Understanding sociability—the degree to which individuals engage and form connections within their social groups—has long posed a challenge for biologists. In many species, which include both insects and mammals, individuals exhibit considerable variation in how socially interactive they are. This variation is influenced by multiple factors including environmental stress, developmental history, neural states, and genetics. However, pinpointing the specific genes and molecular pathways that govern these behaviors has remained elusive, particularly in non-mammalian species. The current research represents a key advance, illuminating some of the conserved genetic mechanisms that shape sociality across distant branches of the evolutionary tree.

The team employed a novel approach by integrating genome-wide analyses with behavioral data from entire honey bee colonies. Using specialized miniaturized barcodes attached to hundreds of individual bees, the scientists tracked the social interactions of these insects in custom-built glass observation hives. This automated monitoring system recorded thousands of trophallaxis events—a behavior where bees share nutritious liquid food mouth-to-mouth, serving both to nourish nestmates and to reinforce social bonds. By correlating this detailed behavioral data with whole-genome sequencing results collected from 357 bees, the researchers identified 18 genetic variants significantly related to the propensity to engage in food-sharing behaviors.

Among these important loci, variants within two key genes—neuroligin-2 and nmdar2—stood out. Both of these genes encode synaptic proteins involved in neuronal communication. Intriguingly, their human orthologs have been implicated in autism spectrum disorders, a set of neurodevelopmental conditions characterized by altered social interactions. The researchers hypothesize that these conserved genes may contribute to fundamental aspects of social cognition across diverse species, despite the stark differences between insect and human nervous systems.

Further insight was gained through transcriptome sequencing of bee brains engaged at differing levels in social interaction. Over 900 genes showed increased expression levels in bees that more frequently engaged in trophallaxis compared to less social individuals. This expansive gene expression signature hints at a widespread molecular network supporting social behaviors, likely encompassing neurotransmission, synaptic plasticity, and metabolic adaptations essential for complex group living. The identification of such a broad gene set reinforces the idea that sociability is polygenic and multifaceted, involving numerous pathways and cellular processes.

What makes these findings especially compelling is the deep evolutionary conservation suggested by this work. Despite the divergence between the lineages leading to bees and humans dating back over half a billion years, there appear to be ancient genetic “building blocks” that have been preserved to support social behaviors. Whether due to convergent evolution or retained ancestral functions, the data reveal shared molecular frameworks enabling social engagement that extend far beyond the traditionally studied mammalian models.

Traniello and his colleagues emphasize that social insects like honey bees offer an unparalleled system for studying sociogenomics at scale. The colony organization of bees allows continuous monitoring of individual experiences and interactions throughout their entire adult lives—an advantage rarely available in vertebrate studies. The coupling of advanced molecular techniques with precise behavioral assays represents a new frontier in behavioral genetics, one that promises to unravel the biological architecture of sociality with unprecedented resolution.

Moreover, the methodological synergy in this study—combining behavioral tracking, whole-genome and RNA sequencing—exemplifies the power of integrative research to penetrate complex biological phenomena. By precisely linking genetic variation to expression changes to observed behavior within the same individuals, the team achieved a multidimensional profile unattainable by traditional approaches. This paradigm illustrates how high-throughput molecular data can be harnessed to address fundamental questions in neuroscience, ethology, and evolutionary biology.

The implications of the study stretch beyond the world of bees, offering important perspectives on human social disorders. Since genes like neuroligin-2 and nmdar2 are associated with autism, these findings suggest ancient genetic components may influence social behavior and its dysfunction across species. Understanding these conserved mechanisms might ultimately pave the way for innovative interventions or therapies targeting social cognitive impairments by illuminating their foundational molecular nature.

At its core, this research also speaks to the universality of social life. Sociability—defined by a spectrum ranging from highly interactive to more isolated individuals—pervades animal societies, shaping survival, reproduction, and group cohesion. The discovery that this variability has deep evolutionary roots highlights the importance of genetic diversity in social traits and invites reconsideration of social behavior as a trait shaped by powerful selective forces operating over hundreds of millions of years.

Ian Traniello remarks on the significance of their approach: “We can follow all these animals throughout most of their lives, identify who interacts with whom, and link these interactions to genomic structure and brain gene expression patterns. By bringing these technologies together, we can test the hypothesis that molecular features underlying social organization might be conserved across species, and indeed our results confirm this fascinating possibility.”

The study sets a new standard for behavioral genomics research and opens exciting avenues for future work. Further analyses might investigate how environmental factors modulate the expression of these conserved genes, or how different social contexts influence molecular pathways contributing to sociability. Additionally, comparative studies across other insect species or vertebrates could reveal the extent of these ancient social molecular frameworks and their evolutionary modifications.

In conclusion, the integration of behavioral data with genomic and transcriptomic analyses in honey bees provides compelling evidence for shared genetic foundations of social behavior across widely divergent species. This convergence of technological innovation and evolutionary insight redefines our understanding of sociability as a deeply rooted, complex, and conserved biological trait, bridging the gap between insect and human social neuroscience.

