Jennifer M. Walker
My primary research interests focus on the systematics and phylogenetics of mollusks. Although my graduate research focused on marine gastropods, my recent research efforts have been focused on a group of freshwater bivalves with a novel system of mitochondrial DNA inheritance termed doubly uniparental inheritance (DUI). In this system, separate male and female mitochondrial DNA genomes are maintained. In most instances, daughters inherit only maternal mitochondrial DNA while sons inherit both maternal and paternal mitochondrial DNA that is segregated within the individual by tissue type. In male individuals with this type of mitochondrial inheritance, male mitochondrial DNA is usually only found in testes tissue while female mitochondrial DNA is found in all other somatic tissues. DUI results in two widely divergent genomes as the male genome evolves at a faster rate than does the female genome. Phylogenetic analyses of DNA sequences from male and female genomes produce distinct female and male lineages with very similar topologies. Recent analyses of concatenated male and female cytochrome c oxidase subunit I and II sequences have produced more resolved trees than female sequences alone. Many of our freshwater ecosystems are highly imperiled. Several North American members of this group have been listed as endangered or are thought to be already extinct. Exploring this novel mode of mitochondrial DNA inheritance will provide more robust tools to determine the relationships within this group and help to aid in the conservation efforts of these organisms.
Along with an interesting mode of mitochondrial DNA inheritance, these bivalves also exhibit several other unique characteristics. One of which is that the larvae are obligate parasites on fish gills or fins for part of their lifecycle. Because the larvae of this group are brooded by the females until they are ready to be released, the females of many species produce fish-attracting structures or lures to increase the survivability of their young by attracting a suitable host. Recent research efforts have been focused on producing a reliable phylogeny that will provide some insight into the evolution of these host-attracting structures. Numerous collaborators are involved in this effort providing information on mussel host specificity, determination of species specific lure types, procurement of specimens, etc.
Further investigation of the molecular evolution of the male mitochondrial cytochrome c oxidase subunit II gene is continuing with collaborators at Kent State University, The University of Southern California, Acadia University, and Saginaw Valley State University.
Walker, Jennifer M., Jason P. Curole, Dan E. Wade, Eric G. Chapman, Arthur E. Bogan, G. Thomas Watters, and Walter R. Hoeh. 2006. Taxonomic distribution and phylogenetic utility of gender- associated mitochondrial genomes in the Unionoida (Bivalvia). Malacologia, 48 (1-2: 265-282).
Walker, Jennifer M., Arthur E. Bogan, Kohar Garo, Gamil N. Soliman, and Walter R. Hoeh. 2006. Hermaphroditism in the Iridinidae (Bivalvia:Etherioidea). Journal of Molluscan Studies, 72:216-217.
Chakrabarti, R., J. M. Walker, D. T. Stewart, R. J. Trdan, S. Vijayaraghavan, J. P. Curole, W. R. Hoeh. 2006. Presence of a unique male-specific extension of C-terminus to the cytochrome c oxidase subunit II protein coded by the male-transmitted mitochondrial genome of Venustaconcha ellipsiformis (Bivalvia: Unionoidea). FEBS Letters, 580(3):862-866.