The Evolution of Invasiveness in Garden Ants

Sylvia Cremer,Bernhard Seifert,Christian Stauffer,Klaus S Petersen,Jørgen Eilenberg,Jes S Pedersen,Florian M Steiner,Falko P Drijfhout,David R Nash,Xavier Espadaler,Birgit C Schlick-Steiner,Line V Ugelvig,Jacobus J Boomsma,Nihat Aktaç,Andreas Schulz,Heino Konrad,Graeme R Jones,Patrizia D’ettorre ,Kadri Kıran ,David Hughes

doi:10.1371/journal.pone.0003838

Abstract

It is unclear why some species become successful invaders whilst others fail, and whether invasive success depends on pre-adaptations already present in the native range or on characters evolving de-novo after introduction. Ants are among the worst invasive pests, with Lasius neglectus and its rapid spread through Europe and Asia as the most recent example of a pest ant that may become a global problem. Here, we present the first integrated study on behavior, morphology, population genetics, chemical recognition and parasite load of L. neglectus and its non-invasive sister species L. turcicus. We find that L. neglectus expresses the same supercolonial syndrome as other invasive ants, a social system that is characterized by mating without dispersal and large networks of cooperating nests rather than smaller mutually hostile colonies. We conclude that the invasive success of L. neglectus relies on a combination of parasite-release following introduction and pre-adaptations in mating system, body-size, queen number and recognition efficiency that evolved long before introduction. Our results challenge the notion that supercolonial organization is an inevitable consequence of low genetic variation for chemical recognition cues in small invasive founder populations. We infer that low variation and limited volatility in cuticular hydrocarbon profiles already existed in the native range in combination with low dispersal and a highly viscous population structure. Human transport to relatively disturbed urban areas thus became the decisive factor to induce parasite release, a well established general promoter of invasiveness in non-social animals and plants, but understudied in invasive social insects.

Highlights

Invasive species use man-made transport networks for their global dispersal and often damage native ecosystems by their high rates of population growth after introduction [1]
Fundamental questions in invasive biology are still largely unanswered: Are key invasive traits already present in the native range, and if so, are they only selected in novel ecological environments? Do invasive traits arise as mutations in small founder populations? Or do they originate later when invasive founder populations grow and adapt to their novel habitats?
Origin and Range of Lasius neglectus We sampled 18 populations assumed to be introduced and invasive across the entire currently known distribution of L. neglectus, plus 25 populations of L. turcicus in Turkey [supporting information, Fig. S1, Table S1], and found that sympatry is restricted to low altitude habitats (,400 m; Fig. 1C)

Summary

Introduction

Invasive species use man-made transport networks for their global dispersal and often damage native ecosystems by their high rates of population growth after introduction [1]. Behavior, population genetics, chemical cues and parasite loads of multiple populations of L. neglectus and L. turcicus to determine the social structure and invasive potential of both species.

Results

Conclusion