Genetic Structure of Pacific Trout at the Extreme Southern End of Their Native Range

Abstract

Salmonid fishes are cold water piscivores with a native distribution spanning nearly the entire temperate and subarctic northern hemisphere. Trout in the genus Oncorhynchus are the most widespread salmonid fishes and are among the most important fish species in the world, due to their extensive use in aquaculture and valuable fisheries. Trout that inhabit northwestern Mexico are the southernmost native salmonid populations in the world, and the least studied in North America. They are unfortunately also facing threats to their continued existence. Previous work has described one endemic species, the Mexican golden trout (O. chrysogaster), and one endemic subspecies, Nelson’s trout (O. mykiss nelsoni), in Mexico, but previous work indicated that there is vastly more biodiversity in this group than formally described. Here we conducted a comprehensive genetic analysis of this important group of fishes using novel genetic markers and techniques to elucidate the biodiversity of trout inhabiting northwestern Mexico, examine genetic population structure of Mexican trout and their relationships to other species of Pacific trout, and measure introgression from non-native hatchery rainbow trout. We confirmed substantial genetic diversity and extremely strong genetic differentiation present in the Mexican trout complex, not only between basins but also between some locations within basins, with at least four species-level taxa present. We also revealed significant divergence between Mexican trout and other trout species and found that introgression from non-native rainbow trout is present but limited, and that the genetic integrity of native trout is still maintained in most locations. This information will help to guide effective conservation strategies for this important group of fishes.

Genetic Differentiation and Origin of Naturalized Rainbow Trout Populations From Southern Chile, Revealed by the mtDNA Control Region Marker

“…These groups represent five groups of mitochondrial DNA (mtDNA) genotypes according to phylogenetic analysis, a result that mostly shows agreement with the morphological data (Bagley and Gall, 1998). This strong genetic structuring of rainbow trout has also been supported in other regions across their native distribution range (Nielsen et al, 1997;Narum et al, 2004;Brunelli et al, 2010;Taylor et al, 2010;Abadía-Cardoso et al, 2015).…”

Population genetic structure and ancestry of steelhead/rainbow trout (Oncorhynchus mykiss) at the extreme southern edge of their range in North America

“…Among the populations in tributaries of rivers that run through the highly urbanized areas of Southern California, only three groups of populations contained significant evidence of native coastal steelhead ancestry: (1) populations from the San Gabriel River system, (2) Coldwater Canyon in the Santa Ana River, and (3) the San Luis Rey River. The analyses also further established the native origin of O. mykiss nelsoni from the Sierra San Pedro Martir in Baja California as the southernmost representative of the coastal steelhead lineage in North America (Abadía-Cardoso et al 2015). The geographic distribution of the US populations in the context of their respective BPGs is shown in Jacobson et al (2014).…”

Dam trout: Genetic variability in Oncorhynchus mykiss above and below barriers in three Columbia River systems prior to restoring migrational access

“…This similarity might be related to the origin of the Skamania Hatchery stock, which included fish from the Washougal River and Klickitat River, Columbia River tributaries adjacent to the White Salmon River [ 39 ]. The absence of hatchery genetic introgression in our work is interesting [ 12 , 25 , 26 ] considering that this is a major concern in other locales [ 76 ].…”