Specificity of a Y‐linked gene in the flea beetle Phyllotreta nemorum for defences in Barbarea vulgaris

Abstract

AbstractA Y‐linked gene (R‐gene) in the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) confer the ability of larvae to survive on types of the plant Barbarea vulgaris R.Br. (Brassicaceae) which are immune to attack by susceptible conspecifics. Two near‐isogenic flea beetle lines were developed. The YE‐line contained the Y‐linked R‐gene, and male larvae from this line survived on B. vulgaris. The ST‐line did not contain the gene and did not survive on the plant. The YE‐line had been developed through 8–9 generations of backcrosses (YE‐males with ST‐females) and the two lines were considered to be isogenic except for genes located on the Y‐chromosome.A single copy of the Y‐linked gene is sufficient to transfer a susceptible genotype (ST) into a resistant genotype (YE) which is able to utilize a plant that is immune to attack by specimens without R‐genes. The Y‐linked gene had no effects on survival on other plant species tested. The gene did not have any effect on developmental times and weights of adult beetles reared on other plants than B. vulgaris. Developmental times of larvae with the Y‐linked gene were longer on B. vulgaris than on normal host plants, R. sativus and S. arvensis, but the adults obtained the same size on these plant species. No trade‐offs of the Y‐linked gene were discovered. The results suggest that the occurrence of the Y‐linked gene is a derived trait which has enabled the flea beetle to expand its host plant range. The evolution of a host shift to B. vulgaris seems not to be favoured by the presence of this single gene.