POPULATION GENETICS, DEMOGRAPHIC CONNECTIVITY, AND THE DESIGN OF MARINE RESERVES

TLDR

Marine population genetics often reveals only slight geographic differentiation, making it hard to discern whether limited demographic exchange or sampling error underlies the signal, and this uncertainty hampers the design of reserve systems that depend on understanding larval transport and connectivity. The study aims to use genetic isolation‑by‑distance patterns to better assess slight genetic differentiation and to inform appropriate spatial scales for marine reserve design. The authors simulate one‑dimensional stepping‑stone populations under various larval dispersal regimes to demonstrate that isolation‑by‑distance signals are strongest when populations are 2–5 times the mean dispersal distance apart. Applying the simulation framework to fish and invertebrate data estimates mean larval dispersal distances of 25–150 km.

Abstract

Genetic analyses of marine population structure often find only slight geographic differentiation in species with high dispersal potential. Interpreting the significance of this slight genetic signal has been difficult because even mild genetic structure implies very limited demographic exchange between populations, but slight differentiation could also be due to sampling error. Examination of genetic isolation by distance, in which close populations are more similar than distant ones, has the potential to increase confidence in the significance of slight genetic differentiation. Simulations of one-dimensional stepping stone populations with particular larval dispersal regimes shows that isolation by distance is most obvious when comparing populations separated by 2–5 times the mean larval dispersal distance. Available data on fish and invertebrates can be calibrated with this simulation approach and suggest mean dispersal distances of 25–150 km. Design of marine reserve systems requires an understanding of larval transport in and out of reserves, whether reserves will be self-seeding, whether they will accumulate recruits from surrounding exploited areas, and whether reserve networks can exchange recruits. Direct measurements of mean larval dispersal are needed to understand connectivity in a reserve system, but such measurements are extremely difficult. Genetic patterns of isolation by distance have the potential to add to direct measurement of larval dispersal distance and can help set the appropriate geographic scales on which marine reserve systems will function well.