Exudation rates and δ13C signatures of tree root soluble organic carbon in a riparian forest
Genomic signals of selection predict climate-driven population declines in a migratory bird
Forest structure in space and time: Biotic and abiotic determinants of canopy complexity and their effects on net primary productivity
The structural dynamics of forest canopies involve complex interactions among the abiotic environment, stand structure, species composition and disturbance regimes. How the re-arrangement of tree canopies in space and time affects forest aboveground net primary productivity (ANPP) remains poorly understood, however. In this study, we analyzed a long-term dataset from a temperate deciduous forest in Northern Michigan, USA, to investigate two primary objectives: 1) what abiotic and biotic factors influence canopy complexity and its inter-annual variability, and 2) the direct and indirect effects that abiotic, biotic and canopy complexity variables have on ANPP. We hypothesized that inter-annual variability in canopy complexity would be lower in high complexity canopies and that temporal variability in complexity metrics would be inversely related to ANPP. We found that canopy complexity was highest in more taxonomically diverse stands with high variability in tree diameters and in stands dominated by Populus tremuloides and Populus grandidentata. Canopy complexity was lowest in stands dominated by Quercus rubra and Pinus strobus, which also had lower ANPP. Stands with a high stem density had lower inter-annual variation in canopy complexity, exhibited more height growth and an increase in canopy open space, which in turn enhanced ANPP. Our results provide novel empirical evidence linking temporal stability in canopy complexity to ANPP, and suggest that variability in canopy complexity over time, in addition to the overall mean canopy complexity, may be important when considering drivers of forest carbon uptake.
Extent of pollen-mediated gene flow and seed longevity in switchgrass (Panicum virgatum L.): Implications for biosafety procedures
New switchgrass (Panicum virgatum L.) bioenergy cultivars are being bred through genetic engineering; however, baseline information is urgently needed to establish guidelines for small-scale field trials prior to commercialization. In this study, we documented the pattern of pollen-mediated gene flow and the extent of seed longevity in field experiments. To mimic crop-to-wild, pollen-mediated gene flow, we planted wild recipient switchgrass ramets at various distances away from cultivar donor ramets at two sites in Ohio. Percent hybridization at each distance was estimated from seed set on recipient ramets, which were self-incompatible clones. The pattern of gene flow was best described by negative exponential models, and the minimum isolation distance for a 0.01% gene flow threshold was predicted to be 69 m and 109 m away from the pollen source at the two sites. To investigate seed longevity, we buried seeds of six cultivars and ten wild biotypes in Ohio and Iowa in 2011. A subset of the seeds were exhumed, germinated, and tested for dormancy over three years. Cultivars lost seed viability and dormancy significantly sooner than wild biotypes at both locations in the first year, and most biotypes lost dormancy by the second year. Cultivar seeds buried in the cooler, drier Iowa site had an overall greater longevity than those buried in Ohio. Our findings suggest that substantial amounts of pollen-mediated gene flow could occur in the immediate vicinity of switchgrass pollen sources, and current switchgrass cultivars are unlikely to persist in the seed bank for more than three years.
Evaluating the adaptive evolutionary convergence of carnivorous plant taxa through functional genomics
Combining allele frequency and tree-based approaches improves phylogeographic inference from natural history collections
M Ruffley, M L Smith, A Espíndola, B C Carstens, J Sullivan, D C Tank. 2018. Mol Ecol. doi:10.1111/mec.14491
Model selection approaches in phylogeography have allowed researchers to evaluate the support for competing demographic histories, which provides a mode of inference and a measure of uncertainty in understanding climatic and spatial influences on intraspecific diversity. Here, to rank all models in the comparison set, and determine what proportion of the total support the top-ranked model garners, we conduct model selection using two analytical approaches –allele frequency-based, implemented in fastsimcoal2, and gene tree-based, implemented in PHRAPL. We then expand this model-selection framework by including an assessment of absolute fit of the models to the data. For this, we utilize DNA isolated from existing natural history collections that span the distribution of red alder (Alnus rubra) in the Pacific Northwest of North America to generate genomic data for the evaluation of 13 demographic scenarios. The quality of DNA recovered from herbarium specimen leaf tissue was assessed for its utility and effectiveness in demographic model selection, specifically in the two approaches mentioned. We present strong support for the use of herbarium tissue in the generation of genomic DNA, albeit with the inclusion of additional quality control checks prior to library preparation and analyses with multiple approaches that incorporate various data. Analyses with allele frequency spectra and gene trees predominantly support A. rubra having experienced an ancient vicariance event with intermittent and frequent gene flow between the disjunct populations. Additionally, the data consistently fit the most frequently selected model, corroborating the model selection techniques. Finally, these results suggest that the A. rubra disjunct populations do not represent separate species.
Geographical range size and latitude predict population genetic structure in a global survey
Tara A. Pelletier, Bryan C. Carstens. 2018. Royal Society Publishing Biology Letters. January 2018 Volume 14, issue 1. DOI: 10.1098/rsbl.2017.0566
While genetic diversity within species is influenced by both geographical distance and environmental gradients, it is unclear what other factors are likely to promote population genetic structure. Using a machine learning framework and georeferenced DNA sequences from more than 8000 species, we demonstrate that geographical attributes of the species range, including total size, latitude and elevation, are the most important predictors of which species are likely to contain structured genetic variation. While latitude is well known as an important predictor of biodiversity, our work suggests that it also plays a key role in shaping diversity within species.
Revision of the world species of the genus Habroteleia Kieffer (Hymenoptera, Platygastridae, Scelioninae)