# Genetic data suggest gene flow within a narrow hybrid zone between two recently separated species in the genus Parnassius (Lepidoptera: Papilionidae)

## TL;DR

Genetic analysis of Clouded Apollo butterflies reveals a narrow hybrid zone between two recently separated species, suggesting ongoing gene flow.

## Contribution

The study identifies a narrow introgression zone and clinal genetic variation between Parnassius mnemosyne and P. turatii.

## Key findings

- Genetic data indicate incomplete reproductive isolation between Parnassius mnemosyne and P. turatii.
- A narrow introgression zone of 50–100 km is identified in the mid Piave valley.
- Intermediate genetic makeup suggests clinal variation rather than F1 hybrids.

## Abstract

Length polymorphism analysis of six microsatellite loci for 540 Clouded Apollo butterflies from Italy and Switzerland revealed a clear separation between sister species Parnassius mnemosyne and P. turatii and provided updated limits for their respective ranges. Correspondence analysis and Structure clustering of a subset of 140 individuals from the Eastern Alps determined intermediate genetic makeup for three small samples collected in the mid Piave valley (northern Italy). The genotypes of the intermediate individuals are not consistent with F1 hybrids, hinting at clinal genetic variation. Our data indicate a narrow introgression zone with a shallow depth of 50–100 km in what is likely to be the only area of contact between the proposed species P. mnemosyne and P. turatii. Our findings indicate incomplete reproductive isolation between the two species, and are consistent with selection against hybrids or with a recent establishment of a secondary contact. The latter may result from slow recolonization of the Eastern Alps from glacial refugia or from very recent changes in traditional land management practices such as grazing and mowing at semi-natural grasslands.