Locomotor activity in the Namaqua rock mouse (Micaelamys namaquensis): entrainment by light manipulations

Abstract

The locomotor activity rhythms of wild-caught Namaqua rock mice (Micaelamys namaquensis Smith, 1834) were examined under four light cycle regimes in order to quantitatively describe the daily expression of locomotor activity and to study the innate relationship between activity and the light-dark cycle. Activity was always significantly higher at night than in the day: 1) The LD1 light cycle (12L: 12D) established a distinct light-entrained and strongly nocturnal activity rhythm (99.11% nocturnal activity). The activity onset was prompt (ZT 12.2 ± 0.04) and activity continued without any prominent peaks or extended times of rest until the offset of activity at ZT 23.73 ± 0.08. 2). Evidence for the internal maintenance of locomotor activity was obtained from the constant dark cycle (DD) in which locomotor activity free ran (mean τ = 23.89 h) and 77.58% of the activity was expressed during the subjective night. 3) During re-entrainment (LD2; 12L: 12D), a nocturnal activity rhythm was re-established (98.65% nocturnal activity) and, 4) the inversion of the light cycle (DL; 12D: 12L) evoked a shift in activity that again revealed dark-induced locomotor activity (95.69% nocturnal activity). Females were consistently more active than males in all of the light cycles, but only under the DD and LD2 cycles were females significantly more active than males. Although this species is considered nocturnal from field observations, information regarding its daily expression of activity and the role of light in its entrainment is lacking. To the best of our knowledge this study is the first to report quantitatively on the species' daily rhythm of activity and to investigate its relationship to the light-dark cycle.

Effects of the colour of photophase light on locomotor activity in a nocturnal and a diurnal South African rodent

“…As in R. pumilio, activity under red lighting increased during the day and reduced during the night. Under 'normal' lighting conditions, locomotor activity of M. namaquensis appears to be strongly masked by light, restricting locomotor activity to complete darkness, but under constant darkness (DD), although the activity rhythm is endogenous, activity is also displayed during the subjective day [26].…”

“…M. namaquensis is nocturnal, whereas R. pumilio is diurnal with marked peaks around dawn and dusk [24]. The general locomotor activity rhythms have been characterized in the laboratory for both R. pumilio and M. namaquensis [25,26]. Furthermore, the retinal photoreceptor compositions of both species appear to be complementary to their temporal niches [27].…”

The topography of rods, cones and intrinsically photosensitive retinal ganglion cells in the retinas of a nocturnal (Micaelamys namaquensis) and a diurnal (Rhabdomys pumilio) rodent

“…As M . namaquensis is almost exclusively active by night [ 43 ], its vision is largely mediated by rods and a homogeneous distribution should contribute to increased visual acuity across the visual field. Photoreceptor distributions often form areae centrales in animals that inhabit closed or complex environments [ 24 ].…”

Effects of photophase illuminance on locomotor activity, urine production and urinary 6-sulfatoxymelatonin in nocturnal and diurnal South African rodents

“…Locomotor activity is robustly entrained by the light-dark cycle in both of these species, with M. namaquensis expressing a strongly nocturnal activity rhythm and R. pumilio expressing a strongly diurnal activity rhythm, but with marked activity at dusk and dawn (Schumann et al, 2005;Skinner and Chimimba, 2005;van der Merwe et al, 2014). The retinal photoreceptor arrangements of these two species have previously been described as overall complementary to their temporal lifestyles.…”