Brown seaweeds often display complex life cycles and remarkable developmental plasticity. For example, the model brown seaweed, Ectocarpus siliculosus, alternates between two morphologically distinct multicellular forms, each of which is generated by a fundamentally different pattern of initial cell division: the sporophyte generation is produced by a symmetrical initial cell division, the gametophyte generation is produced by an asymmetrical initial cell division.
The brown seaweeds are responsible for more than 75% of temperate coastal primary productivity and also support biodiversity hotspots in deeper sea waters. Their early development is a critical period during which seaweed settlement patterns - and hence coastal ecosytem structures - are established. In collaboration with Professor Colin Brownlee at the Marine Biological Association in Plymouth, I use the common intertidal brown seaweed Fucus serratus, or serrated wrack, as a model organism in which to study this early development. As with many brown seaweeds, the spherical F. serratus zygote divides asymmetrically to give a polarized embryo; this first asymmetric cell division defines the embryonic axes that ensure correct multicellular patterning in the adult organism. For more details on the mechanisms behind this cell division, see Bothwell et al., (2008) Development, 135: 2173-2181 and Coelho et al. (2008). Planta, 227: 1037-1046.
However, the significance of such complex life cycles remains unclear. Because seaweed embryogenesis takes place in the intertidal zone and is very sensitive to environmental change, I am carrying out laboratory experiments to see whether different life cycle stages confer selective advantages in response to a variety of environmental stresses. Using bioimaging and molecular approaches - including lifecycle mutants - I am also investigating how a single genome may support two multicellular generations.
Ulva and Enteromorpha are two of the most common seaweeds found around European coastlines, where they are both economically and environmentally important. They are easily distinguishable because of their dramatically different shapes: Ulva are flat, lettuce-like blades two cell layers thick, while Enteromorpha form hollow, branched, tubes one cell thick (see Figure left). These two species are, however, very closely related and their respective morphologies are thought to reflect two outcomes of a single developmental program.