Singapore International Science Challenge

1. Singapore International Science Challenge Group D1: NUS High School

2. Our Assumptions We found an organism which has very similar characteristics to the snow puppy: • Body Length: 8-10cm • Mass: 30-35g • Living conditions: Tunnel system • Living in total darkness • Eusocial colonies • Nearly cold-blooded metabolism Naked Mole Rat Heterocephalus glaber Citations: http://nationalzoo.si.edu/publications/zoogoer/2002/3/nakedmolerats.cfm Naked Mole Rat by Rodney L. Honeycutt

3. Possible mechanisms that might account for the long lifespan of snow puppies

4. Live in well-protected and thermally buffered underground environment Life-history traits that facilitate early reproduction would not be evolved Exhibit reproductive altruism Low extrinsic mortality Longer life spans Low extrinsic mortality • The evolutionary theory of aging: • Snow puppies: Animals living in DANGEROUS environment High extrinsic mortality Facilitate early reproduction Shorter life spans

5. Low metabolism • In ectothems, colder temperatures elicit lower metabolic rates and vice versa for endothems. • Metabolic rates, more specifically, Daily Energy Expenditure, has a negative relationship between lifespan • Comparison of mammals’ (comparable size as snow puppies) life spans • Snow puppies, having an almost cold blooded metabolism, would have a longer life span than these animals

6. Oxidative Stress Imbalance between production of reactive oxygen and a biological system's ability to detoxify the reactive intermediates and repair resulting damages What is oxidative stress? A significant contributor to aging

7. Oxidative Stress • According to a recent study… • Naked mole-rats have more oxidative stress than mice because of reduced glutathione observed • Something unusual observed: Their ability to fend off occasional oxidative insults despite suffering great oxidative damage It has been proposed that their long life spans are caused by their abilities to defend against acute bouts of oxidative stress Citation: Study of “High oxidative damage levels in the longest-living rodent, the naked mole-rat by Blazej Andzaik and Rochelle Buffenstein, of The City College of New York, and the University of Texas Health Science Center, San Antonio

8. Suggests some possible mechanisms that increase the efficiency of oxygen uptake in snow puppies

9. Lung volume is larger • Alveolar surface area and alveolar capillary volume are larger • Diffusion barrier reduced • Higher diffusion rates VL, lung volume; VV(s,L), septum volume per lung volume; V(C), volume of capillaries per lung; SA, alveolar surface area per lung; V(C)/S(A), capillary loading

10. Higher erythrocyte (red blood cell) count and decreased size • Increases surface area • Increases oxygen exchange • Large capillary length density • Short diffusion distances to cells • Increases rate oxygen/carbon dioxide exchange from blood to cells

11. Tissue thickness between alveolar surface and erythrocytes is small • High pulmonary oxygen diffusing capacity τhb, harmonic mean tissue thickness between alveolar surface and erythrocytes; and DLO2, pulmonary oxygen diffusing capacity

12. Explain the seemingly altruism of the workers helping the queen snow puppy

13. Definition of Altruism: The selfless concern for the welfare of others • In eusocial societies, workers sacrifice their own opportunities to survive and reproduce • the individual acts for the good of the species • Increase frequency of its genes in the gene pool • Ensure its genes to be passed on

14. Haploid male Diploid female genes Diploid female Haploid male genes genes

15. Genetic probabilities show that the relatedness of sisters (average 75%) is greater than the relatedness of a parent to his/her offspring (average 50%). • By helping their parents raise siblings, workers increase the representation of their own genetic characteristics.

16. Do their behaviour contradict with the theory of evolution for natural selection?

17. No, it does not contradict • Genetic-relatedness studies of the naked mole-rat suggest that costs of altruism of non-breeders are offset by inclusive fitness benefits • Results from a high degree of intra-colony genetic relatedness

18. Suggest reasons why the snow puppies would evolve to become eusocial • Advantages of kin selection • passing on the same genes • the breeder female can devote all her time with the offspring • Maximize inclusive fitness • all members of the colony benefit more from indirect fitness than individual fitness

19. Suggest how the snow puppies’ tunnel system would be like in order for them to survive the harsh cold of the tundra and yet allow sufficient air circulation in the tunnels

20. Systems of Tunnels 1. Deep underground burrows • Near cold-blooded characteristics results in the need for temperatures between 25oC to 30oC. • Complex systems of tunnels have large surface area • Burrows have to be deep to reduce too much thermal conductivity and thermoregulation • A relatively high temperature underground may tell us that the temperature is maintained under geothermal conditions.

