GENOME DUPLICATION AND REPRODUCTIVE COMPLEXITY IN VASCULAR PLANTS

Whole genome duplication (WGD) events are common in plants and have been linked to shifts in diversification rate and the origin of phenotypic novelties, particularly in angiosperms, which are the most taxonomically and morphologically diverse land plant clade. The exact causal relationships, if any, between WGD, diversification, and morphological evolution remain debated, however. Here I explore the relationship between morphological complexity and WGD across vascular plants, using a previously published complexity metric based on the number of part types present in reproductive structures. I analyzed relationships among two genomic features gathered from published sources, genome size and the inferred number of WGD events in the history of a lineage, and several major reproductive and life history traits including pollination biology and herbaceous versus woody growth habit. Phylogenetic regressions of these data suggest no significant relationship between reproductive complexity and WGD across vascular plants generally or within major subclades (monilophytes, seed plants, angiosperms). Higher complexity is associated with basic differences in reproductive biology, however; greater complexity occurs in seed-producing structures relative to spore or pollen-producing structures, in taxa with biotic pollination syndromes, and is an intrinsic feature of angiosperms. Within angiosperms, there is no significant association between floral complexity as measured here and the number of inferred WGDs, although there is a slight positive association between complexity and herbaceous growth habit. Although it is tempting to link the high reproductive complexity of angiosperms to their numerous WGDs, a broad perspective suggests the group is simply different from other vascular plants in many ways, including in their genomes. This uniqueness makes it difficult to tease apart causal relationships among characteristic angiosperm genomic features such as small genome size and numerous WGDs and their distinctive reproductive complexity and diversity.