Behavioural genetic analysis of biorhythms in the melanogaster subgroup of Drosophila

Differences in Drosophila courtship song components are considered to play an important role in species sexual isolation, because of the observed lack of variation within individuals of a species, and the relatively large differences between closely related species. When a male courts a female, a song is produced, usually consisting of a hum song and trains of pulses. Song recordings from the 8 members of the D. melanogaster subgroup, as well as from several types of interspecific hybrid crosses reveal that the Interpulse Intervals (IPIs) oscillate rhythmically about their mean, in a species-specific fashion, as courtship progresses. Various other song components, such as Intrapulse Frequency (IPF), Sine Song Frequency (SSF), Cycles per Pulses (CPP), Mean Burst Duration (MBD), and Mean Interburst Interval (MIBI) which are also thought to contribute to the maintenance of species-specific differences, thus sustaining species barriers were also studied in different species. Hybridisation between species gave evidence for possible X-linked factors in song rhythms, but generally, autosomal factors appear to be involved in controlling the other song characters.;Another behavioural trait that may contribute to the species isolation of the members of the melanogaster subgroup are the circadian locomotor activity patterns. Locomotor activity profiles in constant darkness conditions revealed species-specific differences between the species in the period of their circadian oscillator, while locomotor activity profiles in light/dark cycles demonstrated phenotypic differences between the various species of the melanogaster subgroup. Hybridisations were used to assess the relative contribution of maternal and paternal factors. The overall species pattern of activity appeared to be determined by the sex-chromosomes, whereas other characteristics were primarily autosomally controlled. The implication of these findings on song and circadian behavioural cycles with respect to the current molecular analysis of circadian clock genes is discussed.