The effect of geographical scale of sampling on DNA barcoding.

Eight years after DNA barcoding was formally proposed on a large scale, CO1 sequences are rapidly accumulating from around the world. While studies to date have mostly targeted local or regional species assemblages, the recent launch of the global iBOL project (International Barcode of Life), highlights the need to understand the effects of geographical scale on Barcoding's goals. Sampling has been central in the debate on DNA Barcoding, but the effect of the geographical scale of sampling has not yet been thoroughly and explicitly tested with empirical data. Here, we present a CO1 data set of aquatic predaceous diving beetles of the tribe Agabini, sampled throughout Europe, and use it to investigate how the geographic scale of sampling affects 1) the estimated intraspecific variation of species, 2) the genetic distance to the most closely related heterospecific, 3) the ratio of intraspecific and interspecific variation, 4) the frequency of taxonomically recognized species found to be monophyletic, and 5) query identification performance based on 6 different species assignment methods. Intraspecific variation was significantly correlated with the geographical scale of sampling (R-square = 0.7), and more than half of the species with 10 or more sampled individuals (N = 29) showed higher intraspecific variation than 1% sequence divergence. In contrast, the distance to the closest heterospecific showed a significant decrease with increasing geographical scale of sampling. The average genetic distance dropped from > 7% for samples within 1 km, to < 3.5% for samples up to > 6000 km apart. Over a third of the species were not monophyletic, and the proportion increased through locally, nationally, regionally, and continentally restricted subsets of the data. The success of identifying queries decreased with increasing spatial scale of sampling; liberal methods declined from 100% to around 90%, whereas strict methods dropped to below 50% at continental scales. The proportion of query identifications considered uncertain (more than one species < 1% distance from query) escalated from zero at local, to 50% at continental scale. Finally, by resampling the most widely sampled species we show that even if samples are collected to maximize the geographical coverage, up to 70 individuals are required to sample 95% of intraspecific variation. The results show that the geographical scale of sampling has a critical impact on the global application of DNA barcoding. Scale-effects result from the relative importance of different processes determining the composition of regional species assemblages (dispersal and ecological assembly) and global clades (demography, speciation, and extinction). The incorporation of geographical information, where available, will be required to obtain identification rates at global scales equivalent to those in regional barcoding studies. Our result hence provides an impetus for both smarter barcoding tools and sprouting national barcoding initiatives-smaller geographical scales deliver higher accuracy.

Spatio-temporal variation in water beetle assemblages across temperate freshwater ecosystems.

Ecological communities are structured by several mechanisms, including temporal, spatial and environmental factors. However, the simultaneous effects of these factors have rarely been studied. Here, we investigated their role on water beetle assemblages sampled over a period of 18 years. Water beetles were sampled in the spring of each year in lotic and lentic water bodies from mainland region of Kalmar and Öland Island in southeastern Sweden. We assessed how past assemblage structure, environmental factors and spatial variables correlated with current assemblage structure using a variation partitioning approach. We also tested for correlates of temporal beta diversity of water beetle assemblages with multiple regressions. We found that past water beetle assemblage structure explained current water beetle assemblage structure better than the environmental and spatial correlates. We also observed that temporal beta diversity of water beetle assemblages was mainly due to species gain rather than to species loss. Finally, environmental variables (e.g., hydroperiod, habitat size and hydrology) and timespan between sampling events explained part of temporal beta diversity and contribution of species loss to total assemblage dissimilarity variation. Despite the fact that most variation remained unexplained, we found that ecological factors that have been thought to be important for water beetle richness and abundance in past studies (e.g. water body size, water permanence, shore slope, and whether the water body is lentic or lotic) were also correlated to temporal beta diversity. From a conservation point of view, our study suggest that temporal variability of assemblage structure should be included in biological monitoring because of its potential to predict current assemblage structure.