The Influence of History and Contemporary Stream Hydrology on the Evolution of Genetic Diversity Within Species: An Examination of Microsatellite Dna Variation in Bull Trout, Salvelinus Confluentus (Pisces: Salmonidae)

Abstract

An understanding of the relative roles of historical and contemporary factors in structuring genetic variation is a fundamental, but understudied aspect of geographic variation. We examined geographic variation in microsatellite DNA allele frequencies in bull trout (Salvelinus confluentus, Salmonidae) to test hypotheses concerning the relative roles of postglacial dispersal (historical) and current landscape features (contemporary) in structuring genetic variability and population differentiation. Bull trout exhibit relatively low intrapopulation microsatellite variation (average of 1.9 alleles per locus, average H e ϭ 0.24), but high levels of interpopulation divergence (F ST ϭ 0.39). We found evidence of historical influences on microsatellite variation in the form of a decrease in the number of alleles and heterozygosities in populations on the periphery of the range relative to populations closer to putative glacial refugia. In addition, one region of British Columbia that was colonized later during deglaciation and by more indirect watershed connections showed less developed and more variable patterns of isolation by distance than a similar region colonized earlier and more directly from refugia. Current spatial and drainage interconnectedness among sites and the presence of migration barriers (falls and cascades) within individual streams were found to be important contemporary factors influencing historical patterns of genetic variability and interpopulation divergence. Our work illustrates the limited utility of equilibrium models to delineate population structure and patterns of genetic diversity in recently founded populations or those inhabiting highly heterogeneous environments, and it highlights the need for approaches incorporating a landscape context for population divergence. Substantial microsatellite DNA divergence among bull trout populations may also signal divergence in traits important to population persistence in specific environments.

Phylogeography of Schizothorax o’connori (Cyprinidae: Schizothoracinae) in the Yarlung Tsangpo River, Tibet

“…Gorges and waterfalls were well known to inhibit gene flow in many fishes and had a substantial effect on their genetic structure (e.g., Currens et al, 1990;Costello et al, 2003;Taylor et al, 2003;Crispo et al, 2006). We also observed that waterfalls restricted upstream gene flow within S. o'connori and increased its genetic divergence.…”

“…In others, geographic patterns of genetic structure may be more a product of current environments, involving restricted gene flow, demographic processes (e.g., bottlenecks or founder events), or selection (Templeton et al, 1995). Consequently, assessing the relative influence of these historical and contemporary factors on extant genetic structure has clear implications for questions related to evolutionary change and has become an important consideration in terms of conservation (Costello et al, 2003;Crispo et al, 2006;Hubert et al, 2007).…”

Assessing connectivity in salmonid fishes with DNA microsatellite markers

“…The authors concluded that insufficient time had elapsed since the initial colonization of this area to allow detectable differences among watersheds to accrue, but that contemporary factors modulating dispersal were important in shaping relationships among populations at smaller spatial scales, such as within watersheds. In a large-scale study of bull charr, all populations had low genetic variability, which is likely attributable to post-glacial founding events (Costello et al 2003). In addition, peripheral populations, which were colonized more recently, exhibited lower levels of genetic diversity compared to those central to the species' distribution.…”

“…In addition, peripheral populations, which were colonized more recently, exhibited lower levels of genetic diversity compared to those central to the species' distribution. Isolation by distance was weaker in these peripheral populations, indicating that historical colonization effects continue to mask the influence of current dispersal in these populations (Costello et al 2003). Using canonical correspondence analysis (CCA) to relate various environmental factors to genetic variability, Angers et al (1999) found that altitude contributed significantly to population genetic differentiation in brook charr.…”

Linking habitat quality with genetic diversity: a lesson from great bustards in Spain

“…Attempts to use measures of habitat quality to predict current genetic variation in wild populations are in their infancy. Thus far, they rarely appear to be able to explain the partitioning of diversity in natural populations (Angers et al 1999;Costello et al 2003). This might reflect our incomplete understanding of the complex nature of the relationship between habitat quality and population dynamics.…”