The Sweet Lab
Coevolution of birds and their parasitic lice
We use genomic data to reconstruct and compare the phylogenetic and population genetic patterns between birds and their parasitic feather lice. Making these comparisons is a powerful approach for understanding what processes shape bird-louse interactions over different evolutionary scales (codiversification, host switching, etc.). We work with many different bird/louse systems, including pigeons and doves, ptarmigan and grouse, passerine songbirds, and Tyrannus flycatchers. We also work at different geographical scales, from specific regions in the U.S. to a global (multi-continent) scale.
Tanglegrams comparing the phylogenies of ground-doves and their lice.
Mitogenome evolution in lice
Fragmented mitogenomes from four species of bird lice
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 a dozen 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.
Phylogeography of Caribbean birds (and their lice)
The Caribbean islands are home to many different species of birds. This includes a mix of species endemic to a specific island, species that are found on many islands, and species that are found on both islands and the mainland. The birds also act as "islands" to different groups of parasites. We are interested in the phylogeography of several groups of Caribbean birds and their ectoparasites. Some questions we are pursuing include: How/when have different species colonized the islands? Do their parasites show similar phylogeographic patterns, or is there evidence for more independent evolutionary histories? Currently, we are addressing these questions in Common ground-doves (Columbina passerina) and Loggerhead kingbirds (Tyrannus caudifasciatus).
Range map of Common ground doves
Regional prevalence and dispersal of bird lice
Parasites can have considerable variation in their prevalence across geographical space, but relatively little is understood about the factors that drive this variation at a regional scale. To address this gap, we are focusing on prevalence of parasitic lice across different ecoregions in Arkansas. We are primarily sampling lice from Northern Cardinals (Cardinalis cardinalis) and Mourning Doves (Zenaida macroura) to estimate prevalence and abundance of lice in these regions. We are also obtaining genomic information to better understand dispersal of the lice and their hosts both within and among different habitats and ecoregions.
Prevalence of lice from Northern Cardinals in Arkansas
Arthropod biodiversity of northeast Arkansas
Arthropods are the most diverse group of animals, but most of this biodiversity is undescribed. This shortcoming poses major challenges for conserving arthropods in the face of a massive biodiversity crises. Formerly describing new species relies on the knowledge of taxonomic experts, but genetic data can be a good first-pass for assessing the diversity of a group and/or geographic region. We are applying the latest DNA sequencing approaches to assess arthropod biodiversity in northeast Arkansas. We are primarily using DNA barcoding data generated from large pools of samples to get an initial glimpse into the regional biodiversity (including potentially new taxa!).
Haplotype network based on mitochondrial cox1 sequences from mites collected in northeast Arkansas
Phylogeny of endosymbionts from two groups of bird lice
Evolutionary History of Bacterial Endosymbionts in Parasitic 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.