Department Chair

I. Martha Skerrett, PhD.

Date of Award


Access Control

Open Access

Degree Name

Biology, M.A.


Biology Department


Robert J. Warren, PhD.

Department Home page

First Reader

Robert J. Warren, PhD.

Second Reader

Amy M. McMillan, PhD.

Third Reader

Gary W. Pettibone, PhD.


Seed dispersal by ants is a cosmopolitan mutualism involving thousands of plant species. Ants gain a food reward (elaiosomes) from the plant seed, and ant-mediated plants gain several presumed benefits, including dispersal away from parent plants and placement in 'safe site' microhabitat. Higher plant germination and survival in ant nest soils has been attributed to higher levels of nutrients, aeration, and soil moisture than surrounding soils, but evidence in support of these benefits is inconsistent. Ants secrete anti-microbial compounds that inhibit microbial pathogens. I explore the possibility that ants transfer anti-microbial properties to the soil they inhabit, and there is some evidence that the anti-microbial body chemistry may benefit plants. Hence, an additional benefit of ant-mediated seed dispersal might be that myrmecochores (ant-dispersed plants) gain pathogenic fungal protection from anti-microbial ant secretions. If so, I expect that seed-dispersing ants inhibit plant pathogenic (phytopathogenic) fungi. I first re-analyzed published data to determine whether ant-occupied soil contained fewer phytopathogenic fungi. I then conducted two experiments to test for anti-fungal effects on plant pathogen fungi. In the first, I used assays of known phytopathogenic fungi (Alternaria alternata and Fusarium oxysporum) with ant soaked hexane. I measured the zone of inhibition on agar plates and calculated area to compare the effect of the treatments. In the second experiment, I conducted a metagenomic-sequencing analysis to determine fungal diversity in ant nests as compared to control soils. The reanalysis of published data showed plant pathogenic fungal diversity decreased within ant nests but not control soil. I found no evidence of direct iii pythotopathic inhibition in the fungal assays, but I also found that the methodology did not have enough power to detect effects. The metagenomic analysis did confirm significantly less fungal diversity in ant-colonized than control soils. More importantly, the colonized soils contained significantly less diversity of plant pathogenic fungi than control soils. These results suggest ant presence in soils reduces fungal diversity and that ant-mediated seed dispersal provides a heretofore unexplored benefit to myrmecochores: fungal pathogen protection. The added benefit of fungal protection strengthens the evidence for myrmecochore dependency on their dispersal partner, and provides a more consistent explanation for why plants recruit better in ant nest soil. Pathogenic fungal protection may be a key evolutionary benefit to the worldwide phenomenon of ant-mediated seed dispersal.