Comparative Neurobiology
The groups of mollusks that we study contain species with nervous systems that vary widely in their complexity and degree of centralization. We are using comparative approaches to study how and why complex, centralized nervous systems evolve from those that are simpler and more dispersed. In particular, we are interested in the co-evolutionary relationships between brains, new sensory systems, and new forms of locomotion. We are also using scallops and chitons as model systems for studying the neurobiology of dispersed visual systems. Techniques we employ for these studies include:
- Neurohistology.
- Electrophysiology.
- Exploring the evolutionary histories and expression patterns of brain-related genes.
- Axon-tracing in collaboration with the Poulain Lab at USC.
Co-evolution of eyes and brains
Bivalves and chitons tend to have decentralized nervous systems. Unlike other bivalves, scallops have a large central ganglion known as the parietovisceral ganglion (PVG). Previous work indicates that this ganglion includes specialized lobes that process visual information gathered by the eyes. The diagram above illustrates the nervous system of the scallop Pecten ziczac (diagram modified from Wilkens, L.A., 1981. Neurobiology of the scallop. Proc. R. Soc. Lond. B. 211, 341-372).
Bivalves and chitons tend to have decentralized nervous systems. Unlike other bivalves, scallops have a large central ganglion known as the parietovisceral ganglion (PVG). Previous work indicates that this ganglion includes specialized lobes that process visual information gathered by the eyes. The diagram above illustrates the nervous system of the scallop Pecten ziczac (diagram modified from Wilkens, L.A., 1981. Neurobiology of the scallop. Proc. R. Soc. Lond. B. 211, 341-372).
- Species of scallops and their close relatives differ in the complexities of their eyes and swimming-related behaviors. What are the relationships between neural complexity, visual acuity, and swimming ability in these animals? For example, do stronger swimmers tend to have better vision and bigger brains?
- Like bivalves, do chitons with eyes have nervous systems that are relatively centralized and complex compared to their eyeless relatives?
Neurobiology of dispersed visual systems
Most research on the processing of visual information has been conducted on animals that have a pair of eyes located on their head. Generally, information gathered separately by the right and left eyes is transmitted along a pair of optic nerves that travel to a central location within an animal’s brain. Here, information from the two eyes is integrated so that a single reconstruction of the visual environment is formed. Such integration is necessary if an animal is to accurately gauge the number and relative positions of objects in its environment. Paired cephalic eyes are not the only eyes found in the natural world, however, and we may have much to learn from visual systems -- such as those of scallops and chitons -- that deviate from this familiar arrangement by containing dozens or hundreds of separate image-forming structures. Currently, the Speiser Lab is asking:
Most research on the processing of visual information has been conducted on animals that have a pair of eyes located on their head. Generally, information gathered separately by the right and left eyes is transmitted along a pair of optic nerves that travel to a central location within an animal’s brain. Here, information from the two eyes is integrated so that a single reconstruction of the visual environment is formed. Such integration is necessary if an animal is to accurately gauge the number and relative positions of objects in its environment. Paired cephalic eyes are not the only eyes found in the natural world, however, and we may have much to learn from visual systems -- such as those of scallops and chitons -- that deviate from this familiar arrangement by containing dozens or hundreds of separate image-forming structures. Currently, the Speiser Lab is asking:
- Do scallops and/or chitons integrate the images gathered by their many separate eyes in a way that allows them to form a single reconstruction of their visual environment?
- If they do, how may such a system be accomplished neurally?
- If they do not, what are the possible functions of a visual system in which many separate, over-lapping images are perceived simultaneously?