Divergence genetics analysis reveals historical population genetic processes leading to contrasting phylogeographic patterns in co‐distributed species

Abstract

Coalescent samplers are computational time machines for inferring the historical demographic genetic processes that have given rise to observable patterns of spatial genetic variation among contemporary populations. We have used traditional characterizations of population structure and coalescent-based inferences about demographic processes to reconstruct the population histories of two co-distributed marine species, the frilled dog whelk, Nucella lamellosa, and the bat star, Patiria miniata. Analyses of population structure were consistent with previous work in both species except that additional samples of N. lamellosa showed a larger regional genetic break on Vancouver Island (VI) rather than between the southern Alexander Archipelago as in P. miniata. Our understanding of the causes, rather than just the patterns, of spatial genetic variation was dramatically improved by coalescent analyses that emphasized variation in population divergence times. Overall, gene flow was greater in bat stars (planktonic development) than snails (benthic development) but spatially homogeneous within species. In both species, these large phylogeographic breaks corresponded to relatively ancient divergence times between populations rather than regionally restricted gene flow. Although only N. lamellosa shows a large break on VI, population separation times on VI are congruent between species, suggesting a similar response to late Pleistocene ice sheet expansion. The absence of a phylogeographic break in P. miniata on VI can be attributed to greater gene flow and larger effective population size in this species. Such insights put the relative significance of gene flow into a more comprehensive historical biogeographic context and have important implications for conservation and landscape genetic studies that emphasize the role of contemporary gene flow and connectivity in shaping patterns of population differentiation.

Genealogical approaches to the temporal origins of the Central American gap: Speciation and divergence in Pacific <i>Chthamalus</i> (Sessilia: Chthamalidae)

“…However, these methods require data from a larger number of taxa. Separating the influences of temporal isolation and recurrent gene flow is often critical in assessing alternate historical scenarios that could produce patterns of extant diversity (McGovern et al 2010).…”

“…What we have come to recognize is the dynamic nature of habitat and species distributions through time. Histories of allopatry, expansion, and habitat loss are not always readily apparent from contemporary species distributions (McGovern et al 2010). it is of interest to characterize these historical events when they appear to have influenced large numbers of taxa.…”

Genetic Analysis of Larval Dispersal, Gene Flow, and Connectivity

“…Are these assumptions justified, or would other measures of migration and gene flow (e.g., McGovern et al 2010;Crandall et al 2012) more closely reflect the dispersal capabilities of larvae? Most of these assumptions are difficult to test.…”

Population Genomics of Marine Zooplankton

“…The usefulness of F-statistics is further limited by the very large population sizes of many zooplankton, which result in relatively larger confidence intervals for very small F values (Waples 1998), and thus a lack of statistical significance for high gene flow species (see Waples et al 2008). At least partly for this reason, population genetic studies of marine species have also employed various measures of oceanographic distance (Hansen and Hemmer-Hansen 2007;McGovern et al 2010;Alberto et al 2011;Schunter et al 2011) and approaches such as seascape genetics (Galindo et al 2010). …”