Yeasts from temperate forests.

Yeasts are ubiquitous in temperate forests. While this broad habitat is well-defined, the yeasts inhabiting it and their life cycles, niches, and contributions to ecosystem functioning are less understood. Yeasts are present on nearly all sampled substrates in temperate forests worldwide.

Breaking a species barrier by enabling hybrid recombination.

Hybrid sterility maintains reproductive isolation between species by preventing them from exchanging genetic material. Anti-recombination can contribute to hybrid sterility when different species' chromosome sequences are too diverged to cross over efficiently during hybrid meiosis, resulting in chromosome mis-segregation and aneuploidy. The genome sequences of the yeasts Saccharomyces cerevisiae and Saccharomyces paradoxus have diverged by about 12% and their hybrids are sexually sterile: nearly all of their gametes are aneuploid and inviable.

Failure to progress.

Experiments on yeast cells that are hosts to a killer virus confirm that natural selection can sometimes reduce fitness.

Defining and Disrupting Species Boundaries in .

The genus is an evolutionary paradox. On the one hand, it is composed of at least eight clearly phylogenetically delineated species; these species are reproductively isolated from each other, and hybrids usually cannot complete their sexual life cycles. On the other hand, species have a long evolutionary history of hybridization, which has phenotypic consequences for adaptation and domestication.

A Saccharomyces paradox: chromosomes from different species are incompatible because of anti-recombination, not because of differences in number or arrangement.

Many species are able to hybridize, but the sterility of these hybrids effectively prevents gene flow between the species, reproductively isolating them and allowing them to evolve independently. Yeast hybrids formed by Saccharomyces cerevisiae and Saccharomyces paradoxus parents are viable and able to grow by mitosis, but they are sexually sterile because most of the gametes they make by meiosis are inviable. The genomes of these two species are so diverged that they cannot recombine properly during meiosis, so they fail to segregate efficiently.

Recombining Your Way Out of Trouble: The Genetic Architecture of Hybrid Fitness under Environmental Stress.

Hybridization between species can either promote or impede adaptation. But we know very little about the genetic basis of hybrid fitness, especially in nondomesticated organisms, and when populations are facing environmental stress. We made genetically variable F2 hybrid populations from two divergent Saccharomyces yeast species.

Spore-autonomous fluorescent protein expression identifies meiotic chromosome mis-segregation as the principal cause of hybrid sterility in yeast.

Genome-wide sequence divergence between populations can cause hybrid sterility through the action of the anti-recombination system, which rejects crossover repair of double strand breaks between nonidentical sequences. Because crossovers are necessary to ensure proper segregation of homologous chromosomes during meiosis, the reduced recombination rate in hybrids can result in high levels of nondisjunction and therefore low gamete viability. Hybrid sterility in interspecific crosses of Saccharomyces yeasts is known to be associated with such segregation errors, but estimates of the importance of nondisjunction to postzygotic reproductive isolation have been hampered by difficulties in accurately measuring nondisjunction frequencies.

Modeling the contributions of chromosome segregation errors and aneuploidy to Saccharomyces hybrid sterility.

Errors in meiosis can be important postzygotic barriers between different species. In Saccharomyces hybrids, chromosomal missegregation during meiosis I produces gametes with missing or extra chromosomes. Gametes with missing chromosomes are inviable, but we do not understand how extra chromosomes (disomies) influence hybrid gamete inviability.

Diminishing Returns on Intragenic Repeat Number Expansion in the Production of Signaling Peptides.

Signaling peptides enable communication between cells, both within and between individuals, and are therefore key to the control of complex physiological and behavioral responses. Since their small sizes prevent direct transmission to secretory pathways, these peptides are often produced as part of a larger polyprotein comprising precursors for multiple related or identical peptides; the physiological and behavioral consequences of this unusual gene structure are not understood. Here, we show that the number of mature-pheromone-encoding repeats in the yeast α-mating-factor gene MFα1 varies considerably between closely related isolates of both Saccharomyces cerevisiae and its sister species Saccharomyces paradoxus.

Ribosome reinitiation can explain length-dependent translation of messenger RNA.

Models of mRNA translation usually presume that transcripts are linear; upon reaching the end of a transcript each terminating ribosome returns to the cytoplasmic pool before initiating anew on a different transcript. A consequence of linear models is that faster translation of a given mRNA is unlikely to generate more of the encoded protein, particularly at low ribosome availability. Recent evidence indicates that eukaryotic mRNAs are circularized, potentially allowing terminating ribosomes to preferentially reinitiate on the same transcript.

A systematic forest survey showing an association of Saccharomyces paradoxus with oak leaf litter.

Although we understand the genetics of the laboratory model yeast Saccharomyces cerevisiae very well, we know little about the natural ecology and environment that shaped its genome. Most isolates of Saccharomyces paradoxus, the wild relative of S. cerevisiae, come from oak trees, but it is not known whether this is because oak is their primary habitat.

