Mapping unexplored genomes II: genetic architecture of species differences in the woody Sonchus alliance (Asteraceae) in the Macaronesian Islands.

Despite numerous, well-documented evolutionary histories of plant groups which underwent rapid radiation in various oceanic archipelagos, very little is known about the genetic basis of species differences and adaptive radiation. This paper represents the first such study in the Macaronesian Islands using non-model endemic plants, the woody Sonchus alliance. Here I inferred the genetic basis of species differences between two Canary Island endemics, the herbaceous perennial, shade tolerant Lactucosonchus webbii and the woody, coastal desert perennial Sonchus radicatus by quantitative trait locus (QTL) mapping using AFLP markers. A total of 23 QTL (7.3-23.8% PVE; phenotypic variance explained) for 11 morphological traits were found, one for flowering time (31% PVE), and five QTL (7-10.7% PVE) for two physiological traits (intrinsic water use efficiency and stomatal conductance). Interpreted cautiously, these results suggest that major morphological and some physiological differences between the two species are controlled by numerous genes with small to moderate effect. This implies that major morphological changes in island plants can be more complex than suggested by other studies, such as in Tetramolopium in the Hawaiian Islands. The genetic basis of arborescence on islands, one of the most spectacular convergent features of plants across different lineages and archipelagos, is also discussed.