Impacts of Microbiomes on Mutualisms

November 16, 2018 by wpeeb

Jonathan Dickey, a graduate student in the Fordyce lab, investigates the mediation of pollinator network assembly by rhizospheric soil microbiota through reproductive plant traits and aboveground fitness consequences in the genus Salvia. He demonstrates this by sampling soil microbiomes of Salvia lyrata at various phenological stages of development while measuring traits like photosynthetic biomass and floral abundance.

“We have seen before that the main driver of pollinator visitation and community composition relative to ecoregion and soil context is driven by plant composition, floral traits, and rewards, but how do belowground communities influence plant distribution and relative attractiveness towards insects?” Jonathan says.

Jonathan plans to quantify soil microbial communities based on 16S rRNA gene abundance using Illumina next-generation sequencing for each plant replicate per phenological stage. Jonathan’s exploration of community assembly with Salvia lyrata is multidisciplinary and connects community ecology with population level, evolutionary processes like the phenotypic selection. Furthermore, he has been optimizing a protocol for seed sterilization and germination for the genus Salvia by repeated processes that include seed coat surface sterilization and heat treatments to remove all potential endophytic microbiota. Upon successful germination, Jonathan plans to use soil microbial slurries associated with juveniles and flowering individuals to measure flowering time, abundance, corolla tube length, and ultimately pollinator visitation rates.

Additionally, he uses species distribution modeling (SDMs) to inspect how nutrient based mutualisms can breakdown in future climate scenarios. Through this exploration, he explicitly states the spatial extent at which potential niche divergence could occur in Eastern North America and the implications for conservation and effects on higher trophic levels. From yet another avenue, Jonathan is writing an R package employing MuSSE, a phylogenetic method, to analyze population size as a trait dependent on the presence of a stress-tolerant gene. The utility of this package is versatile and can provide a nuanced look at community disassembly in light of climate change or various disturbance events.

“We’re just now beginning to fully appreciate the vital role that microbial communities play across levels of ecological organization,” Fordyce says. “Jonathan’s project, entirely of his own design, is timely and novel. I’m looking forward to seeing what he discovers.”

Ants as Seed Dispersers

November 16, 2018 by wpeeb

Although it is likely most people have experienced ants at a picnic, they may not realize ants are important seed dispersers, a mutualism referred to by ecologists as myrmecochory. Seed dispersal by ants exists worldwide, but the eastern deciduous forests are a hotspot for this ant-plant interaction. Approximately 35 percent of the herbaceous plants in the understory of forests in eastern North America rely on ants for seed dispersal. Plant species that have coevolved myrmecochory have an oil-rich appendage, known as an elaiosome. The elaiosome attracts the ants with chemical cues. Ants pick up the seed by the elaiosome and return with it to their nest where they feed the elaiosome to their brood. The seed either remains in the nest or is taken outside of the nest. Thus, in myrmecochory, ants gain food, and seeds receive dispersal away from their parent plant, protection from seed predators, and a nutrient-rich germination site in or around ant nests.

Additional organisms likely play a role in this interaction. Microbes, such as bacteria and fungi, are abundant in soil and decaying wood environments where ants nest and seeds germinate. Some of these microbes are harmful to plants or ants, so ants and plants have defenses against these pathogens. Each partner in the ant seed dispersal mutualism has the potential to affect the other partner’s microbes. Chloe Lash, a graduate student in the Kwit Lab, is investigating the effects of chemicals and microbes in this mutualism for her dissertation.

Chloe uses advanced chemical identification techniques to investigate plant and ant chemicals and their potential antimicrobial properties. A combination of traditional and next generation sequencing techniques allows Chloe to understand the microbial loads that both ants and seeds encounter and how those microbial communities change when the partners interact with each other. This novel incorporation of chemical and microbial facets into myrmecochory will contribute to understanding the evolution and persistence of the myrmecochory mutualisms and can help scientists predict the consequences of global change-related disruptions.