Origins of Nuclear Genomes in Hybrid Unisexual Salamanders

Academy Of Natural Sciences Philadelphia, Philadelphia PA

Investigators

Abstract

DEB-0075856 Christina M. Spolsky Thomas M. Uzzell Drs. Christina M. Spolsky and Thomas M. Uzzell of the Academy of Natural Sciences, Philadelphia, have been awarded a grant to study the interaction of genomic imprinting and unusual reproductive lifestyles in salamanders. Mole salamanders (genus Ambystoma) include a variety of clonally-reproducing lineages that are almost exclusively female. Such clonal females are hybrids between sexually reproducing species, and might be expected to be sterile. Nevertheless, the clonal females are capable of reproducing and have broad geographic ranges in which they are common. The mitochondrial DNA of the clonal forms, although distinct, most resembles that in a species in one species group of Ambystoma, whereas the nuclear genetic material (DNA contained in chromosomes) resembles that of two species in another species group. This award will be used to obtain genetic material from tissues of selected sexual species and clonal individuals. All the genes that encode proteins will be archived in so-called cDNA libraries. Two of the nuclear genes (serum albumin and serpin) will be isolated from these libraries and sequenced. These sequences will be used to design and test primers that permit identification of the genomic composition of clonal individuals. The mitochondrial genomes of clonally-reproducing mole salamanders are distinctive, and suggest that these lineages have existed for 3-5 million years. This is far longer than expected according to evolutionary theory, because gradual accumulation of deleterious mutations should eventually doom any strictly clonal lineage to extinction. The paradox posed by the long independent survival of the mitochondrial DNA given the brief survival expected from theory suggests that occasionally nuclear chromosome sets of the clonal salamanders are replaced, in sexual rather than clonal reproduction, by nuclear chromosome sets from males of sexual species. Genome-specific primers will permit an assessment of the frequency with which such chromosomal replacements occur. The data are important for theories about the persistence of sexual reproduction despite the short-term advantages of clonal reproduction. Comparison of variability in mitochondrial and nuclear DNA will provide a basis for evaluating the relative effects of natural selection on these two kinds of DNA in the clonal lineages.