Adenosine-to-inosine (A-to-I) RNA editing, capable of protein recoding, has evolved independently in animals and fungi. This study proposes adaptive hypotheses regarding its origins and phenotypic significance, suggesting that A-to-I editing enhances adaptability by alleviating genetic trade-offs. In metazoans, its emergence may have been driven by a development-defense trade-off associated with transposable element activation during the evolution of multicellularity. Late Devonian cooling and End-Permian warming are hypothesized to have driven the emergence of extensive A-to-I recoding in coleoid nervous systems and Sordariomycete sexual fruiting bodies, respectively. These adaptations may have influenced key evolutionary innovations, including the evolution of metazoan nervous systems, coleoid intelligence, and shell loss, and fungal sexual reproductive structures. Additionally, extensive A-to-I recoding is proposed to facilitate accelerated development and specific life-history strategies in both animals and fungi. This paper provides new perspectives on the evolutionary forces shaping A-to-I RNA editing and its role in phenotypic diversity across taxa.

Abstract Simple multicellularity evolves readily in diverse unicellular species, but nascent multicellular groups are prone to reversion to unicellularity. Successful transitions to multicellularity therefore require subsequent mutations that promote the entrenchment of the higher-level unit, stabilizing it through time. Here we explore the causes of entrenchment using digital evolution. When faced with a trade-off between cellular metabolic productivity and information fidelity, digital “multicells” often evolve reproductive division of labor. Because digital “unicells” cannot circumvent this trade-off, unicellular revertants tend to exhibit low fitness relative to their differentiated multicellular ancestors. Thus, division of labor can drive the entrenchment of multicellularity. More generally, division of labor may play a crucial role in major transitions, enriching the complexity and functionality of higher-level units while enhancing their evolutionary stability.

Abstract The evolution of multicellularity paved the way for significant increases in biological complexity. Although multicellularity has evolved many times independently, we know relatively little about its origins. Directed evolution is a promising approach to studying early steps in this major transition, but current experimental systems have examined only a subset of the possible evolutionary routes to multicellularity. Here we consider egalitarian routes to multicellularity, in which unrelated unicellular organisms evolve to become a multicellular organism. Inspired by microbial syntrophies and lichens, we outline three such routes from a system of different species to an interdependent relationship that replicates. We compare these routes to contemporary experimental systems and consider how physical structure, the threat of invasion, division of labour and co-transmission affect their evolution. Models to Study the Evolutionary Origins of Multicellularity The evolution of multicellular organisms from unicellular ancestors is one of the major transitions of evolution (Maynard Smith & Szathmáry 1995).

A crucial step in several major evolutionary transitions is the division of labor between components of the emerging higher-level evolutionary unit. Examples include the separation of germ and soma in simple multicellular organisms, appearance of multiple cell types and organs in more complex organisms, and emergence of casts in eusocial insects. How the division of labor was achieved in the face of selfishness of lower-level units is controversial. I present a simple mathematical model describing the evolutionary emergence of the division of labor via developmental plasticity starting with a

Throughout its nearly four-billion-year history, life has undergone evolutionary transitions in which simpler subunits have become integrated to form a more complex whole. Many of these transitions opened the door to innovations that resulted in increased biodiversity and/or organismal efficiency. The evolution of multicellularity from unicellular forms represents one such transition, one that paved the way for cellular differentiation, including differentiation of male and female gametes. A useful model for studying the evolution of multicellularity and cellular differentiation is the volvoci

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. Over the next 220 days, snowflake yeast evolved to settle 44% more quickly. Throughout the experiment the clusters evolved faster settling by thr

At the origin of multicellularity, cells may have evolved aggregation in response to predation, for functional specialisation or to allow large-scale integration of environmental cues. These group-level properties emerged from the interactions between cells in a group, and determined the selection pressures experienced by these cells. We investigate the evolution of multicellularity with an evolutionary model where cells search for resources by chemotaxis in a shallow, noisy gradient. Cells can evolve their adhesion to others in a periodically changing environment, where a cell’s fitness solely depends on its distance from the gradient source. We show that multicellular aggregates evolve because they perform chemotaxis more efficiently than single cells. Only when the environment changes too frequently, a unicellular state evolves which relies on cell dispersal. Both strategies prevent the invasion of the other through interference competition, creating evolutionary bi-stability. Therefore, collective behaviour can be an emergent selective driver for undifferentiated multicellularity.

The evolution of complexity remains one of the most challenging topics in biology to teach effectively. We present a novel laboratory activity, modeled on a recent experimental breakthrough, in which students experimentally evolve simple multicellularity using single-celled yeast ("Saccharomyces cerevisiae"). By simply selecting for faster settling through liquid media, yeast evolve to form snowflakeshaped multicelled clusters that continue to evolve as multicellular individuals. We present core experimental and curriculum tools, including discussion topics and assessment instruments, and prov

Issues of directionality in the history of life can be framed in terms of six major evolutionary steps, or megatrajectories (cf. Maynard Smith and Szathmary 1995): (1) evolution from the origin of life to the last common ancestor of extant organisms, (2) the metabolic diversification of bacteria and archaea, (3) evolution of eukaryotic cells, (4) multicellularity, (5) the invasion of the land and (6) technological intelligence. Within each megatrajectory, overall diversification conforms to a pattern of increasing variance bounded by a right wall as well as one on the left. However, the expand

Prion proteins undergo self-sustaining conformational conversions that heritably alter their activities. Many of these proteins operate at pivotal positions in determining how genotype is translated into phenotype. But the breadth of prion influences on biology and their evolutionary significance are just beginning to be explored. We report that a prion formed by the Mot3 transcription factor, [MOT3⁺], governs the acquisition of facultative multicellularity in the budding yeast Saccharomyces cerevisiae. The traits governed by [MOT3⁺] involved both gains and losses of Mot3 regulatory activity.

The emergence of the basement membrane (BM), a specialized form of extracellular matrix, was essential in the unicellular transition to multicellularity. However, the mechanism is unknown. Goodpasture antigen– binding protein (GPBP), a BM protein, was uniquely poised to play diverse roles in this transition owing to its multiple isoforms (GPBP-1, -2, and -3) with varied intracellular and extracellular functions (ceramide trafficker and protein kinase). We sought to determine the evolutionary origin of GPBP isoforms. Our findings reveal the presence of GPBP in unicellular protists, with GPBP-2