Nonrandom larval dispersal can steepen marine clines

Area of Science:

• Population Genetics
• Marine Ecology
• Evolutionary Biology

Background:

• Classical models assume random gene flow homogenizes populations, hindering local adaptation across environmental gradients.
• Marine species with larval dispersal often exhibit sharp phenotypic and genotypic clines, contradicting random gene flow expectations.
• Coastal hydrodynamics can lead to nonrandom larval dispersal patterns, potentially explaining these sharp clines.

Purpose of the Study:

• To investigate how nonrandom larval dispersal, influenced by hydrodynamics, can accentuate sharp phenotypic clines in marine species.
• To model the interplay between directional dispersal, selection gradients, and dispersal barriers in shaping clinal variation.
• To understand the conditions under which marine transition zones generate steep clines despite high gene flow.

Main Methods:

• Developed a population genetic model for a linear species range with a selection gradient and uniform population densities.
• Incorporated convergent larval advection and semipermeable dispersal barriers to simulate nonrandom dispersal patterns.
• Analyzed the impact of factors like current speed, barrier permeability, and advection distance on phenotypic differentiation.

Main Results:

• Convergent larval advection coupled with a dispersal barrier can amplify phenotypic differentiation, creating sharp clines.
• Directional dispersal introduces migration load, shifting phenotypic means away from local optima near convergence zones.
• Disjunctions in quantitative traits were enlarged by faster currents or more complete dispersal barriers, with significant trait differences observed.

Conclusions:

• Nonrandom larval dispersal, particularly convergent advection near dispersal barriers, can generate surprisingly steep phenotypic clines in marine species.
• Hydrographic phenomena in marine transition zones play a crucial role in balancing gene flow and selection, leading to pronounced local adaptation.
• These findings challenge the assumption of random gene flow in marine systems and highlight the importance of hydrodynamics in evolutionary processes.