Courtship behavior in fruit fly Drosophila melanogaster male consists of multiple stereotypic behavioral elements. For successful mating, a male needs to firmly detect sensory cues derived from conspecific female, and once he starts courting, he needs to interact with the female by expressing the behavioral elements in a coordinated manner. P1 neurons, a class of male specific interneurons that express the sex determination gene fruitless, have been identified as “trigger neurons” that can initiate male courtship. P1 neurons are activated upon a pheromonal stimulus derived from a female thereby activate visually guided behavioral elements of courtship including female following and courtship song generation. In vivo functional imaging revealed that P1(pC1) neurons show Ca²⁺ rises that coincide with locomotion turns during courtship following, suggesting that, in addition to courtship initiation, they are involved in the control of visually-guided orientation behavior towards the female during courtship. Here I summarize our studies on the relations between sensory cues, Ca²⁺ activities in P1(pC1) neurons and behavioral outputs and describe the current knowledge on the neural basis of courtship behavior in Drosophila.

In the vertebrate retina, there are two types of visual photoreceptor cells, rods and cones. Both rods and cones convert light signals to neural signals, and the resultant light responses in rods and cones are different in two aspects, light sensitivity and duration of a light response. Light sensitivity is higher in rods than in cones. Thus, rods mediate night vision, and cones mediate daylight vision. Duration of a cone light response is much shorter than that of a rod, so that the time-resolution of daylight vision is higher than that of scotopic vision. Fortunately, we succeeded in purification of rods and cones form carp (Cyprinus carpio) retina, which enables us to investigate biochemically the molecular bases of these differences in the light response between rods and cones. Our studies showed that the signal amplification in the signal transduction cascade is higher in rods than in cones, and that the reactions to terminate a photoresponse are much faster in cones than in rods. These results well explain the lower light sensitivity and shorter duration of a light response in cones than in rods.

For ectothermic animals such as insects, ambient temperature is a vastly important environmental factor, as it severely affects their life activities. For example, low temperature often causes low activity, and its long-term exposure may result in death. High temperature is a more life-threatening condition for insects, as even a short-term exposure could be lethal. Since ambient temperature changes in a circadian manner, insects have the capability to predict the time of these changes using an internal clock −circadian clock. Since the 1990s, the molecular mechanisms of the circadian clock have been unveiled in some model animals, flies and mice. Particularly, the fruit fly Drosophila melanogaster has been a very useful model to investigate molecular and neuronal basis of the clock and has developed excellent genetic tools for manipulating neurons responsible for the clock in the brain. Drosophila researchers, including the authors, have studied the reciprocal relationship between the clock and daily temperature adaptations in Drosophila. In this review, we would like to summarize the progress that has been made in this field.