Predicted questions for the article

1. The naked mole rat is a burrowing rodent. What adaptations does this animal show to its burrowing lifestyle?This eusocial rodent lives in complete darkness in a harsh underground environment. Living mainly in the dark, this unique animal has very small eyes and poor vision. Communication is mainly by sound, smell and with the aid of modified hairs called vibrissae (whiskers) which are positioned around the nose. The legs are short and thin allowing the animals to move forward and in reverse within the narrow tunnels. The huge protruding incisors are used for excavating their tunnels and the lips are sealed behind the teeth to prevent soil from filling their mouth as they dig to find root tubers. The skin is devoid of hair, an adaptation which facilitates heat loss or gain in an environment where the temperature may be fluctuating. It is possible that the thickened epidermis and reduction in sweat glands compensate for the lack of fur. The wrinkled skin may provide a larger surface area for the heat exchanges which are essential for poikilothermic temperature regulation. The ability to vary blood flow through the skin may certainly help thermoregulation. The light-coloured pink skin may reflect light of give a degree of camouflage above the ground when some of the animals disperse from their burrows. Any form of camouflage when the animals are exposed above ground could give a degree of protection from predators or rival naked mole rats.Physiologically the mole rats have small lungs and their blood has a high affinity for oxygen, increasing the efficiency of oxygen uptake in an environment where oxygen levels are low. These animals have a low respiratory rate and therefore a low metabolic rate so food requirements are also low.

2. What do you understand by a eusocial society?Eusociality is a term used in animal behaviour studies which describes complex organizations which exist on colonial animal species. Eusociality encompasses societies which exhibit a highly specialized division of labour i.e. with different members of the society performing specific tasks. Some members of the society may be sterile showing kin altruism while cooperative care of the young is also characteristic of Eusociality.

3. Using data from paragraph 7 calculate the % difference in lifespan shown by the naked mole rat when compared to a rat.Difference between the lifespan of a naked mole rat and a rat:30-3 = 27 years% difference in lifespan;27/30 * 100 = 90% increase

4. How are free radicals implicated to malignancy processes?Cell damage, such as mutagenesis, caused by oxygen free radicals produced in aerobic respiration and inflammatory responses, is a frequently occurring process in

living cells. Mutagenesis may create variation in the genetic code which can then alter gene expression and protein functionality. Damage which does not result in cell death can stimulate cancer by expanding tumour clones which may then become malignant. Certainly, free radicals can suppress DNA repair genes and they can also block tumour suppressor genes. Changes to normal cell cycling may also increase the risk of cancer. In fact, any disturbance to cell homeostasis may lead to permanent changes associated with carcinogenesis. Experiments with transgenic and knockout mice support the role of free radicals in the promotion of malignant tumours.

5. In para 3 it is stated that there are 12 species of mole rat in sub-Sahara Africa. Describe how these 12 species could have arisen from a single original population.The original population may have been subjected to allopatric (geographic) isolation mechanisms or to sympatric (prezygotic/post zygotic) mechanisms. In both cases the isolated populations would experience random mutations which would accumulate over time. As a result, natural selection may operate in different ways on these genetically diverse populations by selective mortality natality processes. The mole rat may develop preferences for slightly different niches as competition within the populations increase, producing sub-populations. Advantageous alleles are likely to favour survival and may be passed on to future generations. Different selection pressures in the isolated populations produce phenotypic behavioural diversity over time. When mating rituals change reproductive isolation may occur in sympatric populations, preventing breeding. Such processes give rise to new species of mole rats. Species are not immutable. They undergo continuous change and evolve into new forms better able to cope with changes in local conditions. The principle agent of this change is natural selection.

