D3140: Microbe-mediated stabilization of mosquito-pitcher plant interactions

Wyeomyia smithii mosquitoes form an obligate symbiosis with the northern carnivorous pitcher plant, Sarracenia purpurea—completing their entire life cycle in the plant’s water-filled leaves (pitchers). S. purpurea relies on both developing W. smithii larvae and the diverse bacterial community present in its pitchers for prey digestion. However, little is known about the impact of W. smithii-bacteria interactions on the structure and stability of this micro-ecosystem. We tested the hypothesis that W. smithii-bacteria interactions reinforce stability of this symbiosis via two aims: (1) Assess whether viable bacteria are dispersed by individual adult female W. smithii mosquitoes during oviposition, and (2) Characterize the relative contributions of maternally-transmitted and pitcher-associated bacteria to larval fitness. Individual oviposition assays indicated that viable bacteria can be recovered from eggs laid by females under sterile conditions and viable bacterial density was positively associated with egg hatch rate. Bioassays of larval offspring from each female further indicated that maternally-transmitted bacteria are sufficient to support development to the adult stage, although the proportion of larvae that survived to the final instar or pupated and emerged as adults varied substantially between females. This variability was diminished when females laid eggs under non-sterile conditions, and the fitness of larvae reared in the presence of both maternally-transmitted and pitcher-associated bacteria was significantly higher than that of larvae reared in the presence of only one source of bacteria. Altogether, these results support our hypothesis and have important implications for our understanding of the function of animal-microbe interactions in natural ecosystems.