Plant kleptomaniacs: geographic genetic patterns in the amphi-apomictic Rubus ser. Glandulosi (Rosaceae) reveal complex reticulate evolution of Eurasian brambles.

Abstract

Rubus ser. Glandulosi represents a unique model of geographic parthenogenesis on a homoploid (2n = 4x) level. We aim to characterize evolutionary and phylogeographic patterns in this taxon and shed light on the geographic differentiation of apomicts and sexuals. Ultimately, we aim to evaluate the importance of phylogeography in the formation of geographic parthenogenesis. R. ser. Glandulosi was sampled across its Eurasian range together with other co-occurring Rubus taxa (587 individuals in total). Double digest restriction-site associated DNA sequencing (ddRADseq) and modelling of suitable climate were employed for evolutionary inferences. Six ancestral species were identified that contributed to the contemporary gene pool of R. ser. Glandulosi. While sexuals were introgressed from R. dolichocarpus and R. moschus in West Asia and from R. ulmifolius agg., R. canescens and R. incanescens in Europe, apomicts were characterized by alleles of R. subsect. Rubus. Gene flow between sexuals and apomicts was also detected, as well as occasional hybridization with other taxa. We hypothesize that sexuals survived the last glacial period in several large southern refugia, whereas apomicts were mostly restricted to southern France from whence they quickly recolonized Central and Western Europe. The secondary contact of sexuals and apomicts was probably the principal factor that established geographic parthenogenesis in R. ser. Glandulosi. Sexual populations are not impoverished in genetic diversity along their borderline with apomicts and maladaptive population genetic processes likely did not shape the geographic patterns.