Altruism and social cheating in the social amoeba Dictyostelium discoideum

Testing the coordination hypothesis: incompatibilities in aggregative development of an experimentally evolved social amoeba

Multicellular organisms that form by aggregation of cells arguably do not achieve high levels of complexity. Conflict among the cells is a widely accepted explanation for this, but an alternative hypothesis is that mixing cells of different genotypes leads to failures of coordination, which we call the "coordination hypothesis." We empirically tested the coordination hypothesis in the social amoeba Dictyostelium discoideum. We mixed D. discoideum clones that had evolved in isolation for generations and acquired mutations that have not been tested against each other by selection. To quantify the effect of incompatibilities, we measured performance in terms of the developmental traits of slug migration and spore production. Importantly, we mixed lines evolved from the same ancestor under conditions that would not select for the evolution of de novo kin recognition. Our results show no evidence of incompatibilities in four traits related to the coordinated movement of slugs toward light in the social amoeba. Spore production was higher than expected in mixtures, in apparent contradiction to the coordination hypothesis. However, we found support for coordination incompatibilities in an interaction between migration and spore production: in mixtures, fewer cells succeeded at both migrating and becoming spores.

Sociobiology meets oncology: unraveling altruistic cooperation in cancer cells and its implications

Altruism, an act of benefiting others at a cost to the self, challenges our understanding of evolution. This Perspective delves into the importance of altruism in cancer cells and its implications for therapy. Against the backdrop of existing knowledge on various social organisms found in nature, we explore the mechanisms underlying the manifestation of altruism within breast tumors, revealing a complex interplay of seemingly counteracting cancer signaling pathways and processes that orchestrate the delicate balance between cost and benefit underlying altruistic cooperation. We also discuss how evolutionary game theory, coupled with contemporary molecular tools, may shed light on understudied mechanisms governing the dynamics of altruistic cooperation in cancer cells. Finally, we discuss how molecular insights gleaned from these mechanistic dissections may fuel advancements in our comprehension of altruism among cancer cells, with implications across multiple disciplines, offering innovative prospects for therapeutic strategies, molecular discoveries, and evolutionary investigations.

Adaptive evolutionary trajectories in complexity: Transitions between unicellularity and facultative differentiated multicellularity

Multicellularity spans a wide gamut in terms of complexity, from simple clonal clusters of cells to large-scale organisms composed of differentiated cells and tissues. While recent experiments have demonstrated that simple forms of multicellularity can readily evolve in response to different selective pressures, it is unknown if continued exposure to those same selective pressures will result in the evolution of increased multicellular complexity. We use mathematical models to consider the adaptive trajectories of unicellular organisms exposed to periodic bouts of abiotic stress, such as drought or antibiotics. Populations can improve survival in response to the stress by evolving multicellularity or cell differentiation-or both; however, these responses have associated costs when the stress is absent. We define a parameter space of fitness-relevant traits and identify where multicellularity, differentiation, or their combination is fittest. We then study the effects of adaptation by allowing populations to fix mutations that improve their fitness. We find that while the same mutation can be beneficial to populations of different complexity, e.g., strict unicellularity or life cycles with stages of differentiated multicellularity, the magnitudes of their effects can differ and alter which is fittest. As a result, we observe adaptive trajectories that gain and lose complexity. We also show that the order of mutations, historical contingency, can cause some transitions to be permanent in the absence of neutral evolution. Ultimately, we find that continued exposure to a selective driver for multicellularity can either lead to increasing complexity or a return to unicellularity.

Convergent pairs of highly transcribed genes restrict chromatin looping in Dictyostelium discoideum

Dictyostelium discoideum is a unicellular slime mold, developing into a multicellular fruiting body upon starvation. Development is accompanied by large-scale shifts in gene expression program, but underlying features of chromatin spatial organization remain unknown. Here, we report that the Dictyostelium 3D genome is organized into positionally conserved, largely consecutive, non-hierarchical and weakly insulated loops at the onset of multicellular development. The transcription level within the loop interior tends to be higher than in adjacent regions. Loop interiors frequently contain functionally linked genes and genes which coherently change expression level during development. Loop anchors are predominantly positioned by the genes in convergent orientation. Results of polymer simulations and Hi-C-based observations suggest that the loop profile may arise from the interplay between transcription and extrusion-driven chromatin folding. In this scenario, a convergent gene pair serves as a bidirectional extrusion barrier or a 'diode' that controls passage of the cohesin extruder by relative transcription level of paired genes.

Strain identity effects contribute more to Pseudomonas community functioning than strain interactions

Microbial communities can shape key ecological services, but the determinants of their functioning often remain little understood. While traditional research predominantly focuses on effects related to species identity (community composition and species richness), recent work increasingly explores the impact of species interactions on community functioning. Here, we conducted experiments with replicated small communities of Pseudomonas bacteria to quantify the relative importance of strain identity versus interaction effects on two important functions, community productivity and siderophore production. By combining supernatant and competition assays with an established linear model method, we show that both factors have significant effects on functioning, but identity effects generally outweigh strain interaction effects. These results hold irrespective of whether strain interactions are inferred statistically or approximated experimentally. Our results have implications for microbiome engineering, as the success of approaches aiming to induce beneficial (probiotic) strain interactions will be sensitive to strain identity effects in many communities.

Ecological histories govern social exploitation by microorganisms

Exploitation is a common feature of social interactions, which can be modified by ecological context. Here, we investigate effects of ecological history on exploitation phenotypes in bacteria. In experiments with the bacterium Myxococcus xanthus, prior resource levels of different genotypes interacting during cooperative multicellular development were found to regulate social fitness, including whether cheating occurs. Responses of developmental spore production to manipulation of resource-level histories differed between interacting cooperators and cheaters, and relative-fitness advantages gained by cheating after high-resource growth were generally reduced or absent if one or both parties experienced low-resource growth. Low-resource growth also eliminated exploitation in some pairwise mixes of cooperative natural isolates that occurs when both strains have grown under resource abundance. Our results contrast with previous experiments in which cooperator fitness correlated positively with concurrent resource level and suggest that resource-level variation may be important in regulating whether exploitation of cooperators occurs in a natural context.

