Bridgehead effect and multiple introductions shape the global invasion history of a termite

Alexander J Blumenfeld,Changlu Wang,Thomas Chouvenc,Pierre-André Eyer,Shichen Wang,Laura N L Johnson,Edward L Vargo,J Kenneth Grace,Claudia Husseneder,Jianchu Mo

doi:10.1038/s42003-021-01725-x

Abstract

Native to eastern Asia, the Formosan subterranean termite Coptotermes formosanus (Shiraki) is recognized as one of the 100 worst invasive pests in the world, with established populations in Japan, Hawaii and the southeastern United States. Despite its importance, the native source(s) of C. formosanus introductions and their invasive pathway out of Asia remain elusive. Using ~22,000 SNPs, we retraced the invasion history of this species through approximate Bayesian computation and assessed the consequences of the invasion on its genetic patterns and demography. We show a complex invasion history, where an initial introduction to Hawaii resulted from two distinct introduction events from eastern Asia and the Hong Kong region. The admixed Hawaiian population subsequently served as the source, through a bridgehead, for one introduction to the southeastern US. A separate introduction event from southcentral China subsequently occurred in Florida showing admixture with the first introduction. Overall, these findings further reinforce the pivotal role of bridgeheads in shaping species distributions in the Anthropocene and illustrate that the global distribution of C. formosanus has been shaped by multiple introductions out of China, which may have prevented and possibly reversed the loss of genetic diversity within its invasive range.

Highlights

Introduction inLouisiana/Texas (52 migrants) from the already invasive population in Hawaii through bridgehead (1k generations ago) c groupedIntroduced Native averaged Hawaii LouisianaNucleotide diversity the native and the introduced US ranges (Fig. 5b)
Substantial structure was observed among the C. formosanus populations from fastSTRUCTURE, with K = 15 best explaining the structure in the data (Fig. 1a, b; FST values between all pairs of populations are supplied in Supplementary Fig. 2)
Our findings reveal that the global distribution of C. formosanus has been shaped by multiple introductions out of eastern Asia, coupled with a bridgehead event

Summary

Introduction

Introduction inLouisiana/Texas (52 migrants) from the already invasive population in Hawaii through bridgehead (1k generations ago) c groupedIntroduced Native averaged Hawaii LouisianaNucleotide diversity the native and the introduced US ranges (Fig. 5b). Louisiana/Texas (52 migrants) from the already invasive population in Hawaii through bridgehead (1k generations ago) c grouped. Nucleotide diversity the native and the introduced US ranges (Fig. 5b). Most native populations have experienced a gradual decline in their effective population size, while Fuzhou, Hangzhou, Jieyang, and the two Japanese populations experienced a bottleneck followed by a period of rapid growth. In the US populations, Hawaii and Louisiana both underwent a gradual decline in their effective population size, while Florida experienced a bottleneck followed by a period of rapid growth (Fig. 5b), corroborating the ABC results of an additional and distinct introduction event within Florida

Objectives

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Conclusion