Meeting Abstract
It is widely known that during electronics design complex circuits are made from standardized components. Many individuals often think biological systems are organized in this same way. It is attractive to hypothesize that homologous neurons should participate in similar circuits to produce homologous behaviors between species. However, differences in neuronal activity of homologous neurons have been observed in shell-less mollusks. This work has shown, in swimming behavior, that homologous neurons form different circuit connections in two closely related species. Despite this, little research has been done on differences in homologous neurons in different species analyzing similar behaviors. This research analyzed the circuits involved in reproductive behavior in two closely related leech species, Hirudo verbana and Macrobdella decora. Both species respond to a hormone (hirudotocin) by progressing through the same reproductive behaviors. Additionally, both synthesize this hormone in two segmentally repeated neurons called Leydig cells. Furthermore, both species have the same cohort of motor neurons that produce behaviors. We hypothesized that if a species-specific circuit difference existed, we might observe it in different motorneuron activity. We have found that there are significant differences in the reproductive behavioral circuit. Quantifiable differences in motorneuron dynamics include: burst duration, inter-burst interval, burst frequency, and the number of spikes per burst. These results indicate that there is a difference in neuronal participation between the two species when producing the same reproductive behavior. The outcome of this research raises a question as to why evolutionarily two closely related species producing the same behavior do so using different circuitry.
