Maternal effect by stem females in Brachionus plicatilis: effect of starvation on mixis induction in offspring Atsushi Hagiwara 1, *, Yoji Kadota 1 & Akinori Hino 2 1 Graduate School of Science & Technology, Nagasaki University, Bunkyo 1-14, 852-8521, Nagasaki, Japan 2 Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, 113-8657, Tokyo, Japan (*Author for correspondence: E-mail: hagiwara@net.nagasaki-u.ac.jp) Key words: rotifera, Brachionus plicatilis, stem female, maternal effect, starvation, mixis Abstract We examined whether starvation during the initial period of life in stem females affected reproductive characteristics of the offspring. Starvation treatment had different effects on rotifers hatched from resting eggs and those hatched from amictic eggs. When stem females experienced starvation after hatching, this induced a higher percentage of mixis in their offspring. When the same starvation treatment was applied to rotifers hatched from amictic eggs, there was no effect on the induction of mixis. It is probable that stem females hatched from resting eggs have specific features that are vulnerable to unfavorable environmental conditions, and that these features can be inherited by their offspring through the maternal cytoplasm. Introduction Rotifers hatched from resting eggs are diploid amictic females. These are known as stem females. Stem females are difficult to distinguish from asex- ually produced amictic females by their morphology alone. The only observable difference is the presence of some yolk derived from the cytoplasm of the resting egg for a few hours after hatching. Several biological features of stem females have been reported. For example, external conditions such as incubation temperature and salinity during resting egg formation affect the frequency of mixis of a rotifer clone initiated by stem females (Hino & Hirano, 1985, 1988). Variations in food availabil- ity during population growth and resting egg for- mation affect the hatchability of resting eggs and the population growth rate of the derived clones (Hagiwara & Hino, 1990). External conditions during initial developmental stages to complete resting egg maturation affect the hatching patterns of the eggs (either sporadic or simultaneous), frequency of mixis induction and the population growth rate of the derived clones (Hagiwara & Hino, 1989). It is possible that stem females are especially vulnerable to environmental effects, and that these features may be inherited by their offspring through the maternal cytoplasm. In support of this hypothesis, Hino & Hirano (1977) found that a change of food decreased mixis induction in Brachionus plicatilis cultures, except when the food was changed to that ingested by stem females. In order to investigate this hypothesis further, we conducted research to determine whether the starvation of stem females immediately after hatching affects the reproductive characteristics of their offspring. Materials and methods We used Brachionus plicatilis Russian strain, which was obtained from Terry W. Snell, Georgia Institute of Technology, USA. This strain was selected for the experiments because, among all Hydrobiologia (2005) 546:275–279 Ó Springer 2005 A. Herzig, R.D. Gulati, C.D. Jersabek & L. May (eds.) Rotifera X: Rotifer Research: Trends, New Tools and Recent Advances DOI 10.1007/s10750-005-4208-0