Measuring microbial fitness in a field reciprocal transplant experiment.

Microbial fitness is easy to measure in the laboratory, but difficult to measure in the field. Laboratory fitness assays make use of controlled conditions and genetically modified organisms, neither of which are available in the field. Among other applications, fitness assays can help researchers detect adaptation to different habitats or locations.

Fungal diversity and ecosystem function data from wine fermentation vats and microcosms.

Grape must is the precursor to wine, and consists of grape juice and its resident microbial community. We used Illumina MiSeq® to track changes in must fungal community composition over time in winery vats and laboratory microcosms. We also measured glucose consumption and biomass in microcosms derived directly from must, and glucose consumption in artificially assembled microcosms.

Asynchronous spore germination in isogenic natural isolates of Saccharomyces paradoxus.

Spores from wild yeast isolates often show great variation in the size of colonies they produce, for largely unknown reasons. Here we measure the colonies produced from single spores from six different wild Saccharomyces paradoxus strains. We found remarkable variation in spore colony sizes, even among spores that were genetically identical.

Ecology: Tribal Warfare Maintains Microbial Diversity.

When two tribes of Myxococcus bacteria attack each other, the most numerous usually wins. Established colonies can therefore resist invaders by outnumbering them. This shows how positive frequency dependence can maintain diversity across spatially structured environments.

Experimental Evolution of Species Recognition.

Sex with another species can be disastrous, especially for organisms that mate only once, like yeast. Courtship signals, including pheromones, often differ between species and can provide a basis for distinguishing between reproductively compatible and incompatible partners. Remarkably, we show that the baker's yeast Saccharomyces cerevisiae does not reject mates engineered to produce pheromones from highly diverged species, including species that have been reproductively isolated for up to 100 million years.

Saccharomyces cerevisiae: a nomadic yeast with no niche?

Different species are usually thought to have specific adaptations, which allow them to occupy different ecological niches. But recent neutral ecology theory suggests that species diversity can simply be the result of random sampling, due to finite population sizes and limited dispersal. Neutral models predict that species are not necessarily adapted to specific niches, but are functionally equivalent across a range of habitats.

The interaction of Saccharomyces paradoxus with its natural competitors on oak bark.

The natural history of the model yeast Saccharomyces cerevisiae is poorly understood and confounded by domestication. In nature, S. cerevisiae and its undomesticated relative S.

Spore germination determines yeast inbreeding according to fitness in the local environment.

Gene combinations conferring local fitness may be destroyed by mating with individuals that are adapted to a different environment. This form of outbreeding depression provides an evolutionary incentive for self-fertilization. We show that the yeast Saccharomyces paradoxus tends to self-fertilize when it is well adapted to its local environment but tends to outcross when it is poorly adapted.

Origins of multicellular evolvability in snowflake yeast.

Complex life has arisen through a series of 'major transitions' in which collectives of formerly autonomous individuals evolve into a single, integrated organism. A key step in this process is the origin of higher-level evolvability, but little is known about how higher-level entities originate and gain the capacity to evolve as an individual. Here we report a single mutation that not only creates a new level of biological organization, but also potentiates higher-level evolvability.

Hybridization facilitates evolutionary rescue.

The resilience of populations to rapid environmental degradation is a major concern for biodiversity conservation. When environments deteriorate to lethal levels, species must evolve to adapt to the new conditions to avoid extinction. Here, we test the hypothesis that evolutionary rescue may be enabled by hybridization, because hybridization increases genetic variability.

The ecology and evolution of non-domesticated Saccharomyces species.

Yeast researchers need model systems for ecology and evolution, but the model yeast Saccharomyces cerevisiae is not ideal because its evolution has been affected by domestication. Instead, ecologists and evolutionary biologists are focusing on close relatives of S. cerevisiae, the seven species in the genus Saccharomyces.

Size and competitive mating success in the yeast .

In unicellular organisms like yeast, mating with the right partner is critical to future fitness because each individual can only mate once. Because cell size is important for viability, mating with a partner of the right size could be a significant advantage. To investigate this idea, we manipulated the size of unmated yeast cells and showed that their viability depended on environmental conditions; large cells do better on rich medium and small cells do better on poor medium.

Effects of honeybee (Apis mellifera) venom on keratinocyte migration in vitro.

Background: Since the ancient times the skin aging application of honeybee venom (BV) is practiced and persisted until nowadays. The present study evaluated the effect of the honeybee venom (BV) on keratinocyte migration in wound healing model in vitro.

Objective: To access BV further as a cosmetic ingredient and a potential external application for topical uses, we performed studies to investigate the biologic effect of BV treatment on keratinocyte proliferation and migration in vitro.