Host-parasite coevolution

Comparing the evolutionary histories of hosts and their parasites is a powerful approach for understanding host-parasite interactions. In the Sweet Lab, we use genomic data to compare phylogenetic and population genetic patterns between hosts and parasites. Most of our work focuses on parasitic bird lice, which has yielded important insights into the factors that shape bird-louse relationships. It is especially useful to compare multiple groups of lice from the same group of birds. For example, comparing phylogenetic and population genetic patterns in two groups of lice from doves indicated that the dispersal ability of lice plays an important role in shaping bird-louse relationships over evolutionary time. Another study of different groups of lice from Ptarmigan in Alaska revealed evidence of interactions between different populations of Ptarmigan, patterns that were not evident from host data alone. Future work will incorporate data from other parasites, such as hippoboscid flies, to get a more complete picture of different host-parasite systems.

Tanglegrams comparing the phylogenies of ground-doves and their lice.


Fragmented mitogenomes from four species of bird lice

Parasite biodiversity

Parasites likely make up more than half of earth's biodiversity, but relatively little is known about the scale and generators of this diversity, especially on a regional level. The Sweet Lab is committed to closing this knowledge gap by focusing on ectoparasites of birds from Arkansas and the Mid-South region. This research combines field surveys, identification, and molecular analysis of parasites from many species of birds. Molecular work is especially key because many parasites, including parasitic bird lice, can have a high amount of cryptic diversity. Results from these projects will not only improve our understanding of parasite diversity in the Mid-South, but will also give us insight into what factors are important for generating parasite diversity and shaping parasite communities. 

Most organisms have a single, circular mitochondrial genome (mitogenomes). However, several species of parasitic lice are known to have fragmented mitogenomes. The same set of genes are present, but they are separated on two or more smaller fragments ("chromosomes"). We are pursuing two general questions related to these fragmented mitogenomes in parasitic lice. First, how common is this phenomenon in lice? Fragmented mitogenomes appear to have arisen from single mitogenomes at least 12 times within lice, but it is unknown how common fragmentation is across the diversity of lice. Second, why are fragmented mitogenomes relatively common in lice, when the phenomenon is rare and often detrimental across all other animals? We are currently focusing on testing links between fragmentation and selection, mito-nuclear interactions, and mitogenome nucleotide composition. Stay tuned!

Phylogeny showing cryptic diversity in lice from doves


Phylogeny of endosymbionts from two groups of bird lice

Endosymbiotic bacteria are another player in the bird-louse system. These bacteria are likely maternally inherited and provide essential nutrients that lice are not able to get in their diets. Lice as a group harbor several different types of endosymbionts, usually depending on the species or genus of louse. The Sweet Lab uses genetic data to understand the diversity and evolutionary relationships of endosymbiotic bacteria from lice. How diverse are these bacteria? Do different species of lice harbor unique clades of bacteria? Do the phylogenies of bacteria mirror that of their louse hosts? We can address these questions by bioinformatically obtaining bacterial genes from whole genome sequences of lice. Because we use an entire louse specimen for DNA extraction, the bacterial DNA is sequenced as "by-catch." From these data we are able to construct phylogenetic relationships among the bacteria.

Avian phylogenetics and biogeography

Part of understanding a host-parasite system is focusing on the hosts. As a result, we are also interested in the evolutionary history of different groups of birds. Most of this work has focused on the phylogenetics, systematics, biogeography, and trait evolution of doves. This work is not only useful for understanding the evolutionary history of the birds themselves, but also for incorporating into a framework for understanding bird-parasite coevolution. For example, the biogeographic history of New World ground-doves can help explain relationships with their lice. Future work will focus on other groups of birds as we focus on different groups of bird parasites. 

Phylogeny of New World ground-doves showing an ancestral reconstruction of plumage dimorphism.