Differential locomotor activity responses to day-time light intensity in juvenile and adult solitary Cape mole-rats, Georychus capensis (Rodentia: Bathyergidae)

ABSTRACT

The Cape mole-rat (Georychus capensis) is a solitary, strictly subterranean rodent that is responsive to light and entrains to photic cues despite having a reduced visual system. Circadian entrainment is maintained throughout life, but age can alter the amplitude of the response and re-entrainment time. Mole-rats are long-lived for their size which raises questions regarding the robustness of their circadian rhythms and how impacts their locomotor activity rhythms. The locomotor activity rhythms of juvenile and adult Cape mole-rats were investigated. They were exposed to pre-experimental and post-experimental control cycles under fluorescent lights, six 12 h light:12 h dark cycles of decreasing intensities and a constant dark cycle (DD). All animals exhibited more activity during the dark phases of all light regimes. Juveniles were more active than adults and displayed more variable activity during both the light and dark phases. Adults exhibited relatively stable levels of activity under all experimental conditions, whereas juvenile activity decreased as the light intensity was reduced. The amplitude of Cape mole-rat rhythms was consistently low, but similar across light regimes and between adults and juveniles. Cape mole-rats have functional circadian systems, are primarily nocturnal and respond differentially to light intensity depending on their age. Light intensity does not affect the locomotor activity responses of Cape mole-rats in a predictable manner, and could indicate more complex interactions with light wavelengths. The circadian systems of juveniles appear to be more sensitive than those of adults, although the mechanism of the light response remains unclear.

KEYWORDS:

• Juvenile
• adult
• Cape mole-rat
• light intensity
• circadian rhythm
• locomotor activity

Acknowledgments

Thank you to Joshua Webber, Giséle Cumming, and Chase McAlpine for assistance with animal maintenance.

Author contributions

SB – student, experimental setup, performed experiment, analysis, wrote original draft

NCB – co-supervisor, conceptualisation, funding, revision of final manuscript

CV – animal capture, revision of final manuscript

MKO – supervisor, conceptualisation, experimental setup, analysis, writing and revision of final manuscript

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, MKO, upon reasonable request.

Supplementary data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/07420528.2023.2253298.

Additional information

Funding

The authors acknowledge a DST-NRF South African Research Chair for Behavioural Ecology and Physiology (GUN 64756) for funding to NCB.