Changes in frequencies of genes that enable Phyllotreta nemorum to utilize its host plant, Barbarea vulgaris, vary in magnitude and direction, as much within as between seasons

Abstract

The interaction between the flea beetle, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae), and its host plants is well suited to study the dynamics of a geographic mosaic of (co)evolution. The flea beetle can either be resistant or susceptible to the defense of one of its host plants, Barbarea vulgaris R.Br. G‐type (Brassicaceae). Previous findings suggested that the frequency of resistant beetles on host plants other than the G‐type of B. vulgaris had decreased over time within the period of 1999–2003. In 2008 and 2009 new sampling was performed to investigate whether or not this decrease in frequency of resistance of the flea beetles formed a continuing trend and whether or not the frequency of resistant beetles also varies within the year. The frequency of resistant beetles on different host plants was determined during the reproductive season of the flea beetles in both years. Overall, the frequencies of resistant beetles on B. vulgaris (G‐type) remained close to 100%, as found before, but those on other host plants did not consistently decrease across the years, in contrast to what had been suggested. Furthermore, the repeated sampling revealed that the frequency of resistant beetles differed significantly within a season. The present data show that relative frequencies of different resistance phenotypes of P. nemorum on other host plants than B. vulgaris (G‐type) are highly dynamic, both within and across years. Therefore, monitoring the changes in these resistance frequencies should involve season‐wide sampling efforts. Although the monitoring in this study does not provide an explanation for the observed dynamics, we propose a testable scenario.

Comparative genetics of invasive populations of walnut aphid, Chromaphis juglandicola, and its introduced parasitoid, Trioxys pallidus, in California

“…If as expected, coevolutionary interactions are both spatially and temporally dynamic (Torres, ) and are important for biological control services (Holt & Hochberg, ; Jones et al., ; Kraaijeveld & Godfray, , ), then localized breakdowns in biological control services might be a common and transitory occurrence as predicted by the geographic mosaic theory of coevolution (Thompson, , ). While geographic mosaics have been observed for interactions between herbivores and plants (Muola et al., ; Siepielski & Benkman, ; Vermeer, Verbaarschot, & de Jong, ), predators and prey (Brodie & Ridenhour, ), and hosts and parasites (Dixon, Craig, & Itami, ; Lorenzi & Thompson, ; Thompson, ; Vergara, Lively, King, & Jokela, ), as of yet there are no known documented examples from the biological control literature. It has been proposed, however, that a geographic mosaic of coevolution may have played an important role in the establishment of invasive knapweeds ( Centaurea maculosa Lamarck and C. diffusa Lamarck) in North America (Callaway, Hierro, & Thorpe, ).…”

“…If as expected, coevolutionary interactions are both spatially and temporally dynamic (Torres, 2009) and are important for biological control services (Holt & Hochberg, 1997;Jones et al, 2014;Kraaijeveld & Godfray, 1999, then localized breakdowns in biological control services might be a common and transitory occurrence as predicted by the geographic mosaic theory of coevolution (Thompson, 1994(Thompson, , 2005. While geographic mosaics have been observed for interactions between herbivores and plants (Muola et al, 2010;Siepielski & Benkman, 2005;Vermeer, Verbaarschot, & de Jong, 2012), predators and prey (Brodie & Ridenhour, 2002), and hosts and parasites (Dixon, Craig, & Itami, 2009;Lorenzi & Thompson, 2011;Thompson, 2009b This is in part due to the fact that there have been very few longterm, postrelease studies of biological control agents and their targets (McCoy & Frank, 2010;Mills, 2000Mills, , 2017, and that it can be difficult to identify a priori which adaptive traits to measure when studying coevolutionary interactions. In this context, comparative population genomics may provide a useful approach to obtain preliminary evidence for the presence and/or potential importance of coevolution in biological control systems.…”

Adaptation of flea beetles to Brassicaceae: host plant associations and geographic distribution of Psylliodes Latreille and Phyllotreta Chevrolat (Coleoptera, Chrysomelidae)

“…Although the saponin-based defence of B.vulgaris is a dead-end for most Ph.nemorum genotypes, resistant individuals that performed well on the G-type were found at varying frequencies in all sampled populations (Nielsen and de Jong 2005; Nielsen 2012; Vermeer et al 2012). The ability to use the G-type as a host plant clearly shows that resistant individuals can tolerate or detoxify saponins by an unknown mechanism.…”

Role of Saponins in Plant Defense against the Diamondback Moth, Plutella xylostella (L.)

“…However, it showed that the presence or absence of leaf pubescence in B. vulgaris var. arcuata seemed to be correlated with many chemical and biological features (Agerbirk et al, 2001;Vermeer et al, 2012;de Jong and Nielsen, 2013), which differed significantly between the two types. It's suggested a greater taxonomic distance between the two types of B. vulgaris var.…”