Colonization history of Metrioptera roeselii in northern Europe indicates human‐mediated dispersal

Abstract

Aim The bush‐cricket Metrioptera roeselii is an example of an insect which has expanded its indigenous range beyond expectations based on its natural dispersal potential. Understanding how species colonize new areas is vital for formulating effective species conservation programmes and managing invasive species. The aim of this research is to use mitochondrial sequence and microsatellite data to delineate the likely origin and dispersal pathways of M. roeselii in northern Europe. The well‐known ecology of the species and the detailed colonization data make it a very suitable model species for addressing questions relating to invasiveness. Location Fennoscandia, Baltic Sea coast, northern Europe. Methods Using a 676 bp fragment of the mitochondrial cytochrome oxidase subunit I (COI) gene and seven polymorphic microsatellite loci, we genotyped and compared populations at 28 sites within the continuous range of M. roeselii along the Baltic Sea coast, and 10 isolated populations in Denmark, islands in the Baltic Sea and the Scandinavian Peninsula. The acquired data, information on the species' ecology and historical population establishment records were used to infer the colonization history and pathways of this species. Results Both mitochondrial DNA and microsatellite data indicated that several of the isolated populations did not originate from their nearest locations within the continuous distribution area of M. roeselii. Instead, the likeliest source populations were in some cases situated > 500 km from the isolated populations. Hence the first records of appearance in the isolated sites did not coincide with the species' natural expansion but agreed well with the time of colonization of the founder sites inferred from the genetic data. Main conclusions The limited ability of M. roeselii to cross geographical barriers through active dispersal, the inferred colonization pathways from this study, and the knowledge that transport of eggs can potentially occur with agricultural products collectively suggest that at least some of the isolated populations originate from human‐mediated introductions rather than natural dispersal.

Contrasted invasion processes imprint the genetic structure of an invasive scale insect across southern Europe

“…Moreover, all the populations sampled in Corsica had the same allelic pools and were genetically not differentiated, suggesting one unique colonization event followed by a step-by-step local expansion between neighbouring host patches, as was shown for the Cedar seed wasp Megastigmus schimitscheki (AugerRozenberg et al, 2012). Similar findings of severe bottlenecks at introduction in different species suggested that successful invasions can also result from a very small number of original migrants, which is sometimes considered as a characteristic of successful invasive species (Kaň uch et al, 2013). Diverse genetic and/or ecological mechanisms may circumvent the loss of genetic variation occurring during introduction events (Lye et al, 2011; Auger-Rozenberg et al, 2012).…”

“…The colonization of the northern Mediterranean coast was a pre-requisite for a successful invasion of Corsica, South-Eastern France acting as a 'bridgehead' , that is, as a new potential source population to reach new territories (Lombaert et al, 2010). A similar situation was observed for the bush cricket Metrioptera roeselii that crossed the Baltic Sea once introduced along the coast (Kaň uch et al, 2013). Larvae may be regularly transported from the French and Italian coasts to Corsica, but the probability of settlement is rather low, because the larvae need a suitable host to survive and found an invasive population.…”

“…Passive mechanisms can involve natural currents, such as winds or water flows that can sometimes carry individuals over long distances, or human activities, when the initial migrants are for instance introduced with transported goods (Kaňuch et al, 2013). Deciphering between natural and human-aided long-distance dispersal events may be difficult, even though anthropogenic dispersal usually occurs from (and to) urbanised areas or regions with active human transport networks such as large harbours, motorways and railways (Robinet et al, 2009;Carrasco et al, 2010;Kaň uch et al, 2013). Invasive species may colonize distant patches and new environments by long-distance dispersal and/or expand into adjacent habitats by regional diffusion.…”

“…In the last decade, molecular markers have been widely used to link the invasive populations to potential sources based on genetic distances or assignment methods (for example, Ciosi et al, 2008;Estoup and Guillemaud, 2010;Kaň uch et al, 2013). The main drawback of the classical analyses performed with molecular data is that they do not take into account the demographic history and the stochasticity involved in introduction scenarios (bottleneck effects, drift, population expansions, admixture from several sources) and do not allow to formally test competing scenarios .…”

Using citizen‐reported data to predict distributions of two non‐native insect species in Sweden

“…Although studies on phytophagous shield bugs similar to G. lineatum have shown that individuals move only short distances (mainly to the next food patch) a yearly range expansion estimate of 1.07 km is not surprising because of general differences between individual dispersal rates and species expansion rates. Species expansion is the sum of the movement dynamics of geographically distributed populations where extinction and colonization events are controlled both by species' ecology and the environment, and may not be directly predictable by individual movement patterns (Berggren et al 2009, Preuss et al 2011, Kaň uch et al 2013). …”