# Fitness and Morphology Support Genetic Differentiation Across Different Geographic Scales in a Native Insect Utilising Native vs. Invasive Host Plants

## TL;DR

The Australian soapberry bug shows genetic and morphological differences based on the host plants it feeds on, even with gene flow between populations.

## Contribution

This study demonstrates rapid genetic and morphological adaptation in a native insect feeding on invasive versus native host plants.

## Key findings

- Genetic differentiation was moderate between Northern Territory insects and those from New South Wales and Queensland.
- Proboscis length in insects feeding on invasive host plants shows ongoing adaptation likely due to fruit size differences.
- Hybridisation experiments showed high heritability in proboscis length and body size, and F1 hybrids outperformed controls.

## Abstract

Native species can evolve rapidly in response to utilising invasive species as novel resources. We investigated the genetic and trait differentiation of the Australian soapberry bug Leptocoris tagalicus across three biotypes: those feeding on invasive
Cardiospermum grandiflorum
in New South Wales (NSW) and Queensland (Qld), invasive
C. halicacabum
in the Northern Territory (NT), and on the native host Alectryon tomentosus (in Qld). Genetic analyses revealed moderate differentiation between NT insects and those from NSW and Qld (F
ST = 0.033). Conversely, insects from NSW and Qld had low genetic differentiation, irrespective of their host plant associations (F
ST = 0.008). Field data and data from a multi‐generation experiment indicated ongoing adaptation in proboscis length in insects feeding on the two invasive host plant species, likely in response to the sizes of their fruits. Multi‐generation hybridisation experiments demonstrated high narrow sense heritability in insect proboscis length and body size (H2 = 0.48 and 0.4, respectively). Crosses involving F1 hybrids of insect biotypes generally outperformed inter‐biotype and control crosses. Taken together, these findings support ongoing genetic differentiation among L. tagalicus biotypes across different spatial scales, even in instances of high gene flow.

Native species can rapidly evolve when utilising invasive species as novel resources. We found that the Australian soapberry bug Leptocoris tagalicus exhibits genetic differentiation and morphological adaptation across biotypes feeding on different native and invasive host plants. Hybridisation experiments revealed high heritability of key insect traits, supporting ongoing evolutionary divergence despite gene flow.