Neuronal composition of early stages of visual processing in a highly visual crab revealed by reduced-silver methods.

JULIETA SZTARKER, NICHOLAS STRAUSFELD AND DANIEL TOMSIC

Suecia

Congreso; The second International Conference on Invertebrate Vision; 2008

Lund University

Crustaceans are among the most vastly distributed phylogenetic groups. They occupy many different ecologies and have very diverse lifestyles. There exist numerous reports on behavioral adaptations and modifications in the external morphology of the eyes of crustaceans living in different habitats. The eye stalk length, eye separation and acute zones for vertical resolving power have been correlated with the structure of the animals environment. However, up to the present it is unclear whether such changes are accompanied by differences in the cellular organization of their optic lobes and, if so, whether they are due to structural modification of existing cell lineages or by incorporation of new cell types. Compared with insects, relatively little is known about the morphology of cells and neural organization of crustacean optic neuropils. Anatomical data available in the literature relates almost exclusively to the first optic neuropil, the lamina, and detailed anatomical information of deeper structures is lacking. In addition, the species commonly analyzed are few and most of them live in turbid or deep waters and thus probably don’t rely on vision as the most important sensory modality. Chasmagnathus granulatus is a semiterrestrial crab very sensitive and reactive to visual stimuli. He lives in large colonies, socially interacts, and is subject to attack by aerial predators. The present study describes the rich cellular composition of the visual neuropils of Chasmagnathus revealed by Bodian and Golgi techniques. We found several commonalities with previous descriptions in decapods along with some novel elements not previously described. Among them, we find a stratified wide field monopolar neuron and two types of Small-field T-neurons (SFT) linking the lamina with the medulla. SFT neurons are thought to interact with retinula cell endings probably providing a multicartridge (the dendritic tree extends over 3-4 cartridges in the lamina, see figure) centripetal channel of information. This network might act as a sensitive channel working in conditions of dim light. In fact, albeit passing long periods in land Chasmagnathus also spends part of the day submerged in turbid water. Therefore, SFT might confer additional processing capacities adaptive for the changing necessities of these animals. In addition, we stained an unequaled large number of T-neuron and  centrifugal cell types. Considering our results, it appears that Chasmagnathus nervous system is very susceptible to being impregnated using reduced silver techniques and can provide a thorough description of the cell types present in the brains of decapods.