Seascape drivers of Macrocystis pyrifera population genetic structure in the northeast Pacific |
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| Authors: | Mattias L Johansson Filipe Alberto Daniel C Reed Peter T Raimondi Nelson C Coelho Mary A Young Patrick T Drake Christopher A Edwards Kyle Cavanaugh Jorge Assis Lydia B Ladah Tom W Bell James A Coyer David A Siegel Ester A Serrão |
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| Institution: | 1. Department of Biological Sciences, University of Wisconsin – Milwaukee, Milwaukee, WI, USA;2. Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Canada;3. Marine Science Institute, University of California, Santa Barbara, CA, USA;4. Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA, USA;5. Ocean Sciences Department, University of California, Santa Cruz, 95064, USA;6. Department of Geography, University of California, Los Angeles, CA, USA;7. Center of Marine Sciences, University of Algarve, Faro, Portugal;8. Department of Biological Oceanography, CISESE, Ensenada, Baja California, México;9. Earth Research Institute, University of California, Santa Barbara, CA, USA;10. Shoals Marine Laboratory, Cornell University, Portsmouth, NH, USA |
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| Abstract: | At small spatial and temporal scales, genetic differentiation is largely controlled by constraints on gene flow, while genetic diversity across a species' distribution is shaped on longer temporal and spatial scales. We assess the hypothesis that oceanographic transport and other seascape features explain different scales of genetic structure of giant kelp, Macrocystis pyrifera. We followed a hierarchical approach to perform a microsatellite‐based analysis of genetic differentiation in Macrocystis across its distribution in the northeast Pacific. We used seascape genetic approaches to identify large‐scale biogeographic population clusters and investigate whether they could be explained by oceanographic transport and other environmental drivers. We then modelled population genetic differentiation within clusters as a function of oceanographic transport and other environmental factors. Five geographic clusters were identified: Alaska/Canada, central California, continental Santa Barbara, California Channel Islands and mainland southern California/Baja California peninsula. The strongest break occurred between central and southern California, with mainland Santa Barbara sites forming a transition zone between the two. Breaks between clusters corresponded approximately to previously identified biogeographic breaks, but were not solely explained by oceanographic transport. An isolation‐by‐environment (IBE) pattern was observed where the northern and southern Channel Islands clustered together, but not with closer mainland sites, despite the greater distance between them. The strongest environmental association with this IBE pattern was observed with light extinction coefficient, which extends suitable habitat to deeper areas. Within clusters, we found support for previous results showing that oceanographic connectivity plays an important role in the population genetic structure of Macrocystis in the Northern hemisphere. |
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| Keywords: | giant kelp Lagrangian particle simulation landscape genetics marine connectivity microsatellites spatial genetic structure |
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