Dissertation Paul Hime: The Search for Sex-Linked Genes in Cryptobranchid Salamanders: Genome-Wide Gene Discovery and Marker Development

The emerging synthesis of genomic analysis and conservation biology is empowering new and powerful approaches for the management of endangered species. As such, I seek to use massively-parallel DNA sequencing to develop a genetic sex diagnostic for hellbender salamanders in order to: better understand the demographic structure ofwild populations; to inform management of captive populations; and to investigate the effects ofendocrine disrupting hormone pollution on declining wild populations. Although the accurate diagnosis of sex is an important aspect ofconservation management efforts with endangered species, sex can be difficult to determine reliably in monomorphic species. Such is the case with cryptobranchid salamanders, including the North American hellbender. Several non-genetic methods exist for determining hellbender sex, but each has limitations and none are universally reliable. Because non-homologous sex-linked genes have evolved independently in many different amphibian lineages, genetic sex diagnostics must typically be designed de-novo in unstudied taxa. Sex chromosomes exist in cryptobranchids, but they are weakly differentiated, suggesting that only a small portion ofthe genome varies between males and females. This study set out to design a genetic marker diagnostic for sex in hellbenders by identifying a region ofthe genome unique to one sex. Amplification ofcandidate sex-linked loci known from other amphibians and a preliminary AFLP analysis both failed to detect sex-linkage in a panel ofknown-sex hellbenders. Efforts are currently underway to identify hellbender-specific candidate sex-linked genes with high-throughput transcriptome sequencing ofovary and testis tissues, followed by in-silico subtraction of shared transcripts. I seek funding to screen one-hundred ofthese differentially expressed genes in a panel ofknown-sex cryptobranchids in an effort to design a genetic sex assay for hellbenders. Ifidentified and validated, a genetic sex diagnostic for hellbenders would have profound implications for in-situ and ex-situ conservation ofthis endangered species.