Subterranean mammals inhabit an environment that is normally devoid of light and are therefore deprived of photoperiodic information that can be used to time important life-history events. An assessment was made of whether melatonin secretion in a strictly subterranean rodent, the Damaraland mole-rat Cryptomys damarensis, can be modified by photoperiod. In experiment 1, a clear diurnal rhythm of melatonin secretion in animals housed under a neutral photoperiod (12L:12D) was observed, with significantly higher melatonin concentrations in the dark compared to the light phase. The same diurnal melatonin rhythm was found 1 day after animals were transferred to either continuous light or continuous dark, suggesting that a circadian rhythm was maintained under acute exposure to light and dark. In experiment 2, melatonin secretion was monitored in a long (14L:10D) and short day (10L:14D) photoperiod and was found to be modified by the photoperiodic change. We therefore suggest that the Damaraland mole-rat possesses a circadian melatonin rhythm that can be physiologically modulated in response to photoperiod.

Temperature and respiratory gas (CO2 and O2) concentrations were measured in the foraging tunnels of burrows naturally inhabited by two species of southern African mole-rats, the Cape mole-rat Georhychus capensis and the Damaraland mole-rat Cryptomys damarensis. Both species are completely fossorial and inhabit closed burrow systems. Tunnels of G. capensis burrows had a mean diameter of 8.7 cm and a depth, measured to the roof of the tunnel, of 6.2 cm; those of C. damarensis had a mean diameter of 6.5 cm and depth of 40 cm. In both species, the mean concentration of CO2 was higher, and mean concentration of O2 lower, in burrows than in the surrounding soil or in ambient air. Mean and minimum values of O2 were 20.4% and 19.8%, respectively, in G. capensis and 20.4% and 19.9% in C. damarensis; mean and maximum values of CO2 were 0.4% and 1.2% in G. capensis and 0.4% and 6.0% in C. damarensis. Temperature varied between 18.5 and 24.2 °C in burrows of G. capensis by comparison with an ambient range of 16.9 to 26.8 °C; and from 19.6 to 29.3 °C in burrows of C. damarensis by comparison with an ambient range of 8.6 to 30.8 °C. Thus a burrowing habit seems to offer both species protection from extremes of temperature without entailing the cost of a grossly abnormal respiratory environment. From a review of the relevant literature, we conclude that average concentrations of CO2 and O2 in mammalian burrows often do not differ greatly from ambient values. However, more work is needed to determine the respiratory gas concentrations in the immediate vicinity of active, burrowing animals.

Conspecific recognition was investigated in the eusocial and subterranean Damaraland mole-rat Cryptomys damarensis. This species out-breeds and is xenophobic. Differences in the frequency of agonistic behaviours between male–male pairs were used as an indication of recognition. Focal males were tested with familiar, unfamiliar, and foreign conspecifics. Males directed significantly more aggression towards unfamiliar colony mates and foreign conspecifics than towards familiar colony mates. This happened even though both focal and test animals retained contact with their natal colonies and, therefore, any group cue. Furthermore, when male–male pairs were returned to their natal colonies they continued directing aggression towards each other but not towards the rest of the colony. These results suggest that the Damaraland mole-rat uses individually distinct cues rather than kin-specific cues based on genetic relatedness.

The relationship between reproductive status and reproductive physiology was investigated in male Damaraland mole-rats Cryptomys damarensis, an eusocial rodent that exhibits a marked reproductive division of labour. Testicular anatomical and histological morphometrics, selected sperm motion parameters and measurements of circulating plasma testosterone were studied in 44 males (17 reproductive and 27 non-reproductive). Reproductive males were significantly larger than non-reproductive males. Testicular mass of reproductive males, corrected for body mass, was significantly larger than in non-reproductives. However, corrected testicular volume did not vary significantly between the two groups. Circulating plasma testosterone concentrations of reproductives and non-reproductives were not significantly different (reproductive males 201.5 ± 56.5 pg/l vs 187.5 + 91 pg/l for non-reproductive males). The quality of sperm was measured by the percentage of spermatozoa produced and the amount of immature sperm, and differed between the two groups. Reproductive males produced a greater proportion of motile sperm (77.8%) than non-reproductives (56.3%). Non-reproductive males were characterized by a greater proportion of immature sperm in the epididymis (79%) than the reproductives (25%). Interestingly, the spermatozoa of reproductive males were characterized by a greater percentage of head and tail defects. Oligospermia may be the result of a reduction in circulating follicle stimulating hormone, which acts upon the Sertoli cells of the seminiferous tubules, that in turn may be due to a lack of an opportunity to mate while in the confines of the colony in this obligate outbreeder.