Soil Amoebae Are Unexpected Hotspots of Environmental Antibiotics and Antibiotic Resistance Genes

Antibiotic resistance poses a significant threat to human health. While most studies focus on bacteria, interactions between antibiotics and other crucial microbial groups like protists remain uncertain. This study investigates how protists interact with antibiotics and examines how these interactions impact the fate of resistance genes. It reveals that amoebae exhibit high resistance to eight high-risk environmental antibiotics, accumulating significant quantities within their cells. Wild amoeboid strains from distant locations carry substantial antibiotic resistance genes (ARGs) and metal resistance genes (MRGs), with significant heterogeneity within a single species. Amoeboid symbionts and pathogens predominantly carry these genes. Paraburkholderia symbionts have reduced genomes and fewer resistance genes compared to free-living strains, while amoeba-endogenous Stenotrophomonas maltophilia does not exhibit a significantly reduced genome size. This suggests that the amoeboid hosts serve as a temporary medium facilitating its transmission. In summary, the study unveils that soil amoebae represent unexpected hotspots for antibiotics and resistance genes. Future research should assess the effects of antibiotics on often-overlooked protists and explore their role in spreading ARGs and MRGs in ecosystems. Incorporating protists into broader antibiotic resistance research is recommended, highlighting their significance within a One Health perspective.

Going against the family: Perturbation of a greenbeard pathway leads to falsebeard cheating

Greenbeards facilitate cooperation by encoding a perceptible signal, the ability to detect it, and a tendency to help others that display it. Falsebeards are hypothetical cheaters that display the signal without being altruistic. Despite many examples of greenbeards, evidence for falsebeards is scarce. The Dictyostelium discoideum tgrB1-tgrC1 allorecognition pathway encodes a greenbeard. It allows development, which yields fruiting bodies with altruistic stalks that increase spore dispersal. Here we show that cells lacking rapgapB, a tgrB1-tgrC1 signaling element, cheat by avoiding the stalk fate and generating more spores in chimeras than in pure populations. rapgapB - cells cheat only on partners with compatible tgrB1-tgrC1 allotypes, suggesting that beard display and recognition are intact but decoupled from altruism. The rapgapB - falsebeard provides a model to study greenbeard maintenance and subversion.

Evolutionary stability of developmental commitment

Evolution of unicellular to multicellular organisms must resolve conflicts in reproductive interests between individual cells and the group. The social amoeba Dictyostelium discoideum is a soil-living eukaryote with facultative sociality. While cells grow in the presence of nutrients, cells aggregate under starvation to form fruiting bodies containing spores and altruistic stalk cells. Once cells socially committed, they complete formation of fruiting bodies, even if a new source of nutrients becomes available. The persistence of this social commitment raises questions as it inhibits individual cells from swiftly returning to solitary growth. I hypothesize that traits enabling premature de-commitment are hindered from being selected. Recent work has revealed outcomes of the premature de-commitment through forced refeeding; The de-committed cells take an altruistic prestalk-like position due to their reduced cohesiveness through interactions with socially committed cells. I constructed an evolutionary model assuming their division of labor. The results revealed a valley in the fitness landscape that prevented invasion of de-committing mutants, indicating evolutionary stability of the social commitment. The findings provide a general scheme that maintains multicellularity by evolving a specific division of labor, in which less cohesive individuals become altruists.

Multiple distinct evolutionary mechanisms govern the dynamics of selfish mitochondrial genomes in Caenorhabditis elegans

Cells possess multiple mitochondrial DNA (mtDNA) copies, which undergo semi-autonomous replication and stochastic inheritance. This enables mutant mtDNA variants to arise and selfishly compete with cooperative (wildtype) mtDNA. Selfish mitochondrial genomes are subject to selection at different levels: they compete against wildtype mtDNA directly within hosts and indirectly through organism-level selection. However, determining the relative contributions of selection at different levels has proven challenging. We overcome this challenge by combining mathematical modeling with experiments designed to isolate the levels of selection. Applying this approach to many selfish mitochondrial genotypes in Caenorhabditis elegans reveals an unexpected diversity of evolutionary mechanisms. Some mutant genomes persist at high frequency for many generations, despite a host fitness cost, by aggressively outcompeting cooperative genomes within hosts. Conversely, some mutant genomes persist by evading inter-organismal selection. Strikingly, the mutant genomes vary dramatically in their susceptibility to genetic drift. Although different mechanisms can cause high frequency of selfish mtDNA, we show how they give rise to characteristically different distributions of mutant frequency among individuals. Given that heteroplasmic frequency represents a key determinant of phenotypic severity, this work outlines an evolutionary theoretic framework for predicting the distribution of phenotypic consequences among individuals carrying a selfish mitochondrial genome.

The greenbeard gene tgrB1 regulates altruism and cheating in Dictyostelium discoideum

Greenbeard genetic elements encode rare perceptible signals, signal recognition ability, and altruism towards others that display the same signal. Putative greenbeards have been described in various organisms but direct evidence for all the properties in one system is scarce. The tgrB1-tgrC1 allorecognition system of Dictyostelium discoideum encodes two polymorphic membrane proteins which protect cells from chimerism-associated perils. During development, TgrC1 functions as a ligand-signal and TgrB1 as its receptor, but evidence for altruism has been indirect. Here, we show that mixing wild-type and activated tgrB1 cells increases wild-type spore production and relegates the mutants to the altruistic stalk, whereas mixing wild-type and tgrB1-null cells increases mutant spore production and wild-type stalk production. The tgrB1-null cells cheat only on partners that carry the same tgrC1-allotype. Therefore, TgrB1 activation confers altruism whereas TgrB1 inactivation causes allotype-specific cheating, supporting the greenbeard concept and providing insight into the relationship between allorecognition, altruism, and exploitation.

Prestalk-like positioning of de-differentiated cells in the social amoeba Dictyostelium discoideum

The social amoeba Dictyostelium discoideum switches between solitary growth and social fruitification depending on nutrient availability. Under starvation, cells aggregate and form fruiting bodies consisting of spores and altruistic stalk cells. Once cells socially committed, they complete fruitification, even if a new source of nutrients becomes available. This social commitment is puzzling because it hinders individual cells from resuming solitary growth quickly. One idea posits that traits that facilitate premature de-commitment are hindered from being selected. We studied outcomes of the premature de-commitment through forced refeeding. Our results show that when refed cells interacted with non-refed cells, some of them became solitary, whereas a fraction was redirected to the altruistic stalk, regardless of their original fate. The refed cells exhibited reduced cohesiveness and were sorted out during morphogenesis. Our findings provide an insight into a division of labor of the social amoeba, in which less cohesive individuals become altruists.

In the social amoeba Dictyostelium discoideum, shortened stalks may limit obligate cheater success even when exploitable partners are available

Cooperation is widespread across life, but its existence can be threatened by exploitation. The rise of obligate social cheaters that are incapable of contributing to a necessary cooperative function can lead to the loss of that function. In the social amoeba Dictyostelium discoideum, obligate social cheaters cannot form dead stalk cells and in chimeras instead form living spore cells. This gives them a competitive advantage within chimeras. However, obligate cheaters of this kind have thus far not been found in nature, probably because they are often enough in clonal populations that they need to retain the ability to produce stalks. In this study we discovered an additional cost to obligate cheaters. Even when there are wild-type cells to parasitize, the chimeric fruiting bodies that result have shorter stalks and these are disadvantaged in spore dispersal. The inability of obligate cheaters to form fruiting bodies when they are on their own combined with the lower functionality of fruiting bodies when they are not represent limits on obligate social cheating as a strategy.

