Combined effects of temperature and salinity on sexual reproduction and colonial growth ofBotryllus schlosseri(Tunicata)

Abstract

Abstract Combined effects of temperature and salinity on sexual reproduction and colonial growth of Botryllus schlosseri have been studied in nine experimental samples at several combinations of temperature (from 13° to 25°C) and salinity (from 25% to 40% S). Within such bounds the two environmental parameters do not influence the initial growth (at least not up to the 5th blastogenetic generation) or the formation of gonads in buds. A marked effect of experimental conditions is noted, instead, on the subsequent colonial growth and gonad maturation. The two processes present opposite thermosaline optima. The high temperature and the intermediate salinity stimulate the maturation of gonads, the low temperature and extreme salinities stimulate colonial growth. The ecological meaning of such behaviour is discussed also in the light of previous work in the field.