Current research projects

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Evolution of mtDNA in sponges and other animals

Mitochondrial DNA of bilaterian animals is typically a small, circular-mapping molecule that encodes 37 tightly packed genes. MtDNA of choanoflagellate Monosiga brevicollis, the closest unicellular out-group, is four times larger and contains 1.5 times as many genes. Comparative studies can provide valuable insights into the mechanisms responsible for this remarkable transition in mtDNA evolution, but the scarcity of data from non-bilaterian animals (phyla Placozoa, Porifera, Ctenophora, and Cnidaria) severely limits these studies (Lavrov, 2007). Our group aims to sample and analyze mitochondrial genomes from all major groups of non-bilaterian animals. To date we determined complete mitochondrial sequences from 21 species of demosponges (Wang and Lavrov, 2008), 2 species of glass sponges (Haen et al. 2007), and two previously unsampled classes of cnidarians (Shao et al., 2006; Kayal and Lavrov, 2008). Our analyses revealed a large extent of mitochondrial diversity in non-bilaterian animals. These genomes are usually larger in size compared to their counterparts in bilaterian animals, show more variation in the gene content, contain introns, often use a minimally-modified genetic code for mitochondrial translation, and usually display low rates of sequence evolution (Lavrov, 2007). We also discovered a remarkable example of parallel genomic evolution in glass sponges and bilaterian animals (Haen et al. 2007).

Demosponge relationships based on mtDNA data

The class Demospongiae, one of three classes in the phylum Porifera, encompasses most of sponges' morphological and species diversity. This class also represents one of the most challenging groups in animal phylogenetics, due to the ancient origin, scarcity of useful phylogenetic characters, and morphological plasticity of demosponges. Reflecting these difficulties, the higher-level phylogeny of demosponges remains largely unresolved. Among many unanswered questions are the most fundamental, including the interrelationships of Demospongiae with two other classes in the phylum Porifera, and the relationships among the 14 recognized orders within the class. In addition, the monophylies of several orders, two out of three proposed subclasses, and even the class Demospongiae itself remain suspect. The lack of resolved phylogeny hampers progress in studies of demosponge biology, evolution and biodiversity and interferes with efficient conservation and economic use of this group. We aim to elucidate the phylogeny of Demospongiae by using two independent datasets based on complete mitochondrial genomes - gene sequences and gene orders (Lavrov et al. 2008).

Cell-cell communication in sponges (in collaboration with Michael Nickel)

We are currently constructing a cDNA library for the demosponge Tethya wilhelma, which we plan to search for the elements of signaling pathways. These data will then become the basis for further studies of cell-cell interaction in sponges.

MtDNA in Nasonia wasps

Nasonia are small parasitoid wasps (Hymenoptera: Pteromalidae) that are being developed as a model system for Basic, Developmental and Evolutionary Genetics. We are in the process of determining mtDNA sequences for three closely related and interfertile species N. vitripennis, N. longicornis, and N. giraulti, which should provide an excellent system for comparative and evolutionary studies. To learn more about Nasonia go here.