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Circadian rhythms of locomotor activity have been investigated in several African mole-rat species. Even though mole-rats spend most of their lives in underground burrows devoid of light, studies have shown that they do possess circadian rhythms to some extent. We investigated the circadian rhythms of locomotor activity in 11 male Ansell's mole-rats Fukomys anselli from Zambia. In order to determine whether these animals can entrain to light and have endogenous rhythms, they were subjected to different light regimes: first, 12 h light/12 h dark, followed by constant darkness, then returned to 12 h light/12 h dark, which was later inversed to 12 h dark/12 h light. Only two individuals displayed arrhythmic activity patterns whereas the other nine (81.8%) exhibited entrainment of their activity to the light regimes. Locomotory activity of Ansell's mole-rat was predominantly during the dark phase in all light regimes. During constant darkness (DD), only five individuals (45.5%) displayed very weak circadian rhythms that free ran but became more indistinct towards the end of the cycle. Under the second LD light cycle, 90.1% of the animals were active during the night phase of the cycle and when placed under an inverse light cycle, seven individuals still displayed activity predominantly during the dark phase. In conclusion, these results suggest that Ansell's mole-rat does have a weak circadian clock and is able to perceive light and entrain to light cycles. [ABSTRACT FROM AUTHOR]

The hearing and visual ecology of mole-rats, Spalax ehrenbergi (Spalacidae) from Israel and Fukomys (formerly Cryptomys) anselli (Bathyergidae) from Zambia, two rodent taxa that have independently adapted to subterranean life, are reviewed and compared with epigeic counterparts, the laboratory rat and the guinea pig. In burrows, airborne sounds of low frequencies (200-800 Hz) are least attenuated and even accentuated over short distances. In both mole-rat species the frequency range of the best hearing is shifted to match the frequencies best propagated in tunnels: hearing sensitivity in the lower frequency range (<16 kHz) has been conserved or further improved. Compared to the rat, the hearing range (covering about eight octaves) in mole-rats is not restricted but only shifted towards lower frequencies. Morphologies of the middle and inner ears of mole-rats and the guinea pig are similar in some aspects and suggest tuning to low frequencies. The middle ear morphology of mole-rats does not seem to explain the lower high-frequency limit of hearing. Middle ear is not reduced or degenerated. On the contrary, the incus and the stapedial footplate are markedly enlarged, resulting in reduced sensitivity. These features can be considered an adaptation to compensate for local sound amplification in burrows. The cochlea and its components are highly specialised for sensitive perception and high resolution of low frequencies. Despite living in the same optic environment, Spalax and Fukomys show different degrees of regression and specialisation of the visual system. The eye in Spalax is severely regressed and shortwave-opsin cones are missing. Spalax is blind but the retina has retained its role for photoperiodic perception. Fukomys has small, yet morphologically normal, eyes, with a retina rich in 'blue' cones. It has retained basic visual capabilities; however, the role of light as a zeitgeber is not conclusive. [ABSTRACT FROM AUTHOR]