Genetic architecture of adaptation to biotic invasions in soapberry bugs

Abstract

On the Florida peninsula, the soapberry bug (Jadera haematoloma) has been able to colonize the golden rain tree, Koelreuteria elegans, since the introduction of this invasive tree only a few decades ago. The populations feeding on the new host have been rapidly differentiating from the native populations. Possibly the most dramatic differentiation is that of the beak (mouthpart) length. Derived populations showed shorter beaks more appropriate for feeding on the flattened pods of the new host. Previous studies have shown that the divergence of the beak length has a genetic basis and involves non-additive genetic effects. However, to date, the soapberry bug divergence has not been studied at the molecular level. In the current study, I 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 QTL controlling beak length and body size in J. haematoloma. Using the AFLP technique and a two-way pseudo-testcross design I produced two parental maps. The maternal map covered six linkage groups and the paternal map covered five; the expected number of chromosomes was recovered and the putative X chromosome was identified. For beak length, QTL analyses revealed one significant QTL. Three QTL were found for body size. Interestingly, the most significant body size QTL co-localized with the beak length QTL, suggesting linkage disequilibrium or pleiotropic effects of related traits. Through single marker regression analysis, nine single markers that could not be placed on the map were also found to be associated with either trait. However, I found no evidence for epistasis. Overall, my findings support an oligogenic model of genetic control on beak length and body size, and the underlying genetic architectures were complex. This study is the first to look at the molecular basis underlying adaptive traits in the soapberry bug, and contributes to understanding of the genetic changes involved in early stages of ecological divergence.