Subject of Research: Animals

Article Title: Genetic variation influences food-sharing sociability in honey bees

News Publication Date: September 16, 2025

Web References: http://dx.doi.org/10.1371/journal.pbio.3003367

References:
Traniello IM, Avalos A, Gachomba MJM, Gernat T, Chen Z, Cash-Ahmed AC, et al. (2025) Genetic variation influences food-sharing sociability in honey bees. PLOS Biol 23(9): e3003367. https://doi.org/10.1371/journal.pbio.3003367

Image Credits: Dr. Zachary Huang (CC-BY 4.0)

Keywords: Honey bees, sociability, genetics, neurogenomics, trophallaxis, Apis mellifera, social behavior, autism-related genes, neuroligin-2, nmdar2, transcriptomics, evolutionary biology

A recent groundbreaking study published in PLOS Biology, led by Dr. Robert Brocklehurst of Harvard University’s Department of Organismic and Evolutionary Biology, employs cutting-edge biomechanical analysis to unravel this intricate evolutionary narrative. The team meticulously examined the humerus — the upper arm bone — from over 60 fossil specimens of non-mammalian synapsids alongside more than 140 specimens of extant species including reptiles, amphibians, and diverse mammals. By integrating fossil data with advanced computational techniques, they reconstructed the locomotor postures and forelimb functions of these ancient species with unprecedented precision.

The researchers utilized a novel “slice-based” landmarking method, innovatively adapted from an existing R software package, to map the complex surface morphology of humeral bones. This approach enabled precise quantification of crucial anatomical traits such as bone length, mass distribution, muscle leverage, and torsion — a measure of the bone’s twist along its longitudinal axis. These parameters serve as biomechanical proxies, providing insight into muscle attachments and locomotor capabilities, thereby illuminating the postural adaptations that ancient synapsids and their descendants underwent during their evolutionary journey.

Contrary to the prevailing paradigm of a neat, stepwise evolutionary progression from sprawling to semi-sprawling and finally to upright parasagittal postures, the study revealed a more labyrinthine adaptive landscape. This landscape is characterized by multiple, distinct adaptive peaks, each corresponding to specialized functional regimes in forelimb posture and movement. Importantly, extinct synapsid lineages occupied a variety of these peaks, evincing a rich tapestry of biomechanical experimentation rather than a straightforward linear trend.

This complex evolutionary pattern suggests that mammalian ancestors engaged in repeated episodes of adaptive radiation, wherein each major group explored a spectrum of locomotor strategies. Some of these postures approximated the modern upright stance, while others represented alternative solutions fine-tuned to specific ecological contexts. Such evolutionary plasticity underscores the dynamic interplay between morphology, function, and environmental pressures throughout the mammalian lineage’s deep history.

One particularly intriguing finding relates to a fossil species closely allied to modern marsupials and placentals, which exhibited humeral features congruent with the fully upright, parasagittal posture typical of extant mammals. This discovery implies that the definitive upright gait, long assumed to be an early hallmark of mammals, actually evolved relatively late, in contrast to traditional hypotheses. These results dovetail with recent comparative studies on vertebral and hindlimb morphology, collectively reshaping our understanding of mammalian locomotor evolution.

Moreover, the study challenges the long-held assumption that early non-mammalian synapsids exhibited sprawling postures analogous to modern reptiles such as lizards and crocodilians. Rather, the forelimb biomechanics of these ancient synapsids differ substantially, indicating unique functional adaptations absent in contemporary reptiles. This finding accentuates the distinct evolutionary identity of synapsids, highlighting their departure from basal reptilian locomotor modes well before the rise of crown mammals.

The methodology employed surmounted formidable technical hurdles inherent in comparing morphological traits across a vast taxonomic and temporal spectrum. Traditional geometric morphometric techniques, often limited to homologous structures with similar shapes, proved inadequate for such a diverse dataset spanning species separated by hundreds of millions of years. By adapting and innovating analytical tools, the research team generated a robust framework capable of translating complex fossil morphology into biomechanical function, paving the way for future evolutionary biomechanical investigations.

This research builds upon a storied scientific legacy, tracing intellectual lineages back to early 20th-century pioneers like Alfred Sherwood Romer and Farish Jenkins Jr., who first grappled with the origins of mammalian posture. With contemporary tools and computational power, the team now revisits these classic questions with renewed rigor and resolution, bringing clarity to long-standing evolutionary puzzles.

Looking ahead, the research group aims to develop detailed biomechanical models of limb articulation and muscle function in select fossil taxa. Such models promise to further elucidate the functional dynamics underlying posture and locomotion during key evolutionary transitions, offering deeper insight into the anatomical and ecological contexts that shaped mammalian evolution.

In sum, this groundbreaking study reveals an intricate and nonlinear evolutionary pathway from sprawling to upright forelimb function and posture in mammals. It highlights the evolutionary plasticity and innovation that characterized the mammalian lineage, challenging simplistic narratives and enriching our understanding of vertebrate evolution. As Dr. Brocklehurst emphasizes, deciphering how mammals came to stride upright transcends mere bone morphology; it opens a window into the dynamic history of life on Earth.

Subject of Research: Evolution of forelimb posture and locomotor biomechanics in mammals and their synapsid ancestors

Article Title: Adaptive landscapes unveil the complex evolutionary path from sprawling to upright forelimb function and posture in mammals

News Publication Date: 24-Jun-2025

Web References:

• PLOS Biology Article DOI: 10.1371/journal.pbio.3003188
• Related studies on backbone and hindlimb evolution:
  • Royal Society Publishing: Mammalian backbone evolution
  • Science Advances: Hindlimb evolution

Image Credits: Magdalen Mercado