UC Berkeley

Life can be hierarchically organized into units of reproduction that function as “individuals”. In evolutionary theory, individuals are typically cells or multicellular bodies, but the boundaries or definitions of individuals are ambiguous. A working definition for biological individuals will likely always be circumstantial and debated, but biologists are not the only ones constructing boundaries around the organizations of living things. Cells, bodies, societies, and even species construct their own boundaries to their identities through recognition systems that filter what components are allowed to exist in these levels of organization. My dissertation broadly investigates social recognition in eusocial animals, specifically ants and trematodes. Ants are the model system for “superorganisms”, or social groups that collectively reproduce using a reproductive division of labor. Trematodes (i.e. flatworms, blood flukes) are parasitic worms that are recently argued to possess a eusocial life stage while living in snail intermediate hosts. I begin with a review arguing why trematodes are comparable to other eusocial taxa, also explaining why the definitions and evolutionary theories of eusociality struggle to include polyembryonic parasites, such as the trematodes. Next, I report my experiments on colony recognition in my trematode species of interest, Himasthla rhigedana. I demonstrate that H. rhigedana are capable of distinguishing between conspecific colonies from different coastal marshes, directing more aggression towards trematodes from geographically distant subpopulations. I also suggest that this species is “facultatively” eusocial, as its soldier caste is not strictly composed of non-reproducing trematodes. Finally, I investigate the functions of the chemical cues used in social recognition in the invasive Argentine ant, Linepithema humile. Argentine ants use cuticular hydrocarbons to recognize members of their invasive “supercolonies”, but these compounds also influence their desiccation resistance. Our experiments show that the ratio of compound classes from an ant’s hydrocarbon profile determines their survival in desiccation assays. Virtually every level of life’s hierarchical organization employs recognition systems, but we are far from universal theories explaining the function and evolution of recognition from cells to societies. This dissertation is intended to contribute to a comparative biology of recognition systems across taxa, and also validate the inclusion of parasite sociality as comparable to other forms of animal sociality.