(full paper is archived in the Miller Library)
Title: Development of behavioral responses to visual stimuli in Pacific bonito (Sarda chiliensis)
Student Author(s): Easton, Katrina
Faculty Advisor(s): Thompson, Stuart
Location: Final Papers Biology 175H
Date: June 1999
Abstract: During development, organisms must establish properly functioning and well coordinated sensory and motor systems in order to survive. Pacific bonito (Sarda chiliensis), pelagic fishes belonging to the tuna family, undergo a relatively rapid developmental transformation in the <24-hour period after hatching. The two major morphological changes that occur are enlargement of the jaw and pigmentation of the eye (retinal ephithelium). In addition, dramatic behavioral changes take place. For example, early (stage L1) animals frequently exhibit fast start escape responses, while in the later stage (L2), more controlled sustained swimming movements are present. L1 larvae are also more sensitive to touch and vibration stimuli than L2. To test the hypothesis that the emerging visual system changes the activity of descending motor systems, I recorded field potentials in the hindbrain and spinal cord during this developmental period. Recordings of spontaneous activity showed that there was essentially no difference between L1 and L2 larvae, either in the light or dark. The same was true for L2 larvae reared in the dark. Looking at the strong visual stimuli, larvae reared in dark exhibit a movement response but recover more slowly than those reared under normal (daylight) conditions. This finding suggests that dark rearing negatively affects the sensitivity of the developing visual system, however appropriate connections with the hindbrain still appear to be made. Based on these observations, it appears that visual imputs might be sufficient to modify the activity of an identified reflex circuit, and more specific experiments are warranted to identify the physiological basis for this change.