21. Circulation in Tunnels 2. Vertical openings to tunnels (convection) cool Ground Air flow Convection currents Air gets warmed up Nesting area Warm

22. 3. Pressure Differences • Have one of the conditions below: • Having the openings of the burrow shaped as to the left • Having one of the openings at a location with higher wind speed than the other openings Ground

23. By applying Bernoulli’s theorem, a higher fluid speed would result in lower pressure and vice versa. • By having a bulge in one of the openings, air is made to flow longer distance at a same amount of time, hence a lower pressure. • By having openings of the tunnels at locations with larger wind speed would decrease the pressure.

24. This circulation of air would replace the oxygen levels with fresh air. Lower Pressure Higher Pressure Ground Air Flow

25. Suggest how the snow puppies need to change the design of their tunnel system in order to survive in the future?

26. 1. Physical effects • Due to the rise in temperature, temperature gradient between underground and the surface decreases • Convection current is not as significant as before global warming • Air circulation must be increased

27. Increase in opening diameters • An increase in opening diameters would increase the rate of air flow into the tunnel to balance the decrease in convection currents.

28. 2. Biological effects • Melting of the permafrost layers, leading rise in water levels. • Increasing soil moisture content • increases difficulties in digging (Buffenstein, chapter 2, underground life – the biology of subterranean rodents) • Warmer and more humid conditions makes it favorable for plant growth – more food

29. Increasing difficulty in digging and food sources causes the snow puppies to have tunnels slightly closer to the surface. • Predatory effect changes are mild as subterranean ecology is buffered against predators.

30. Conclusion and Extensions • Study the snow puppy in detail for example, size of blood cells to compare against the naked mole rat • In the case of global warming, the tunnel system would change • Serves as an indicator for global warming

31. References • Judith Korb (2003) Thermoregulation and ventilation of termite mounds. Naturwissenschaften (2003) 90:212–219 • HANS R. WIDMER, HANS HOPPELER, EVIATAR NEVO, C.RICHARD TAYLOR, AND EWALD R. WEIBEL (1996) Working underground: Respiratory adaptations in the blind mole rat. Proc. Natl. Acad. Sci. USA Vol. 94, pp. 2062–2067, • J. N. Maina, Y. Gebreegziabher, R. Woodley and R. Buffenstein (2000) Effects of change in environmental temperature and natural shifts in carbon dioxide and oxygen concentrations on the lungs of captive naked mole-rats (Heterocephalus glaber): a morphological and morphometric study. J. Zool., Lond. (2001) 253, 371±382

32. References • F. G. Hall (Nov., 1937) Adaptations of Mammals to High Altitudes. Journal of Mammalogy, Vol. 18, No. 4. , pp. 468-472. • Rodney L. Honeycutt. Naked Mole-Rats • Robert W. Bullard, Cyrus Broumand, and Frederick R. Meyer (1965) Blood characteristics and volume in two rodents native to high altitude. J. Appl. Physiol. 2I(3): 994-998. • Timothy P. O’Connor, Angela Lee, Jennifer U.M. Jarvis, Rochelle Buffenstein (2001) Prolonged longevity in naked mole-rats: age-related changes in metabolism, body composition and gastrointestinal function. Comparative Biochemistry and Physiology Part A 133 (2002) 835-842

33. References • John R. Speakman (2005) Body size, energy metabolism and lifespan. The Journal of Experimental Biology 208, 1717-1730 • Arthur Svihla anf Howard C. Bowman (1952) Oxygen carrying capacity of the blood of dormant ground squirrels. • Eileen A. Lacey, James L. Dalton, Guy N. Cameron. Life Underground – the biology of subterannean rodents. University of Chicago press. Chicago and London

34. References • http://www.bio.davidson.edu/people/vecase/Behavior/Spring2002/Poulton/Eusociality.html