Abstract
The leaf-miner moth Cameraria ohridella, a pest in Central Europe, causes severe damage to trees. Host-associated differentiation (HAD) for this species has been suggested previously based on the occurrence of a specific mitochondrial haplotype. We assessed genetic diversity and population structure for sympatrically occurring individuals collected in association with two host species, Ohio buckeye (Aesculus glabra) and horse chestnut (Ae. hippocastanum), using six microsatellite loci (SSR) and mtDNA sequences that encode parts of cytochrome oxidase I and II. To infer population structure and assign individuals to clusters, we employed Bayesian clustering. We further characterized the relationships between genetic distance and geographical distance (IBD) in analyzed samples. Although our results derived from the SSR loci analyses demonstrating that there was no population substructuring caused by the hosts, we found evidence of differences in wing size, which might be attributed to the quality of food resources available to larvae. The population structure with K = 2 cannot be interpreted as the result of IBD; rather, it reflects a population differentiation due to demographic or genetic processes (e.g., an origin of invaders). Although genetic diversity was relatively high (He> 0.5), the population had a deficiency of heterozygotes (FIS > 0), which was most likely due to nonrandom mating and, possibly, a Wahlund effect. A star-like haplotype network and negative Tajima’s D support the genetic effect of bottleneck followed by population expansion. Based on presumably neutral markers, we conclude that C. ohridella appeared to be a good model for studying evolution toward a generalist invasive species, rather than HAD.
Highlights
There is growing evidence that plant-feeding insects frequently diversify in sympatry as a result of host shifts referred to as “any gain of a novel host plant taxon by phytophagous insect population” (Vertacnik and Linnen 2017, p. 186; see Rice 1987; Via 1999; Craig et al 2001)
In order to get an overview of the genetic diversity and population structure of C. ohridella occurring on Ae. hippocastanum and Ae. glabra, we evaluated 72 accessions collected from one site using six SSR markers (Mena et al 2008)
Based on our data, we could carefully conclude that C. ohridella appeared to be a good model for studying evolution toward a generalist invasive species, rather than host-specific associations
Summary
There is growing evidence that plant-feeding insects frequently diversify in sympatry (i.e., within dispersal radius of the insects) as a result of host shifts referred to as “any gain of a novel host plant taxon by phytophagous insect population” (Vertacnik and Linnen 2017, p. 186; see Rice 1987; Via 1999; Craig et al 2001). Diversification via host or organ shifts, followed by host-associated differentiation (HAD) and race/species formation (Drès and Mallet 2002), is a dynamic and continuous process that involves some degree of genetic divergence due to differences in ecologically important traits of insects developing on the ancestral and novel host. These traits may contribute to barriers against gene flow, leading to reproductive isolation between conspecific populations, neutral genetic differentiation, and race/full species formation. HAD is probably at least partially responsible for the astonishing diversity of phytophages seen today, making this type of study a significant component in our understanding of the role of host plant species in ecological speciation (Heard 2012)
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