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The coexistence between sexual and unisexual Ambystoma salamanders
The maintenance of sexual reproduction is one of the fundamental questions in evolutionary biology. Sexual taxa are expected to be more robust to extinction in the evolutionary long-term due to increased genetic variability in offspring. In contrast, asexual taxa are released from the burden of producing two sexes, one of which does not directly reproduce, and so are expected to outcompete related sexual taxa in the evolutionary short-term but suffer a cost in terms of reduced genetic variation limiting long-term persistence. This appears to be the case, as asexual taxa are well-recognized for their young lineage ages compared to related sexual species. Nonetheless, there are some “asexual” lineages that are unexpectedly old, which raises the question: what are the evolutionary mechanisms that allow these “anomalous” asexual lineages to persist over evolutionary time?
I study the wonderfully strange unisexual Ambystoma salamanders, an all-female lineage of salamanders that are widespread across Eastern North America. These salamanders are proposed to reproduce uniquely among vertebrates by "stealing" sperm from the males of other sexual species. This has resulted in a single line of females with multiple genomes from other species, all without a male in sight! I've sought to explain how these unisexuals get away with this mode of reproduction without driving sexual species, or themselves, extinct. I mainly attempt to do this using by combining molecular biology with basic ecology, physiology, and behavior.
The discordance between mitochondrial and nuclear genomes
Hybridization between species is a well-studied phenomenon that has vast evolutionary and ecological implications. However, an underappreciated consequence of hybridization is the one-way infiltration of mitochondrial genomes from one species into another. When these genomes spread, a species can have a mismatch between the nuclear genomes of their own species and the mitochondrial genomes of another.
Along with Katy Greenwald (E. Michigan University) and Lisle Gibbs (Ohio State University), we've identified this pattern of mitonuclear discordance in two species of Ambystoma salamander, the Smallmouth Salamander (A. texanum) and the Streamside Salamander (A. barbouri) and are currently studying how and why these foreign mitochondrial genomes spread.
Amphibians are quickly disappearing across the globe, and habitat alteration is one of the major drivers of their extinction. I continue to be interested in how humans can construct wetlands to mitigate the prior removal of breeding habitat and preserve natural, healthy amphibian communities.