Insufficient sampling constrains our characterization of plant microbiomes

Plants host diverse microbial communities, but there is little consensus on how we sample these communities, and this has unknown consequences. Using root and leaf tissue from showy milkweed (Asclepias speciosa), we compared two common sampling strategies: (1) homogenizing after subsampling (30 mg), and (2) homogenizing bulk tissue before subsampling (30 mg). We targeted bacteria, arbuscular mycorrhizal (AM) fungi and non-AM fungi in roots, and foliar fungal endophytes (FFE) in leaves. We further extracted DNA from all of the leaf tissue collected to determine the extent of undersampling of FFE, and sampled FFE twice across the season using strategy one to assess temporal dynamics. All microbial groups except AM fungi differed in composition between the two sampling strategies. Community overlap increased when rare taxa were removed, but FFE and bacterial communities still differed between strategies, with largely non-overlapping communities within individual plants. Increasing the extraction mass 10 × increased FFE richness ~ 10 ×, confirming the severe undersampling indicated in the sampling comparisons. Still, seasonal patterns in FFEs were apparent, suggesting that strong drivers are identified despite severe undersampling. Our findings highlight that current sampling practices poorly characterize many microbial groups, and increased sampling intensity is necessary for increase reproducibility and to identify subtler patterns in microbial distributions.

Asclepias speciosa (Apocynaceae, Asclepiadoideae): a rare or unrecognized alien species in Europe?

Studies on populations of Asclepiassyriaca L. in Lithuania revealed the occurrence of a new alien plant species, the North American native Asclepiasspeciosa Torr. (Apocynaceae, Asclepiadoideae), in southern parts of Lithuania – the first report of the latter species in Europe. Interestingly, a thorough analysis of herbarium specimens revealed that A.speciosa had first been collected in Lithuania in 1962, but the specimen was misidentified at the time as A.syriaca. The newly discovered population of A.speciosa occupies mesic grasslands, tall-herb fringe communities and arable field habitats. Sexual reproduction of this species was not recorded; it spreads locally by means of vegetative reproduction. We present here an exhaustive analysis of morphological characteristics and differences between A.speciosa and A.syriaca and other species of the genus, as well as a key for identification of alien Asclepias species in Europe. We predict that the effect of A.speciosa on native habitats and communities, and its economic impact, are comparable to those of the highly invasive A.syriaca. Although A.speciosa currently occurs very rarely as an alien species in Europe, its existence in other regions of Europe is highly probable.

Spectral efficiency and microstructure of the compound eyes of Synanthedon myopaeformis (Lepidoptera: Sesiidae)

The apple clearwing moth, Synanthedon myopaeformis (Borkhausen) (Lepidoptera: Sesiidae), is a day-flying species that feeds on floral nectar of many plants. In British Columbia, Canada, this invasive moth is often observed feeding on visually conspicuous showy milkweed, Asclepias speciosa Torrey (Apocynaceae). We measured the spectral efficiency of the compound eyes of S. myopaeformis in the context of their capacity to discriminate the measured spectral reflectance from inflorescences of A. speciosa, and conducted histological examination of these eyes to determine whether they possess apposition type ommatidia, as commonly observed in diurnal butterflies. Light micrographs of the compound eyes in S. myopaeformis revealed eucone apposition type ommatidia, which is consistent with the diurnal behaviour of the moth. Electroretinograms on compound eyes revealed they were particularly efficient at absorbing ultraviolet (UV) wavelengths in the 335–370 nm range and green wavelengths in the 495–560 nm range. These results support the conclusion that the compound eyes of S. myopaeformis have the capacity for dichromatic vision based on UV and green photoreceptors. However, spectral reflectance curves obtained from inflorescences and foliage of A. speciosa revealed no evidence of UV reflectance, making it less likely that colour plays a primary role in the attraction of S. myopaeformis to A. speciosa.