Reproduction in a carnivorous sponge: the significance of the absence of an aquiferous system to the sponge body plan
Reproduction in a carnivorous sponge: the significance of the absence of an aquiferous system to the sponge body plan
复制标题
DOI：
10.1111/j.1525-142x.2007.00200.x
复制
发表时间：
2007-11-01
影响因子：
2.9
通讯作者：
Leys, Sally P.
中科院分区：
文献类型：
--
作者：
Riesgo, Ana;Taylor, Chantel;Leys, Sally P.
海绵通常通过含水系统产生、释放和捕获配子，因此在肉食性海绵中既没有节细胞又没有含水系统，这导致了这一门的不寻常的发育特征。精子是高度特化的细长细胞，紧密地包裹在海绵周围组织中的精囊中。成熟精子前端有顶体前小泡，鞭毛周围有纤毛孔。由四到五个卵母细胞组成的集群处于同步的卵裂阶段，这表明受精是同步的。胚胎的所有阶段都发生在同一个人身上。2、4、8细胞期胚胎卵裂球致密，16细胞期胚胎为双层。晚期胚胎沿前后轴可见三个细胞区：前半球细胞异质性，中区细胞垂直于A-P轴的胶原基质，后极小细胞。非同寻常的是，Porifera的多纤毛细胞覆盖了除后极外的所有细胞。据推测，受精是通过捕获完整的精囊而发生的，精囊周围的钳针被困在邻近海绵的异形藻中。细长形状的精子可能被设计成穿透松散的胶原膜，这样一包精子的到来将导致卵母细胞同时受精。食肉海绵失去了水渠系统，使得这种动物栖息地高度专门化的特征得以进化，但这种修改并不一定是后生动物随后进化的先决条件。考虑到海绵中配子发生、胚胎发生和组织/身体结构的极其多样的机制，关于基础后生动物的繁殖、发育和结构的概括必须谨慎对待。
Sponges usually produce, release, and capture gametes via the aquiferous system, and so the absence of both choanocytes and an aquiferous system in the carnivorous sponge Asbestopluma occidentalis has led to unusual characteristics of development for this Phylum. Sperm are highly specialized elongate cells tightly packed into spermatic cysts in the peripheral tissue of the sponge. Mature spermatozoa have proacrosomal vesicles at the anterior end and a ciliary pit surrounding the flagellum. Clusters of four to five oocytes are in synchronous stages of cleavage, suggesting that fertilization is synchronous. All stages of embryos occur in the same individual. Early cleavage was holoblastic and equal; blastomeres in two-, four- and eight-cell embryos were compact and 16-cell stage embryos were bi-layered. Late-stage embryos show three cellular regions along the anterior-posterior axis: the anterior hemisphere with heterogeneous cells, a mid-region with cells lying perpendicular to the A-P axis in a collagenous matrix, and small cells at the posterior pole. Unusually for Porifera, multiciliated cells cover all but the posterior pole. It is inferred that fertilization occurs by capture of intact spermatic cysts whose surrounding forceps spicules become trapped in the anisochelae of neighboring sponges. The elongate shape of sperm may be designed to penetrate the loose collagenous mesohyl, such that the arrival of a packet of sperm would lead to simultaneous fertilization of oocytes in a cluster. Loss of the water canal system in carnivorous sponges has allowed the evolution of features that are highly specialized for the habitat of this animal, but such modifications were not necessarily a prerequisite for the subsequent evolution of metazoans. Given the extremely versatile mechanisms of gametogenesis, embryogenesis, and tissue/body structure in sponges, generalizations regarding basal metazoan reproduction, development, and structure must be approached with caution.