Dissertation Proposal - The University of Arizona Campus Repository

(i.e. D4 colonies with small germ cells, increased NS/NR ratio) at the expense of fecundity
in environments where higher motility capabilities are needed (e.g. permanent lakes). I
return to these issues in the Discussion (Section V).
The results of the hydrodynamics model show that larger colonies need to invest in a
higher proportion of somatic cells specialized in flagellar motility to avoid sinking and be
motile, and that increasing investment in reproductive tissue decreases motility and vice
versa. These results are based on several assumptions, some conservative, others not. If
the difference in density between the ECM and water is not negligible, the need to invest
in somatic cells would be even higher since ∆M would increase. Since species differ in
their cell surface concentration pattern, not using the intercellular space term A when
analyzing the model might lead to an understatement of R, therefore also leading to an
understatement of the need of somatic cells for motility. For example, V. gigas reaches a
diameter of 3mm or more, but usually contains less than 2,000 cells (Van de Berg and
Starr 1971). Besides, the assumption of a fixed f, rS, and ∆ρC needs to be confirmed for
real colonies. The average force per flagellated cell f, reproductive or somatic, might be
dependent on colony and cell size. As a result of constructive or destructive interference,
the change in Nq per colony and per unit area may increase or decrease the force
efficiency of each cell. Also, the sizes of flagellated cells (r or rS) vary between species
and flagellated cells grow as the colony develops. I do not yet know whether there is any
relationship between cell size and flagellar beating force. Cell density ∆ρC may also vary
between cell types and species, changing ∆M.
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