Evol Ecol Res 16: 351-361 (2014)     Full PDF if your library subscribes.

Is there specificity in a defensive mutualism against soil versus laboratory nematodes, Dictyostelium discoideum farmers and their bacteria?

Boahemaa Adu-Oppong, David C. Queller and Joan E. Strassmann

Department of Biology, Washington University in St. Louis, St. Louis, Missouri, USA

Correspondence: B. Adu-Oppong, Department of Biology, CB 1137, Washington University in St. Louis, St. Louis, MO 63130, USA.
e-mail: badu-oppong@wustl.edu


Background: The social amoeba Dictyostelium discoideum is a soil-dwelling microbe, which lives most of its life cycle in the vegetative stage as a predator of bacteria and as prey for nematodes. When bacteria are sparse, amoebae aggregate into a multicellular fruiting body. Some clones of D. discoideum have agriculture (Brock et al., 2011). They carry bacteria through the social stage, eat them prudently, and use some bacteria as defence against non-farming D. discoideum competitors. Caenorhabditis elegans preys on D. discoideum in the laboratory but does not encounter it in nature because C. elegans lives on rotten fruit. The nematode Oscheius tipulae is abundant in the soil.

Questions: Do the defensive bacteria that farmers carry also protect farmers from nematodes? Is this protection specific to nematodes that reside with D. discoideum?

Hypotheses: Many organisms evolve defensive mutualisms against predators. The natural habitat of D. discoideum is populated with nematodes. Therefore, we hypothesize that farming D. discoideum clones use non-food bacteria for protection from nematodes. We predicted higher fitness of farmers than non-farmers in the presence of nematodes. We also predicted to see this change of fitness only in the presence of the soil nematode, O. tipulae.

Organisms: Amoeba Dictyostelium discoideum, nematodes Caenorhabditis elegans and Oscheius tipulae, bacteria Klebsiella pneumoniae and Burkholderia xenovorans.

Methods: We compared spore production of D. discoideum farmers and non-farmers with and without nematodes. We also looked at nematode proliferation in the presence of farmers, non-farmers, K. pneumonia, and B. xenovorans.

Results: Overall, farmer D. discoideum produced fewer spores than non-farmers. There was a decrease in the spore counts in the presence of nematodes for both farmers and non-farmers. There was a significant decrease in the percentage change in spore production for the farmers in the presence of soil nematodes but not laboratory nematodes. Nematode proliferation with the laboratory nematode and soil nematode did not vary in the presence of farmers, non-farmers, K. pneumoniae or B. xenovorans.

Conclusion: The non-food bacteria that farmers carry do not provide defence against nematodes. In fact, it was a disadvantage for farmers to carry bacteria, since the soil nematode decreased spore production for farmers compared with non-farmers. However, the differences between the laboratory nematode and the soil nematode are marked enough to conclude that different species of nematodes respond differently to D. discoideum as a food source.

Keywords: defensive mutualisms, Dictyostelium discoideum, Caenorhabditis elegans, Oscheius tipulae, bacteria.

IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.


        © 2015 Boahemaa Adu-Oppong. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

       Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.

       All copies of abstracts and articles must preserve their copyright notice without modification.