Factors Influencing Mate Choice in a Eusocial Mammal, the Damaraland Mole-Rat (Fukomys damarensis)

Factors Influencing Mate Choice in a Eusocial Mammal, the Damaraland Mole-Rat (Fukomys damarensis

Out-breeding behaviour and xenophobia in the Damaraland mole-rat, Cryptomys damarensis

Out-breeding behaviour and xenophobia were investigated in laboratory colonies of the Damaraland mole-rat, Cryptomys damarensis. Foreign males and/or females were introduced into reproductively quiescent colonies and colonies which were actively breeding. Although males attempted to mate with familiar or related females, females only mated with foreign males. This suggests that female avoidance of incest is responsible for outbreeding in this species. Resident males in reproductively quiescent colonies did not attack foreign males or females. However, resident males in actively breeding colonies attacked and kilted foreign males. Resident females in reproductively quiescent colonies attacked foreign females but attempted to mate with foreign males. However, in colonies in which the breeding female was approaching parturition, resident non-breeding females also attacked foreign males. Once foreign females attained reproductive status in the colony into which they were introduced they killed all the resident females. These results suggest that xenophobia in the Damaraland mole-rat is influenced by whether or not the colony is actively breeding, and by the reproductive state of the breeding female

Social Structure Predicts Genital Morphology in African Mole-Rats

BACKGROUND:African mole-rats (Bathyergidae, Rodentia) exhibit a wide range of social structures, from solitary to eusocial. We previously found a lack of sex differences in the external genitalia and morphology of the perineal muscles associated with the phallus in the eusocial naked mole-rat. This was quite surprising, as the external genitalia and perineal muscles are sexually dimorphic in all other mammals examined. We hypothesized that the lack of sex differences in naked mole-rats might be related to their unusual social structure. METHODOLOGY/PRINCIPAL FINDINGS:We compared the genitalia and perineal muscles in three African mole-rat species: the naked mole-rat, the solitary silvery mole-rat, and the Damaraland mole-rat, a species considered to be eusocial, but with less reproductive skew than naked mole-rats. Our findings support a relationship between social structure, mating system, and sexual differentiation. Naked mole-rats lack sex differences in genitalia and perineal morphology, silvery mole-rats exhibit sex differences, and Damaraland mole-rats are intermediate. CONCLUSIONS/SIGNIFICANCE:The lack of sex differences in naked mole-rats is not an attribute of all African mole-rats, but appears to have evolved in relation to their unusual social structure and reproductive biology

A PRELIMINARY INVESTIGATION INTO THE EXTENDED LIFESPAN OF BAT SPECIES: THE RELATIONSHIP BETWEEN THE EXTRACELLULAR MATRIX PROTEIN HAS2 AND LONGEVITY

Investigation into physiological and molecular factors influencing the extended lifespan of long-lived species significantly contributes to clinical research aimed at improving the lives of humans. Bats have a significantly longer lifespan than other mammals of similar size and have not been recorded to develop cancer. The longevity and anti-cancer properties displayed by bats are features shared by another well-studied mammal, the naked mole rat. The naked mole rat is currently the longest living rodent with a maximum lifespan of over 30 years, and the species exhibits a novel anti-cancer mechanism involving the rapid production of hyaluronan. The naked mole rat has a unique sequence of hyaluronan synthase 2 (HAS2) which rapidly produces high molecular mass hyaluronan and contributes to reduced activity of hyaluronan degrading enzymes. Known genomic sequences of several species of bats were analyzed to determine differences in amino acid sequence for the HAS2 gene. Furthermore, RNA extracted from captured bats was subjected to real-time polymerase chain reaction to measure the expression level of HAS2 in various tissues. Genomic sequence analysis revealed that the bat species examined did not have the same amino acid substitutions in HAS2 as the naked mole rat. Real-time PCR trials using multiple primers designed to be specific for the HAS2 region resulted in inconclusive data. Therefore, gene expression analysis conclusions cannot be made until successful HAS2 primers are generated to amplify the HAS2 region. Further research needs to be directed towards determining alternative methods to study the longevity and anti-cancer mechanisms bats possess

Morphological and genomic shifts in mole-rat 'queens' increase fecundity but reduce skeletal integrity.

In some mammals and many social insects, highly cooperative societies are characterized by reproductive division of labor, in which breeders and nonbreeders become behaviorally and morphologically distinct. While differences in behavior and growth between breeders and nonbreeders have been extensively described, little is known of their molecular underpinnings. Here, we investigate the consequences of breeding for skeletal morphology and gene regulation in highly cooperative Damaraland mole-rats. By experimentally assigning breeding 'queen' status versus nonbreeder status to age-matched littermates, we confirm that queens experience vertebral growth that likely confers advantages to fecundity. However, they also upregulate bone resorption pathways and show reductions in femoral mass, which predicts increased vulnerability to fracture. Together, our results show that, as in eusocial insects, reproductive division of labor in mole-rats leads to gene regulatory rewiring and extensive morphological plasticity. However, in mole-rats, concentrated reproduction is also accompanied by costs to bone strength

The Role of the Gonads and Incest Avoidance in the Regulation of Sexual Behavior in Damaraland Mole-Rats

The Damaraland mole-rat (DMR; Fukoymys damarensis) is one of a small number of mammals that are eusocial. In this mating system, only a single pair reproduce while the other remaining colony members are non-reproductive. Non-breeders exhibit sexual behavior only when paired with unfamiliar opposite-sex individuals. The role of the gonads in the regulation of reproductive behaviors in non-breeders remains unknown; however, inbreeding avoidance has been hypothesized to account, in part, for the lack of reproductive behavior in non-breeding individuals. The mechanism that regulates incest avoidance also remains unknown. The aims of this study were twofold; first, to investigate the role of the gonads in the expression of sexual behaviors and second, to identify the mechanism of incest avoidance. The results indicate 1) that the expression of sexual behavior is largely independent of the gonads and 2) that rather than incest avoidance per se, DMR avoid mating with familiar individuals irrespective of relatedness

