Into the weeds: Matching importation history to genetic consequences and pathways in two widely used biological control agents

Abstract

The intentional introduction of exotic species through classical biological control programs provides unique opportunities to examine the consequences of population movement and ecological processes for the genetic diversity and population structure of introduced species. The weevils Neochetina bruchi and N. eichhorniae (Coleoptera: Curculionidae) have been introduced globally to control the invasive floating aquatic weed, Eichhornia crassipes , with variable outcomes. Here, we use the importation history and data from polymorphic microsatellite markers to examine the effects of introduction processes on population genetic diversity and structure. We report the first confirmation of hybridization between these species, which could have important consequences for the biological control program. For both species, there were more rare alleles in weevils from the native range than in weevils from the introduced range. N. eichhorniae also had higher allelic richness in the native range than in the introduced range. Neither the number of individuals initially introduced nor the number of introduction steps appeared to consistently affect genetic diversity. We found evidence of genetic drift, inbreeding, and admixture in several populations as well as significant population structure. Analyses estimated two populations and 11 sub‐clusters for N. bruchi and four populations and 23 sub‐clusters for N. eichhorniae , indicating divergence of populations during and after introduction. Genetic differentiation and allocation of introduced populations to source populations generally supported the documented importation history and clarified pathways in cases where multiple introductions occurred. In populations with multiple introductions, genetic admixture may have buffered against the negative effects of serial bottlenecks on genetic diversity. The genetic data combined with the introduction history from this biological control study system provide insight on the accuracy of predicting introduction pathways from genetic data and the consequences of these pathways for the genetic variation and structure of introduced species.

Effects of contemporary shifts of range margins on patterns of genetic structure and mating system in two coastal plant species

“…These studies often involved surveys of historical range shifts since the ice retreat of last glacial maximum or rapidly expanding invasive species (e.g. Hewitt, 2000;Hampe and Petit, 2005;Colautti et al, 2010;Leys et al, 2014;Hopper et al, 2019). Nonetheless, ongoing humandriven environmental changes trigger current geographical expansion or retraction of species' geographical ranges and local adaptation to changing conditions through the evolution of key life-history traits related to dispersal and reproductive traits (Jump and Peñuelas, 2005;Colautti et al, 2010;e.g.…”

The pattern of genetic diversity of different breeds of pigs based on microsatellite analysis

“…One of the most commonly used indicators in population genetic studies is the standard method for estimating the F ST fixation index, described by Weir and Cockerham (1984). However, when calculating the genetic distances based on the variability of highly polymorphic markers, the values of the indicator may be shifted (Meirmans, Hedrick, 2011;Hopper et al, 2018). Therefore, we additionally performed calculations of the D index proposed by Jost (2008) that takes into account the proportion of allelic variations in populations (Table 3).…”

Climate Mismatch between Introduced Biological Control Agents and Their Invasive Host Plants: Improving Biological Control of Tropical Weeds in Temperate Regions

“…In New Zealand, genetic bottlenecks upon importation of the heather beetle (Lochmaea suturalis (Thomson) (Coleoptera: Chrysomelidae)) are thought to have led to poor establishment and overwintering survival in introduced populations [47]. In contrast, Neochetina eichhorniae Warner (Coleoptera: Brachyceridae) was imported into Australia from the USA where, subsequently, populations were found to be more cold tolerant [10] and less genetically diverse [48] than several USA populations. To reduce the importance of founder effects and reduced genetic diversity in introduced agent populations, multiple introductions from various source areas could be accomplished [48], although this may increase the regulatory burden for scientists if safety assessments are required for all unique source populations (see Section 7).…”

“…In contrast, Neochetina eichhorniae Warner (Coleoptera: Brachyceridae) was imported into Australia from the USA where, subsequently, populations were found to be more cold tolerant [10] and less genetically diverse [48] than several USA populations. To reduce the importance of founder effects and reduced genetic diversity in introduced agent populations, multiple introductions from various source areas could be accomplished [48], although this may increase the regulatory burden for scientists if safety assessments are required for all unique source populations (see Section 7). Additionally, because different source areas may have unique host plant genotypes, an understanding of how agents will perform on genotypes present in the introduced range is important and can also be determined pre-release.…”