Genetic structure and gene flow in French populations of two Ostrinia taxa: host races or sibling species?

Abstract

Most models of ecological speciation concern phytophagous insects in which speciation is thought to be driven by host shifts and subsequent adaptations of populations. Despite the ever-increasing number of studies, the current evolutionary status of most models remains incompletely resolved, as estimates of gene flow between taxa remain extremely rare. We studied the population genetics of two taxa of the Ostrinia genus--one feeding mainly on maize and the other on mugwort and hop--occurring in sympatry throughout France. The actual level of divergence of these taxa was unknown because the genetic structure of populations had been investigated over a limited geographical area and the magnitude of gene flow between populations had not been estimated. We used 11 microsatellite markers to investigate the genetic structure of populations throughout France and the extent of gene flow between the two Ostrinia taxa at several sites at which they are sympatric. We observed clear genetic differentiation between most populations collected on the typical respective hosts of each taxon. However, populations displaying intermediate allelic frequencies were found on hop plants in southern France. Individual assignments revealed that this result could be accounted for by the presence of both taxa on the same host. Gene flow, estimated by determining the proportion of hybrids detected, was low: probably<1% per generation, regardless of site. This indicates that the two Ostrinia taxa have reached a high level of genetic divergence and should be considered sibling species rather than host races.

A Helitron-Like Transposon Superfamily from Lepidoptera Disrupts (GAAA)n Microsatellites and is Responsible for Flanking Sequence Similarity within a Microsatellite Family

“…Microsatellites that originate at independent loci have unique flanking DNA that is used to design locus-specific genetic markers (Pemberton et al 1995) that are desirable due to high levels of allelic variation (Tautz 1989;Weber and May 1989). Polymorphic microsatellite markers from Lepidoptera have been used for linkage mapping (Miao et al 2005) and population genetic studies (Reddy et al 1999;Prasad et al 2005;Malausa et al 2007), but problems often arise during genotype analyses. PCR coamplification of fragments primed at [1 microsatellite locus often occur due to the presence of multilocus microsatellites (microsatellite families) that share nucleotide sequence similarity at genome regions that flank the tandem repeat (Zhang 2004;Meglécz et al 2004; Van't Hof et al 2007).…”

From Russia with lobe: genetic differentiation in trilobed uncus Ostrinia spp. follows food plant, not hairy legs

“…However, it is most unlikely that our samples were not polymorphic at all for male mid-tibiae, as they originate from the area between Kharkov (Ukraine), Kazan, Stavropol and Rostov-on-theDon, where populations were highly polymorphic at both loci in the 1970-1980s (Table 1, (Table 1). The latter population pair fills a gap that existed between a more 'northern' and a more 'southern' group of populations in Malausa et al (2007b). Each of the six pairs or triplets in Malausa et al (2007b) included one population from maize, and one or two populations from hop and/or mugwort.…”

“…We also collected one population on hemp in Kazakhstan (Sorbulak, B40 km north-west from Almaty, October 2008). In the FSU, we sampled larvae on hemp rather than hop-the second dicotyledon from which Ostrinia larvae had been collected in France (Malausa et al, 2007b, see below)-because it was more difficult to locate infested hop, whereas wild hemp was common and often infested by Ostrinia. Moreover, hemp was reported to be a common host plant for O. narynensis Mutuura and Monroe (syn.…”

“…Conversely, mating success is significantly reduced between individuals collected on maize versus dicotyledons (Frolov et al, 2007). In France, although all males have small mid-tibiae, trilobed uncus Ostrinia populations actually consist of two taxa that are significantly isolated reproductively Malausa et al, 2005;Pélozuelo et al, 2007) and genetically differentiated (Bourguet et al, 2000;Martel et al, 2003;Bontemps et al, 2004;Malausa et al, 2005Malausa et al, , 2007aMalausa et al, , 2007bLeniaud et al, 2006): one feeding mainly on maize and one feeding mainly on two dicotyledonsmugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.).…”

“…(2007) hypothesis by examining the genetic structure of Ostrinia sp. populations collected on maize versus dicotyledons in areas of the FSU where male mid-tibiae are polymorphic on dicotyledons, and by comparing it with that of a similar sample collected in France (Malausa et al, 2007b). If Frolov et al's.…”