Variation among sites and years in the local ecological outcome of interspecific interactions can generate a geographic mosaic of coevolution, as indicated by recent mathematical models. We evaluated whether local temporal dynamics of ecological outcome in the interaction between the moth Greya politella (Prodoxidae) and its host plant Lithophragma parviflorum (Saxifragaceae) are likely to mitigate or magnify geographic differences in ecological outcome found in earlier studies. The moths are highly host-specific pollinating floral parasites, and the mutualism can be swamped in some populations by the presence of effective co-pollinators. Hence, differing community contexts can shift the outcome of the interaction from mutualism to commensalism or antagonism. During each of four years, we evaluated the effect of Greya oviposition on seed development through a paired design that controlled for plant genotype and microenvironment. At Turnbull National Wildlife Refuge in Washington State, the interaction was significantly mutualistic in all four years. Mutualism in this population was indicated by a higher probability of development of capsules visited by ovipositing Greya than capsules not visited by Greya on the same plant. At Rapid River, Idaho, the interaction was commensalistic in three years and antagonistic in one year. Antagonism in this population was indicated by selective withering of capsules containing Greya eggs. Overall, the results suggest stable geographic differences in the range of ecological outcomes in this plant-insect interaction under different community contexts.

Understanding the historical framework in which species interactions have diversified across landscapes may help to partition the effects of vicariance and geographically variable selection in shaping the geographical mosaic of coevolving species. We used phylogeographical analyses of the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) to define the historical processes that may have structured interactions of this species with its host plants across major biogeographical breaks in western North America. Using 648 bp of cytochrome oxidase I and amplified fragment length polymorphisims, we identified deep genetic breaks among some populations consistent with some definitions of cryptic species. A combination of phylogenetic and population genetic approaches indicates that different historical processes may have structured G. politella genetic diversity in four regions: northern Pacific Northwest, southern Oregon, southern Sierra Nevada, and the remainder of California. The northern Pacific Northwest had high genetic diversity likely due to glacial refugia and subsequent spatial expansion, concordant with some other taxa. Populations in southern Oregon possessed unique, closely related haplotypes with restricted gene flow, possibly indicating a long-standing set of populations in this endemic-rich region. Analyses of California populations showed evidence of restricted gene flow and spatial expansion with many closely related haplotypes that occupy a broad geographical range. Southern Sierra Nevada populations were genetically distinct and highly diverse, possibly due to a localized glacial refugium. Together, these results suggest that vicariance and population expansion, possibly in combination with geographically variable selection, have shaped the diversification of G. politella and its interactions with its host plants.

The common cushion moss Grimmia laevigata (Bridel) Bridel grows on bare rock in a broad range of environments on every continent except Antarctica. As such, it must harbor adaptations to a remarkably broad set of environmental stresses, the extremes of which can include very high temperatures, prolonged nearly complete desiccation, and high ultraviolet B (UVB) exposure. Yet, like many mosses, G. laevigata shows very little morphological variability across its cosmopolitan range. This presents an evolutionary puzzle, the solution to which lies in understanding the phylogeographic structure of this morphologically simple organism. Here we report the results of an analysis of amplified fragment length polymorphisms (AFLPs) in G. laevigata, focusing on individuals from the California Floristic Province. We found evidence that populations within California constitute two distinct geographically overlapping cryptic species. Each clade harbors multiple private alleles, indicating they have been genetically isolated for some time. We suggest that the existence of cryptic species within G. laevigata, in combination with its life history, growth habits, and extreme desiccation tolerance, makes this moss an ideal research tool and a candidate for a biological indicator of climate change and pollution.amplified fragment length polymorphisms ͉ bioindication ͉ California Floristic Province ͉ Grimmiaceae ͉ phylogeography