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Circadian Rhythms of Locomotor Activity in Ansell’s mole-rat, Fukomys anselli:

Circadian Rhythms of Locomotor Activity in Ansell’s mole-rat, Fukomys anselli: are mole-rats clocks ticking?. J. L. de Vries M. K. Oosthuizen N. C. Bennett Photographs by J. L. de Vries. Introduction. Circadian rhythms Circadian rhythms are endogenous and self-sustaining

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Circadian Rhythms of Locomotor Activity in Ansell’s mole-rat, Fukomys anselli:

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  1. Circadian Rhythms of Locomotor Activity in Ansell’s mole-rat, Fukomys anselli: are mole-rats clocks ticking? J. L. de Vries M. K. Oosthuizen N. C. Bennett Photographs by J. L. de Vries

  2. Introduction Circadian rhythms • Circadian rhythms are endogenous and self-sustaining • In the absence of external cues (zeitgebers), the rhythm free-runs with a period (tau) of close to 24 hours • Suprachiasmatic nucleus (SCN) – Master clock • Allows animals to anticipate changes • Light most common cue (sun) (Goldman et al. 1995; Reuss 1996)

  3. Introduction Previous studies • Solitary species • Cape mole-rat (Georychus capensis) • Social species • Common mole-rat, Cryptomys hottentotus • Mashona mole-rat, Fukomys darlingi • Damaraland mole-rat, Fukomys damarensis (Lovegrove & Papenfus 1995; Oosthuizen et al 2003; Hart et al. 2004; Vasicek, et al 2005; Schöttner et al. 2006)

  4. Introduction Visual capabilities • Blind mole-rat Spalax ehrenbergi • Subcutaneous, atrophied eyes, but are still able to entrain to light cycles • Suggested that African mole-rats (Bathyergidae) have better visual capabilities • Ansell’s mole-rat Fukomys anselli • Visual system that is involved in coordination of visuomotor reflexes • Subsystems which are involved in perception of photoperiod, form and brightness are well developed Fukomys anselli (Cooper 1993; Cernuda-Cernuda et al. 2003; Němec et al. 2004)

  5. Introduction Temporal activity patterns • Very inconsistent data • G. capensis • Nocturnal • F. damarensis • Diurnal • C. hottentotus • Diurnal and nocturnal Georychus capensis (Lovegrove & Papenfus 1995; Hart et al. 2004; Schöttner et al. 2006)

  6. Introduction Ansell’s mole-rat • Herbivorous African mole-rat that is endemic to the savannas of Zambia • Extensive burrow systems that are completely sealed from the surface • Little chance to be exposed to light • Colonies range in size from 2 to 25 animals, but normally found in colonies of 12 Fukomys anselli (Bennett, N.C. & Aguilar, G. H. 1995)

  7. Aims • 1) Determine whether the mole-rats are able to entrain their locomotor activity to • light cues. • 2) Investigate whether the mole-rats exhibited an endogenous rhythm of locomotory • activity in constant darkness.

  8. Materials and Methods Animal capture • West of Lusaka, Zambia • February to April 2007 • Modified Hickman traps • Blocking the tunnel with a hoe Animals care • Housed in plastic containers • Fed on chopped sweet potatoes and apples • Cages cleaned after lighting cycle Experimental room • Light controlled • Kept at 25 ± 1°C • Extractor fan (Hickman 1979)

  9. Materials and Methods Experimental model • Animals kept in darkness for 30 days • Placed under various light regimes lasting 20 days each • 12L: 12 D (08:00 – 20:00 L) • DD • 12L :12D (08:00 – 20:00 L) • 12D :12L (08:00 – 20:00 D) Activity measures • Infrared capture placed above each cage • Activity measures captured by Vital view on a Mini Mitter computer

  10. Materials and Methods Data analysis • Double plotted Actograms • Actiview Biological Rhythm Analyses 1.2 software • Percentages determined for activity during dark phase of all cycles • Microsoft Excel

  11. Arrhythmic Entraining Results LD1 DD LD2 DL

  12. DD cycle Results LD1 cycle

  13. DL cycle Results LD2 cycle

  14. Results

  15. Discussion Entrainment of activity • Activity patterns not robust, large variation • Same in three subspies of Cryptomys hottentotus • Same in two species of Fukomys genera • Light not a strong zeitgeber • Other external cues might have more influence Cryptomys hottentotus (Hart et al. 2004; Oosthuizen et al. 2003; Vasicek et al 2005; Schöttner et al. 2006)

  16. Discussion Endogenous circadian rhythms • Social cues • F. damarensis • Castor canadensis • Octodon degus • More beneficial for mole-rat • Variation might be due to weak coupling to pacemaker Fukomys damarensis (Bovet & Oertli 1974; Lovegrove et al. 1993; Goel & Lee 1995)

  17. Discussion Endogenous circadian rhythms • Tested during DD lighting regime • Six individuals had arrhythmic activity patterns • Five individual had weak circadian rhythms close to 24h • Lesotho mole-rat • Little advantage of circadian rhythms in subterranean environment • Aseasonl breeder • Low latitude Cryptomys hottentotus (Bennett & Aguila 1995; Sharma 2003; Schöttner et al. 2006)

  18. Discussion Temporal distribution of activity • Majority display nocturnal activity • Largest part of activity took place in dark phase • Large variations

  19. Conclusion • Entrain to light cues • Able to distinguish between light and dark • Active mainly during dark phase • Weak circadian rhythms • Clocks ticking, but very weakly

  20. Acknowledgements • Alfred Sichilima

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