Signatures of vicariance, postglacial dispersal and spawning philopatry: population genetics of the walleyeSander vitreus

Abstract

Population genetic relationships reveal the signatures of current processes such as reproductive behaviour and migration, as well as historic events including vicariance and climate change. We analyse population structure of native walleye Sander vitreus across North America, encompassing 10 nuclear DNA microsatellite loci, 26 spawning sites and 921 samples from watersheds across the Great Lakes, Lake Winnipeg, upper Mississippi River, Ohio River and Mobile Bay of the Gulf Coast. Geographical patterning is assessed using phylogenetic trees, pairwise F(ST) analogues, hierarchical partitioning, Mantel regression, Bayesian assignment and Monmonier geographical networks. Results reveal congruent divergences among population groups, corresponding to historic isolation in glacial refugia, dispersal patterns and basin divisions. Broad-scale relationships show genetic isolation with geographical distance, but reproductive groups within basins do not -- with some having pronounced differences. Greatest divergence distinguishes outlying Gulf Coastal and northwest populations, the latter tracing to dispersal from the Missourian refugium to former glacial Lake Agassiz, and basin isolation approximately 7000 ya. Genetic barriers in the Great Lakes separate groups in Lakes Superior, Huron's Georgian Bay, Erie and Ontario, reflecting contributions from Mississippian and Atlantic refugia, and changes in connectivity patterns. Walleye genetic patterns thus reflect vicariance among watersheds and glacial refugia, followed by re-colonization pathways and changing drainage connections that established modern-day northern populations, whose separations are maintained through spawning site fidelity. Conservation management practices should preserve genetic identity and unique characters among these divergent walleye populations.

Population genetics of walleye and yellow perch in the St. Marys River

“…Walleye populations in the SMR expressed a relatively large number of alleles at each microsatellite locus and heterozygosities that were similar to those documented in other populations throughout the midwest by Stepien et al (2009), and in the southeast by Palmer et al (2006). There is no historical genetic baseline to which the current populations in the SMR can be compared, nor historic samples that could be used to generate such a baseline.…”

“…As population size is reduced, allele frequencies will drift due to a smaller number of breeders, eventually leading to fewer alleles in the population and a decrease in heterozygosity (Cornuet and Luikart, 1996). Microsatellite DNA loci have been used extensively to assess genetic structure of populations (Miller, 2003;Strange and Stepien, 2007;Stepien et al, 2009), and they were chosen as the markers to assess the genetic status and to establish a baseline for future monitoring of the yellow perch and walleye populations in the SMR.…”

Microsatellite and mitochondrial DNA markers show no evidence of population structure in walleye (Sander vitreus) in Lake Winnipeg

“…When present, philopatry results in a spatial separation of spawning aggregations across the lake, providing potential for genetic variation to develop over several generations, and for potentially discrete genetic stocks to form within the lake. Genetic work in the Laurentian Great Lakes using both mitochondrial (Stepien and Faber, 1998;Gatt et al, 2002) and nuclear Stepien et al, 2009) DNA variation has revealed genetic differences among walleye spawning sites consistent with those expected from reduced gene flow as a result of philopatry.…”

A geographical genetics framework for inferring homing reproductive behavior in fishes

“…This lack of a correlation would occur because there would be no particular reason that close waterheads would be more similar to each other than would waterheads located further apart (e.g., Stepien et al 2009). Although genetic distance will increase with time, there is no reason for time and space to be correlated in this scenario because the processes driving homing behavior are not geographically structured among the subsamples (waterheads).…”

“…The absence of spatial patterns will be predicted to occur appear only in the absence of a long-term history of differentiation in the species as well as the presence of a stable migration system (i.e., the waterheads and main river course), geographically independent waterheads and a low ''failure'' of individual homing behavior. Although examples of these assumptions are hard to find in nature, this prediction leads to a different but interesting challenge: the identification of a significant spatial pattern among waterheads will require an additional explanation for the structure of the population beyond that strictly involving homing behavior (see Beheregaray and Sunnucks 2001;Stepien et al 2009). Thus, ironically, the existence of Fig.…”