Regional Variation in Feeding Preferences of the Marine Herbivore Ampithoe Longimana
McCarty, Amanda Terry
Sotka, Erik E.
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In many shallow water marine ecosystems, herbivores control the abundance and diversity of seaweeds. Therefore, understanding interactions between seaweeds and herbivores provides insight into the ecological structure and evolutionary history of benthic ecosystems. I explored the ecology and evolution of geographic variation in the feeding preferences and host use of the generalist marine herbivore Ampithoe longimana, which has a broad geographic range spanning 2,000 km of the Atlantic coast of North America. I specifically tested whether populations of this amphipod from New England, North Carolina and Florida consistently evolve greater feeding preferences for locally important macroalgal using field surveys, laboratory based feeding assays and molecular analyses. Field surveys indicated that seaweeds in the genus Dictyota are important hosts for A. longimana from North Carolina but not amphipods from New England or Florida. A series of laboratory based feeding assays revealed that North Carolina amphipods consumed proportionally more of the chemically defended seaweed D. ciliolata and its lipophilic secondary metabolites than amphipods from New England and Florida. In contrast, when offered eleven seaweeds that also represent locally important seaweed hosts ( e.g., Hypnea, Acanthophora, Gracilaria ), regional variation in feeding preference was not detected. Therefore, although populations of marine herbivores are capable of evolving greater feeding preferences for locally abundant seaweeds, they do not necessarily do so.