Pratt Marney C
Department of Biology, Duke University, Durham, North Carolina 27708-0338, USA.
Biol Bull. 2004 Aug;207(1):17-27. doi: 10.2307/1543625.
Most Recent bryozoan species are encrusting sheets, and many of these colonies have densely packed feeding zooids. In this study, I tested whether tight packing of feeding zooids affects food capture. Colonies of a bryozoan with an encrusting sheet form (Membranipora membranacea) were dissected to produce individuals whose feeding zooids were (1) closely packed, (2) more widely spaced, or (3) isolated. For each type, rates of particle ingestion were measured in still water and in a freestream velocity of 2.7 cm s(-1). Ingestion rate increased when zooids were closest together, probably because of reduced refiltration and increased feeding current strength farther from the lophophores. The mean incurrent velocity within 0.02 cm above the center of the lophophore was 0.28 cm s(-1) regardless of zooid spacing; however, when the incurrent velocity was measured more than 0.1 cm from the lophophores, zooids that were close together or spaced one zooid's width apart had significantly faster incurrent velocities than single zooids. Flow visualization suggests that isolated zooids and those spaced far apart refilter more water than zooids that are close together. These results along with the observed trend of increased zooid integration over evolutionary time suggest that the benefits of increasing coordination outweigh the consequences of intrazooid competition.
大多数现代苔藓虫物种呈覆盖状薄片，而且许多这样的群体都有紧密排列的摄食类虫体。在本研究中，我测试了摄食类虫体的紧密排列是否会影响食物捕获。解剖了一种具有覆盖状薄片形态的苔藓虫（膜孔苔藓虫）群体，以得到其摄食类虫体处于以下三种状态的个体：（1）紧密排列、（2）间隔更宽、或（3）孤立分布。对于每种类型，分别在静水和2.7厘米/秒的自由流速度下测量颗粒摄取率。当类虫体靠得最近时，摄取率会增加，这可能是由于再过滤减少以及离触手冠较远位置的摄食水流强度增加所致。无论类虫体间距如何，在触手冠中心上方0.02厘米内的平均入流速度均为0.28厘米/秒；然而，当在离触手冠超过0.1厘米处测量入流速度时，靠在一起或间隔一个类虫体宽度的类虫体的入流速度明显快于单个类虫体。流动可视化显示，孤立的类虫体和间隔较远的类虫体比靠在一起的类虫体再过滤更多的水。这些结果以及在进化时间里观察到的类虫体整合增加的趋势表明，增加协调性的益处超过了类虫体内竞争的后果。
