Population and Fishery Genetics of Smallmouth Bass
Genetic studies: Across Lake Erie
Smallmouth bass: Work to date has analyzed 686 specimens for 8 microsatellite loci and 28 populations, including the Great Lakes and outlying samples. Samples have included 425 specimens from spawning locations in Lake Erie. We are continuing to increase the number of loci in order to more accurately resolve fine-scale relationships in Lake Erie.
Carol A. Stepien, Douglas J. Murphy and Rex Meade Strange
Molecular Ecology (2007) volume 16, pages 1605-1624
Abstract: Analysis of population genetic relationships reveals the signatures of current processes such as spawning behaviour and migration, as well as those of historical events including vicariance and climate change. This study examines these signatures through testing broad to fine-scale genetic patterns among smallmouth bass Micropterus dolomieu spawning populations across their native Great Lakes range and outgroup areas, with fine-scale concentration in Lake Erie. Our primary hypotheses include whether genetic patterns result from behavioural and/or geographical isolation, specifically: (i) Are spawning groups in interconnected waterways genetically separable? (ii) What is the degree of isolation across and among lakes, basins, and tributaries? (iii) Do genetic divergences correspond to geographical distances? and (iv) Are historical colonization patterns from glacial refugia retained? Variation at eight nuclear microsatellite DNA loci are analysed for 666 smallmouth bass from 28 locations, including 425 individuals in Lake Erie; as well as Lakes Superior, Huron, and Ontario, and outgroups from the Mississippi, Ohio, St. Lawrence, and Hudson River drainages. Results reveal marked genetic differences among lake and river populations, as well as surprisingly high divergences among closely spaced riverine sites. Results do not fit an isolation-by-geographical-distance prediction for fine-scale genetic patterns, but show weak correspondence across large geographical scales. Genetic relationships thus are consistent with hypotheses regarding divergent origins through vicariance in glacial refugia, followed by colonization pathways establishing modern-day Great Lakes populations, and maintenance through behavioural site fidelity. Conservation management practices thus should preserve genetic identity and unique characters among smallmouth bass populations.
Figure 1. (a) Map showing locations of collection sites for smallmouth bass spawning groups across the Great Lakes drainage system (enclosed in solid line) and outgroup samples in the Mississippi, Ohio, Hudson, and St. Lawrence River drainages. Lake Erie sites are lettered in Fig. 1b. Latitude and longitude coordinates of these sites are given in Table 1. Triangles denote riverine locations and circles designate lacustrine reef sites. Lines denote primary genetic break divisions among populations using the Manni et al. (2004a, b) barrier approach, designated with Roman numerals from greatest to less pronounced(I to IX). (b) Spawning sites for smallmouth bass sampled from lacustrine sites in Lakes Erie and St. Clair (circles) and tributaries (triangles). Latitude and longitude coordinates of these sites are given in Table 1. Divisions of Lake Erie into three physiographic basins are indicated by dotted lines. Shaded portion inside modern Lake Erie depicts ancient Lake Erie 7000–10 000 years bp, based on Bolsenga & Herdendorf (1993) and Holcombe et al. (2003).
Table 1. Summary of population divergence calculated using θST (Weir & Cockerham 1984) and nonparametric genetic differentiation tests (Goudet et al. 1996) for smallmouth bass by Great Lakes basin or river drainage for systems with multiple sampling locations and high potential connectivity among the sites
Figure 2. Examples of allelic frequencies at the Mdo8 locus for smallmouth bass among tributary spawning sites locations in the upper Mississippi River drainage system (upper three) and the central basin of Lake Erie (lower three). Note: alleles 221 and 223 do not appear in these particular rivers.
Figure 3. Pairwise relationship between genetic distance (θST/1 − θST) vs. the natural logarithm of geographical distance (km). (a), Across Great Lakes region. Test of isolation by distance: P = 0.002**,R2 = 0.201, equation is 10.1148 + 0.1425 (ln km). (b), Across Lake Erie, without river sites. Test of isolation by distance: P = 0.002**, R2 = 0.043, equation is −0.0244 + 0.0119 (ln km).
Figure 4. Neighbour-joining tree (Saitou & Nei 1987; constructed in phylip) showing relationships among major population areas for smallmouth bass based on Nei (1972) genetic distances. The tree calculated from (Cavalli-Sforza & Edwards 1967) chord distances was similar in topology and resolution, and is thus not shown. Tree is ‘rooted’ with its sister species, the spotted bass. Values at nodes denote relative support from 1000 bootstrap iterations.
Figure 5. Estimated population structure for smallmouth bass from structure analysis for K = 5(a), 9(b), and 12(c) groups (with the latter number having the greatest mean likelihood and posterior probability values). Each individual is represented by a thin vertical line, which is partitioned into K coloured segments that represent the individual’s estimated membership fractions. Black lines separate individuals from different spawning sites, which are labelled below the figure. Ten structure runs at each K produced nearly identical individual membership coefficients, having pairwise similarity coefficients above 0.95, and the figure illustrating a given K is based on the highestprobability run at that K.
Figure 6. Examples of allelic frequency patterning for smallmouth bass among spawning sites in Lake St. Clair, Lake Erie (western, central, and eastern basins), Lake Ontario(combined sites), and the Cuyahoga River(located off central basin of Lake Erie).Upper = Mdo3 locus, Lower = Mdo11 locus.
Genetic studies: Across Lake Erie