Implicating microbes in regulation of host phenology

It is fundamentally important for organisms to coordinate developmental and behavioral milestones throughout their lifetimes in accordance with the abiotic and biological conditions of their environment. This may take the form of seasonality of reproduction (e.g., reproduce in the spring) or periods of reduced metabolic activity (e.g., hibernate in the winter). However, it is no small task to accurately anticipate the onset of environmental conditions, requiring integration of complex cues like temperature and day length (i.e., photoperiod). The cost of incorrectly anticipating the changing of the seasons is steep, not only in terms of having organismal physiology appropriate for local conditions, but also for matching the seasonal dynamics of other organisms with which an organism may interact. For example, it would be disadvantageous for a plant to flower in the absence of its insect pollinators. The seasonal timing of life history events is known as phenology, and cases where interacting organisms are misaligned in their timing are known as phenological mismatch.

Global change can drive phenological mismatch, with errant temperature events eliciting an inappropriate change in organismal biology or the early onset of warm temperatures contradicting the locally-adapted response to day length. What is unknown is to what extent microbes might play a role in buffering organismal response to global change (e.g., offering an extended phenotype which may confer more adaptive plasticity) or the role host-associated microbes play in coordinating seasonal phenology in the first place. In my PhD I began work in the pitcher plant mosquito to explore the essentiality of microbes to coordinate host hibernal diapause (some mosquito larvae go to sleep for the winter!) and on-going work is exploring the division of metabolic labor in the overwintering mosquito host.

W. smithii mosquitoes undergo photoperiod-programmed diapause during the onset of winter, when day lengths get short, these mosquitoes go to sleep! Individuals overwinter as third instar larvae, sometimes completely freezing in the water-filled pitchers where they live. Our research hopes to elucidate the importance of microbes in host coordination of diapause. We will also explore the microbe- and host-derived products that differentiate the host active state and diapause.

Work in the diapausing mosquito system will also be conducted across temperatures, to more accurately explore the effects of mismatched seasonal cues on diapause survival and host-associated microbiota (e.g., warm temperatures during diapause). This work is only possible through on-going collaboration with PhD student Heidi McKee in Dr. Kerri Coon’s Lab of Vector Biology and Microbiology.

(Left) We conduct simulated diapause experiments on larval W.smithii across a range of temperature conditions. (Right) We can measure host physiological variables like gut transit time for sleeping mosquito larvae, even though their metabolic activity is reduced, it is not fully stopped even in diapause. Here we see fluorescently-tagged bacteria are still uptaken by larval mosquitoes in diapause.

Associated references:

Arellano, A.A.*, McKee, H.*, Lee, J. †, Prack, J.P.†, Young, E.B., Coon, K.L. Bacterial community composition and function associated with population bottlenecks and temperature during pitcher plant mosquito seasonal metabolism. (In prep)

McKee, H.*, Arellano, A.A.*, Lee, J. †, Young, E.B., Coon, K.L. Host-microbe divisions of labor during seasonal metabolism revealed by global metabolomics and microbiota swaps. (In prep)

* authors contributed equally
† undergraduate mentee