Determination of genetic taxonomic units within the native Mexican trout from northwestern México

Authors: Anna Belia De Los Santos, Francisco J. García de León, Richard L. Mayden, Irene D.L.A. Barriga Sosa, Grupo Truchas Mexicanas

Year: 2008 (xl)

Abstract

A high diversity of native salmonids, commonly recognized as Mexican trout and members of the genus Oncorhynchus are found in the mountain creeks and rivers of the northern part of the Sierra Madre Occidental in Mexico. From these diverse groups of fishes, only two of them are formally described, Oncorhynchus mykiss nelsoni which inhabits the Sierra San Pedro Martir in Baja California, and Oncorhynchus chrysogaster from the rivers El Fuerte, Culiacan and Sinaloa in the SMO, remaining an extensive group of fishes still to be describe. This species complex in under an impending treat of extinction due to habitat degradation, global climate change, and the introduction of exotic species mainly the rainbow trout which are cultivated in almost all the rivers where the natives inhabit without a good control. Here, we describe the genetic diversity of those group salmonids using 11 microsatellite loci with the aim to determine taxonomic units that contribute to the species delimitation as well as to assess the impact and possible genetic introgression with the introduced rainbow trout. The genetic biodiversity parameters showed an average of 24 alleles per locus, allelic richness values between 1.707 and 4.8, Ho from 0.085 to 0.7234, and a total of 70 exclusive alleles distributed in the different basins. Neighbor-joining phylogeny reconstruction using Cavalli-Sforza & Edward´s genetic distances indicate the formation of seven genetically homogeneous groups (Guzmán/Yaqui-Bavispe, Yaqui-Sirupa/Mayo, Conchos, San Lorenzo/Piaxtla, Acaponeta/Baluarte/Presidio, one group in the Sidra stream from San Lorenzo basin and one more group in the Aparique stream belonging to the Fuerte basin groups) besides of the formally described O. mykiss nelsoni and O. chrysogaster and introduced rainbow trout. This grouping was corroborated by assignation analysis using the Bayesian method, gene flow estimates, and AMOVA. The results of the different analyses support the existence of seven taxonomic units corresponding to each of the mentioned groups. Furthermore, assignation analysis and genetic flow estimates showed that contrary to what we thought, only Presidio and Acaponeta basins indicate introgressions with rainbow trout, however, these results should be further corroborated with an appropriate sampling method in order to specify the impact.