The effect of cooperator recognition on competition among clones in spatially structured microbial communities

In spatially structured microbial communities, clonal growth of stationary cells passively generates clusters of related individuals. This can lead to stable cooperation without the need for recognition mechanisms. However, recent research suggests that some biofilm-forming microbes may have mechanisms of kin recognition. To explore this unexpected observation, we studied the effects of different types of cooperation in a microbial colony using spatially explicit, agent-based simulations of two interacting strains. We found scenarios that favor a form of kin recognition in spatially structured microbial communities. In the presence of a "cheater" strain, a strain with greenbeard cooperation was able to increase in frequency more than a strain with obligate cooperation. This effect was most noticeable in high density colonies and when the cooperators were not as abundant as the cheaters. We also studied whether a polychromatic greenbeard, in which cells only cooperate with their own type, could provide a numerical benefit beyond a simple, binary greenbeard. We found the greatest benefit to a polychromatic greenbeard when cooperation is highly effective. These results suggest that in some ecological scenarios, recognition mechanisms may be beneficial even in spatially structured communities.

Linked selection and the evolution of altruism in family-structured populations

Much research on the evolution of altruism via kin selection, group selection, and reciprocity focuses on the role of a single locus or quantitative trait. Very few studies have explored how linked selection, or selection at loci neighboring an altruism locus, impacts the evolution of altruism. While linked selection can decrease the efficacy of selection at neighboring loci, it might have other effects including promoting selection for altruism by increasing relatedness in regions of low recombination. Here, we used population genetic simulations to study how negative selection at linked loci, or background selection, affects the evolution of altruism. When altruism occurs between full siblings, we found that background selection interfered with selection on the altruistic allele, increasing its fixation probability when the altruistic allele was disfavored and reducing its fixation when the allele was favored. In other words, background selection has the same effect on altruistic genes in family-structured populations as it does on other, nonsocial, genes. This contrasts with prior research showing that linked selective sweeps can favor the evolution of cooperation, and we discuss possibilities for resolving these contrasting results.

Determination of Neuronal Activity and Its Meaning for the Processes of Learning and Memory

Despite the years of studies in the field of systems neuroscience, the functions of neural circuits and behavior-related systems are still not entirely understood. The systems description of brain activity has recently been associated with cognitive concepts, e.g., a cognitive map, reconstructed via place-cell activity analysis and the like, and a cognitive schema, modeled in consolidation research. The issue we find of importance is that cognitive concepts reconstructed in neuroscience research are mainly formulated in terms of the environment. In this chapter, we present the idea of an element of individual experience that serves as a model of behavioral interaction with the environment, rather than a model of the environment itself. This intangible difference entails the need for substantial revision of several well-known phenomena, including long-term potentiation. The principal questions we address are: how do elements of experience appear and change during learning and performance; and how do the links between these elements create the whole structure of individual experience? We argue that learning and memory research need a clear distinction between processes that provide the emergence of new elements of experience (functional systems) and processes underlying the retrieval and/or changes in the existing experience. We propose to view the activity of a neuron as an "action" directed to the future adaptive "microresult," essential for meeting its metabolic needs. This anticipatory neuronal activity is coordinated with the activity of many other cells of the body in the organism-wide functional system, ensuring the achievement of an adaptive "macroresult" at the behavioral level. From this perspective, the mechanisms of learning are considered as the formation of functional systems, and memory is considered as a dynamic structure constituted by systems formed at different stages of individual development.

Parallel evolution of the G protein-coupled receptor GrlG and the loss of fruiting body formation in the social amoeba Dictyostelium discoideum evolved under low relatedness

Aggregative multicellularity relies on cooperation among formerly independent cells to form a multicellular body. Previous work with Dictyostelium discoideum showed that experimental evolution under low relatedness profoundly decreased cooperation, as indicated by the loss of fruiting body formation in many clones and an increase of cheaters that contribute proportionally more to spores than to the dead stalk. Using whole-genome sequencing and variant analysis of these lines, we identified 38 single nucleotide polymorphisms in 29 genes. Each gene had 1 variant except for grlG (encoding a G protein-coupled receptor), which had 10 unique SNPs and 5 structural variants. Variants in the 5' half of grlG-the region encoding the signal peptide and the extracellular binding domain-were significantly associated with the loss of fruiting body formation; the association was not significant in the 3' half of the gene. These results suggest that the loss of grlG was adaptive under low relatedness and that at least the 5' half of the gene is important for cooperation and multicellular development. This is surprising given some previous evidence that grlG encodes a folate receptor involved in predation, which occurs only during the single-celled stage. However, non-fruiting mutants showed little increase in a parallel evolution experiment where the multicellular stage was prevented from happening. This shows that non-fruiting mutants are not generally selected by any predation advantage but rather by something-likely cheating-during the multicellular stage.

Reduced social function in experimentally evolved Dictyostelium discoideum implies selection for social conflict in nature

Many microbes interact with one another, but the difficulty of directly observing these interactions in nature makes interpreting their adaptive value complicated. The social amoeba Dictyostelium discoideum forms aggregates wherein some cells are sacrificed for the benefit of others. Within chimaeric aggregates containing multiple unrelated lineages, cheaters can gain an advantage by undercontributing, but the extent to which wild D. discoideum has adapted to cheat is not fully clear. In this study, we experimentally evolved D. discoideum in an environment where there were no selective pressures to cheat or resist cheating in chimaeras. Dictyostelium discoideum lines grown in this environment evolved reduced competitiveness within chimaeric aggregates and reduced ability to migrate during the slug stage. By contrast, we did not observe a reduction in cell number, a trait for which selection was not relaxed. The observed loss of traits that our laboratory conditions had made irrelevant suggests that these traits were adaptations driven and maintained by selective pressures D. discoideum faces in its natural environment. Our results suggest that D. discoideum faces social conflict in nature, and illustrate a general approach that could be applied to searching for social or non-social adaptations in other microbes.

Ecological histories determine the success of social exploitation

Ecological context often modifies biotic interactions, yet effects of ecological history are poorly understood. In experiments with the bacterium Myxococcus xanthus , resource-level histories of genotypes interacting during cooperative multicellular development were found to strongly regulate social fitness. Yet how developmental spore production responded to variation in resource-level histories between interactants differed greatly between cooperators and cheaters; relative-fitness advantages gained by cheating after high-resource growth were generally reduced or absent if one or both parties experienced low-resource growth. Low-resource growth also eliminated facultative exploitation in some pairwise mixes of cooperation-proficient natural isolates that occurs when both strains have grown under resource abundance. Our results contrast with previous studies in which cooperator fitness correlated positively with resource level and suggest that resource-level variation may be important in regulating whether exploitation of cooperators occurs in a natural context.

