[
International Worm Meeting,
2005]
We are studying the evolution of behavior by taking a comparative approach to address behavioral variation among different nematode species. C. elegans has a simple nervous system consisting of 302 neurons to detect and respond to diverse environmental stimuli. Some neurons respond to a single stimulus whereas others respond to multiple (polymodal) stimuli. A question that arises is how does a single neuron evolve multiple functions to sense different stimuli?? Is polymodality necessary to circumvent some constraint or to efficiently use the small number of neurons? The goal of the present study is to understand whether polymodality evolves or is a general property of nematode nervous systems. We chose the ASH mediated behavior for our comparative analyses. The ASH neuronal circuitry is known to detect several different stimuli such as mechanical, osmotic and chemical stimuli and has been well characterized in C. elegans(1,2). The activation of the ASH neurons leads to a synaptic input to the interneurons which regulate/cause spontaneous reversals and backward locomotion (3). Given the prolific nature of nematodes and the availability of a good phylogenetic tree, we tested the following species i) C. elegans (N2), ii) C. briggsae (AF16), iii) Caenorhabditis sp (CB5161), iv) Caenorhabditis sp. (PS1010), v) P. pacificus (PS312) vi) Cruznema sp. (PS1351) and vii) Panagrellus redivivus. We tested all the ASH mediated behaviors viz. a) osmotic avoidance b) response to nose touch c) volatile chemical repellence using the assays standardised in C. elegans. The osmotic avoidance assay was performed using the standard drop assay (4). Our assays indicate some differences in ASH mediated behavior in some species of nematodes. For the osmotic avoidance drop assay, we observed that all species we tested avoided the high osmolarity. However the response time for some of the species was different than C. elegans We also observed differences in behavior for the nose touch and volatile repellant assays. Using DIC microscopy, we identified the ASH neuron in the other species. In general, the ASH neuron is in a similar position as C. elegans in the other species. To test whether these behaviors are mediated by ASH in the other species, we are examining the behavior of ASH-ablated animals. References: 1.Kaplan and Horvitz PNAS, 1993 2.Hart et al. Nature, 1995 3. Zheng et al. Neuron, 1999 4. Hilliard et al Curr Biol. 2002