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Hybridization and Introgression in a Managed, Native Population of Yellowstone Cutthroat Trout: Genetic Detection and Management Implications
Author(s) -
Campbell Matthew R.,
Dillon Jeff,
Powell Madison S.
Publication year - 2002
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(2002)131<0364:haiiam>2.0.co;2
Subject(s) - introgression , trout , rainbow trout , biology , broodstock , hatchery , hybrid , oncorhynchus , population , fishery , stocking , zoology , ecology , aquaculture , genetics , botany , fish <actinopterygii> , demography , sociology , gene
Since the mid‐1920s, the Idaho Department of Fish and Game has cultured Yellowstone cutthroat trout Oncorhynchus clarki bouvieri at Henrys Lake to offset declines in natural production and for use in stocking programs throughout Idaho. Since the mid‐1970s, they have also produced F 1 hybrids: female Yellowstone cutthroat trout × male rainbow trout O. mykiss . The ability of fishery managers, when selecting broodstock, to visually distinguish returning cutthroat trout from F 1 hybrids is, therefore, crucial to avoid accidental introduction of rainbow trout genes into the hatchery‐supplemented cutthroat trout population. To evaluate this ability, fish identified by staff as putative cutthroat trout or hybrids (an array of phenotypic characters are used), were sampled during two spawning seasons. Phenotypically identified fish were genetically tested using species‐specific restriction fragment length polymorphisms (RFLPs) of nuclear and mitochondrial DNA gene loci and diagnostic allozyme loci. Current levels of rainbow trout introgression in the cutthroat trout population at Henrys Lake were also investigated by analyzing samples collected from the lake and several of its tributaries. Results indicated that staff's phenotypic identifications were highly accurate in distinguishing cutthroat trout from F 1 hybrids when selecting broodstock (no F 1 hybrids were detected among 80 samples identified as pure). However, backcrosses of F 1 hybrids were identified in random collections of adults from the lake as well as fry from Henrys Lake tributaries, indicating introgression. Present levels of rainbow trout introgression are most likely the product of past rainbow trout introductions and limited, intermittent spawning of hatchery‐produced F 1 hybrids with wild Yellowstone cutthroat, rather than the accidental crossing of F 1 hybrids with cutthroat trout at the hatchery. Current levels of introgression are inadvertently maintained by (1) the inability of managers to phenotypically identify and exclude as broodstock individuals with low levels of rainbow trout introgression and (2) the limited, intermittent reproductive success of straying, hatchery‐produced F 1 hybrids.