ASEXUAL DIAPAUSE INDUCED BY FOOD LIMITATION IN THE ROTIFERSYNCHAETA PECTINATA

Abstract

In some clones of Synchaeta pectinata, females parthenogenetically produce two types of eggs: thin-shelled, subitaneous eggs and thicker-shelled eggs that undergo a brief diapause. The stimulus for producing diapausing eggs is food limitation, either throughout the life-span or for short intervals during early adult life. Inductive food concentrations are well above the threshold food concentration (where rm = 0). Even when severely food limited, some females produce only subitaneous eggs, and some produce a mixture of subitaneous and diapausing eggs. Production of both types of eggs may be a risk-spreading strategy: diapausing eggs provide a refuge from short periods of very low food availability, and subitaneous eggs permit some population growth as long as food availability remains above the threshold food concentration. While prolonged food limitation reduces the birth rate, the diapause response is not always associated with, and thus probably is not directly caused by, a decreased birth rate. This supposition is consistent with the fact that the presence of a toxic cyanobacterium at high food concentrations reduces the birth rate but does not induce the diapause response. The mechanism by which food limitation is assessed by the rotifer is not known. While diapause induced by food limitation is common in microorganisms, it has rarely been reported in aquatic invertebrates.