Scirpus olneyi
Three-square (Scirpus olneyi) is one of several species that propagates clonally in brackish wetlands at SERC. It is of interest to us because of the variability we find in how individual plants allocate their resources to growth, especially to clonal growth, a non-sexual form of plant propagation. Many wetland species are clonal, and most ecologists believe that this has been a successful evolutionary strategy because it uses less energy and nutrients than sexual reproduction (i.e. seed production) and it enables plants to occupy space and exclude other species.

First, a little terminology will help explain our research on Three-square. Most clonal species produce new plants that remain connected to each other. The connected plants all have the same genetic makeup and the entire group is called a genet. The individual plants within the genet are called ramets.

Maki Ikegami is studying ecological and evolutionary aspects of ramet specialization in Three-square for his Ph.D. degree at Utrecht University (The Netherlands). He has observed that in some habitats, genets produce short rhizomes, while in other areas, new ramets are produced at the end of long underground stems. In shaded patches, plants allocate proportionally more biomass to aboveground parts and ramet production continues throughout the growing season. In habitats that are not shaded, Three-square allocates more biomass belowground and ramet production stops early in the growing season. Plants in patches of high shoot density produce more seeds than plants in patches with a low shoot density.

These field observations, combined with controlled experiments and computer simulations, suggest that groups of connected ramets may obtain greater benefit for the genet by a process called "Division of Labor". Division of Labor occurs when ramets within a genet specialize in resource acquisition. Because of ramet specialization, the genet is able to acquire more resources, and thus do better, than it would if there were not ramet specialization.

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