Thermal sensitivity and seasonal change in the gut microbiome of a desert ant, Cephalotes rohweri

Microorganisms within ectotherms must withstand the variable body temperatures of their hosts. Shifts in host body temperature resulting from climate change have the potential to shape ectotherm microbiome composition. Microbiome compositional changes occurring in response to temperature in nature have not been frequently examined, restricting our ability to predict microbe-mediated ectotherm responses to climate change. In a set of field-based observations, we characterized gut bacterial communities and thermal exposure across a population of desert arboreal ants (Cephalotes rohweri). In a paired growth chamber experiment, we exposed ant colonies to variable temperature regimes differing by 5 °C for three months. We found that the abundance and composition of ant-associated bacteria were sensitive to elevated temperatures in both field and laboratory experiments. We observed a subset of taxa that responded similarly to temperature in the experimental and observational study, suggesting a role of seasonal temperature and local temperature differences amongst nests in shaping microbiomes within the ant population. Bacterial mutualists in the genus Cephaloticoccus (Opitutales: Opitutaceae) were especially sensitive to change in temperature-decreasing in abundance in naturally warm summer nests and warm growth chambers. We also report the discovery of a member of the Candidate Phlya Radiation (Phylum: Gracilibacteria), a suspected epibiont, found in low abundance within the guts of this ant species.

Culturable bacteria are more common than fungi in floral nectar and are more easily dispersed by thrips, a ubiquitous flower visitor

Variation in dispersal ability among taxa affects community assembly and biodiversity maintenance within metacommunities. Although fungi and bacteria frequently coexist, their relative dispersal abilities are poorly understood. Nectar-inhabiting microbial communities affect plant reproduction and pollinator behavior, and are excellent models for studying dispersal of bacteria and fungi in a metacommunity framework. Here, we assay dispersal ability of common nectar bacteria and fungi in an insect-based dispersal experiment. We then compare these results with the incidence and abundance of culturable flower-inhabiting bacteria and fungi within naturally occurring flowers across two coflowering communities in California across two flowering seasons. Our microbial dispersal experiment demonstrates that bacteria disperse via thrips among artificial habitat patches more readily than fungi. In the field, incidence and abundance of culturable bacteria and fungi were positively correlated, but bacteria were much more widespread. These patterns suggest shared dispersal routes or habitat requirements among culturable bacteria and fungi, but differences in dispersal or colonization frequency by thrips, common flower visitors. The finding that culturable bacteria are more common among nectar sampled here, in part due to superior thrips-mediated dispersal, may have relevance for microbial life history, community assembly of microbes, and plant-pollinator interactions.

The timing of leaf damage affects future herbivory in mountain sagebrush (Artemisia tridentata)

Many plants respond to herbivory by increasing expression of defensive traits. The defensive response of plants can vary depending on plant condition, seasonality, and time of day. Due to a lack of field-based studies, it is unclear how temporal variability in defensive response may alter future rates of herbivory within ecological communities. In a series of simulated herbivory experiments, I quantified how the timing of leaf damage in mountain sagebrush (Artemisia tridentata ssp. vaseyana) affects future herbivory. An identical leaf damage treatment was applied across 12 time windows to test how the effectiveness of response to herbivore damage changes along three interacting temporal scales: diel, seasonal, and annual. In contrast to several studies demonstrating induced resistance to herbivory in sagebrush, prevention of future herbivory was only detected following summer afternoon leaf damage in one of three years. These findings suggest that the timing of experimental leaf damage is one of many factors contributing to variability in field-based plant defensive induction studies.