Many animals and plants have evolved symbiotic relationships with bacteria. These bacteria provide their hosts with nutrients lacking in the natural diet. Most studies have focused on insects that feed on vertebrate blood or plant sap because these insects are recognized as important medical, veterinary and agricultural pests. This project will study the role of symbiotic bacteria in feather-feeding lice that are obligate parasites of birds. These lice are an important model system for understanding why parasites specialize to a single species of host. Initially, DNA-based analyses will be used to survey lice for bacterial symbionts. Microscopic and genomic techniques will then be used to evaluate the relationships between different lice and their symbiotic bacteria.
To appreciate the nature of symbiosis, it is essential to understand the full spectrum of these interactions. This project represents one of the first studies of symbiosis in insects that feed on hair or feathers (a group consisting of several thousand species). The project will provide in depth training for a Ph.D. student, as well as training for undergraduate research assistants. This training will further contribute to educating students, and the public alike, about important issues in microbiology, such as the evolution of antibiotic resistance.
"If you want to be incrementally better: Be competitive. If you want to be exponentially better: Be cooperative." Unknown Our project concerned the evolution of symbiotic relationships between insects and their internal bacteria. The study of symbiosis examines the relationship between organisms that work cooperatively for mutual benefit. A well known example is the relationship between termites and their internal microbes that help them digest wood. The termite supplies wood and the microbes break it down into useable food for the termites. Both partners benefit from this relationship. Like termites, other groups of insects have evolved symbiotic relationships with internal microbes like bacteria and protozoa (amoeba-like single celled organisms). These symbiotic relationships are thought to have allowed some groups of insects to evolve the ability to live in extreme or harsh environments. One example is the group of parasitic insects known as feather lice that live exclusively on birds. Feather lice spend all of their time on feathers and they even feed one them. This is a rather remarkable feat, given that feathers - like fingernails or hair - are made almost entirely of Keratin. Keratin is very difficult to digest and is lacking in critical nutrients such as B vitamins. One goal of our project was to test the hypothesis that feather lice are able to live on Keratin because they get "help" from endosymbiotic bacteria. Another goal of our project was to trace the evolutionary history of the bacteria to determine how closely their evolution has paralleled that of the feather lice. In other systems, such as endosymbiotic bacteria in aphids, the evolutionary trees of the bacteria and aphids are mirror images of one another. The reason is that whenever new species of aphids form, their endosymbiotic bacteria form new species in tandem. We wanted to determine if this has occurred with the bacteria in feather lice. We chose to concentrate on species of feather lice found on pigeons and doves from around the world. All of the feather lice we studied were members of the single genus Columbicola. PI Clayton has studied this group of insects for many years and has a collection of specimens from which we were able to extract DNA and determine the evolutionary relationships between the bacteria. We also kept live cultures of feather lice on pigeons and mourning doves, which enabled us to perform physiological experiments to test whether the bacteria are important in the ability of the feather lice to digest feathers. Our results showed that the bacteria do indeed help lice survive on a diet of feathers, probably by producing B vitamins. Our work also yielded the surprising result that the evolutionary history of the bacteria does not parallel the evolutionary history of the lice in which they reside. Instead, we found evidence indicating that feather lice periodically acquire new symbionts from the environment, replacing existing representatives and potentially providing enhanced functions. This is a novel result that sheds light on the early evolution of endosymbiotic associations. It means that the evolution of endosymbiotic relationships is not as rigid as we previously observed. This work will serve as a primer for a more in-depth understanding of co-evolution between insects and their bacterial partners.
