The phylogeography and conservation of the brassy minnow, Hybognathus hankinsoni

• Main Author: Nowosad, Damon M.
• Language: English
• Published: University of British Columbia 2011
• Online Access: http://hdl.handle.net/2429/33139

Brassy minnow, Hybognathus hankinsoni, is a little-studied cyprinid fish with highly disjunct distributions in western Canada. Phylogeographic scenarios on the origins of brassy minnow in British Columbia (BC) were explored using two mitochondrial loci (cyt b and ND4) that were sequenced for up to 32 localities. This revealed an approximate ‘east-west’ geographic split, suggesting that BC populations are likely post-glacial colonists from the Mississippi-Missouri refugium. However, certain ‘eastern’ populations exhibited incongruences between gene and species trees, suggesting complex evolutionary histories in brassy minnow. Sampling brassy minnow within BC revealed highest catch rates in the Interior of the province, and a year-long survey conducted in the Lower Mainland (n = 60 sites), revealed that brassy minnow abundances were highest at Westham Island. A logistic-regression habitat model was performed incorporating seven physical habitat parameters over 37 sites, identifying conductivity as a near significant parameter for predicting brassy minnow presence. Additionally, in the Lower Mainland, eight invasive species constituted 28 % of the relative abundance of species sampled. Compared to historical records from the University of BC Fish Museum, sites exhibited a significant decline in the number of cypriniform species, including brassy minnow, but showed no significant change in the number of invasive species present. A detrended correspondence analysis (DCA) of species abundance across sites suggested brassy minnow overlapped most closely with two invasive species: bullfrogs, Lithobates catesbieanus, and brown bullhead, Ameiurus nebulosus. To explore the impact of brown bullhead on brassy minnow, pools with and without adult brown bullhead were compared at Tamboline Slough, Westham Island, and showed significant differences in the native fish species abundances across pools, including brassy minnow. Additionally, growth experiments were conducted over 90 days with brassy minnow, young-of-year brown bullhead, and redside shiner, Richardsonius balteatus, kept in all possible combinations for a total of four treatments per species. Treatments showed that brassy minnow were the only species to exhibit weight loss and mortality when with other species. In addition to providing insights into the biogeography, ecology, and conservation implications of brassy minnow, my thesis provides a quantitative baseline for invasive species found within the Lower Mainland.