G. Baghdasarian et L. Muscatine, Preferential expulsion of dividing algal cells as a mechanism for regulating algal-cnidarian symbiosis, BIOL B, 199(3), 2000, pp. 278-286
A wide range of both intrinsic and environmental factors can influence the
population dynamics of algae in symbiosis with marine cnidarians. The prese
nt study shows that loss of algae by expulsion from cnidarian hosts is one
of the primary regulators of symbiont population density. Because there is
a significant linear correlation between the rate of algal expulsion and th
e rate of algal division, factors that increase division rates (e.g., eleva
ted temperature) also increase expulsion rates. Additionally, H-3-thymidine
is taken up to a greater extent by algae destined to be expelled than by a
lgae retained in the host cnidarians. Taken together, data for rates of exp
ulsion, rates of division at different temperatures, and uptake of 3H-thymi
dine suggest that dividing algal cells are preferentially expelled from the
ir hosts. The preferential expulsion of dividing cells may be a mechanism f
or regulation of algal population density, where the rate of expulsion of a
lgae may be an inverse function of the ability of host cells to accommodate
new algal daughter cells. This kind of regulation is present in some cnida
rian species (e.g., Aiptasia pulchella, Pocillopora damicornis), but not in
all (e.g., Montipora verrucosa, Porites compressa, and Fungia scutaria).