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Dung beetles and their nematode parasites as ecosystem engineers and agents of disease




Boze, Broox G. V., author
Moore, Janice, advisor
Naug, Dhruba, committee member
Lacy, Michael, committee member
Ubelaker, John, committee member

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Dung beetles (Order Coleoptera, Subfamily Scarabaeoidea), are a magnificent group of insects noted for both their physical beauty and ecologically significant role in parasite suppression and agricultural management. These insects feed on feces in both their larval and adult forms and are classified into one of three groups based on the way they procure fecal resources to their young. Paracoprid dung beetles collect chunks of feces and bury them in tunnels/nests dug directly below the site of deposition, telocoprid beetles create carefully crafted balls of dung and roll them away from the pat before burying them in underground nests, and endocoprid beetles create nests in the feces without moving it from the original deposition site. Because dung beetles interact with feces on a regular basis, and because many parasites use feces as a medium for distributing their eggs, it is not uncommon for dung beetles to come in contact with parasite propagules at a rate higher than that seen in other animals. While the majority of parasite propagules cannot survive consumption by a dung beetle, several nematode species have found a way to use these insects as their intermediate hosts. After being consumed by a dung beetle, both Streptopharagus pigmentatus (found throughout East Asia) and Physocephalus sexalatus (found in the Southeastern United States) migrate from the dung beetle's digestive tract into the body cavity of the beetle where they wait to be consumed by their final host. Trophically transmitted parasites often change the behavior of their host and examples of behavioral modification have been found in most major host taxa. This study asks whether these two nematodes alter dung beetle behavior in ways that affect transmission dynamics and/or their role as ecosystem engineers. Indeed, when nematode infections are present, both paracoprid and telocoprid beetles reduce their feeding rate and interaction with feces. Paracoprid beetles (from the genus Onthophagus and Phaneaus) infected with nematodes consume only half of the feces consumed by uninfected beetles. Further studies on beetles from the genera Phaneaus indicate that these beetles also bury less feces and do so at a shallower depth. This is relevant because dung beetles are responsible for removing and processing the majority of fecal material in both agricultural areas and forest ecosystems. Feces serve as breeding grounds for many insect pests and carry nutrients that, when buried by dung beetles, are essential for plant health. I show that both S. pigmentatus and P. sexalatus, through alterations in their host's behavior, alter the availability of fecal resources to both plant and animal communities and should therefore be classified as an ecosystem engineers. Telocoprid beetles infected by the nematode parasite P. sexalatus also exhibit reduced feeding behavior and provide a unique opportunity to quantify the fecal resources provided to young. It is not uncommon for males and females of many host to respond to infection in different ways and indeed that is what we see in telocoprid beetles from the genus Canthon. Both C. pilularis and C. nigricornis females show reduced feeding whereas this difference in consumption is not present in male beetles. Male beetles of both C. pilularis and C. nigricornis consistently make smaller brood balls than beetles that are not infected. Because of the direct correlation between adult size and fecal resources available at emergence, this type of behavioral modification in adults is relevant to the outcome of competitive interactions seen in future offspring. Typical tests for predator avoidance (use of shelter, use of substrate, and activity level) did not indicate a change behavior based on infection for any of the species studied. The fact that activity, shelter use and substrate use are not altered is interesting given that a large number of parasites with complex lifecycles play an active role in increasing the probability of transmission. While this study asks if the most common forms of predator avoidance in dung beetles are changed by parasites, it is not exhaustive and it is possible that the parasite alters its host's predator avoidance behavior in some other way. Uninfected dung beetles are extremely beneficial and a variety of countries have actually imported exotic dung beetles because of the services they provide. Some of the most common and beneficial dung beetles in the United States (Onthophagus Taurus and O. gazelle) were introduced from Asia and Africa in the early 1980s and continue flourish throughout the country. These insects are so important in agricultural and disease management and are believed to save the American cattle industry $380 million per year. It is therefore imperative that we understand how the parasites transmitted by dung beetles alter host behavior, especially if the behavioral changes affect their role as ecosystem engineers.


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behavioral change
dung beetle


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