# Testing the Island Effect in a Highly Mobile Pollinator: Wing Morphological Divergence in Euglossa mixta from Continental and Insular Panama

## TL;DR

This study shows that even highly mobile orchid bees can develop subtle wing shape differences in island versus mainland environments.

## Contribution

The study demonstrates that insular isolation can lead to fine-scale morphological divergence in a highly mobile pollinator species.

## Key findings

- Wing shape differences in Euglossa mixta are more pronounced between distant islands and the mainland.
- Geometric morphometrics reveal subtle but consistent morphological structuring in insular populations.
- Results suggest that isolation can drive early morphological differentiation in highly mobile species.

## Abstract

Islands provide unique opportunities to explore how isolation affects the lives of organisms. Although orchid bees are strong fliers, which leads to the assumption that their mobility prevents significant population differences, our study examined the wing shape of the orchid bee Euglossa mixta from the Coiba archipelago islands and a nearby mainland site in Panama. By using geometric morphometrics, we identified subtle yet consistent differences in wing shape across different sites. These variations were more pronounced between the distant islands and the mainland, indicating that even highly mobile pollinators can develop fine-scale morphological differences in insular environments.

Islands provide valuable opportunities to study how isolation affects phenotypic variation. Even though orchid bees are highly mobile, their movement can still be restricted by marine barriers. In this study, we assessed whether insular isolation impacts wing shape in the orchid bee Euglossa mixta across the Coiba archipelago and a nearby mainland site in Western Panama. Our study analyzed 271 individuals using geometric morphometrics, focusing on forewing venation landmarks, and evaluated the variation using multivariate analyses of shape variation and quantifying the shape of Mahalanobis distances. Additionally, we conducted a Mantel test to explore the relationship between geographic distance and morphological divergence. Our findings reveal that wing shape variation in E. mixta is largely conserved but shows fine-scale structuring consistent with spatial patterns expected in insular systems. These results suggest that even highly mobile pollinators may experience enough isolation for subtle phenotypic shifts to occur, highlighting the sensitivity of geometric morphometrics for detecting early stages of morphological differentiation.