Kin-recognition and predation shape collective behaviors in the cannibalistic nematode Pristionchus pacificus

Kin-recognition is observed across diverse species forming an important behavioral adaptation influencing organismal interactions. In many species, the molecular mechanisms involved are difficult to characterize, but in the nematode Pristionchus pacificus molecular components regulating its kin-recognition system have been identified. These determine its predatory behaviors towards other con-specifics which prevents the killing and cannibalization of kin. Importantly, their impact on other interactions including collective behaviors is unknown. Here, we explored a high altitude adapted clade of this species which aggregates abundantly under laboratory conditions, to investigate the influence of the kin-recognition system on their group behaviours. By utilizing pairwise aggregation assays between distinct strains of P. pacificus with differing degrees of genetic relatedness, we observe aggregation between kin but not distantly related strains. In assays between distantly related strains, the aggregation ratio is frequently reduced. Furthermore, abolishing predation behaviors through CRISPR/Cas9 induced mutations in Ppa-nhr-40 result in rival strains successfully aggregating together. Finally, as Caenorhabditis elegans are found naturally occurring with P. pacificus, we also explored aggregation events between these species. Here, aggregates were dominated by P. pacificus with the presence of only a small number of predators proving sufficient to disrupt C. elegans aggregation dynamics. Thus, aggregating strains of P. pacificus preferentially group with kin, revealing competition and nepotism as previously unknown components influencing collective behaviors in nematodes.

SOCfinder: a genomic tool for identifying social genes in bacteria

Bacteria cooperate by working collaboratively to defend their colonies, share nutrients, and resist antibiotics. Nevertheless, our understanding of these remarkable behaviours primarily comes from studying a few well-characterized species. Consequently, there is a significant gap in our understanding of microbial social traits, particularly in natural environments. To address this gap, we can use bioinformatic tools to identify genes that control cooperative or otherwise social traits. Existing tools address this challenge through two approaches. One approach is to identify genes that encode extracellular proteins, which can provide benefits to neighbouring cells. An alternative approach is to predict gene function using annotation tools. However, these tools have several limitations. Not all extracellular proteins are cooperative, and not all cooperative behaviours are controlled by extracellular proteins. Furthermore, existing functional annotation methods frequently miss known cooperative genes. We introduce SOCfinder as a new tool to find bacterial genes that control cooperative or otherwise social traits. SOCfinder combines information from several methods, considering if a gene is likely to [1] code for an extracellular protein [2], have a cooperative functional annotation, or [3] be part of the biosynthesis of a cooperative secondary metabolite. We use data on two extensively-studied species (P. aeruginosa and B. subtilis) to show that SOCfinder is better at finding known cooperative genes than existing tools. We also use theory from population genetics to identify a signature of kin selection in SOCfinder cooperative genes, which is lacking in genes identified by existing tools. SOCfinder opens up a number of exciting directions for future research, and is available to download from https://github.com/lauriebelch/SOCfinder.

Open questions in the social lives of viruses

Social interactions among viruses occur whenever multiple viral genomes infect the same cells, hosts, or populations of hosts. Viral social interactions range from cooperation to conflict, occur throughout the viral world, and affect every stage of the viral lifecycle. The ubiquity of these social interactions means that they can determine the population dynamics, evolutionary trajectory, and clinical progression of viral infections. At the same time, social interactions in viruses raise new questions for evolutionary theory, providing opportunities to test and extend existing frameworks within social evolution. Many opportunities exist at this interface: Insights into the evolution of viral social interactions have immediate implications for our understanding of the fundamental biology and clinical manifestation of viral diseases. However, these opportunities are currently limited because evolutionary biologists only rarely study social evolution in viruses. Here, we bridge this gap by (1) summarizing the ways in which viruses can interact socially, including consequences for social evolution and evolvability; (2) outlining some open questions raised by viruses that could challenge concepts within social evolution theory; and (3) providing some illustrative examples, data sources, and conceptual questions, for studying the natural history of social viruses.

Adaptation in the face of internal conflict: the paradox of the organism revisited

The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.

Signatures of kin selection in a natural population of the bacteria Bacillus subtilis

Laboratory experiments have suggested that bacteria perform a range of cooperative behaviors, which are favored because they are directed toward relatives (kin selection). However, there is a lack of evidence for cooperation and kin selection in natural bacterial populations. Molecular population genetics offers a promising method to study natural populations because the theory predicts that kin selection will lead to relaxed selection, which will result in increased polymorphism and divergence at cooperative genes. Examining a natural population of Bacillus subtilis, we found consistent evidence that putatively cooperative traits have higher polymorphism and greater divergence than putatively private traits expressed at the same rate. In addition, we were able to eliminate alternative explanations for these patterns and found more deleterious mutations in genes controlling putatively cooperative traits. Overall, our results suggest that cooperation is favored by kin selection, with an average relatedness of r = .79 between interacting individuals.

Reuniting philosophy and science to advance cancer research

Cancers rely on multiple, heterogeneous processes at different scales, pertaining to many biomedical fields. Therefore, understanding cancer is necessarily an interdisciplinary task that requires placing specialised experimental and clinical research into a broader conceptual, theoretical, and methodological framework. Without such a framework, oncology will collect piecemeal results, with scant dialogue between the different scientific communities studying cancer. We argue that one important way forward in service of a more successful dialogue is through greater integration of applied sciences (experimental and clinical) with conceptual and theoretical approaches, informed by philosophical methods. By way of illustration, we explore six central themes: (i) the role of mutations in cancer; (ii) the clonal evolution of cancer cells; (iii) the relationship between cancer and multicellularity; (iv) the tumour microenvironment; (v) the immune system; and (vi) stem cells. In each case, we examine open questions in the scientific literature through a philosophical methodology and show the benefit of such a synergy for the scientific and medical understanding of cancer.

Genetic variance and indirect genetic effects for affiliative social behavior in a wild primate

Affiliative social behaviors are linked to fitness components in multiple species. However, the role of genetic variance in shaping such behaviors remains largely unknown, limiting our understanding of how affiliative behaviors can respond to natural selection. Here, we employed the "animal model" to estimate environmental and genetic sources of variance and covariance in grooming behavior in the well-studied Amboseli wild baboon population. We found that the tendency for a female baboon to groom others ("grooming given") is heritable (h2 = 0.22 ± 0.048), and that several environmental variables-including dominance rank and the availability of kin as grooming partners-contribute to variance in this grooming behavior. We also detected small but measurable variance due to the indirect genetic effect of partner identity on the amount of grooming given within dyadic grooming partnerships. The indirect and direct genetic effects for grooming given were positively correlated (r = 0.74 ± 0.09). Our results provide insight into the evolvability of affiliative behavior in wild animals, including the possibility for correlations between direct and indirect genetic effects to accelerate the response to selection. As such they provide novel information about the genetic architecture of social behavior in nature, with important implications for the evolution of cooperation and reciprocity.

