Pharaoh ant Monomorium pharaonis queen and workers,©Luigi Pontieri

We study the genetic and behavioral underpinnings of complex social systems in order to understand how these systems function and evolve. We are especially interested in how social interactions affect genetic architecture and trait evolution.

We use social insects, such as the pharaoh ant pictured above, as a study system because they are exemplar social systems and are also well-established models for research in social evolution, behavioral genetics, and collective behavior.

word cloud illustrating common words used in publications

Recent Publications

Pontieri, L., Schmidt A. M., Singh R., Pedersen J. S., & Linksvayer T. A. (2017).  Artificial selection on ant female caste ratio uncovers a link between female-biased sex ratios and infection by Wolbachia endosymbionts. Journal of Evolutionary Biology. 30, 225-234. Abstract

Social insect sex and caste ratios are well-studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short-term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female-biased in the two replicate high selection lines and less female-biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female-biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia-infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.

Warner, M. R., Mikheyev A. S., & Linksvayer T. A. (2017).  Genomic signature of kin selection in an ant with obligately sterile workers. Molecular Biology and Evolution. AbstractWebsite

Kin selection is thought to drive the evolution of cooperation and conflict, but the specific genes and genome-wide patterns shaped by kin selection are unknown. We identified thousands of genes associated with the sterile ant worker caste, the archetype of an altruistic phenotype shaped by kin selection, and then used population and comparative genomic approaches to study patterns of molecular evolution at these genes. Consistent with population genetic theoretical predictions, worker-upregulated genes showed relaxed adaptive evolution compared to genes upregulated in reproductive castes. Worker-upregulated genes included more taxonomically-restricted genes, indicating that the worker caste has recruited more novel genes, yet these genes also showed relaxed selection. Our study identifies a putative genomic signature of kin selection and helps to integrate emerging sociogenomic data with longstanding social evolution theory.

Warner, M. R., Kovaka K., & Linksvayer T. A. (2016).  Late-instar ant worker larvae play a prominent role in colony-level caste regulation. Insectes Sociaux. doi:10.1007/s00040-016-0501-3, Abstract

The success of social insect societies is often attributed to an efficient reproductive division of labor between queen and worker castes. At the group level, social insect colonies must decide both the timing and amount of resources to allocate to each caste. Queen production is typically restricted by factors such as season or the presence of fertile queens in colonies. In the absence of such inhibition, the relative production of new queens versus workers varies between and is regulated by colonies. Here, we investigate social regulation of caste in the ant Monomorium pharaonis through a series of experiments manipulating the environment in which developing larvae are reared. The number of new queens produced depended strongly on diet as well as the number of late-instar worker larvae in the colony at the time of caste regulation. Given that these late-instar larvae are known to process solid protein for the rest of the colony, their stimulatory effect on queen production is likely a result of their contribution to a colony’s nutrient assimilation. Our results emphasize the need to consider late-instar larvae as critical social players and effectors of colony regulatory dynamics.

Linksvayer, T. A., & Wade M. J. (2016).  Theoretical predictions for sociogenomic data: the effects of kin selection and sex-limited expression on the evolution of social insect genomes. Frontiers in Ecology and Evolution. 4, 65. Abstractlinksvayer_and_wade_2016_predictions_for_sociogenomic_data.pdf

Kin selection theory has always been explicitly genetic and has long been invoked to explain the evolution of the sterile worker caste in the social insects. However, sociogenomic studies of the evolution and genomic basis of social insect caste have been largely disconnected from kin selection theory and other related genetic theories of social evolution. Two previous population genetic models make testable predictions for patterns of sequence diversity for genes shaped indirectly by kin selection compared to genes shaped directly by natural selection, but there is some confusion in the literature regarding the predicted effects of kin selection and sex-limited expression on molecular evolution. We review the previous models and then use a simple parental effect model to clarify that the two factors, kin selection and sex-limited expression, are distinct and each has a separate effect on the expected patterns of molecular evolution. We further build on the previous models to show how categories of genes in social insect genomes with diverse combinations of fitness effects (direct, parental, sib, and offspring) and patterns of sex-limitation are predicted to evolve. We discuss how caste- and sex-specific transcriptomic profiling, coupled with population genomic data, can be used to identify different functional categories of genes and subsequently test whether observed patterns of molecular evolution fit theoretical predictions.

