Disparity between morphology and genetics in Urtica dioica (Urticaceae)

Polyploidization is generally considered a major evolutionary force that can alter the genetic diversity, morphology, physiology and ecology of plants. One striking example is the polyploid Urtica dioica complex, in which diploid taxa are often found in remote and partly relictual geographical ranges, in contrast to tetraploid individuals, which have an unknown evolutionary history and occur in a variety of synanthropic habitats. We used a set of 279 plants, evenly representing the geographical and morphological variation of U dioica al. in Europe and Southwest Asia, and employed multivariate and geometric morphometrics and Hyb-Seq sequencing to estimate the extent of differentiation of diploid taxa and the ubiquitous tetraploid cytotype. Diploid subspecies form more-or-less separate clusters in morphological analyses, but our molecular evaluation did not reveal any structure. Moreover, tetraploids coalesced with diploids in both morphological and molecular analyses. This disparity between morphological and molecular data might be driven by (1) local adaptation of the diploid cytotype that is mirrored in specific phenotypes, (2) only recent genetic diversification of the group and (3) homoploid and heteroploid hybridization events.

Automated summary

This study used multivariate and geometric morphometrics as well as Hyb-Seq sequencing to study the diploid taxa and tetraploid cytotype of U dioica al. plants. The results showed that diploid subspecies form distinct clusters in morphological analyses, but there was no structure revealed in molecular evaluation, and tetraploids coalesced with diploids in both morphological and molecular analyses.