Aspects of memory in the Damaraland mole-rat, Cryptomys damarensis spatial learning and kin recognition /
Professor N.C. Bennett, Department of Zoology and Entomology,University of
Pretoria, Pretoria, 0002, South Africa
African mole-rats (Bathyergidae) exhibit a wide range of social structures
ranging from solitary to eusocial. This allows for studies looking at links between
sociality and measurable characteristics such as spatial learning and kin-recognition.
Furthermore, the existence of species with differing level of sociality allows for
comparison between the highly social species and the solitary species.
The existence of differences in spatial learning ability and memory between
the sexes has long been debated. Eusocial Damaraland mole-rats (Cryptomys
damarensis) and solitary Cape mole-rats (Georychus capensis) were tested to see if
there were sex or species differences in the ability to locate food in an artificial maze
task with the express purpose of investigating spatial learning and memory.
Measurements of the time taken to complete the task, the distance travelled, wrong
turns taken, and the average velocity at which animals travelled were used to compare
performance between animals. Both sexes in each of the species exhibited learning
and a decay in memory over time. The Damaraland mole-rat exhibited superior
learning and memory retention when compared to the Cape mole-rat. Male Cape
mole-rats had superior learning and longer term memory retention when compared to
females of the same species. There was no significant difference in learning curves
between male and female Damaraland mole-rats, but this species did exhibit a
tendency for females to show better medium term memory retention while males
performed better on long term memory trials. Species differences are likely to be
linked to social organization and possibly the resultant burrow-structure in the natural
environment, while sex-differences may be due to differing life histories.
Kin-recognition is important in maintaining the social structure and hierarchy
in the eusocial species of African mole-rat, Cryptomys damarensis. Opposite sex
sibling pairs from reproductively quiescent colonies were tested to see if exposure to
colony urine odour would reinforce recognition of opposite sex siblings and the
concomitant incest avoidance. Control sibling pairs from the same colonies were
exposed to water. Mating, social, and non-social behaviours were measured in all
sibling pairs. In addition, urinary levels of cortisol, progesterone and testosterone
were measured to examine the interaction between four factors: colony olfactory cues
(urinary odour), hormone levels, mating behaviour and relatedness. Exposure to
urinary odour reinforced recognition and was correlated to a decrease in mating
behaviour. Hormonal assays suggest that female hormone levels are modified based
on exposure to colony urine odour, while males are not affected. Olfactory cues such
as colony urinary odour is linked to the alteration and correlation of hormone levels
and mating behaviour.
The Damaraland mole-rat and other species in the family Bathyergidae
provide a useful system for investigating aspects of learning and memory, as well as
the potential correlation between cognitive processes and sociality.