Document: ERI-3-43-12

Population-level variation in herbivore performance on a toxic seaweed: A mechanistic and phylogenetic approach.

SOTKA, E.* ¹ and M.E.HAY ²

University of North Carolina, Chapel Hill, NC U.S.A. ¹
Georgia Institute of Technology, Atlanta, GA U.S.A. ²

Abstract:
Widely distributed herbivores are subject to locally distinct flora and consequently, geographically separated populations often, though not always, prefer and perform best on local host plants. Theory which can explain such within-species variation has been developed largely from insects, and may profit from tests utilizing herbivores phylogenetically distinct from yet ecologically similar to insects. In this vein, the tube-dwelling amphipod Ampithoe longimana (Crustacea) is found in estuaries along most of the Atlantic coast of North America. Where the amphipod co-occurs with the tropical seaweed Dictyota, the seaweed provides protection from omnivorous fishes as well as a quality food source. One such population has higher fitness on and shows greater affinity toward Dictyota than does a population which is not in sympatry with Dictyota. This difference in preference for Dictyota appears to be mediated by tolerance toward one or more diterpene alcohols found in the seaweed. A pertinent question is whether tolerance to these metabolites has been lost in herbivore populations which have spread beyond the zone of sympatry (via selection or drift) or alternatively, whether it has been gained by sympatric populations through natural selection. To answer this, two independent loci were sequenced (the mitochondrial COI and nuclear ITS regions) in order to determine the historical patterns of differentiation among these populations. Preliminary data indicates that rather than one group of populations being ancestral to the other, they are in fact reciprocally monophyletic at both loci, indicating a very long historical isolation from each other. Thus, we can't currently assess whether loss or gain of tolerance to Dictyota may have occurred, or whether both occurred simultaneously.

Keywords: amphipod, seaweed, Ampithoe, Dictyota, secondary metabolites, molecular phylogeny

This abstract is being presented at: 8:15 AM in session:
Oral Session #4: Herbivore Responses to Plants.