Geographic Variation in Phenotypic and Genetic Differentiation within Populations
A variety of plant and animal studies have demonstrated that strong selection or lack of dispersal across a steep environmental gradient can result in differentiation between conspecifics. However, local environmental gradients are nested within latitudinal gradients, and processes at these larger spatial scales may mediate selection and dispersal on the local scale. Thus, the degree of differentiation between conspecifics across a steep environmental gradient may vary among larger geographic regions.
I am using the brown seaweed Fucusvesiculosus, a foundation species in Gulf of Maine rocky shore communities, to address this hypothesis. This species has a broad distribution along the intertidal gradient - occurring from the low to high intertidal zone. Using molecular tools to quantify population structure at multiple spatial scales and field experiments to compare phenotypic response to tide height, I have found evidence of adaptation and genetic differentiation in some but not all regions of the Gulf of Maine. This is likely driven by among population variation in dispersal between individuals along the intertidal gradient. Importantly phenotypic differentiation in traits such as nutrient uptake and resource use efficiency have been identified, which could have consequences for associated communities and ecosystems.
Phenological study of Phaeosaccion collinsii Farlow in Nahant, MA
Phaeosaccion, epiphytic on seagrass (2x mag.)
In 1882, W.G. Farlow described a new genus of epiphytic algae on seagrass, Zostera marina, collected from Little Nahant, Massachusetts – Phaeosaccion collinsii. Almost nine decades later Chen, Craigie, McLachlan, et al. made some of the first laboratory observations on morphological, life-history, and chemical characteristics. We collected data in situ over two growing seasons, and found that Phaeosaccion collinsii is highly sensitive to changes in environmental conditions, particularly temperature. During the unusually warm winter of 2012, we found that Phaeosaccion did not complete its full life-cycle and individuals were restricted to smaller morphological forms. In 2013, when winter temperatures were considerably cooler, completion of the life-cycle, including zoospore production was observed. Additionally, we identified variation in storm damage and ambient nutrient supply as other possible factors that may influence Phaeosaccion; factors that had not been previously considered for this species.
Modification of Secondary Succession by a Foundation Species
Foundation species alter the availability of abiotic and biotic resources, thereby shaping the distribution and abundance of associated organisms. This can occur through mechanisms such as modification of competitive outcomes, environmental filtering, and/or changes in recruitment patterns. In temperate marine communities, kelps are conspicuous foundation species that alter the distribution and abundance of both benthic seaweed and invertebrate species. The reduced light levels, imposed by the kelp canopies, have long been thought to shape competitve outcomes of understory species with low light tolerant dominating understory communities. However, data on spore and larval dispersal in these ecosystems suggests that kelp canopies also could limit dispersal into these habitats thereby althering recruitment and succession in understory communities.
Using a canopy manipulation experiment and observations of seaweed spore settlement, we found that the kelp Eisenia arborea, limits dispersal and/or survival of seaweed spores in the understory environment. Due to this limited dispersal, recruitment and secondary succession is slow in understory communities. This allows red seaweed species, which are competitively inferior in canopy-free environments, to persist and even dominate in understory communities. In canopy-free zones however, high recruitment and high light, allow for relatively rapid succession, and competitive interactions shape the community assemblage. These results demonstrating that foundation species alter the distribution and abundance of species by affecting not only interspecific interactions (i.e., competition) but also dispersal and recruitment limitation.