singapore international science challenge group d1: nus high school
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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.
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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
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