Minor variations in multicellular life cycles have major effects on adaptation

Multicellularity has evolved several independent times over the past hundreds of millions of years and given rise to a wide diversity of complex life. Recent studies have found that large differences in the fundamental structure of early multicellular life cycles can affect fitness and influence multicellular adaptation. Yet, there is an underlying assumption that at some scale or categorization multicellular life cycles are similar in terms of their adaptive potential. Here, we consider this possibility by exploring adaptation in a class of simple multicellular life cycles of filamentous organisms that only differ in one respect, how many daughter filaments are produced. We use mathematical models and evolutionary simulations to show that despite the similarities, qualitatively different mutations fix. In particular, we find that mutations with a tradeoff between cell growth and group survival, i.e. "selfish" or "altruistic" traits, spread differently. Specifically, altruistic mutations more readily spread in life cycles that produce few daughters while in life cycles producing many daughters either type of mutation can spread depending on the environment. Our results show that subtle changes in multicellular life cycles can fundamentally alter adaptation.

Social Diversification Driven by Mobile Genetic Elements

Social diversification in microbes is an evolutionary process where lineages bifurcate into distinct populations that cooperate with themselves but not with other groups. In bacteria, this is frequently driven by horizontal transfer of mobile genetic elements (MGEs). Here, the resulting acquisition of new genes changes the recipient's social traits and consequently how they interact with kin. These changes include discriminating behaviors mediated by newly acquired effectors. Since the producing cell is protected by cognate immunity factors, these selfish elements benefit from selective discrimination against recent ancestors, thus facilitating their proliferation and benefiting the host. Whether social diversification benefits the population at large is less obvious. The widespread use of next-generation sequencing has recently provided new insights into population dynamics in natural habitats and the roles MGEs play. MGEs belong to accessory genomes, which often constitute the majority of the pangenome of a taxon, and contain most of the kin-discriminating loci that fuel rapid social diversification. We further discuss mechanisms of diversification and its consequences to populations and conclude with a case study involving myxobacteria.

Disease association and comparative genomics of compositional bias in human proteins

Background: The evolutionary rate of disordered proteins varies greatly due to the lack of structural constraints. So far, few studies have investigated the presence/absence patterns of intrinsically disordered regions (IDRs) across phylogenies in conjunction with human disease. In this study, we report a genome-wide analysis of compositional bias association with disease in human proteins and their taxonomic distribution. Methods: The human genome protein set provided by the Ensembl database was annotated and analysed with respect to both disease associations and the detection of compositional bias. The Uniprot Reference Proteome dataset, containing 11297 proteomes was used as target dataset for the comparative genomics of a well-defined subset of the Human Genome, including 100 characteristic, compositionally biased proteins, some linked to disease. Results: Cross-evaluation of compositional bias and disease-association in the human genome reveals a significant bias towards low complexity regions in disease-associated genes, with charged, hydrophilic amino acids appearing as over-represented. The phylogenetic profiling of 17 disease-associated, low complexity proteins across 11297 proteomes captures characteristic taxonomic distribution patterns. Conclusions: This is the first time that a combined genome-wide analysis of low complexity, disease-association and taxonomic distribution of human proteins is reported, covering structural, functional, and evolutionary properties. The reported framework can form the basis for large-scale, follow-up projects, encompassing the entire human genome and all known gene-disease associations.

Disease association and comparative genomics of compositional bias in human proteins

Background: The evolutionary rate of disordered protein regions varies greatly due to the lack of structural constraints. So far, few studies have investigated the presence/absence patterns of compositional bias, indicative of disorder, across phylogenies in conjunction with human disease. In this study, we report a genome-wide analysis of compositional bias association with disease in human proteins and their taxonomic distribution. Methods: The human genome protein set provided by the Ensembl database was annotated and analysed with respect to both disease associations and the detection of compositional bias. The Uniprot Reference Proteome dataset, containing 11297 proteomes was used as target dataset for the comparative genomics of a well-defined subset of the Human Genome, including 100 characteristic, compositionally biased proteins, some linked to disease. Results: Cross-evaluation of compositional bias and disease-association in the human genome reveals a significant bias towards biased regions in disease-associated genes, with charged, hydrophilic amino acids appearing as over-represented. The phylogenetic profiling of 17 disease-associated, proteins with compositional bias across 11297 proteomes captures characteristic taxonomic distribution patterns. Conclusions: This is the first time that a combined genome-wide analysis of compositional bias, disease-association and taxonomic distribution of human proteins is reported, covering structural, functional, and evolutionary properties. The reported framework can form the basis for large-scale, follow-up projects, encompassing the entire human genome and all known gene-disease associations.

Heterogeneous individual motility biases group composition in a model of aggregating cells

Aggregative life cycles are characterized by alternating phases of unicellular growth and multicellular development. Their multiple, independent evolutionary emergence suggests that they may have coopted pervasive properties of single-celled ancestors. Primitive multicellular aggregates, where coordination mechanisms were less efficient than in extant aggregative microbes, must have faced high levels of conflict between different co-aggregating populations. Such conflicts within a multicellular body manifest in the differential reproductive output of cells of different types. Here, we study how heterogeneity in cell motility affects the aggregation process and creates a mismatch between the composition of the population and that of self-organized groups of active adhesive particles. We model cells as self-propelled particles and describe aggregation in a plane starting from a dispersed configuration. Inspired by the life cycle of aggregative model organisms such as Dictyostelium discoideum or Myxococcus xanthus, whose cells interact for a fixed duration before the onset of chimeric multicellular development, we study finite-time configurations for identical particles and in binary mixes. We show that co-aggregation results in three different types of frequency-dependent biases, one of which is associated to evolutionarily stable coexistence of particles with different motility. We propose a heuristic explanation of such observations, based on the competition between delayed aggregation of slower particles and detachment of faster particles. Unexpectedly, despite the complexity and non-linearity of the system, biases can be largely predicted from the behavior of the two corresponding homogenous populations. This model points to differential motility as a possibly important factor in driving the evolutionary emergence of facultatively multicellular life-cycles.

