Dorman, Hanna , Wallace, Lisa .
Phylogeography of Acmispon dendroideus (Fabaceae) on the California Channel Islands tracked through variation in Nsp1.
Phylogeographic patterns emerging from studies of taxa that inhabit the California Channel Islands suggest that oceans are major barriers to dispersal for many insular species. Clearly, this has contributed to the evolution of unique plant species in this archipelago, many of which are single-island endemics. We are interested in whether barriers to inter-island dispersal could also result in the evolution of variation in symbiotic relationships, particularly between legumes and rhizobia. Symbiotic specificity has been found to vary among plants of the same species, among rhizobia strains, and in concert with geographical variation. Given the extensive variation in soils,communities, and geology across the California Channel Islands, we hypothesized that conspecific populations on different islands would exhibit variation in rhizobial relationships. To test this hypothesis we examined sequence variation in Nsp1, an early-acting gene that controls nodule formation, within and across 14 populations of Acmispon dendroideus (Fabaceae) on the southern islands of San Clemente and Santa Catalina and the northern islands of Anacapa, Santa Rosa,Santa Cruz, and San Miguel. We found high sequence similarity between A. dendroideus and model legumes, which suggests homology and conservation of function of this gene in the focal species. Eight unique alleles were identified in A. dendroideus, and there was considerable structure across the islands. Of the three common alleles, two occurred in populations on the northern and southern islands and the third was restricted to San Clemente. This latter allele contains a unique insertion that was also found in two samples from Santa Catalina and outgroups from mainland California.The similarity between these alleles and those in outgroup species in a median joining network suggests a direction of colonization from mainland California to Santa Catalina and/or San Clemente followed by dispersal to the northern islands. The presence of numerous alleles on Santa Catalina that are more closely related to alleles on northern islands suggests colonization of Santa Catalina from the north as well. Among the northern islands, one allele was found throughout all four islands, which is consistent with the prediction of panmixia associated with the formation of Santa Rosae during the last glacial period. This is one of the first studies to demonstrate intraspecific variation in genes involved in the legume-rhizobium symbiosis. Further studies of rhizobial diversity across the islands are needed to confirm the functional significance of the observed variation in A. dendroideus.
Log in to add this item to your schedule
1 - Mississippi State University, PO Box GY, Mississippi State, MS, 39762, USA
Presentation Type: Poster:Posters for Topics
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM