Singapore International Science Challenge

Group D1: NUS High School

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

Citations: http://nationalzoo.si.edu/publications/zoogoer/2002/3/nakedmolerats.cfm

Naked Mole Rat by Rodney L. Honeycutt

Naked Mole Rat

Heterocephalus glaber

Possible mechanisms that might account for the long lifespan of

snow puppies

Low extrinsic mortality

The evolutionary theory of aging:

Snow puppies:

Animals living in DANGEROUS environment

High extrinsic mortality

Facilitate early reproduction

Shorter life spans

Live in well-protected and

thermally buffered

underground environment

Exhibit reproductive

altruism

Low extrinsic mortality

Longer life spans

Life-history traits that

facilitate early reproduction would not be

evolved

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

Animal Naked mole rat Rabbit Hamster Rat

Life span (years)

25-30 9-12 2-3 2-4

Oxidative Stress

Imbalance between production of reactive oxygen and a biological system's ability to detoxify the reactive intermediates and repair resulting damages

A significant contributor to aging

What is oxidative stress?

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

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

It has been proposed that their long life spans are caused by their abilities to defend against

acute bouts of oxidative stress

Suggests some possible mechanisms that increase the efficiency of oxygen

uptake in snow puppies

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

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

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

Explain the seemingly altruism of the workers helping the queen

snow puppy

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

Haploid male Diploid female

genes

Haploid maleDiploid female

genes genes

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.

Do their behaviour contradict with the theory of evolution for natural

selection?

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

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

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

Systems of Tunnels

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.

1. Deep underground burrows

Circulation in Tunnels

2. Vertical openings to tunnels (convection)

Convection currents

Ground

Nesting area

Warm

cool

Air flow

Air gets warmed up

3. Pressure Differences

Have one of the conditions below:

1.Having the openings of the burrow shaped as to the left

2.Having one of the openings at a location with higher wind speed than the other openings

Ground

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.

22221

21111 2

1

2

1vghPvghP

Ground

Lower Pressure Higher Pressure

Air Flow

This circulation of air would replace the oxygen levels with fresh air.

Suggest how the snow puppies need to change the design of their tunnel

system in order to survive in the future?

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

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.

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

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.

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

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

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

References

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

References

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