Role of Dead Cells in Collective Stress Tolerance in Microbial Communities: Evidence from Yeast

A substantial part of yeast life cycle takes place in the communities where the cells are surrounded by their own clones. Meanwhile, yeast cell fitness depends not only on its own adaptations but also on the processes in the neighboring cells. Moreover, even if a cell loses its clonogenic ability, it is still capable of protecting surrounding cells that are still alive. Dead cells can absorb lipophilic antibiotics and provide nutrients to their kin neighbors. Some enzymes can be released into the environment and detoxify exogenous toxins. For example, cytosolic catalase, which degrades hydrogen peroxide, can stay active outside of the cell. Inviable cells of pathogenic yeast species can suppress host immune responses and, in this way, boost spread of the pathogen. In this review, we speculate that biochemical processes in dying cells can facilitate increase of stress resistance in the alive kin cells and therefore be a subject of natural selection. We considered possible scenarios of how dead microbial cells can increase survival of their kin using unicellular fungi - baker's yeast Saccharomyces cerevisiae - as an example. We conclude that the evolutionary conserved mechanisms of programmed cell death in yeast are likely to include a module of early permeabilization of the cell plasma membrane rather than preserve its integrity.

The evolution of manipulative cheating

A social cheat is typically assumed to be an individual that does not perform a cooperative behaviour, or performs less of it, but can still exploit the cooperative behaviour of others. However, empirical data suggests that cheating can be more subtle, involving evolutionary arms races over the ability to both exploit and resist exploitation. These complications have not been captured by evolutionary theory, which lags behind empirical studies in this area. We bridge this gap with a mixture of game-theoretical models and individual-based simulations, examining what conditions favour more elaborate patterns of cheating. We found that as well as adjusting their own behaviour, individuals can be selected to manipulate the behaviour of others, which we term 'manipulative cheating'. Further, we found that manipulative cheating can lead to dynamic oscillations (arms races), between selfishness, manipulation, and suppression of manipulation. Our results can help explain both variation in the level of cheating, and genetic variation in the extent to which individuals can be exploited by cheats.

An evolutionary perspective on increasing net benefits to crops from symbiotic microbes

Plant-imposed, fitness-reducing sanctions against less-beneficial symbionts have been documented for rhizobia, mycorrhizal fungi, and fig wasps. Although most of our examples are for rhizobia, we argue that the evolutionary persistence of mutualism in any symbiosis would require such sanctions, if there are multiple symbiont genotypes per host plant. We therefore discuss methods that could be used to develop and assess crops with stricter sanctions. These include methods to screen strains for greater mutualism as resources to identify crop genotypes that impose stronger selection for mutualism. Single-strain experiments that measure costs as well as benefits have shown that diversion of resources by rhizobia can reduce nitrogen-fixation efficiency (N per C) and that some legumes can increase this efficiency by manipulating their symbionts. Plants in the field always host multiple strains with possible synergistic interactions, so benefits from different strains might best be compared by regressing plant growth or yield on each strain's abundance in a mixture. However, results from this approach have not yet been published. To measure legacy effects of stronger sanctions on future crops, single-genotype test crops could be planted in a field that recently had replicated plots with different genotypes of the sanction-imposing crop. Enhancing agricultural benefits from symbiosis may require accepting tradeoffs that constrained past natural selection, including tradeoffs between current and future benefits.

Multicellularity in animals: The potential for within-organism conflict

Metazoans function as individual organisms but also as “colonies” of cells whose single-celled ancestors lived and reproduced independently. Insights from evolutionary biology about multicellular group formation help us understand the behavior of cells: why they cooperate, and why cooperation sometimes breaks down. Current explanations for multicellularity focus on two aspects of development which promote cooperation and limit conflict among cells: a single-cell bottleneck, which creates organisms composed of clones, and a separation of somatic and germ cell lineages, which reduces the selective advantage of cheating. However, many obligately multicellular organisms thrive with neither, creating the potential for within-organism conflict. Here, we argue that the prevalence of such organisms throughout the Metazoa requires us to refine our preconceptions of conflict-free multicellularity. Evolutionary theory must incorporate developmental mechanisms across a broad range of organisms—such as unusual reproductive strategies, totipotency, and cell competition—while developmental biology must incorporate evolutionary principles. To facilitate this cross-disciplinary approach, we provide a conceptual overview from evolutionary biology for developmental biologists, using analogous examples in the well-studied social insects.

Evolving social behaviour through selection of single-cell adhesion in Dictyostelium discoideum

The social amoeba Dictyostelium discoideum commonly forms chimeric fruiting bodies. Genetic variants that produce a higher proportion of spores are predicted to undercut multicellular organization unless cooperators assort positively. Cell adhesion is considered a primary factor driving such assortment, but evolution of adhesion has not been experimentally connected to changes in social performance. We modified by experimental evolution the efficiency of individual cells in attaching to a surface. Surprisingly, evolution appears to have produced social cooperators irrespective of whether stronger or weaker adhesion was selected. Quantification of reproductive success, cell-cell adhesion, and developmental patterns, however, revealed two distinct social behaviors, as captured when the classical metric for social success is generalized by considering clonal spore production. Our work shows that cell mechanical interactions can constrain the evolution of development and sociality in chimeras and that elucidation of proximate mechanisms is necessary to understand the ultimate emergence of multicellular organization.

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Cooperative behavior evolved as a pleiotropic effect of selection for surface adhesion

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Multicellular development of evolved lines with the ancestor follows two different paths

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A metric of social behavior including clonal development differentiates these two paths

Developmental constraints enforce altruism and avert the tragedy of the commons in a social microbe

Organisms often cooperate through the production of freely available public goods. This can greatly benefit the group but is vulnerable to the "tragedy of the commons" if individuals lack the motivation to make the necessary investment into public goods production. Relatedness to groupmates can motivate individual investment because group success ultimately benefits their genes' own self-interests. However, systems often lack mechanisms that can reliably ensure that relatedness is high enough to promote cooperation. Consequently, groups face a persistent threat from the tragedy unless they have a mechanism to enforce investment when relatedness fails to provide adequate motivation. To understand the real threat posed by the tragedy and whether groups can avert its impact, we determine how the social amoeba Dictyostelium discoideum responds as relatedness decreases to levels that should induce the tragedy. We find that, while investment in public goods declines as overall within-group relatedness declines, groups avert the expected catastrophic collapse of the commons by continuing to invest, even when relatedness should be too low to incentivize any contribution. We show that this is due to a developmental buffering system that generates enforcement because insufficient cooperation perturbs the balance of a negative feedback system controlling multicellular development. This developmental constraint enforces investment under the conditions expected to be most tragic, allowing groups to avert a collapse in cooperation. These results help explain how mechanisms that suppress selfishness and enforce cooperation can arise inadvertently as a by-product of constraints imposed by selection on different traits.

