Here we review how evolving species concepts have been applied to understand yeast diversity. Initially, a phenotypic species concept was utilized taking into consideration morphological aspects of colonies and cells, and growth profiles. Later the biological species concept was added, which applied data from mating experiments. Biophysical measurements of DNA similarity between isolates were an early measure that became more broadly applied with the advent of sequencing technology, leading to a sequence-based species concept using comparisons of parts of the ribosomal DNA. At present phylogenetic species concepts that employ sequence data of rDNA and other genes are universally applied in fungal taxonomy, including yeasts, because various studies revealed a relatively good correlation between the biological species concept and sequence divergence. The application of genome information is becoming increasingly common, and we strongly recommend the use of complete, rather than draft genomes to improve our understanding of species and their genome and genetic dynamics. Complete genomes allow in-depth comparisons on the evolvability of genomes and, consequently, of the species to which they belong. Hybridization seems a relatively common phenomenon and has been observed in all major fungal lineages that contain yeasts. Note that hybrids may greatly differ in their post-hybridization development. Future in-depth studies, initially using some model species or complexes may shift the traditional species concept as isolated clusters of genetically compatible isolates to a cohesive speciation network in which such clusters are interconnected by genetic processes, such as hybridization.

The purpose of this review is to introduce Metschnikowia to the yeast researcher community and to convince readers that the genus is a worthwhile object of study in developmental biology, genetics, ecology and biotechnology. Metschnikowia sits at the foundation of modern immunology, having been instrumental in the discovery of animal phagocytosis. Some 81 species form a monophyletic group within the Metschnikowiaceae, which also include the smaller genus Clavispora and a few clades of Candida species. The family stands out by the habit of forming, by meiosis, only two ascospores, which in Metschnikowia are needle shaped. In some cases, the spores can reach enormous proportions, exceeding 200 µm in length; in others, ascus formation is preceded by the development of chlamydospores. The adaptive value of such features remains to be elucidated. Extensive genetic studies are lacking, but attempts to apply methods developed for model species have been successful. Some species are found at the plant–insect interface whereas others are pathogens of aquatic animals and have served as model organisms in the exploration of host‐parasite theory. Some species are globally distributed and others exhibit extreme endemism. Many species are remarkably easy to recover by sampling their known habitats. M. pulcherrima and close relatives may play an important role in wine quality and produce pulcherrimin, an iron‐dipeptide complex that can interfere with the growth of other microorganisms. Some symbiotic species incapable of growth in culture media have been assigned to the genus, but their kinship with the group remains to be demonstrated. Copyright © 2016 John Wiley & Sons, Ltd.

Floral nectar harbours a diverse microbiome of yeasts and bacteria that depend predominantly on animal visitors for their dispersal. Since pollinators visit specific sets of flowers and carry their own unique microbiota, we hypothesize that plant species visited by the same set of pollinators may support non‐random nectar microbial communities linked together by the type of pollinator. Here we explore the importance of plant–pollinator interactions in the assembly of nectar microbiome and study the role of plant geographic location as a determinant of microbial community composition. We intensively sampled the nectar of 282 flowers of 48 plant species with beetles, birds, long‐tongued and short‐tongued insects as pollinators in wild populations in South Africa, one of the world's biodiversity hotspots, and using molecular techniques we identified nectar yeast and bacteria taxa. The analyses provided new insights into the richness, geographic structure and phylogenetic characterization of nectar microbiome, and compared patterns of composition of bacteria and yeast communities in relation to plant and pollinator guild. Our results showed that plant–pollinator interactions played a crucial role in shaping nectar microbial communities. Plants visited by different pollinator guilds supported significantly different yeast and bacterial communities. The pollinator guild also contributed to the maintenance of beta diversity and phylogenetic microbial segregation. The results revealed different patterns for yeast and bacteria; whereas plants visited by beetles supported the highest richness and phylogenetic diversity of yeasts, bacteria communities were significantly more diverse in plants visited by other insect groups. We found no clear microbial spatial segregation at different geographical scales for bacteria, and only the phylogenetic similarity of yeast composition was correlated significantly with geography. Synthesis. Interactions of animal vector, plant host traits and microbe physiology contribute to microbial community assemblages in nectar. Our results suggest that plants visited by the same pollinator guild have a characteristic nectar microbiota signature that may transcends the geographic region they are in. Contrasted patterns for yeast and bacteria stress the need for future work aimed at better understanding the causes and consequences of the importance of plants and pollinators in shaping nectar microbial communities in nature.

Three heterothallic, haplontic yeast species,Metschnikowia hamakuensis,Metschnikowia kamakouanaandMetschnikowia mauinuiana, are described from isolates associated with endemic nitidulid beetles living on various endemic plants on three Hawaiian islands. As morphospecies, they are similar toMetschnikowia hawaiiensis, but based on mating compatibility and ascospore formation, they can be assigned clearly to distinct biological species. Analysis of ITS/5·8S and D1/D2 large subunit rDNA sequences shows that, withM. hawaiiensisand two other isolates, these species form a distinct subclade within the large-sporedMetschnikowiaspecies, indicating that they are Hawaiian endemics. Type cultures are:M. hamakuensis, UWOPS 04-207.1^T=CBS 10056^T=NRRL Y-27834^T(type, h⁺) and UWOPS 04-204.1=CBS 10055=NRRL Y-27833 (allotype, h⁻);M. kamakouana, UWOPS 04-112.5^T=CBS 10058^T=NRRL Y-27836^T(type, h⁺) and UWOPS 04-109.1=CBS 10057=NRRL Y-27835 (allotype, h⁻); andM. mauinuiana, UWOPS 04-190.1^T=CBS 10060^T=NRRL Y-27838^T(type, h⁺) and UWOPS 04-110.4=CBS 10059=NRRL Y-27837 (allotype, h⁻).