The study on allorecognition in colonial animals

1.冈田海绵和日本海绵均表现出同种识别反应。一个个体的碎片与同一个体的另一个碎片融合，但不与另一个个体的碎片融合。这表明控制同种异体识别的基因表现出高度的多态。相反，单个雌性个体幼虫之间的融合率很高。在幼虫中，同种异体识别的机制可能太不成熟，不能排斥不相容的幼虫。苔藓虫群体表现出同种异体识别反应。沿着两个接触群之间的边界观察到动物群系的融合或破坏。已经有报道称，当两个不相容的菌落融合时，双壳类海鞘动物会表现出延迟的同种识别反应。这种反应被称为“群体再吸收”，这种反应表现出一种层次分明的反应。很明显，异种识别能力在群体无脊椎动物中很常见。然而，目前尚不清楚这种识别异体的能力是否只存在于殖民地动物的进化过程中，或者这种能力是所有动物的共同和基本功能。我们需要对海绵和苔藓动物中同种异体识别的遗传学进行更多的研究，才能与脊椎动物的MHC进行比较，还需要对其他门的许多动物进行同种识别的检测。

1. The two species of Japanese sponges, Hilichondria okadai and H.Japonica, showed allorecognition responses. A piece of an individual fused with another piece of the same individual, but did not fuse with the piece of the other individual. This suggests that the genes controlling allorecognition show high polymorphism. On the contrary, the rate of fusion among larvae from a single female individual was very high. In a larva the mechanism of allorecognition might be too immature to reject incompatible larvae.2. Bryozoan colonies showed allorecognition responses. Fusion or destruction of zooeciums was observed along the boundary between two contact colonies.3. It was already reported that botryllid ascidians show the delayd allorecognition responses when two incompatible colonies has fused. This responses are called "colony resorption", and botryllids display a hierarchy of this responses.It becomes clear that the ability of allorecognition is common among colonial invertebrates. However, it is unclear whether the ability of allorecognition has been kept in only colonial animals through their evolution processes or that ability is a common and basic function for all animals. We need much study on the genetics of allorecognition in sponges and bryozoans in order to compare with MHC of vertabrates, and also need examination of many animals of other phylum about the presence of allorecognition.