Discussions of the "Not So Fit": How Ableism Limits Diverse Thought and Investigative Potential in Evolutionary Biology

AbstractEvolutionary biology and many of its foundational concepts are grounded in a history of ableism and eugenics. The field has not made a concerted effort to divest our concepts and investigative tools from this fraught history, and as a result, an ableist investigative lens has persisted in present-day evolutionary research, limiting the scope of research and harming the ability to communicate and synthesize knowledge about evolutionary processes. This failure to divest from our eugenicist and ableist history has harmed progress in evolutionary biology and allowed principles from evolutionary biology to continue to be weaponized against marginalized communities in the modern day. To rectify this problem, scholars in evolutionary research must come to terms with how the history of the field has influenced their investigations and work to establish a new framework for defining and investigating concepts such as selection and fitness.

Paligenosis: Cellular Remodeling During Tissue Repair

Complex multicellular organisms have evolved specific mechanisms to replenish cells in homeostasis and during repair. Here, we discuss how emerging technologies (e.g., single-cell RNA sequencing) challenge the concept that tissue renewal is fueled by unidirectional differentiation from a resident stem cell. We now understand that cell plasticity, i.e., cells adaptively changing differentiation state or identity, is a central tissue renewal mechanism. For example, mature cells can access an evolutionarily conserved program (paligenosis) to reenter the cell cycle and regenerate damaged tissue. Most tissues lack dedicated stem cells and rely on plasticity to regenerate lost cells. Plasticity benefits multicellular organisms, yet it also carries risks. For one, when long-lived cells undergo paligenotic, cyclical proliferation and redif-ferentiation, they can accumulate and propagate acquired mutations that activate oncogenes and increase the potential for developing cancer. Lastly, we propose a new framework for classifying patterns of cell proliferation in homeostasis and regeneration, with stem cells representing just one of the diverse methods that adult tissues employ.

The evolution of mechanisms to produce phenotypic heterogeneity in microorganisms

In bacteria and other microorganisms, the cells within a population often show extreme phenotypic variation. Different species use different mechanisms to determine how distinct phenotypes are allocated between individuals, including coordinated, random, and genetic determination. However, it is not clear if this diversity in mechanisms is adaptive-arising because different mechanisms are favoured in different environments-or is merely the result of non-adaptive artifacts of evolution. We use theoretical models to analyse the relative advantages of the two dominant mechanisms to divide labour between reproductives and helpers in microorganisms. We show that coordinated specialisation is more likely to evolve over random specialisation in well-mixed groups when: (i) social groups are small; (ii) helping is more "essential"; and (iii) there is a low metabolic cost to coordination. We find analogous results when we allow for spatial structure with a more detailed model of cellular filaments. More generally, this work shows how diversity in the mechanisms to produce phenotypic heterogeneity could have arisen as adaptations to different environments.

Cheating Promotes Coexistence in a Two-Species One-Substrate Culture Model

Cheating in microbial communities is often regarded as a precursor to a “tragedy of the commons,” ultimately leading to over-exploitation by a few species and destabilization of the community. While current evidence suggests that cheaters are evolutionarily and ecologically abundant, they can also play important roles in communities, such as promoting cooperative behaviors of other species. We developed a closed culture model with two microbial species and a single, complex nutrient substrate (the metaphorical “common”). One of the organisms, an enzyme producer, degrades the substrate, releasing an essential and limiting resource that it can use both to grow and produce more enzymes, but at a cost. The second organism, a cheater, does not produce the enzyme but can access the diffused resource produced by the other species, allowing it to benefit from the public good without contributing to it. We investigated evolutionarily stable states of coexistence between the two organisms and described how enzyme production rates and resource diffusion influence organism abundances. Our model shows that, in the long-term evolutionary scale, monocultures of the producer species drive themselves extinct because selection always favors mutant invaders that invest less in enzyme production, ultimately driving down the release of resources. However, the presence of a cheater buffers this process by reducing the fitness advantage of lower enzyme production, thereby preventing runaway selection in the producer, and promoting coexistence. Resource diffusion rate controls cheater growth, preventing it from outcompeting the producer. These results show that competition from cheaters can force producers to maintain adequate enzyme production to sustain both itself and the cheater. This is similar to what is known in evolutionary game theory as a “snowdrift game” – a metaphor describing a snow shoveler and a cheater following in their clean tracks. We move further to show that cheating can stabilize communities and possibly be a precursor to cooperation, rather than extinction.

Novel potential functions of amoeboid cells in thraustochytrids revealed by Aurantiochytrium limacinum BL10

The current study investigated the potential functions of amoeboid cell formation and migration in a thraustochytrid strain, Aurantiochytrium limacinum BL10. Our results showed that: (1) When the surface of an agar plate was inoculated with BL10, amoeboid cells mainly emerged on the periphery of isolated colonies. The amoeboid cells then migrated outwards to form small vegetative cell clusters, which favored rapid colony expansion. In addition, amoeboid cells were capable of self-recognition (i.e. they were able to distinguish BL10 from other thraustochytrid species), and could choose whether to evade (self colonies) or approach (non-self colonies). These observations indicated that amoeboid cells were employed by BL10 to help colonize empty territories and to outcompete other thraustochytrid species in previously colonized territories. (2) When the agar medium was soft, amoeboid cells were able to penetrate the surface and migrate throughout, thereby allowing BL10 to colonize the interior of the solid matrix. This finding suggested that amoeboid cell formation and migration may help Aurantiochytrium colonize the interior of solid matrices to obtain additional nutrients and spatial resources. The mechanisms underlying the regulation of amoeboid cell formation and migration as well as the extraordinary microbial social behaviors of BL10 are also discussed in this article.

Reactive/Less-cooperative individuals advance population's synchronization: Modeling of Dictyostelium discoideum concerted signaling during aggregation phase

Orchestrated chemical signaling of single cells sounds to be a linchpin of emerging organization and multicellular life form. The social amoeba Dictyostelium discoideum is a well-studied model organism to explore overall pictures of grouped behavior in developmental biology. The chemical waves secreted by aggregating Dictyostelium is a superb example of pattern formation. The waves are either circular or spiral in shape, according to the incremental population density of a self-aggregating community of individuals. Here, we revisit the spatiotemporal patterns that appear in an excitable medium due to synchronization of randomly firing individuals, but with a more parsimonious attitude. According to our model, a fraction of these individuals are less involved in amplifying external stimulants. Our simulations indicate that the cells enhance the system’s asymmetry and as a result, nucleate early sustainable spiral territory zones, provided that their relative population does not exceed a tolerable threshold.

