SS4.05 Tribute to Thomas Frost
Date: Monday, June 10, 2002
Time: 11:30:00 AM
Location: Sidney
 
GILBERTJJ, DARTMOUTH COLLEGE, HANOVER, USA, John.J.Gilbert@Dartmouth.edu
 
A MULTI-GENERATIONAL PARENTAL EFFECT DELAYS SEXUALITY AND DIAPAUSE IN A ROTIFER LIFE CYCLE
image
Many planktonic rotifers have heterogonic life cycles. Population growth occurs via female parthenogenesis, and a period of bisexual reproduction leads to the production of fertilized resting eggs. In many of these rotifers, sexuality is initiated when specific environmental stimuli induce amictic females--whose eggs develop parthenogenetically into females--to produce mictic daughters--whose haploid eggs develop parthenogenetically into males or, if fertilized, into diapausing amictic-female embryos. An experiment with ten clones of Brachionus calyciflorus demonstrated that the propensity of amictic females to produce mictic daughters in response to a standardized crowding condition is low when they hatch from resting eggs and then gradually increases to a maximum after about 12 parthenogenetic generations. This parental effect ensures that each clone derived from a resting egg in a multi-clonal population can rapidly increase its population size through parthenogenesis before sexual reproduction. Therefore, it should promote random encounters between males and mictic females of the same clone, maximize the number of resting eggs to which a clone can contribute genes, and increase clonal diversity in the population and egg bank.