Helluy S, Sandeman R, Beltz B, Sandeman D
Department of Biological Sciences, Wellesley College, Massachusetts 02181.
J Comp Neurol. 1993 Sep 15;335(3):343-54. doi: 10.1002/cne.903350305.
The freshwater crayfish Cherax destructor and the lobster Homarus americanus have many similarities including life style, body form, and neural organization. However, the ontogenic history is very different in the two species. The development of Cherax is short and direct whereas the development of Homarus comprises three pelagic larval stages and takes more than twice as long from extrusion to benthic stages at constant temperature. In order to determine the progression of maturation of the nervous system in each species and the potential implications of pelagic forms on brain structure, the timing of appearance of 22 general and neural developmental events clearly identifiable in both species was compared. The onset of serotonin antigenicity in the different parts of the brain was chosen as one marker of neural development. During the first month of embryogenesis the timing of morphological, physiological, and neural events is similar in the two species. Morphological development is then accelerated in the crayfish near hatching time and over the two postembryonic stages before the advent of the independent benthic stage. Such heterochronic processes can at least partly account for the different developmental patterns in the two decapods. Among the characters showing similar timing in the two species is the formation of glomeruli (presumptive zones of synaptic contact) in the olfactory lobes of the deutocerebrum, although this event is embryonic in Homarus but postembryonic in Cherax. In contrast, glomerular formation in the accessory lobes is heterochronic: in both species, the glomeruli of the accessory lobes are acquired postembryonically, that is, 3 to 4 months earlier in Cherax than in Homarus. These data suggest that the development of the glomeruli in the olfactory lobes may depend primarily on internal developmental signals, whereas the triggering of glomerular formation in the accessory lobes may depend on external cues. The fact that, in Homarus, only the postlarval stages show mature accessory glomeruli may be a reflection of the functional requirements of benthic life.
淡水小龙虾（Cherax destructor）和美洲龙虾（Homarus americanus）有许多相似之处，包括生活方式、身体形态和神经组织。然而，这两个物种的个体发育史却大不相同。Cherax的发育过程短且直接，而Homarus的发育则包括三个浮游幼虫阶段，在恒温条件下，从孵化到底栖阶段所需的时间是Cherax的两倍多。为了确定每个物种神经系统成熟的进程以及浮游形态对脑结构的潜在影响，我们比较了在这两个物种中都能清晰识别的22个一般发育事件和神经发育事件出现的时间。选择大脑不同部位5-羟色胺抗原性的出现时间作为神经发育的一个标志。在胚胎发育的第一个月，这两个物种的形态、生理和神经事件的发生时间相似。在小龙虾接近孵化时以及在独立底栖阶段出现之前的两个胚后阶段，形态发育加速。这种异时过程至少可以部分解释这两种十足目动物不同的发育模式。在这两个物种中，显示相似时间的特征之一是在中脑嗅觉叶中形成小球（假定的突触接触区域），尽管这一事件在Homarus中是胚胎期的，而在Cherax中是胚后期的。相比之下，副叶中小球的形成是异时的：在这两个物种中，副叶的小球都是在胚后期获得的，也就是说，Cherax比Homarus早3至4个月。这些数据表明，嗅觉叶中小球的发育可能主要依赖于内部发育信号，而副叶中小球形成的触发可能依赖于外部线索。在Homarus中，只有幼体后期显示成熟的副小球，这一事实可能反映了底栖生活的功能需求。
