Diversity and abundance of human‐pathogenic fungi associated with pigeon faeces in urban environments

Pathogenic fungi are a growing health concern worldwide, particularly in large, densely populated cities. The dramatic upsurge of pigeon populations in cities has been implicated in the increased incidence of invasive fungal infections. In this study, we used a culture‐independent, high‐throughput sequencing approach to describe the diversity of clinically relevant fungi (CRF) associated with pigeon faeces and map the relative abundance of CRF across Seoul, Korea. In addition, we tested whether certain geographical, sociological and meteorological factors were significantly associated with the diversity and relative abundance of CRF. Finally, we compared the CRF diversity of fresh and old pigeon faeces to identify the source of the fungi and the role of pigeons in dispersal. Our results demonstrated that both the composition and relative abundance of CRF are unevenly distributed across Seoul. The green area ratio and the number of multiplex houses were positively correlated with species diversity, whereas wind speed and number of households were negatively correlated. The number of workers and green area ratio were positively correlated with the relative abundance of CRF, whereas wind speed was negatively correlated. Because many CRF were absent in fresh faeces, we inferred that most species cannot survive the gastrointestinal tract of pigeons and instead are likely transmitted through soil or air and use pigeon faeces as a substrate for proliferation.     

Divergence thresholds and divergent biodiversity estimates: can metabarcoding reliably describe zooplankton communities?

DNA metabarcoding is a promising method for describing communities and estimating biodiversity. This approach uses high‐throughput sequencing of targeted markers to identify species in a complex sample. By convention, sequences are clustered at a predefined sequence divergence threshold (often 3%) into operational taxonomic units (OTUs) that serve as a proxy for species. However, variable levels of interspecific marker variation across taxonomic groups make clustering sequences from a phylogenetically diverse dataset into OTUs at a uniform threshold problematic. In this study, we use mock zooplankton communities to evaluate the accuracy of species richness estimates when following conventional protocols to cluster hypervariable sequences of the V4 region of the small subunit ribosomal RNA gene (18S) into OTUs. By including individually tagged single specimens and “populations” of various species in our communities, we examine the impact of intra‐ and interspecific diversity on OTU clustering. Communities consisting of single individuals per species generated a correspondence of 59–84% between OTU number and species richness at a 3% divergence threshold. However, when multiple individuals per species were included, the correspondence between OTU number and species richness dropped to 31–63%. Our results suggest that intraspecific variation in this marker can often exceed 3%, such that a single species does not always correspond to one OTU. We advocate the need to apply group‐specific divergence thresholds when analyzing complex and taxonomically diverse communities, but also encourage the development of additional filtering steps that allow identification of artifactual rRNA gene sequences or pseudogenes that may generate spurious OTUs.     

Do Female Western Mosquitofish,Gambusia affinis,Prefer Ornaments That Males Lack?

Some species in the family Poeciliidae are known for extravagant male ornaments and courtship behavior (e.g., guppies), but the majority of poeciliids are characterized by coercive male copulation attempts that seem to circumvent female choice. In some lineages with male ornaments, female sensory bias may have preceded the evolution of corresponding male signals. We examined female preferences for colorful ornaments in Western mosquitofish, Gambusia affinis, in which males lack ornamentation and reproduce primarily through coercive mating attempts. We found that females exhibited a positional affinity for males that were artificially ornamented with blue coloration over males that had been treated with a transparent ornament. Females exhibited the opposite effect for males treated with red ornaments. In contrast, focal females did not exhibit behavioral discrimination between two live stimulus females or two models (silver fishing lures) with blue vs. transparent ornaments. This suggests a sexual context for female discrimination between males based on ornament color and whether an ornament was present. Because tribe Gambusiini is the basal branch of family Poeciliidae, the results of this study are consistent with the hypothesis that female responsiveness to male coloration is the ancestral poeciliid character state.