Latitudinal variation in locomotor activity rhythm in adult Drosophila ananassae

Abstract

The parameters of the circadian rhythm of adult locomotor activity in strains of Drosophila ananassae originating between 6° and 34°N were variable and latitude-dependent. Two representative southern strains became active before sunrise, but one representative northern strain began activity after sunrise in nature. During entrainment to a 12 h light (L) : 12 h dark (D) cycle in the laboratory, the southern strains showed two peaks of activity, at the beginning and end of photophase, whereas the northern strains showed a single uninterrupted activity peak starting about 3 h after the lights-on. Among the strains, the phase angle difference (Ψ) during entrainment to 12 h L : 12 h D varied by about 5 h, the period of free-running rhythm(τ) in constant darkness by 3 h, the duration of the activity phase (α) by 7 h, and the duration of the resting phase (ρ) by 10 h. Lower latitude was correlated with an early Ψ (r = 0.977), a short τ (r = 0.975), a prolonged α (r = -0.995), a short ρ (r = 0.995) and a large α/ρ ratio (r = -0.963).