Nonrandom Larval Dispersal Can Steepen Marine Clines

Abstract

Abstract. Sharp and stable clinal variation is enigmatic when found in species with high gene flow. Classical population genetic models treat gene flow as a random homogenizing force countering local adaptation across habitat discontinuities. Under this view, dispersal over large spatial scales will lower the effectiveness of adaptation by natural selection at finer spatial scales. Thus, random gene flow will create a shallow phenotypic cline across an ecotone in response to a steep selection gradient. In sedentary marine species that disperse primarily as larvae, nonrandom dispersal patterns are expected due to coastal hydrodynamics. Surprisingly sharp phenotypic and genotypic clines have been documented in marine species with high gene flow. We are interested in the extent to which nonrandom dispersal could accentuate such clines. We model a linear species range in which populations have stable and uniform densities along a selection gradient; in contrast to random dispersal, convergent advection of larvae can amplify phenotypic differentiation if coupled with a semipermeable dispersal barrier in the convergence zone. The migration load caused by directional dispersal pushes the phenotypic mean away from the local trait optimum in downstream populations, that is, near the convergence zone. A dispersal barrier is possible as a result of colliding currents if the water and larvae are mostly displaced offshore, away from suitable settlement habitat. Disjunctions in a quantitative trait were enlarged in the convergence zone by faster current flows or a more complete dispersal barrier. With advection of larvae per generation one-third as far as the average dispersal distance by diffusion, convergence on a dispersal barrier with 40% permeability generated a trait disjunction across the convergence zone of two phenotypic standard deviations. Without directional dispersal, similar clines also developed across a habitat gap, where population density was low, or across dispersal barriers with less than 1% permeability. These findings suggest that the types of hydrographic phenomena often associated with marine transition zones can strongly affect the balance between gene flow and selection and generate surprisingly steep clines given the large-scale gene flow expected from larvae.

Identifying and reducing AFLP genotyping error: an example of tradeoffs when comparing population structure in broadcast spawning versus brooding oysters

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Genetic panmixia and demographic dependence across the North Atlantic in the deep-sea fish, blue hake (Antimora rostrata)

“…For marine species occupying a large range of environments and with large effective population sizes, neutral loci may exhibit little divergence despite fairly limited gene flow, whereas loci under strong selection may display a high degree of differentiation (White et al, 2010). Hence, using loci under selection could aid in identifying ecologically and genetically relevant units, while the distribution of different alleles in time and space could also be used to infer dispersal parameters (Barton and Gale, 1993;Hare et al, 2005).…”

A biophysical perspective on dispersal and the geography of evolution in marine and terrestrial systems

“…Taylor & Hellberg 2003;Dawson & Hamner 2005) due to environmental heterogeneity (Gilg & Hilbish 2003;Sotka et al 2004;Hare et al 2005) a synthesis for marine and terrestrial systems seems increasingly tangible. Such a synthesis will necessarily consider a wide diversity of species and situations (e.g.…”

“…The growth of molecular biology, satellite oceanography and chemical tagging methods (among other technologies) since the early 1990s has provided alternative perspectives. Studies applying these techniques have often emphasized abundant cryptic taxa (Knowlton 1993(Knowlton , 2000Goetze 2003;Dawson 2004;Fukami et al 2004), considerable oceanographic structure with ecological and evolutionary consequences (Longhurst 1998;Sotka et al 2004;Hare et al 2005), interacting biological and physical restrictions on dispersal Cowen et al 2006), a high percentage of self-recruitment (Swearer et al 1999;Cowen et al 2000;Jones et al 2005) and strong phylogeographic structure on scales of tens of meters to tens of kilometres (Taylor & Hellberg 2003;Dawson & Hamner 2005). Re-evaluating all available data leads to the conclusion that a variety of processes, acting at various spatial and temporal scales, influence modern patterns of marine biogeography (see also Rosenblatt 1963).…”