Evolutionary consequences of nascent multicellular life cycles.

A key step in the evolutionary transition to multicellularity is the origin of multicellular groups as biological individuals capable of adaptation. Comparative work, supported by theory, suggests clonal development should facilitate this transition, although this hypothesis has never been tested in a single model system. We evolved 20 replicate populations of otherwise isogenic clonally reproducing 'snowflake' yeast (Δ) and aggregative 'floc' yeast (pp) with daily selection for rapid growth in liquid media, which favors faster cell division, followed by selection for rapid sedimentation, which favors larger multicellular groups.

Forecasting of phenotypic and genetic outcomes of experimental evolution in Pseudomonas protegens.

Experimental evolution with microbes is often highly repeatable under identical conditions, suggesting the possibility to predict short-term evolution. However, it is not clear to what degree evolutionary forecasts can be extended to related species in non-identical environments, which would allow testing of general predictive models and fundamental biological assumptions. To develop an extended model system for evolutionary forecasting, we used previous data and models of the genotype-to-phenotype map from the wrinkly spreader system in Pseudomonas fluorescens SBW25 to make predictions of evolutionary outcomes on different biological levels for Pseudomonas protegens Pf-5.

Why have aggregative multicellular organisms stayed simple?

Multicellularity has evolved numerous times across the tree of life. One of the most fundamental distinctions among multicellular organisms is their developmental mode: whether they stay together during growth and develop clonally, or form a group through the aggregation of free-living cells. The five eukaryotic lineages to independently evolve complex multicellularity (animals, plants, red algae, brown algae, and fungi) all develop clonally.

Ecological Advantages and Evolutionary Limitations of Aggregative Multicellular Development.

All multicellular organisms develop through one of two basic routes: they either aggregate from free-living cells, creating potentially chimeric multicellular collectives, or they develop clonally via mother-daughter cellular adhesion. Although evolutionary theory makes clear predictions about trade-offs between these developmental modes, these have never been experimentally tested in otherwise genetically identical organisms. We engineered unicellular baker's yeast (Saccharomyces cerevisiae) to develop either clonally ("snowflake"; Δace2) or aggregatively ("floc"; GAL1p::FLO1) and examined their fitness in a fluctuating environment characterized by periods of growth and selection for rapid sedimentation.

Copper oxide nanoparticles promote the evolution of multicellularity in yeast.

Engineered nanomaterials are rapidly becoming an essential component of modern technology. Thousands of tons of nanomaterials are manufactured, used, and subsequently released into the environment annually. While the presence of these engineered nanomaterials in the environment has profound effects on various biological systems in the short term, little work has been done to understand their consequences over long, evolutionary timescales.

Cellular packing, mechanical stress and the evolution of multicellularity.

The evolution of multicellularity set the stage for sustained increases in organismal complexity. However, a fundamental aspect of this transition remains largely unknown: how do simple clusters of cells evolve increased size when confronted by forces capable of breaking intracellular bonds? Here we show that multicellular snowflake yeast clusters fracture due to crowding-induced mechanical stress. Over seven weeks (~291 generations) of daily selection for large size, snowflake clusters evolve to increase their radius 1.

Apoptosis in snowflake yeast: novel trait, or side effect of toxic waste?

Recent experiments evolving de novo multicellularity in yeast have found that large cluster-forming genotypes also exhibit higher rates of programmed cell death (apoptosis). This was previously interpreted as the evolution of a simple form of cellular division of labour: apoptosis results in the scission of cell-cell connections, allowing snowflake yeast to produce proportionally smaller, faster-growing propagules. Through spatial simulations, Duran-Nebreda and Solé (J.

Experimental evolution of an alternating uni- and multicellular life cycle in Chlamydomonas reinhardtii.

The transition to multicellularity enabled the evolution of large, complex organisms, but early steps in this transition remain poorly understood. Here we show that multicellular complexity, including development from a single cell, can evolve rapidly in a unicellular organism that has never had a multicellular ancestor. We subject the alga Chlamydomonas reinhardtii to conditions that favour multicellularity, resulting in the evolution of a multicellular life cycle in which clusters reproduce via motile unicellular propagules.

Tempo and mode of multicellular adaptation in experimentally evolved Saccharomyces cerevisiae.

Multicellular complexity is a central topic in biology, but the evolutionary processes underlying its origin are difficult to study and remain poorly understood. Here we use experimental evolution to investigate the tempo and mode of multicellular adaptation during a de novo evolutionary transition to multicellularity. Multicelled "snowflake" yeast evolved from a unicellular ancestor after 7 days of selection for faster settling through liquid media.