Genetic Architecture of Contemporary Adaptation to Biotic Invasions: Quantitative Trait Locus Mapping of Beak Reduction in Soapberry Bugs

Biological invasions can result in new selection pressures driven by the establishment of new biotic interactions. The response of exotic and native species to selection depends critically on the genetic architecture of ecologically relevant traits. In the Florida peninsula, the soapberry bug (Jadera haematoloma) has colonized the recently introduced Chinese flametree, Koelreuteria elegans, as a host plant. Driven by feeding efficiency, the populations associated with this new host have differentiated into a new bug ecomorph characterized by short beaks more appropriate for feeding on the flattened pods of the Chinese flametree. In this study, we have generated a three-generation pedigree from crossing the long-beaked and short-beaked ecomorphs to construct a de novo linkage map and to locate putative quantitative trait locus (QTL) controlling beak length and body size in J. haematoloma. Using amplified fragment-length polymorphism markers and a two-way pseudo-testcross design, we have produced two parental maps in six linkage groups, covering the known number of chromosomes. QTL analysis revealed one significant QTL for beak length on a maternal linkage group and the corresponding paternal linkage group. Three QTL were found for body size. Through single marker regression analysis, nine single markers that could not be placed on the map were also found to be significantly associated with one or both of the two traits. Interestingly, the most significant body size QTL co-localized with the beak length QTL, suggesting linkage disequilibrium or pleiotropic effects of related traits. Our results suggest an oligogenic control of beak length.