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1. What Can Mechanisms Underlying Derived Traits Tell Us About the Evolution of Social Behavior?

   https://doi.org/10.1093/aesa/saaa033  

   Treanore, Erin; Derstine, Nathan; Amsalem, Etya (October 2020, Annals of the Entomological Society of America)

   Sun, Qian “Karen” (Ed.)

   Abstract Social behavior, although rare, is a highly successful form of living that has reached its most extreme forms in eusocial insects. A tractable framework to understand social evolution is the study of major transitions in social behavior. This includes the transitions between solitary to social living, from species exhibiting intermediate degrees of sociality to species exhibiting true sociality, and from primitive to advanced eusocial species. The latter transition is characterized by the emergence of traits not previously found in primitive eusocial species, such as fixed morphological differences between castes and task specialization within the sterile caste. Such derived traits appear to exist in a binary fashion, present in advanced eusocial species, and absent or rare in primitive ones, and thus do not exist in a gradient that is easily tracked and compared between species. Thus, they may not be viewed as valuable to explore ultimate questions related to social evolution. Here, we argue that derived traits can provide useful insights on social evolution even if they are absent or rare in species with a lower social organization. This applies only if the mechanism underlying the trait, rather than the function it regulates for, can be traced back to the solitary ancestors. We discuss two examples of derived traits, morphological differences in female castes and primer pheromones regulating female reproduction, demonstrating how their underlying mechanisms can be used to understand major transitions in the evolution of social behavior and emphasize the importance of studying mechanistic, rather than functional continuity of traits. 

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2. Experience, but not age, is associated with volumetric mushroom body expansion in solitary alkali bees

   https://doi.org/10.1242/jeb.238899  

   Hagadorn, Mallory A.; Johnson, Makenna M.; Smith, Adam R.; Seid, Marc A.; Kapheim, Karen M. (March 2021, Journal of Experimental Biology)

   null (Ed.)

   ABSTRACT In social insects, changes in behavior are often accompanied by structural changes in the brain. This neuroplasticity may come with experience (experience-dependent) or age (experience-expectant). Yet, the evolutionary relationship between neuroplasticity and sociality is unclear, because we know little about neuroplasticity in the solitary relatives of social species. We used confocal microscopy to measure brain changes in response to age and experience in a solitary halictid bee (Nomia melanderi). First, we compared the volume of individual brain regions among newly emerged females, laboratory females deprived of reproductive and foraging experience, and free-flying, nesting females. Experience, but not age, led to significant expansion of the mushroom bodies – higher-order processing centers associated with learning and memory. Next, we investigated how social experience influences neuroplasticity by comparing the brains of females kept in the laboratory either alone or paired with another female. Paired females had significantly larger olfactory regions of the mushroom bodies. Together, these experimental results indicate that experience-dependent neuroplasticity is common to both solitary and social taxa, whereas experience-expectant neuroplasticity may be an adaptation to life in a social colony. Further, neuroplasticity in response to social chemical signals may have facilitated the evolution of sociality. 

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3. The Evolution of Queen Pheromone Production and Detection in the Reproductive Division of Labor in Social Insects

   https://doi.org/10.1146/annurev-ento-022124-124437  

   Liebig, Juergen; Amsalem, Etya (January 2025, Annual Review of Entomology)

   Structurally diverse queen pheromones and fertility signals regulate the reproductive division of labor of social insects, such as ants, termites, some bees, and some wasps. The independent evolution of sociality in these taxa allows for the exploration of how natural history differences in sender and receiver properties led to the evolution of these complex communication systems. While describing the different effects and the structural diversity of queen pheromones, we identify two major syndromes that mostly separate ants and wasps from bees and termites in their use of different pheromone classes. We compare olfactory receptor evolution among these groups and review physiological and hormonal links to fecundity and pheromone production. We explore the cases in which queen pheromone evolution is conserved, convergent, or parallel and those in which queen pheromone responses are more likely to be learned or innate. More mechanistic information about the pathways linking fecundity to queen pheromone production and perception could help close major knowledge gaps. 

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4. Co-expression Gene Networks and Machine-learning Algorithms Unveil a Core Genetic Toolkit for Reproductive Division of Labour in Rudimentary Insect Societies

   https://doi.org/10.1093/gbe/evac174  

   Favreau, Emeline; Geist, Katherine S; Wyatt, Christopher D; Toth, Amy L; Sumner, Seirian; Rehan, Sandra M (January 2023, Genome Biology and Evolution)

   Webster, Matthew (Ed.)

   Abstract The evolution of eusociality requires that individuals forgo some or all their own reproduction to assist the reproduction of others in their group, such as a primary egg-laying queen. A major open question is how genes and genetic pathways sculpt the evolution of eusociality, especially in rudimentary forms of sociality—those with smaller cooperative nests when compared with species such as honeybees that possess large societies. We lack comprehensive comparative studies examining shared patterns and processes across multiple social lineages. Here we examine the mechanisms of molecular convergence across two lineages of bees and wasps exhibiting such rudimentary societies. These societies consist of few individuals and their life histories range from facultative to obligately social. Using six species across four independent origins of sociality, we conduct a comparative meta-analysis of publicly available transcriptomes. Standard methods detected little similarity in patterns of differential gene expression in brain transcriptomes among reproductive and non-reproductive individuals across species. By contrast, both supervised machine learning and consensus co-expression network approaches uncovered sets of genes with conserved expression patterns among reproductive and non-reproductive phenotypes across species. These sets overlap substantially, and may comprise a shared genetic “toolkit” for sociality across the distantly related taxa of bees and wasps and independently evolved lineages of sociality. We also found many lineage-specific genes and co-expression modules associated with social phenotypes and possible signatures of shared life-history traits. These results reveal how taxon-specific molecular mechanisms complement a core toolkit of molecular processes in sculpting traits related to the evolution of eusociality. 

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5. Spontaneous Emergence of Multicellular Heritability

   https://doi.org/10.3390/genes14081635  

   Zamani-Dahaj, Seyed Alireza; Burnetti, Anthony; Day, Thomas C.; Yunker, Peter J.; Ratcliff, William C.; Herron, Matthew D. (August 2023, Genes)

   The major transitions in evolution include events and processes that result in the emergence of new levels of biological individuality. For collectives to undergo Darwinian evolution, their traits must be heritable, but the emergence of higher-level heritability is poorly understood and has long been considered a stumbling block for nascent evolutionary transitions. Using analytical models, synthetic biology, and biologically-informed simulations, we explored the emergence of trait heritability during the evolution of multicellularity. Prior work on the evolution of multicellularity has asserted that substantial collective-level trait heritability either emerges only late in the transition or requires some evolutionary change subsequent to the formation of clonal multicellular groups. In a prior analytical model, we showed that collective-level heritability not only exists but is usually more heritable than the underlying cell-level trait upon which it is based, as soon as multicellular groups form. Here, we show that key assumptions and predictions of that model are borne out in a real engineered biological system, with important implications for the emergence of collective-level heritability. 

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