Although DNA metabarcoding of pollen mixtures has been increasingly used in the field of pollination biology, methodological and interpretation issues arise due to its high sensitivity. Filtering or maintaining false positives, contaminants, and rare taxa or molecular features could lead to different ecological results. Here, we reviewed how this choice has been addressed in 43 studies featuring pollen DNA metabarcoding, which highlighted a very high heterogeneity of filtering methods. We assessed how these strategies shaped pollen assemblage composition, species richness, and interaction networks. To do so, we compared four processing methods: unfiltering, filtering with a proportional 1% of sample reads, a fixed threshold of 100 reads, and the ROC approach (Receiver Operator Characteristic). The results indicated that filtering impacted species composition and reduced species richness, with ROC emerging as a conservative approach. Moreover, in contrast to unfiltered networks, filtering decreased network Connectance and Entropy, and it increased Modularity and Connectivity, indicating that using cut-off thresholds better describes interactions. Overall, unfiltering might compromise reliable ecological interpretations, unless a study targets rare species. We discuss the suitability of each filtering type,plead for justifying filtering strategies on biological or methodological bases and for developing shared approaches to make future studies more comparable.
Land-use change, including urbanization, is known to affect wild bee (Hymenoptera: Apoidea) diversity. However, while previous studies have focused on differences across local urbanization gradients, to the best of our knowledge, none focused on differences among cities at a wide geographical scale. We here used published data for wild bee communities in 55 cities across the globe, in order to explore how city traits (population density, city size, climate and land-use parameters) affect both taxonomic (diversity, distinctness, dominance) and functional (body size, nesting strategy, sociality, plant host specialization) profile of urban bee communities. By controlling for sample size and sampling effort, we found that bigger cities host few parasitic and oligolectic species, along with more above-ground-nesting bees. Cities with highly fragmented green areas present a lower proportion of oligolectic species and a higher proportion of both social species and large-bodied bees. Cities with more impervious surfaces seem to host a lower proportion of below-ground-nesting bees. Hotter cities present both a lower richness and diversity, with functional diversity highest at intermediate precipitation values. Overall, it seems that high levels of urbanization—through habitat modification and the “heat island” effect—lead to a strong simplification of the functional diversity of wild bee communities in cities. Our results may help explain the previously observed variable response of some bee community traits across local urbanization gradients.
The first register of Biomphalaria straminea, vector species of schistosomiasis, in Santa Catarina State, South Brazil is described. The specimens were obtained from two ornamental aquaria of private residences. In both cases the ornamental plants and/or fishes were bought from the same supplier. The presence of this species was later confirmed in the farm where these plants and fishes are cultivated, in the city of Governador Celso Ramos, also in Santa Catarina State. The occurrence in natural environments was later detected in two different places of the Island of Santa Catarina.
1. Bees provide important ecosystem services and are subjects of extensive studies on their α-diversity, which is generally calculated with indices that integrate the number of species with their abundances. Variation in social behaviour, though expected to impact genetic diversity, is still largely neglected in such studies.2. We propose a simple method to show how sociality may affect diversity indices, when a surrogate of genetic diversity is taken into account. This method weighs the number of sampled females (N) to obtain new abundance values (N W ), by taking into account relevant biological traits affecting genetic structure of populations, that is, the number of (natal) nests from which the sampled females originated (which depends on brood productivity and sex ratio) and the genetic relatedness among such females.3. Solitary species tend to have greater N W than eusocial ones especially at larger sample sizes. Across studies on 121 bee communities, we found that Taxonomic distinctness, Shannon-Wiener diversity and Gini-Simpson dominance tended to be greater when based on N W rather than on N. Such differences increased in communities with decreasing number of eusocial species and with increasing proportion of individuals from eusocial species.4. The results suggest that taking into account the social organisation of wild bees may have important consequences in estimating α-diversity, thus claiming for future efforts in collecting biological data on as many wild bee species as possible to improve the precision of N W estimations. For example, stressors affecting more solitary bees could impoverish communities dominated by few but abundant eusocial species, more than expected by using unweighted abundances.
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