introgressive hybridization

Banff longnose dace

The Banff longnose dace, Rhinichthys cataractae smithi, was a diminutive version (about five cm. long) of the eastern longnose dace, its range restricted to a small marsh fed by two hot springs in Banff National Park in Banff, Alberta. With water temperatures between 17-24C (63-75F), the area was popular with bathers. Eventually this led to the pollution of the dace's habitat. Introduced guppies, sailfin mollies, and mosquitofish in the 1920s, reproduce year-round in the marsh, while the Banff longnose dace only spawned once a year. The exotic fish out-competed the dace for food and preyed on unhatched eggs. Aquarium plants were also introduced. The few remaining Banff longnose dace hybridized with the Eastern longnose dace from the nearby Bow River. In 1981 a research study showed that the habitat destruction and the introduction of the non-native fish threatened the dace. It is hypothesized that this Banff subspecies' unique genetic structure was irreversibly mixed with another subspecies (termed introgressive hybridization), by 1986 it had disappeared, and it was declared extinct in 1987 by COSEWIC. Currently a study is underway to clarify the taxonomic classification of this putative subspecies.

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