Is breaking up hard to do? Breakage, growth, and survival in the parasitic clonal plant Cuscuta corymbosa (Convolvulaceae).

In a tripartite exploration of the effects of traumatic breakage in the parasitic clonal plant Cuscuta corymbosa, experimental breakage had significant negative effects upon stem extension of ramets distal to a break and the level of that effect depended upon the number of ramets in the severed fragment. Regular monitoring of clonal individuals transplanted onto naturally occurring, native host species revealed that breakage in individuals growing under natural conditions ranged from 2 to 66% of all interramet connections and significantly affected distance between ramets and stolon generation in ramets associated with a break. Simulations revealed that these responses to breakage would significantly change the "shape" of a clonal individual in a manner capable of affecting probabilities of encounter with patchily distributed resources. Nonetheless, the observed levels of breakage had no discernible effect on biomass accumulation, although individuals that survived into the dry season and thus gained the potential to reproduce in additional seasons had a significantly lower rate of breakage than those that did not. We suggest that the lack of a relationship between breakage and within-season biomass accumulation is an indication that parasite response to breakage is gauged to expected levels of breakage for the habitat. We note that the capacity of ramets to survive disconnection significantly decreased the loss of tissue that would occur if subunits did not possess the potential to function independently.