Specific paucity of unmyelinated C-fibers in cutaneous peripheral nerves of the African naked-mole rat: comparative analysis using six species of bathyergidae

In mammalian peripheral nerves, unmyelinated C-fibers usually outnumber myelinated A-fibers. Using transmission electron microscopy we recently showed that the saphenous nerve of the naked mole-rat (Heterocephalus glaber) has a C-fiber deficit manifested as a substantially lower C:A-fiber ratio compared to other mammals. Here we determined the uniqueness of this C-fiber deficit by performing a quantitative anatomical analysis of several peripheral nerves in five further members of the Bathyergidae mole-rat family: silvery (Heliophobius argenteocinereus), giant (Fukomys mechowii), Damaraland (Fukomys damarensis), Mashona (Fukomys darlingi) and Natal (Cryptomys hottentotus natalensis) mole-rats. In the largely cutaneous saphenous and sural nerves we found that the naked mole-rat had the lowest C:A-fiber ratio (~1.5:1 compared to ~3:1), whereas in nerves innervating both skin and muscle (common peroneal and tibial) or just muscle (lateral/medial gastrocnemius), this pattern was mostly absent. We asked whether lack of hair follicles alone accounts for the C-fiber paucity using a mouse model, which loses virtually all its hair as a consequence of conditional deletion of the beta-catenin gene in the skin. These beta-catenin loss-of function mice (beta-cat LOF mice) displayed only a mild decrease in C:A-fiber ratio compared to wild-type mice (4.42 compared to 3.81). We suggest that the selective cutaneous C-fiber deficit in the cutaneous nerves of naked mole-rats is unlikely to be primarily due to lack of skin hair follicles. Possible mechanisms contributing to this unique peripheral nerve anatomy are discussed

Aspects of memory in the Damaraland mole-rat, Cryptomys damarensis : spatial learning and kin recognition

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.Dissertation (MSc (Zoology))--University of Pretoria, 2007.Zoology and Entomologyunrestricte

Burrow architecture of the Damaraland mole-rat (Fukomys damarensis) from South Africa

The burrow architecture (length, internal dimensions, fractal dimension of tunnel systems, number of nesting chambers and surface mounds) was investigated in the Damaraland mole-rat (Fukomys damarensis). A total of 31 animals were caught from five different colonies and their burrow systems were excavated in their entirety. The mean and SD colony size was 6 ± 3.3, with a range of 2-10 mole-rats. The sex ratio was male biased 1.21:1. Males had a body mass of 80.5 ± 33.8g, but were not significantly different to those of females which had a mean body mass of 83.4 ± 24.9g. The burrow system of the Damaraland mole-rats follows the same general architectural plan as recorded for other species of mole-rat with either one or two more centrally based deeper more permanent burrows which often connect to a nest area, which is used for resting and rearing offspring. The burrow systems contained several more superficial secondary tunnels at a shallower depth. The secondary tunnels accounted for up to 80% of the total burrow system. The mean length of the burrow system was 130.4m and covered an area of 1403m². The mean number of secondary branches in a burrow system was 10. The mean fractal dimension was 1.154 which implies the mole-rats do not explore their surrounding environment particularly efficiently when compared to that of other mole-rat species, but this may relate to the size of the main food resource, the Eland bean (Elephantorrhiza elephantina) which is randomly distributed and fed on in situ. Our study showed that colony size influences the size and complexity of the burrow system with larger colonies having a longer burrow system covering a greater area with more secondary tunnels than that of smaller colonies.The University of Pretoria, by the SARChI Chair of Mammal Behavioural Ecology and Physiology and by the National Research Foundation, South Africa to NCB.http://www.nisc.co.za/products/59/journals/african-zoology2017-04-30hb2016Zoology and Entomolog

Density-dependent effects on body size, Philopatry, and dispersal in the Damaraland mole-rat (Fukomys damarensis)

Population density may exert changes in a variety of behavioural and physiological characters in animals. However, the effects of density-dependence and dispersal are poorly studied in subterranean rodents due to the difficulties involved in observing such effects in wild populations. Using the cooperative breeding Damaraland mole-rat (Fukomys damarensis) as a model species, the effects of population density on body size, growth rates, group size, recruitment, philopatry and dispersal were investigated at two sites (one with low density and one with high density) in the Northern Cape of South Africa. Group size, litter size and the probability of recapture were independent of population density. However, individual body size, recruitment, dispersal rate and dispersal distance were density-dependent. Individuals were significantly larger, juveniles exhibited a significantly higher growth rate, and juvenile recruitment was significantly greater when population density was low. At higher densities, significantly more individuals were lost between capture events which may be indicative of increased rates of dispersal. Mean dispersal distances in mole-rats were reduced at higher densities and increased at lower densities. While both sexes dispersed equally, males were significantly more likely to join an established colony and females created new burrow systems. In addition, four times as many single females were found when population density was low. The apparent differences in the study populations may be attributed to variable annual rainfall or food availability. The greater annual rainfall at the high-density site may provide better habitat conditions and therefore result in an increase in the population density and an increased dispersal rate due to the relaxed ecological constraints such as reduced energetic costs to burrowing. However, the larger body size found at the low-density site may indicate that the available food at that location is of better quality. This study revealed that mole-rats were able to disperse over 1km and therefore a much larger study area would be required in capture-mark-recapture studies to ensure the recapture of the majority of dispersers. Lastly, a surprising find of this study was that females may survive a solitary existence for over two years while awaiting the arrival of a mate