ABSTRACT
We investigated the systematic relationships within the pleurocarpous moss genus Plagiothecium, based on cladistic analyses of sequence data from one nuclear (ITS) and two plastid (trnK-psbA (matK) and rpl16 intron) DNA regions for 110 specimens of Plagiothecium and similar hypnalean mosses. Plastid and nuclear trees were mostly similar, but differed in the placement of several species of Plagiothecium, and in the relationships among other genera. The phylogenetic hypotheses based on plastid markers were well resolved; in contrast, nuclear data were insufficient to resolve some of the lowest-level relationships within the genus. In the main Plagiothecium is natural, includes more taxa than are often recognized, and is most closely related to Isopterygiopsis and Herzogiella. Nine sections are recognized within Plagiothecium, four new: Section Pseudo-Neckera to accommodate P. neckeroideum and its allies, Section Ortholimnobium for P. handelii and P. paleaceum, Section Struckia for P. argentatum and P. enerve, and Section Rectithecium for P. piliferum. The geographical distribution of the sections suggests that Plagiothecium originated in Asia. The derived, mainly autoicous sections Plagiothecium and Leptophyllum may have spread to the Southern Hemisphere through long distance dispersal. Three new species in section Leptophyllum (P. funale, P. pacificum and P. rhizolucidum) and two new taxa in section Pseudo-Neckera (P. decoratum and P. neckeroideum fo. exile) are described. A limited phylogenetic hypothesis for the superficially similar hypnalean genus Taxiphyllum, which was used as outgroup, is included. A related genus (Longiella) is described, with a single species (L. plagiothecioides). The aquarium species T. barbieri is transferred to Ectropothecium.
ABSTRACT
Plants are often attacked by pathogens and insects. Their combined impact on plant performance and fitness depends on complicated three-way interactions and the plant's ability to compensate for resource losses. Here, we evaluate the response of Barbarea vulgaris, a wild crucifer, to combined attack by an oomycete Albugo sp., a plant pathogen causing white rust, and a flea beetle, Phyllotreta nemorum. Plants from two B. vulgaris types that differ in resistance to P. nemorum were exposed to Albugo and P. nemorum alone and in combination and then monitored for pathogen infection, herbivore damage, defence compounds, nutritional quality, biomass and seed production. Albugo developed infections in the insect-resistant plants, whereas insect-susceptible plants were scarcely infected. Concentrations of Albugo DNA were higher in plants also exposed to herbivory; similarly, flea beetle larvae caused more damage on Albugo-infected plants. Concentrations of saponins and glucosinolates strongly increased when the plants were exposed to P. nemorum and when the insect-susceptible plants were exposed to Albugo, and some of these compounds increased even more in the combined treatment. The biomass of young insect-susceptible plants was lower following exposure to flea beetles, and the number of leaves of both plant types was negatively affected by combined exposure. After flowering, however, adult plants produced similar numbers of viable seeds, irrespective of treatment. Our findings support the concept that pathogens and herbivores can affect each other's performance on a host plant and that the plant reacts by inducing specific and general defences. However, plants may be able to compensate for biomass loss from single and combined attacks over time.
