Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences

Abstract

The advent of simple and affordable tools for molecular identification of novel insect invaders and assessment of population diversity has changed the face of invasion biology in recent years. The widespread application of these tools has brought with it an emerging understanding that patterns in biogeography, introduction history and subsequent movement and spread of many invasive alien insects are far more complex than previously thought. We reviewed the literature and found that for a number of invasive insects, there is strong and growing evidence that multiple introductions, complex global movement, and population admixture in the invaded range are commonplace. Additionally, historical paradigms related to species and strain identities and origins of common invaders are in many cases being 1 challenged. This has major consequences for our understanding of basic biology and ecology of invasive insects and impacts quarantine, management and biocontrol programs. In addition, we found that founder effects rarely limit fitness in invasive insects and may benefit populations (by purging harmful alleles or increasing additive genetic variance). Also, while phenotypic plasticity appears important post-establishment, genetic diversity in invasive insects is often higher than expected and increases over time via multiple introductions.Further, connectivity among disjunct regions of global invasive ranges is generally far higher than expected and is often asymmetric, with some populations contributing disproportionately to global spread. We argue that the role of connectivity in driving the ecology and evolution of introduced species with multiple invasive ranges has been historically underestimated and that such species are often best understood in a global context.

Effects of Host Variability on the Spread of Invasive Forest Diseases

“…In a landscape still not completely colonized by an invasive pathogen, the connectivity may be increased by additional introductions, which also have the potential to introduce new genotypes [80,81], or by insect vectors that may actively or passively spread the pathogen over long distances. Fusarium circinatum Nirenberg and O'Donnell, the causal agent of pitch canker, is a potentially dangerous invasive pathogen in pine (Pinus sp.)…”

Identification and genetic diversity of two invasive Pissodes spp. Germar (Coleoptera: Curculionidae) in their introduced range in the southern hemisphere

“…This considerable amount of mitochondrial genetic diversity for an exotic insect is likely to have resulted either from a single introduction of a large number of individuals, or from multiple introductions over time, both of which occur with some regularity in invasive organisms (Garnas et al, 2016;Nadel et al, 2010). (Hurley et al, 2010).…”

“…Forest ecosystems are increasingly threatened by invasive insect pests whose spread has been dramatically increased through the movement of wood products and packaging materials, as well as live plant material (Aukema et al, 2011;Tobin, 2015). It has also been shown that multiple introductions frequently increase genetic diversity of many introduced insects, including forest pests (Cognato et al, 2015;Garnas et al, 2016;Nadel et al, 2010). In addition, multiple introductions may allow unintended introductions of different lineages of the same species or cryptic species, as has been shown for the woodwasp, Sirex noctilio (Boissin et al, 2012), and the eucalyptus leaf weevil, Gonipterus spp.…”

“…in South Africa might be the result of the extensive movement of wood material within the country, in addition to natural spread via flight. Given how long the weevil has been known in the country, it is possible that multiple introductions have occurred, as has been observed in a number of other invasive insects in South Africa and elsewhere (Garnas et al, 2016).…”

The interaction between diet breadth, geography and gene flow in herbivorous insects

“…The process of invasion has important evolutionary consequences for invasive populations, affecting the genetic diversity of the initial colonisers (Blows & McGuigan 2015;Colautti & Lau 2015). The genetic history of invasive insects frequently shows that the process has not occurred as a single population simply establishing in a new area (Garnas et al 2016), and multiple invasions can add to the complexity of the genetic structure of invasive populations (Blackburn et al 2011;Walther et al 2009). In such situations, there is potential for secondary contact and the subsequent admixture of genetically distinct and previously allopatric insect populations (Dlugosch et al 2015;Garnas et al 2016).…”