin beta chain protein Karst. This protein is known to be involved in diapause termination in monarchs but has not previously been identified as associated with migratory life history variance. The most strongly associated migratory SNPs are also present at a low frequency in North America, suggesting that the Australian population is leveraging standing variation which persisted across repeated bottlenecks as Monarchs spread across the Pacific.

Our results provide an intriguing example of how the temporary loss of migration—in this case likely over hundreds of generations—may not entail the loss of genetic variation associated with this complex life history strategy.

The online version contains supplementary material available at 10.1186/s12862-025-02384-w.