Spatial heterogeneity in genetic diversity and composition of bacterial symbionts in a single host species population

Aims Revealing genetic diversity in a root nodulation symbiosis under field conditions is critical to understand the formation of ecological communities of organisms associated with hosts and the nitrogen cycle in natural ecosystems. However, our knowledge of the genetic diversity of bacterial mutualists on a local scale is still poor because of the assumption that the genetic diversity of mutualistic bacteria is constrained by their hosts. Methods We thoroughly investigated the genetic diversity ofFrankiain a local forest stand. We collected root nodules from 213Alnus hirsutaseedlings covering the spatial range of the continuous population, which means thatAlnusindividuals occurred in a relatively homogeneous distribution in a continuous forest. Then, a phylogenetic and diversity analysis was performed for thenifD-K IGS region, including globalFrankiasequences fromAlnushosts. Results The genetic diversity ofFrankiadetected even on a local scale measured as high as that shown by previous studies conducted on local and regional scales. Moreover, a genetic structure analysis revealed a spatially mosaic-like distribution of genetic variation inFrankiadespite the small spatial scale. Conclusions The genetic diversity and composition of bacterial mutualists are heterogeneous on a local scale. Our findings demonstrate that genetically different bacterial symbionts simultaneously interact with a single host population and interaction partnerships spatially vary. The standing variation could produce dynamic ecological and evolutionary outcomes in a heterogeneous forest ecosystem

Plant size, latitude, and phylogeny explain within-population variability in herbivory

Interactions between plants and herbivores are central in most ecosystems, but their strength is highly variable. The amount of variability within a system is thought to influence most aspects of plant-herbivore biology, from ecological stability to plant defense evolution. Our understanding of what influences variability, however, is limited by sparse data. We collected standardized surveys of herbivory for 503 plant species at 790 sites across 116° of latitude. With these data, we show that within-population variability in herbivory increases with latitude, decreases with plant size, and is phylogenetically structured. Differences in the magnitude of variability are thus central to how plant-herbivore biology varies across macroscale gradients. We argue that increased focus on interaction variability will advance understanding of patterns of life on Earth