Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Pretoria 0028, South Africa.
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
J Exp Biol. 2024 Sep 15;227(18). doi: 10.1242/jeb.247793. Epub 2024 Sep 24.
Highveld mole-rats (Cryptomys hottentotus pretoriae) are social rodents that inhabit networks of subterranean tunnels. In their natural environment, they are rarely exposed to light, and consequently their visual systems have regressed over evolutionary time. However, in the laboratory they display nocturnal activity, suggesting that they are sensitive to changes in ambient illumination. We examined the robustness of the Highveld mole-rat circadian system by assessing its locomotor activity under decreasing light intensities. Mole-rats were subjected to seven consecutive light cycles commencing with a control cycle (overhead fluorescent lighting at 150 lx), followed by decreasing LED lighting (500, 300, 100, 10 and 1 lx) on a 12 h light:12 h dark (L:D) photoperiod and finally a constant darkness (DD) cycle. Mole-rats displayed nocturnal activity under the whole range of experimental lighting conditions, with a distinct spike in activity at the end of the dark phase in all cycles. The mole-rats were least active during the control cycle under fluorescent light, locomotor activity increased steadily with decreasing LED light intensities, and the highest activity was exhibited when the light was completely removed. In constant darkness, mole-rats displayed free-running rhythms with periods (τ) ranging from 23.77 to 24.38 h, but was overall very close to 24 h at 24.07 h. Our findings confirm that the Highveld mole-rat has a higher threshold for light compared with aboveground dwelling rodents, which is congruent with previous neurological findings, and has implications for behavioural rhythms.
高地鼹鼠（Cryptomys hottentotus pretoriae）是一种社会性啮齿动物，栖息在地下隧道网络中。在其自然环境中，它们很少暴露在光线下，因此它们的视觉系统在进化过程中已经退化。然而，在实验室中，它们表现出夜间活动，这表明它们对环境光照的变化很敏感。我们通过评估高地鼹鼠在逐渐降低的光照强度下的活动来研究其昼夜节律系统的稳健性。鼹鼠经历了七个连续的光照周期，起始于一个对照周期（头顶荧光灯照明 150 lx），随后是逐渐降低的 LED 照明（500、300、100、10 和 1 lx），在 12 小时光照：12 小时黑暗（L:D）光周期下，最后是一个恒定的黑暗（DD）周期。鼹鼠在整个实验光照条件下都表现出夜间活动，在所有周期的黑暗阶段结束时活动明显增加。在荧光灯下的对照周期中，鼹鼠的活动最少，随着 LED 光照强度的降低，活动稳步增加，当光线完全消失时，活动达到最高。在恒定的黑暗中，鼹鼠表现出自由运行的节律，周期（τ）范围在 23.77 到 24.38 小时之间，但总体上非常接近 24 小时，为 24.07 小时。我们的发现证实，高地鼹鼠对光的阈值比地面栖息的啮齿动物高，这与之前的神经学发现一致，并对行为节律有影响。
