Different Geographical Distributions of Two Chemotypes of Barbarea vulgaris that Differ in Resistance to Insects and a Pathogen

Abstract

The interactions of plants with herbivores and pathogens have been suggested to drive the evolution of resistances in plants and in some cases new lineages and taxa. However, such divergence may require reproductive isolation, e.g., in allopatry. In the crucifer Barbarea vulgaris, some plants are resistant to the flea beetle Phyllotreta nemorum, due to production of specific saponins, whereas others are susceptible. Resistant and susceptible plants additionally differ in resistance to the pathogen Albugo candida, content of glucosinolates, and leaf pubescence, and they are genetically strongly divergent and partially reproductively incompatible. This suggests that at some point they were separated for a considerable length of time. Previously, the insect susceptible P-type had been described only from Denmark, Sweden, and Estonia, whereas the resistant G-type is widely distributed in Western Europe. Here, we tested whether the two plant types have divergent geographical distributions and maintain their distinct trait associations throughout their range. The insect-susceptible type was found in Russia, the Baltics, and parts of Fennoscandia, but not in Central Europe. In contrast, the insect resistant type was found from Finland and westwards. Their different trait associations were consistent within the two ranges. We therefore suggest that the two plant types diverged in allopatry at some time in the past, and evolved different resistances in response to local antagonists. The two plant types probably maintain their distinctness due to a hybridization barrier. Thus, the present distributions of the two types may be shaped by both historical processes and current differential biotic selection.

Multiple hydroxyphenethyl glucosinolate isomers and their tandem mass spectrometric distinction in a geographically structured polymorphism in the crucifer Barbarea vulgaris

“…However, two out of three tested G-type plants from a Polish population (Wroc), grown in parallel with other accessions, lacked 6 as well as 7. A slight tendency for presence of P-type genetic markers in plants from this population was observed (Christensen et al, 2014). However, this occasional lack of 6 was tentatively interpreted as a simple genetic variant in the G-type although PxG hybridization followed by recombination could theoretically lead to absence of both GSLs if two different loci control 6 and 7.…”

“…The Ptype may be identical to var. pubescens N. Busch originally described from Eastern Europe (Agerbirk et al, 2003), and this suggestion was recently supported by its main distribution indeed being Eastern Europe (Christensen et al, 2014).…”

“…Glucosinolate profiles were obtained from 26 populations from Central and Eastern Europe (Christensen et al, 2014), composed of 11 G-type populations, 14 P-type populations and one hybrid population as assigned by genetic markers. The investigated populations were intended to represent a random sampling with respect to genotype and GSL profile and represented a huge geographic area including apparent G-type and P-type distribution areas and part of their apparent meeting zone (Fig.…”

“…Comparison with the type-designation based on genetic markers (Christensen et al, 2014) showed that all genetically assigned G-type individuals were dominated by 2S except for deviant individuals from Slovenia (Ljub population) (Section 2.3) while all genetically assigned P-type individuals were dominated by 2R except for deviant individuals from the Caucasian part of Russia (Cauca population) (Section 2.4). A single population in the meeting zone between the two distribution areas was of hybrid nature according to the genetic analysis (Section 2.2).…”

“…As the deviating P-type bears no clear resemblance to other tested Barbarea species (Agerbirk et al, 2003;Toneatto et al, 2012), the second hypothesis has no experimental support yet. In contrast, the theory of past allopatric separation has been supported by a recent demonstration of different geographic distributions of the two types: based on the characteristic genetic profiles of the P and G-types, the P-type was found to be widely distributed in Eastern Europe in contrast to a more western distribution of the G-type (Christensen et al, 2014;Hauser et al, 2012). Resistance properties and metabolite analysis of most of the accessions generally agreed with the genetic assessment of plant type status based on five unlinked microsatellite markers, but GSL data of two accessions were atypical.…”