The interplay of riverscape features and exotic introgression on the genetic structure of the Mexican golden trout (Oncorhynchus chrysogaster), a simulation approach

Abstract

Aim:We explored the factors between riverscape features and exotic introgression of cultured rainbow trout (Oncorhynchus mykiss) that drive the current genetic structure in the endemic Mexican golden trout (Oncorhynchus chrysogaster) using a riverscape genetics simulator.Location: Sierra Madre Occidental, Northwest Mexico, North America. Methods:We created a system model for Mexican golden trout to test various scenarios for the effect of riverscape resistance and rainbow trout introgression on the native genetic structure of the Mexican golden trout. Individual genotypes were used to initialize the model and were based upon empirical allele frequencies from three genetically and spatially distinct groups in the study area. The geographical location of the simulated populations was defined using a species distribution model. We included hypotheses for movement of riverine distance and riverscape resistance. We evaluated model performance by conducting population and landscape genetics analyses on the simulation outputs. Results:The most plausible scenario included riverscape resistance without introgression, which presented a spatial genetic structure matching the observed riverscape genetic structure and fitting expected general life-history patterns for high elevation trout streams. In addition, temperature, precipitation, hydrology and topography were the most important variables influencing species occurrence and dispersal. Main conclusion:This work presents one of the first empirically derived simulation studies of introgression. It highlights the importance of considering riverscape resistance (i.e. hydroclimatic and topographical gradient effects) in models of spatial genetic structure and introgression. Moreover, our modelling suggests that what we characterize as riverscape resistance is acting as a boundary against exotic introgression. The results of this study could help to develop management strategies that preserve native gene pools.

Genotyping-by-sequencing reveals the effects of riverscape, climate and interspecific introgression on the genetic diversity and local adaptation of the endangered Mexican golden trout (Oncorhynchus chrysogaster)

“…This zone has a complex topography and hydrology with sharp slopes and stream orders mostly corresponding to 1, 2 and 3. The annual mean temperature and annual mean precipitation for the zone are 14.4 °C and 911 mm respectively (Escalante et al 2018). The heterogeneous riverscape of this area offers a diversity of terrestrial and aquatic habitats providing high endemism and biodiversity, with O. chrysogaster as one of the main aquatic predators (Hendrickson et al 2006).…”

“…Six variables characterizing the riverscape and with a strong influence on O. chrysogaster occurrence and genetic divergence were obtained from a previous study (Escalante et al 2018): precipitation of the driest month, temperature of the warmest quarter, river length (distance from the lowermost to the uppermost part of the river above 1 500 m), slope, altitude, and stream order. They were generated and/or processed from data available on the worldclim (http://www.worldclim.org/) and the Japanese Space System (http://www.jspacesystems.or.jp/ersdac/GDEM/E/4.html) websites with 1 km and 30 meter resolution, respectively.…”

“…They were generated and/or processed from data available on the worldclim (http://www.worldclim.org/) and the Japanese Space System (http://www.jspacesystems.or.jp/ersdac/GDEM/E/4.html) websites with 1 km and 30 meter resolution, respectively. Worldclim variables were geometrically corrected to 30 meter resolution (for further details see Escalante et al 2018). The effect of latitude and longitude, recorded using GPS, was also tested.…”

“…Wild trout were sampled by electrofishing at 25 sample sites in the Río Fuerte (10 sites), Río Sinaloa (10 sites), and Río Culiacán (5 sites) basins during the winter and spring seasons of 2013, 2014, and 2015 (collection permit numbers SGPA/DGVS/02485/13 and SGPA/DGVS/05052/15). The sampling was conducted from both the core and edges of the O. chrysogaster ecological niche defined in a previous study (Escalante et al 2018), and at multiple locations with high environmental heterogeneity (topographical and hydrological divergence) avoiding spatial autocorrelation (Fig. 1).…”

“…Some studies for this species have revealed a genetic substructure and introgression processes in locations near aquaculture facilities (Escalante et al 2014; Abadía-Cardoso et al 2015). Moreover, a recent simulation study of O. chrysogaster suggested that the riverscape acts as a barrier against exotic introgression and that riverscape resistance (the combined effect of riverine distance, topographic slope, altitude gradient, stream order changes and temperature increase) is the main factor fragmenting populations within basins (Escalante et al 2018). Strong spatial genetic structure and local adaptation processes in O. chrysogaster arising from riverscape factors are therefore to be expected, with the consequence that this complex riverscape will prevent introgression processes in populations not in proximity to aquaculture farms.…”