Chadwick-Furman N E, Weissman I L
Hopkins Marine Station of Stanford University, Pacific Grove, California 93950, USA.
Biol Bull. 1995 Aug;189(1):36-41. doi: 10.2307/1542199.
The colonial ascidian Botryllus schlosseri is a model organism for research on invertebrate histocompatibility, development, and evolutionary biology. Nonetheless, the basic life history of Pacific Ocean populations of the species remains unknown. We determined field rates of growth, reproduction, and senescence in four cohorts of B. schlosseri colonies in Monterey Bay, California. Colonies grew exponentially as juveniles and reached sizes of up to 1400 zooids within 69 days. After a juvenile phase lasting at least 49 days, the colonies began to reproduce sexually. Each zooid produced up to 10 clutches, each with a maximum of 5 eggs, resulting in very high fecundity of up to 8000 eggs per colony. Following a short period (maximum 70 days) of continuous sexual reproduction, colonies abruptly senesced and died while still bearing a full clutch of eggs. Senescence progressed through four distinct stages over 1-2 weeks, and inevitably led to the simultaneous death of all zooids in the colony. Although senescence was the main cause of mortality, some colonies died as a result of predation or undermined causes. Certain life history traits varied significantly between cohorts that settled at different times of year. For example, lifespans in the field varied from about 3 months for spring to 8 months for fall-born colonies, but the lifetime fecundity of colonies did not vary between cohorts. The morphologies and life histories of colonies monitored in the field and reported here differed from those of colonies cultured previously in the laboratory.
群体海鞘Botryllus schlosseri是研究无脊椎动物组织相容性、发育和进化生物学的模式生物。尽管如此，该物种在太平洋种群的基本生活史仍不清楚。我们测定了加利福尼亚州蒙特雷湾四个Botryllus schlosseri群体的生长、繁殖和衰老的野外速率。群体在幼体阶段呈指数生长，在69天内达到多达1400个游动孢子的大小。在持续至少49天的幼体阶段之后，群体开始有性繁殖。每个游动孢子最多产生10个卵囊，每个卵囊最多有5个卵，导致每个群体的繁殖力非常高，可达8000个卵。在短时间（最长70天）的持续有性繁殖之后，群体突然衰老并死亡，同时仍带有一整卵囊的卵。衰老在1-2周内经历四个不同阶段，并不可避免地导致群体中所有游动孢子同时死亡。虽然衰老为死亡的主要原因，但一些群体因捕食或不明原因而死亡。在一年中不同时间定居的群体之间，某些生活史特征存在显著差异。例如，野外寿命从春季出生群体的约3个月到秋季出生群体的8个月不等，但群体的终生繁殖力在不同群体之间没有差异。这里报道的在野外监测的群体的形态和生活史与之前在实验室培养的群体不同。
