Variations in the rate and direction of re-entrainment to acute simulated jet lag in the diurnal North Indian palm squirrel

Abstract

We report the presence of variations in the rate and direction of re-entrainment to acute simulated jet lag in wild-caught North Indian palm squirrels (Funambulus pennanti). Adult laboratory and wheel-acclimated (Lafayette, USA) males (N = 30) were entrained to a 12:12 h light/dark (LD) schedule, followed by a 9 h advance of the LD schedule to simulate acute jet lag. The direction and rate of re-entrainment, i.e. the number of orthodromic (advancing) and antidromic (delaying) transients, the acrophases of daily rhythms in each case, duration of activity (α) and phase angle relationship (ψ) were noted using Clocklab (Coulbourn, USA). The squirrels exhibited distinct variations in their response to simulated acute jet lag, re-entraining either slowly (14/30) or rapidly (10/30) by advancing transients, or undergoing antidromic re-entrainment slowly (5/30), and, in only one individual, rapidly. Acrophases re-entrained slower than onsets. α underwent compression during re-entrainment, particularly during fast orthodromic responses. ψ was not significantly different in any of the groups before or after re-entrainment. This phenomenon has scope for further investigation and highlights the need for individual assessment of re-entrainment patterns before taking preventive measures for jet lag.