Genetically Derived Estimates of Contemporary Natural Straying Rates and Historical Gene Flow among Lake Michigan Lake Sturgeon Populations

Abstract

Natural rates of straying are difficult to quantify over large spatial scales using direct observations, particularly for long‐lived fish species characterized by delayed sexual maturity and long interspawning intervals. Using multilocus microsatellite genotypes and likelihood‐based statistical methods, we quantified rates of immigration and emigration for six genetically differentiated (mean FST = 0.041) lake sturgeon Acipenser fulvescens populations in Lake Michigan based on adults (n = 437) captured in tributaries during the spawning season. Estimated rates of straying were high (mean = 0.105), asymmetrical, and highly variable across populations. We found no significant association between the total length (a surrogate measure of age) of individuals that strayed and those that did not. Linear distance between streams was more predictive of straying rates and FST than least‐cost distances estimated based on lakescape features (bathymetry and lake current patterns). Historical rates of gene flow estimated using coalescent analysis indicated a fully parameterized model with variable evolutionarily effective population sizes (θ range, 0.684–0.989), and variable and nonsymmetrical migration rates best explained the genetic data. Comparatively high estimates of relative historical gene flow from several numerically depressed populations suggest that these populations were once larger contributors to basinwide gene flow than indicated by estimates of contemporary straying rates. High rates of interpopulation straying contrast with high FST, suggesting that straying rates are poor indicators of successful reproduction following dispersal.

Telemetry and genetic data characterize lake sturgeon (Acipenser fulvescensRafinesque, 1817) breeding ecology and spawning site fidelity in Green Bay Rivers of Lake Michigan

“…However, it is interesting to note that transition probabilities were asymmetrical. Data are consistent with basin‐wide straying estimates (Homola et al., ) that showed certain populations characterized by high net rates of immigration or emigration. It is possible that olfactory cues are less distinct between the Wolf and Peshtigo‐Oconto rivers due to the close geographic proximity of the Wolf River spawning grounds to the headwaters of the Peshtigo and Oconto rivers (Homola et al., ), possibly explaining the high movement probability between these two sets of rivers.…”

“…Transition probabilities of individuals tagged in the Peshtigo‐Oconto and Fox‐Wolf rivers and detected elsewhere were higher than transition probabilities of fish tagged in the Menominee River. Transition probabilities characterizing movements of lake sturgeon from rivers of origin into other rivers are consistent with straying rates and with the degree of genetic differentiation among rivers, suggesting individuals that stray successfully reproduce (Homola et al., ). However, it is interesting to note that transition probabilities were asymmetrical.…”

“…PCR conditions were as described in Homola et al. (). PCR products were subjected to electrophoresis on 6% denaturing polyacrylamide gels.…”

“…Spawning population sizes in each Green Bay River remain relatively small, with less than 100 spawners each in the Fox and Oconto rivers, approximately 500 in the Peshtigo River and about 1,000 in the Menominee River (Elliott & Gunderman, ). In addition, contemporary and asymmetrical straying rates among Lake Michigan lake sturgeon populations have been documented (Homola et al., ). However, fidelity to spawning areas in each river was unknown.…”

“…Acipenser fulvescens are a long‐lived potamodromous fish species that reaches sexual maturity at age 15‐25 years (Harkness & Dymond, ; Houston, ). All Green Bay lake sturgeon are highly genetically differentiated from the lake sturgeon originating from eastern (Michigan) rivers to Lake Michigan (DeHaan, Elliott, Libants, & Scribner, ; Homola et al., ; Hill, May, Quinlan, Robinson, & Welsh, ). Genetic analysis has recently allowed scientists to study straying rates and gene flow in A. fulvescens (Homola et al., ).…”