Small-scale genotypic richness stabilizes plot biomass and increases phenotypic variance in the invasive grass Phalaris arundinacea

Aims We aim to understand how small-scale genotypic richness and gen-otypic interactions influence the biomass and potential invasiveness of the invasive grass,Phalaris arundinacea under two different dis-turbance treatments:intact plots and disturbed plots,where all the native vegetation has been removed.Specifically,we address the following questions(i)Does genotypic richness increase biomass production?(ii)Do genotypic interactions promote or reduce bio-mass production?(iii)Does the effect of genotypic richness and gen-otypic interactions differ in different disturbance treatments?Finally(iv)Is phenotypic variation greater as genotypic richness increases?Methods We conducted a 2-year common garden experiment in which we manipulated genotype richness using eight genotypes planted under both intact and disturbed conditions in a wetland in Burlington,Vermont(44°27′23″N,73°11′29″W).The experiment consisted of a randomized complete block design of three blocks,each containing 20 plots(0.5 m2)per disturbed treatment.We calculated total plot biomass and partitioned the net biodiversity effect into three com-ponents:dominance effect,trait-dependent complementarity and trait-independent complementarity.We calculated the phenotypic variance for each different genotype richness treatment under the two disturbance treatments.Important Findings Our results indicate that local genotypic richness does not increase total biomass production of the invasive grass P.arundinacea in either intact or disturbed treatments.However,genotypic interactions underlying the responses showed very different patterns in response to increasing genotypic richness.In the intact treatment,genotypic interactions resulted in the observed biomass being greater than the predicted biomass from monoculture plots(e.g.,overyielding)and this was driven by facilitation.However,facilitation was reduced as genotypic richness increased.In the disturbed treatment,genotypic interactions resulted in underyielding with observed biomass being slightly less than expected from the performance of genotypes in monocultures;however,underyielding was reduced as genotypic richness increased.Thus,in both treatments,higher genotypic rich-ness resulted in plot biomass nearing the additive biomass from indi-vidual monocultures.In general,higher genotypic richness buffered populations against interactions that would have reduced biomass and potentially spread.Phenotypic variance also had contrasting patterns in intact and disturbed treatments.In the intact treatment,phenotypic variance was low across all genotypic richness levels,while in the disturbed treatment,phenotypic variance estimates increased as genotypic richness increased.Thus,under the dis-turbed treatment,plots with higher genotypic richness had a greater potential response to selection.Therefore,limiting the introduction of new genotypes,even if existing genotypes of the invasive species are already present,should be considered a desirable management strategy to limit the invasive behavior of alien species.

Additive and additive × additive interaction make important contributions to spikelets per panicle in rice near isogenic (Oryza sativa L.) lines

Epistasis plays an important role in the genetic basis of rice yield traits. Taking interactions into account in breeding programs will help the development of high-yielding rice varieties. In this study, three sets of near isogenic lines （NILs） targeting three QTLs for spikelets per panicle （SPP）, namely qSPP1, qSPP2 and qSPP7, which share the same Zhenshan 97 genetic background, were used to produce an F 2 population in which the three QTLs segregated simultaneously. The genotypes of the individual F 2 plants at the three QTLs were replaced with three markers that are closely linked to the corresponding QTLs. These QTLs were validated in the F 2 and F 3 populations at the single marker level. qSPP7 exhibited major pleiotropic effects on SPP, plant height and heading date. Multifactor analysis of variance was performed for the F 2 population and its progeny. Additive × additive interaction between qSPP2 and qSPP7 had significant effects on SPP in both the F 2 population and its progeny. Both additive and additive × additive interactions could explain about 73% of the total SPP phenotypic variance. The SPP performance of 27 three-locus combinations was ranked and favorable combinations were rec- ommended for rice breeding in different ecosystems.

Support for the predictions of the pollinator-mediated stabilizing selection hypothesis

Aims Floral traits are frequently used in traditional plant systematics because of their assumed constancy.One potential reason for the apparent constancy of flower size is that effective pollen transfer between flowers depends on the accuracy of the physical fit between the flower and pollinator.Therefore,flowers are likely to be under stronger stabilizing selection for uniform size than vegetative plant parts.Moreover,as predicted by the pollinator-mediated stabilizing selection(PMSS)hypothesis,an accurate fit between flowers and their pollinators is likely to be more important for specialized pollination systems as found in many species with bilaterally symmetric(zygomorphic)flowers than for species with radially symmetric(actinomorphic)flowers.Methods In a comparative study of 15 zygomorphic and 13 actinomorphic species in Switzerland,we tested whether variation in flower size,among and within individuals,is smaller than variation in leaf size and whether variation in flower size is smaller in zygomorphic compared to actinomorphic species.Important findings Indeed,variation in leaf length was significantly larger than variation in flower length and width.Within-individual variation in flower and leaf sizes did not differ significantly between zygomorphic and actinomorphic species.In line with the predictions of the PMSS,among-individual variation in flower length and flower width was significantly smaller for zygomorphic species than for actinomorphic species,while the two groups did not differ in leaf length variation.This suggests that plants with zygomorphic flowers have undergone stronger selection for uniform flowers than plants with actinomorphic flowers.This supports that the relative uniformity of flowers compared to vegetative structures within species,as already observed in traditional plant systematics,is,at least in part,a consequence of the requirement for effective pollination.