The evolution of division of labour in structured and unstructured groups

Recent theory has overturned the assumption that accelerating returns from individual specialisation are required to favour the evolution of division of labour. Yanni et al., 2020, showed that topologically constrained groups, where cells cooperate with only direct neighbours such as for filaments or branching growths, can evolve a reproductive division of labour even with diminishing returns from individual specialisation. We develop a conceptual framework and specific models to investigate the factors that can favour the initial evolution of reproductive division of labour. We find that selection for division of labour in topologically constrained groups: (1) is not a single mechanism to favour division of labour-depending upon details of the group structure, division of labour can be favoured for different reasons; (2) always involves an efficiency benefit at the level of group fitness; and (3) requires a mechanism of coordination to determine which individuals perform which tasks. Given that such coordination must evolve prior to or concurrently with division of labour, this could limit the extent to which topological constraints favoured the initial evolution of division of labour. We conclude by suggesting experimental designs that could determine why division of labour is favoured in the natural world.

Self and non-self recognition affects clonal reproduction and competition in the pea aphid

The spatial interaction of clonal organisms is an unsolved but crucial topic in evolutionary biology. We evaluated the interactions between aphid clones using a colour mutant (yellow) and an original (green) clone. Colonies founded by two aphids of the same clone and mixed colonies, founded by a green aphid and a yellow aphid, were set up to observe population growth for 15 days. We confirmed positive competition effects, with mixed colonies increasing in size more rapidly than clonal colonies. In mixed colonies where reproduction started simultaneously, green aphids overwhelmed yellow aphids in number, and yellow aphids restrained reproduction. However, when yellow aphids started to reproduce earlier, they outnumbered the green aphids. To test whether aphids have the ability to control reproduction according to the densities of self and non-self clones, one yellow aphid or one antennae-excised yellow aphid was transferred into a highly dense green clone colony. Intact yellow aphids produced fewer nymphs in crowded green colonies, whereas the fecundity of antennae-excised aphids did not change. Thus, we conclude that aphid clones can discriminate between self and non-self clones, and can regulate their reproduction, depending on whether they are superior or inferior in number to their competitors.

Response thresholds alone cannot explain empirical patterns of division of labor in social insects

The effects of heterogeneity in group composition remain a major hurdle to our understanding of collective behavior across disciplines. In social insects, division of labor (DOL) is an emergent, colony-level trait thought to depend on colony composition. Theoretically, behavioral response threshold models have most commonly been employed to investigate the impact of heterogeneity on DOL. However, empirical studies that systematically test their predictions are lacking because they require control over colony composition and the ability to monitor individual behavior in groups, both of which are challenging. Here, we employ automated behavioral tracking in 120 colonies of the clonal raider ant with unparalleled control over genetic, morphological, and demographic composition. We find that each of these sources of variation in colony composition generates a distinct pattern of behavioral organization, ranging from the amplification to the dampening of inherent behavioral differences in heterogeneous colonies. Furthermore, larvae modulate interactions between adults, exacerbating the apparent complexity. Models based on threshold variation alone only partially recapitulate these empirical patterns. However, by incorporating the potential for variability in task efficiency among adults and task demand among larvae, we account for all the observed phenomena. Our findings highlight the significance of previously overlooked parameters pertaining to both larvae and workers, allow the formulation of theoretical predictions for increasing colony complexity, and suggest new avenues of empirical study.

This study uses automated tracking of clonal raider ants and mathematical modeling to reveal how previously overlooked traits of larvae and workers might shape social organization in heterogeneous ant colonies. By incorporating the potential for variability in task efficiency among adults and task demand among larvae, the authors were able to account for all empirically observed phenomena.

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. This fact has largely been explained through social evolutionary theory's lens of cooperation and conflict, where cheating within non-clonal groups has the potential to undermine multicellular adaptation. Multicellular organisms that form groups via aggregation could mitigate the costs of cheating by evolving kin recognition systems that prevent the formation of chimeric groups. However, recent work suggests that selection for the ability to aggregate quickly may constrain the evolution of highly specific kin recognition, sowing the seeds for persistent evolutionary conflict. Importantly, other features of aggregative multicellular life cycles may independently act to constrain the evolution of complex multicellularity. All known aggregative multicellular organisms are facultatively multicellular (as opposed to obligately multicellular), allowing unicellular-level adaptation to environmental selection. Because they primarily exist in a unicellular state, it may be difficult for aggregative multicellular organisms to evolve multicellular traits that carry pleiotropic cell-level fitness costs. Thus, even in the absence of social conflict, aggregative multicellular organisms may have limited potential for the evolution of complex multicellularity.

The evolution of strongly-held group identities through agent-based cooperation

Identity fusion represents a strongly-held personal identity that significantly overlaps with that of a group, and is the current best explanation as to why individuals become empowered to act with extreme self-sacrifice for a group of non-kin. This is widely seen and documented, yet how identity fusion is promoted by evolution is not well-understood, being seemingly counter to the selfish pursuit of survival. In this paper we extend agent-based modelling to explore how and why identity fusion can establish itself in an unrelated population with no previous shared experiences. Using indirect reciprocity to provide a framework for agent interaction, we enable agents to express their identity fusion towards a group, and observe the effects of potential behaviours that are incentivised by a heightened fusion level. These build on the social psychology literature and involve heightened sensitivity of fused individuals to perceived hypocritical group support from others. We find that simple self-referential judgement and ignorance of perceived hypocrites is sufficient to promote identity fusion and this is easily triggered by a sub-group of the population. Interestingly the self-referential judgement that we impose is an individual-level behaviour with no direct collective benefit shared by the population. The study provides clues, beyond qualitative and observational studies, as to how hypocrisy may have established itself to reinforce the collective benefit of a fused group identity. It also provides an alternative perspective on the controversial proposition of group selection - showing how fluidity between an individual's reputation and that of a group may function and influence selection as a consequence of identity fusion.

The Grayness of the Origin of Life

In the search for life beyond Earth, distinguishing the living from the non-living is paramount. However, this distinction is often elusive, as the origin of life is likely a stepwise evolutionary process, not a singular event. Regardless of the favored origin of life model, an inherent "grayness" blurs the theorized threshold defining life. Here, we explore the ambiguities between the biotic and the abiotic at the origin of life. The role of grayness extends into later transitions as well. By recognizing the limitations posed by grayness, life detection researchers will be better able to develop methods sensitive to prebiotic chemical systems and life with alternative biochemistries.

Transfer entropy dependent on distance among agents in quantifying leader-follower relationships

Synchronized movement of (both unicellular and multicellular) systems can be observed almost everywhere. Understanding of how organisms are regulated to synchronized behavior is one of the challenging issues in the field of collective motion. It is hypothesized that one or a few agents in a group regulate(s) the dynamics of the whole collective, known as leader(s). The identification of the leader (influential) agent(s) is very crucial. This article reviews different mathematical models that represent different types of leadership. We focus on the improvement of the leader-follower classification problem. It was found using a simulation model that the use of interaction domain information significantly improves the leader-follower classification ability using both linear schemes and information-theoretic schemes for quantifying influence. This article also reviews different schemes that can be used to identify the interaction domain using the motion data of agents.