Advisor(s)

Rebeca Rosengaus

Abstract

Social insects, including ants, face high risks of infection and disease transmission due to their exploitation of microbe-rich environments and their densely-packed colonies of highly-related individuals. Ants use a variety of defense mechanisms to cope with disease, including behavioral, biochemical, and immunological defenses. In this study, the carpenter ant Camponotus pennsylvanicus was used to investigate the transfer of antimicrobial factors among nestmates via mouth-to-mouth regurgitation (trophallaxis). These ants store nutrients in their crop and engage regularly in trophallaxis, feeding all colony members through this "social stomach." We hypothesized that in addition to nutrients, ants may also be transferring antimicrobial peptides (AMPs) or enzymes during these frequent social exchanges. To induce an immune response, worker ants were injected with: a) heat-killed Serratia marcescens, a generalist entomopathogenic Gram-negative bacterium, b) lipopolysaccharide, an immunogenic outer-membrane component of Gram-negative bacteria, or c) sterile Ringer solution. Behavioral observations of relative frequencies of trophallactic behavior were performed, accompanied by analysis of differences in antimicrobial activity of the regurgitate droplet of ants using a zone of inhibition assay. Total protein concentrations of regurgitate droplets were measured with Bradford assays followed SDS-PAGE analysis of protein content. Frequencies of trophallaxis were significantly higher for immune-challenged ants. Moreover, ants in these treatments exhibited increased antimicrobial activity in their regurgitate droplets relative to those of controls. Although no novel proteins were detected in standardized SDS-PAGE, an increase in total protein concentration was observed in immunechallenged ants and a protein between 25 and 35 kD showed consistent enhancement in non-standardized SDS-PAGE following an immune challenge. Our data provide the first evidence that AMPs and/or antibacterial enzymes, including the tentatively identified enzyme cathepsin D, are constitutively expressed in the regurgitate droplet of C. pennsylvanicus. Such AMPs and/or enzymes may then be actively transferred during increased trophallactic behavior. These results suggest trophallaxis as one mechanism by which socially-mediate prophylaxis may occur in social insects.

Date Accepted

5-1-2010

Publication Date

5-1-2010

Keywords

disease transmission, carpenter ant, trophallaxis

Degree Grantor

Northeastern University

Rights Holder

Casey Hamilton

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