On the development and reproduction of Botryllus schlosseri (Tunicata) colonies from the eastern Mediterranean Sea: plasticity of life history traits

Analysis of developmental patterns of Botryllus schlosseri colonies from th e eastern Mediterranean coast has been performed on 143 genets under differ ent temperature regimens (15, 20, 27 degrees C) for up to 22 weeks. While t he average maximal size as the length of the blastogenic cycle (:BC) varied in respect to water temperature, ontogeny at all temperatures was characte rized by 4 developmental stages: 1. the lag phase (the first 1-3 BCs, 1 bud /BC), 2. the exponential growth phase (5.5-7.8 BCs, up to 3 buds/BC), 3. th e plateau phase, (7.4-8.2 BCs, 1 bud/BC), 4. the degenerative or the variab le phase. Many (40.6%) colonies were not sexually reproductive, the others were male only (30.1%) or hermaphrodites. Colonies at the peak of reproduct ion develop 1.2 oocytes/zooid, and up to 57.7% produced >4 clutches. Analys ing onset of reproduction with maximal colony size revealed 4 patterns, two for "male only" colonies and two for hermaphrodites that varied at differe nt sea water temperatures. In two patterns, the onset of reproduction prece des colony maximal size, and in the others it starts at the peak size or th ereafter. Zooids at the colony's periphery developed almost twice as many b uds as did zooids at the center, but produced significantly lower numbers o f eggs. Fragmentation was recorded in large colonies and was temperature de pendent. Results are-compared with the data available on populations from o ther localities indicating for dramatically different developmental modes c haracteristic to this cosmopolitan species.