Landscape-scale effects on genetic and phenotypic variation of Longfin dace, Agosia chrysogaster, in the upper Gila River drainage

Authors: Tyler J. Pilger, Tracy A. Diver, Nathan R. Franssen

Year: 2013 (xlv)

Abstract

Stream fishes can provide an ideal model to assess landscape-level effects on genetic and phenotypic variation in natural populations. The dendritic nature of low-order stream systems allows for repeatability of habitat conditions and predictability of longitudinal environmental characteristics. Longitudinal habitat heterogeneity can result in limited gene flow and variable selective pressures among populations, driving genetic and phenotypic variation across the landscape. We quantified genetic (using 10 variable microsatellite loci) and morphological (body shape) variation in Longfin dace (Agosia chrysogaster) from six sites within the Gila River Basin, NM. Local habitat conditions (mean stream depth, width, and discharge) were also assessed to evaluate environmental factors on phenotypic variation. We predicted that geographic distance among populations would be correlated with genetic distance (estimated from pairwise F_ST) and phenotypic distance (estimated from pairwise P_ST), and phenotypic distance would be related to environmental distance (measured from Euclidean distances among habitat characteristics). We used Mantel tests to correlate genetic, phenotypic, and environmental distances among populations. We found significant genetic and phenotypic divergence among populations, but F_ST and P_ST, and F_ST and geographic distances were not correlated. However, the correlations between P_ST and environmental and geographic distances showed positive trends. Our results suggest there is limited gene flow among populations, but phenotypic variation across the landscape is likely related to local habitat conditions rather than genetic variation.