Research interests

I have a broad interest in understanding the organization and evolution of social life in insect societies. To this end, the research of my group in the Department of Evolutionary Biology at the University of Mainz (Germany) focuses on investigating division of labor in ants. We use different approaches to study the genetic, genomic, epigenetic, behavioral and physiological mechanisms involved in the alternative production of queens and workers, the division of labor among workers, and more generally the regulation of reproduction, nutrition and behavior in several species of ants.

 

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Past research projects

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Postdoc AntEpigenetics project (2013-2016)

@ Rockefeller University, NYC and University of Lausanne, Switzerland

 

As a Marie Curie postdoctoral fellow in the Kronauer lab at The Rockefeller University and in the Keller lab at the University of Lausanne , I have investigated whether epigenetic modifications regulate reproduction and behavior in the parthenogenetic ant Cerapachys biroi. I have used whole-genome bisulfite sequencing and RNA sequencing to compare DNA methylation, gene expression and alternative splicing patterns between brains of individuals that differ in reproduction and behavior, while controlling for their age and genetic background. DNA methylation is a relatively new field in social insects, and there was a need for more controlled, carefully replicated investigations to determine whether different castes (e.g., queen vs worker) are associated with different patterns of DNA methylation. Not only did I find that brain DNA methylation in the clonal raider ant is robust and not associated with different reproductive and behavioral states, but also showed that the current evidence for caste-specific DNA methylation in social insects is actually very weak, thus providing valuable information on the role and mode of action of DNA methylation in insect societies.

Libbrecht R., Oxley P., Keller L., Kronauer, D. (2016) Robust DNA methylation in the clonal raider ant brain. Current Biology 26(3):R391-395.

 

PhD project - (2007-2012) @ University of Lausanne, Switzerland

 

Download PhD dissertation

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During my PhD under the supervision of Prof. Laurent Keller at the University of Lausanne, I developed four projects to investigate how genes and physiology affect the organization and the division of labor in insect societies.

 

Genetic components to caste allocation in ants. Social insect colonies are characterized by a reproductive division of labor and the coexistence of distinct castes. In social insect species with multiple queens per colony, the fitness of nestmate queens directly depends on the process of caste allocation (i.e., the relative investment in queen, sterile worker and male production). The aim of this study was to investigate the genetic components to the process of caste allocation in a multiple-queen ant species. I conducted controlled crosses in the Argentine ant Linepithema humile to identify maternal and paternal family effects on the relative production of new queens, workers and males. In addition to revealing complex non-additive genetic effects on female caste determination in a multiple-queen ant species, this study revealed strong genetic compatibility effects between parental genomes on caste allocation. These results are important because they suggest an epigenetic regulation of caste determination in L. humile and provide a better understanding for the maintenance of queen specialization in multiple-queen ant species.

Libbrecht R., Schwander T., Keller L. (2011) Genetic components to caste allocation in a multiple-queen ant species. Evolution 65: 2907-2915.

 

Genetic compatibility affects division of labor in ants. The second project of my PhD also involved the use of controlled crosses experiments, but focused on the genetics of division of labor among workers. Division of labor is central to the organization of insect societies. Within-colony comparisons between subfamilies of workers (patrilines or matrilines) revealed genetic effects on division of labor in many social insect species. Although this has been taken as evidence for additive genetic effects on division of labor, this conclusion has never been experimentally tested. To determine the relative roles of additive and non-additive genetic effects (i.e., genetic compatibility, epistasis and parent-of-origin specific imprinting effects) on worker behavior, I performed controlled crosses using the Argentine ant Linepithema humile. The results were most consistent with parent-of-origin and genetic compatibility effects on division of labor. The finding of non-additive genetic effects is in strong contrast with the current view and has important consequences for our understanding of division of labor in insect societies.

Libbrecht R. & Keller L. (2012) Genetic compatibility affects division of labor in the Argentine ant Linepithema humile. Evolution 67: 517-524 

 

Mechanisms behind maternal effects on polyphenism. In the second half of my PhD, I developed a project to investigate the maternal regulation of caste polyphenism in ants. Polyphenism is the phenomenon where alternative phenotypes are produced by a single genotype in response to environmental cues. An extreme case is found in social insects, where reproductive queens and sterile workers that greatly differ in morphology and behavior can arise from a single genotype. The first experimental evidence for maternal effects on caste determination, the differential larval development toward the queen or worker caste, was recently documented in Pogonomyrmex seed-harvester ants, in which only colonies with a hibernated queen produce new queens. However, the proximate mechanisms behind those intergenerational effects have remained elusive. I used a combination of artificial hibernation, hormonal treatments, gene expression analyses and vitellogenin quantification to investigate how the combined effect of environmental cues and hormonal signaling affects the process of caste determination in Pogonomyrmex ants. The results show that the interplay between insulin signaling, juvenile hormone and vitellogenin regulates maternal effects on the production of alternative phenotypes and identify vitellogenin as a potential major player in the intergenerational transmission of information. This study revealed how environmental cues experienced by one generation can translate into phenotypic variation in the next generation.

Libbrecht R., Corona M., Wende F., Dihego D., Serrao J. and Keller L. (2013) Interplay between insulin signaling, juvenile hormone and vitellogenin regulates maternal effects on caste allocation in ants. PNAS 110: 11050-11055

 

Evidence for the reproductive ground plan hypothesis in ants. Toward the end of my PhD, I developed a project in collaboration with Dr. Miguel Corona to investigate the regulation of worker reproduction. The reproductive ground plan hypothesis (RGPH), originally developed in honeybees, posits that mechanisms regulating reproduction in solitary species have been co-opted to regulate the behavior of sterile workers in social species. To test whether such mechanisms could regulate division of labor in ants, we compared the expression of two genes (Vg1 and Vg2) involved in the production of vitellogenin (usually involved in reproduction). The finding of differential gene expression between individuals that differ in reproduction (queens and workers) and in behavior (nurses and foragers) supported the RGPH in ants. This study confirmed that the RGPH is likely to be important for the evolution of sociality, as both ants and bees co- opted mechanisms involved in the regulation of reproduction to regulate division of labor among sterile individuals, even though they evolved sociality independently.

*Corona M., *Libbrecht R., Wurm Y., Riba-Grognuz O., Studer R.S. and Keller L. (2013) Vitellogenin underwent subfunctionalization to acquire caste and behavioral specific expression in the harvester ant Pogonomyrmex barbatus. PloS Genetics 9(8): e1003730 *These authors contributed equally to the work