TEMPORAL PATTERNS OF SEXUAL AND ASEXUAL REPRODUCTION IN THE COLONIAL ASCIDIAN METANDROCARPA TAYLORI HUNTSMAN

¹ Hopkins Marine Station of Stanford University, California

1. Metandrocarpa taylori Huntsman (1912) is an ovoviviparous colonial ascidian with separate zooids connected by a common basal tunic, which reproduces asexually by pallial budding.

2. Specimens in collections from field populations show maximum periods of sexual reproduction during the summer months. Although approximately 80% of the 1961 summer samples were reproductively active during this period, sexual reproduction continued during the remainder of the year with no less than 30% of the population active at any time. Eggs and testes develop simultaneously within the individual zooids.

3. Asexual reproduction was quantitatively studied in colonies cultured in the intertidal zone. Budding rates are lowest during the summer and continue at a high level during the remainder of the year. These rates are not dependent upon the size or age of the colony, but do derive from variations in rates at which successive bud generations follow one another and from the number of bud offspring produced by each zooid.

4. Although the two modes of reproduction are not mutually exclusive, it is clear that one form predominates in activity during any single season.

5. There is a general direct relationship between sexual reproductive activity and ocean temperature. There is little correlation of reproductive activity with food supply, since either phytoplankton or suspended organic detritus are abundant in Monterey Bay all year.