Tarpy, D. R., Simone-Finstrom M., & Linksvayer T. A. (2016).  Honey bee colonies regulate queen reproductive traits by controlling which queens survive to adulthood. Insectes Sociaux. 63, 169-174. Abstracttarpy_et_al_2016_insectes_sociaux.pdf

The production of new queens in honey bee colonies is one of the most important determinants of reproductive success, and it involves cooperative behavior among hundreds or thousands of workers. Colony members are generally expected to benefit by optimizing the reproductive traits of prospective replacement queens, but potential conflicts of interest among colony members could result in suboptimal queens. We studied the degree to which colonies regulate adult queen traits by controlling access to developing queens that survived from pupation to adulthood. We also searched for evidence of strong conflict among patrilines by comparing the contribution of patrilines to new queens and new workers, although we found no evidence for the existence of significantly queen-biased patrilines or for any association between patriline contribution to new queens and queen traits. However, adult queens emerging from cells accessible to workers were larger in terms of wet mass and thorax width compared to adult queens emerging from cells that were not accessible to workers. These results suggest that colonies regulate queen quality traits by curtailing low-quality queens from fully developing, which is further evidence that cooperation predominates over potential conflict within honey bee colonies.

Akçay, E., Linksvayer T. A., & Van Cleve J. (2015).  Bridging social evolution theory and emerging empirical approaches to social behavior. Current Opinion in Behavioral Sciences. 6, 59-64. Abstractakcay_et_al_2015_current_opinion.pdf

Spurred on by technological advances, the last several years have seen an explosion of studies of behavioral, genomic, and neurophysiological mechanisms of social behaviors. Yet these empirical studies and the vast amount of data they produce are typically disconnected from well-established social evolution theory. We argue that unlocking the transformative potential of the emerging empirical approaches to social behavior requires new kinds of theoretical approaches that integrate proximate behavioral, genomic, and neurophysiological mechanisms with evolutionary dynamics. We review recent efforts in this direction that show how proximate mechanisms are important for evolutionary dynamics. However, we argue that these frameworks are still too distant from empirical systems to interface with emerging datasets. As an example of improved approaches that can be developed, we focus on the evolution of social gene regulatory networks, and discuss how integrating dynamics of gene regulatory networks with social evolution theory can result in rigorous hypotheses that are testable with sociogenomic data.

Vojvodic, S., Johnson B. R., Harpur B., Kent C., Zayed A., Anderson K. E., & Linksvayer T. A. (2015).  The transcriptomic and evolutionary signature of social interactions regulating honey bee caste development. Ecology and Evolution. DOI: 10.1002/ece3.1720. Abstractvojvodic_et_al-2015-ecology_and_evolution.pdf

The caste fate of developing female honey bee larvae is strictly socially regulated by adult nurse workers. As a result of this social regulation, nurse-expressed genes as well as larval-expressed genes may affect caste expression and evolution. We used a novel transcriptomic approach to identify genes with putative direct and indirect effects on honey bee caste development, and we subsequently studied the relative rates of molecular evolution at these caste-associated genes. We experimentally induced the production of new queens by removing the current colony queen, and we used RNA sequencing to study the gene expression profiles of both developing larvae and their caregiving nurses before and after queen removal. By comparing the gene expression profiles of queen-destined versus worker-destined larvae as well as nurses observed feeding these two types of larvae, we identified larval and nurse genes associated with caste development. Of 950 differentially expressed genes associated with caste, 82% were expressed in larvae with putative direct effects on larval caste, and 18% were expressed in nurses with putative indirect effects on caste. Estimated selection
coefficients suggest that both nurse and larval genes putatively associated with caste are rapidly evolving, especially those genes associated with worker development. Altogether, our results suggest that indirect effect genes play important roles in both the expression and evolution of socially influenced traits such as

Keller, K., Ishak H. D., Linksvayer T. A., & Mueller U. G. (2015).  Bacterial community composition and diversity in an ancestral ant fungus symbiosis. FEMS Microbiology Ecology. 91, fiv073. Abstract

Editor’s Choice article for issue 91.7 of FEMS Microbiology Ecology


Fungus-farming ants (Hymenoptera: Formicidae, Attini) exhibit some of the most complex microbial symbioses because both macroscopic partners (ants and fungus) are associated with a rich community of microorganisms. The ant and fungal microbiomes are thought to serve important beneficial nutritional and defensive roles in these symbioses. While most recent research has investigated the bacterial communities in the higher attines (e.g., the leaf cutter ant genera Atta and Acromyrmex), which are often associated with antibiotic-producing Actinobacteria, very little is known about the microbial communities in basal lineages, labeled as “lower attines”, which retain the ancestral traits of smaller and more simple societies. In this study we used 16S-amplicon pyrosequencing to characterize bacterial communities of the lower attine ant Mycocepurus smithii among seven sampling sites in central Panama. We discovered that ant and fungus garden associated microbiota were distinct from surrounding soil, but unlike the situation in the derived fungus-gardening ants, which show distinct ant and fungal microbiomes, microbial community structure of the ants and their fungi were similar. Another surprising finding was that the abundance of Actinomycete bacteria was low and instead, these symbioses were characterized by an abundance of Lactobacillus and Pantoea bacteria. Furthermore, our data indicate that Lactobacillus strains are acquired from the environment rather than acquired vertically.