Pathogenic pressures : the life and death struggle of dampwood termites during colony foundation

Abstract

Termites are an ecologically dominant taxon that provides many important ecosystem services. In spite their reputation for hardiness, new colonies have an extremely low probability of becoming established. Swarming alates, winged individuals that disperse from their natal nest to initiate colonies, encounter myriad environmental hazards that drastically reduce the likelihood of colony foundation: high rates of predation, desiccation, limited nutrient availability, and infectious agents. Pathogens are a particularly strong threat to soil and wood-dwelling species. Given pathogens pose important selection pressures, I hypothesized that newly established queens and kings have evolved multiple strategies to protect themselves and their offspring from disease. We assessed whether the bacteria, Serratia marcescens-an ecologically relevant, gram-negative, facultative termite pathogen-negatively affected the survival and growth of newly founded termite colonies. In a series of experiments, virgin alates of the dampwood termite, Zootermopsis angusticollis, were subjected to one of four treatments: naïve (untreated), or injection with either sterile saline, heat-killed S. marcescens, or a sublethal does of live S. marcescens, and paired with either treated or untreated mates. The resulting incipient colonies were assessed for colony-level fitness by quantifying king and queen survival, time to onset and likelihood of both oviposition and hatching, overall egg production and hatching success. We identified factors that, under pathogenic stress, influenced these fitness-related milestones, and developed a comprehensive model of colony foundation in this species. While infection significantly reduced the number of successfully established colonies, colony establishment was positively influenced by queen mass as well as the king's survival and mass, suggesting that the contributions of the king as a co-founder are vital to successful colony establishment in termites. We also assessed termite embryos for both antifungal and antibacterial activity, and provide the first evidence that immature termites are capable of inhibiting the growth of both fungal conidia, and a Gram-negative bacteria. Finally, we assayed for both paternal and maternal transgenerational immune priming (TGIP) by running embryonic transcriptomic analyses and functional antibacterial assays. Our results provide the first molecular evidence of TGIP in termites. Infected queens sired embryos with one immune gene, Relish, having more than twice the expression relative to controls. Together, the four chapters in my dissertation have made significant inroads into a new avenue of research: termites as models for mate assistance, parental investment, transgenerational immunity, embryonic immunocompetence, and the influence of pathogenic pressures on shaping all aspects of social interactions in termites during colony foundation.--Author's abstract