6. Discuss the behavioural interactions between the queen and non-breeding males and females.Behavioural interactions between the queen and the non-breeding females results in the suppression of ovulation in the non-breeding females. The queen also ensures that the non-breeding males are infertile. These effects are hormonally regulated by the queen since her interactions with the non-breeding females suppresses the release of the gonadotrophin-releasing factors from the hypothalamus which, in turn, suppresses release of the gonadotrophin FSH and LH from the anterior pituitary gland. Females with suppressed releasing hormones do not ovulate and so cannot breed. A similar process occurs in non-breeding males where suppression of the releasing factors from the hypothalamus suppresses the production of the gonadotrophins ICSH (interstitial cell stimulating hormone) and FSH resulting in lower concentrations of testosterone, lower sperm counts and non-motile sperms. The above processes are reversible and the non-breeders become sexually active e.g. when the queen dies.

7. What is the significance of kin recognition in naked mole rat populations?

Kin recognition provides a mechanism for avoiding in-breeding and promoting out-breeding, in-breeding leads to homozygosity in organisms so that recessive traits are more likely to appear phenotypically leading to depression of the population. Out-breeding promotes heterozygosity and improved fitness in the colony.

8. Briefly describe the phenotypic characteristics which contribute to the considerable length of the lifespan in naked mole rats. (paragraph 7 & 10 inclusive)Naked mole rats have strong bones which would be less likely to break and show high levels of fitness throughout their lives. These unique animals appear to be resistant to heart disease possibly due, in part, to their genetics, frugal diet and active lifestyle. Breeding females are fertile up to the end of their lifespan so they would be producing oestrogen which is known to protect the heart and bones of these females giving them a potentially longer lifespan. In addition, naked mole rats seem resistant to oxidative damage by free radicals and this characteristic together with the fact that these animals occupy a subterranean niche which does not expose them to the damaging UV rays from sunlight, may partly explain why these mole rats do not suffer from cancers.

9. Suggest ways in which the naked mole rat could be protected from free radical damage to molecules present in their bodies.Specific enzymes called preventive antioxidants can remove free radicals. Many vitamins such as vitamins A, C, E and carotenoids breakdown free radicals in cells. Many of these vitamins are antioxidants which are reducing agents with the ability to limit free radical damage.

10. Suggest mechanisms which may operate the naked mole rat from cancerAs DNA damage from free radicals accumulates, so the predisposition towards cancer increases. It has been discovered that the naked mole rat is resistant to cancer. This animal seems to have a variety of mechanisms which confer cancer resistance, including cells damaged by free radicals having arrested cell cycles. Such damaged cells are then marked for senescence and programmed cell death (apoptosis). In addition, naked mole rats have an ‘over-crowding gene’ which blocks cell division when a group of cells reaches a certain size and a p27 gene which prevents cell reproduction later in the cell cycle than p16. These two genes present a double obstruction to cell proliferation. Increased surveillance of contact inhibition may also be a reason why the naked mole rat is so resistant to cancer.

11. How are free radicals implicated to aging process?As age increases so does the oxidative damage caused by very reactive free radicals accumulates and this may culminate in loss of functionality and death of the

organism. Oxidative processes occurring in the mitochondria during aerobic respiration produce these reactive oxygen species which then damage macromolecules including lipids, proteins and mitochondrial DNA. The resulting mutations, in the mitochondrial DNA, greatly increase the build-up of free radicals within cells and accelerate the aging process. Characteristically, free radical processes involve chain reactions which may produce dysfunctional proteins such as enzymes which can no longer catalyze essential metabolic processes. In addition, DNA cross-linking may occur as a result of free radical chain reactions and these cross-linking processes have been associated with the aging process since they, in turn, are associated with cancer. Similar cross-linking processes which occur in lipids promote plaque formation in arteries, heart disease and stroke.

12. Why is the oxygen concentration in the human womb low?The placenta is a temporary organ in which the capillaries of the mother and the fetus come in to close contact without the blood of the mother and fetus mixing. The haemoglobin of the human fetus has a higher affinity for oxygen than the haemoglobin of the mother. The only way the fetus can obtain oxygen is by diffusion from the blood of the mother and this depends on the haemoglobin of the mother having a lower affinity for oxygen than is present in fetal haemoglobin. Therefore, oxygen availability to the fetus is dependent on the oxygen being carried in the RBCs of the mother.