UV Enclosure Experiment
1) Air temperature.
Air temperatures within each enclosure and ambient air temperatures should be taken each day at approximately the same time. Air temperatures should be taken before water temperatures to avoid evaporative cooling of the thermometer. Air temperatures within each enclosure should be taken approximately 1 inch below the mylar filter by inserting the thermometer through a corner of the enclosure. Ambient air temperatures should be taken outside of the enclosures at approximately the same height as the tops of the mylar filters.
2) Water temperature.
Water temperatures within and next to each enclosure should be taken each day at approximately the same time. These should be taken at the same depth within a few inches of one another. For example, take the water temperature outside enclosure #1 on the right side of the enclosure 1 cm beneath the surface, then take a temperature inside enclosure #1 one cm beneath the surface on the right side within 2 or 3 inches of the location where the outside temperature was taken. Repeat for all enclosures.
3) Relative humidity.
We use a Pocket Sling Psychrometer. Obtain a small cup or wide-mouthed bottle of water, preferably distilled, which has come to ambient equilibrium temperature with the lid off. Record the dry bulb temperature. Completely immerse the wick of the wet bulb thermometer in the water. Whirl the psychrometer rapidly for 20 seconds, then quickly read the wet bulb thermometer. Keeping this reading in mind, immediately whirl again and take another reading. Repeat this process three or four times, or more, if necessary, until at least two successive readings of the wet bulb are found to agree very closely, thereby showing that it has reached its lowest temperature. A minute or more is generally required to secure the correct temperature. If the wick begins to dry out, it will be necessary to reimmerse it and start the process over again.
With the wet and dry bulb temperatures, psychrometric tables or charts may be used to determine the percent relative humidity, dew point or saturation temperature, absolute humidity (pounds of water per pound of dry air), etc.
Evaporation from the wick will leave behind any salts or residues which are dissolved in the water. These may be removed by washing the wick in water or soap and water. Be sure to rinse well to remove all trace of the soap (Marvin 1941).
4) Pool measurements.
Measure pool width, length, and water depth at each site. When a pool is first encountered, mark the length and width of the water bounds with stakes. These stakes will be the points at which length and width are measured for future measurements. Depth will be measured at the deepest point of the site along the width axis. Measure and record length, width, and depth of pool dimensions taken along the axis of the stakes at approximately the same time each day.
5) Placing eggs in enclosures.
During the first night of a rain, locate calling amphibians and water sources. Once breeding sites have been located, search for egg masses. If none are found, search elsewhere and return later to see if eggs have been laid. Once egg masses have been located, place enclosures in the breeding site with equal sized rocks in each enclosure to prevent them from floating. Divide the egg mass into three equal groups. You can use scissors to cut up egg masses in a small tupperware container and use a pipette or turkey baster to transfer eggs. Count the eggs and place the same number of eggs (50-100) into each of the enclosures in floating plastic 1/2 gallon plastic milk jug bottoms or 1 litter plastic soda bottle bottoms that have Nitex nylon mesh glued at the base and Styrofoam peanuts glued to their sides to increase buoyancy. The floating plastic containers should contain at least four inches of water and not permit any water to escape or enter the container (if the containers start to lose water, via evaporation, use water from the enclosure to replace lost water). Once this has been done, place one floating plastic container into each of the three enclosures (control, UV penetrable mylar D enclosure, and UV non-penetrable cellulose acetate enclosure). Use zip ties to join adjacent corners of the mylar filter to prevent the filter from blowing away. Enclosures must be placed at similar depths within the pond being careful to select sites that will not dry up rapidly or allow water to enter or leave through the tops of the enclosures. After egg masses are placed in enclosures, it is important to monitor sites daily to ensure enclosures are kept in the water. If the site begins to dry up, move enclosures into deeper areas of the pool to prevent egg or tadpole death. When selecting eggs to put into enclosures, it is important to select eggs from the same individual for each of the three treatments. Eggs need to be put into enclosures the same night they are laid to ensure that the eggs are not exposed to UV radiation.
6) Measuring hatching success.
Within two days of hatching, measure hatching success by counting the number of unhatched eggs and tadpoles in the floating plastic bottles. Divide the number of tadpoles by the combined number of unhatched eggs and tadpoles and then multiply by 100 to get percent hatching success. Wait one day after hatching before counting tadpoles as they are very susceptible to being crushed shortly after they have hatched.
7) Counting newly hatched tadpoles.
One day after tadpoles have hatched, count the number of tadpoles in each floating soda bottle bottom. Use pipettes to remove tadpoles from the floating plastic bottle bottoms, squirt the captured tadpoles into a 16 oz. soda bottle that has been cut in half to count all hatched tadpoles. Record whether tadpoles are alive, dead, or malformed, then place living tadpoles into a holding bucket (with pond water) and discard dead individuals. Once all the tadpoles are counted, release them back into the soda bottle bottoms. Once tadpoles are free-swimming, release tadpoles from the floating soda bottle bottoms into the enclosure.
8) Measuring tadpole growth.
Every three days after tadpoles have been released into the enclosure, randomly select 15 tadpoles from each enclosure and measure total length of each captured individual. Place the tadpole in the V-shaped channel measuring device. This measuring device is made of clear, right-angled 1/2 x 1/2 inch Lexan plastic marked at 1 cm intervals (Jung and Jagoe 1995).
9) Releasing metamorphs.
As tadpoles begin to metamorphose, take individuals that have forelimbs out of the enclosure. Measure SVL, remaining tail length, and weigh on 200 g Scout balance.
Recommendations or possibilities for future UV studies
1) Use cattle tanks for experiments. These do no dry up as quickly as rain pools and are not subjected to flash floods. Possibilities: Paint Gap Tank, Beaver Pond, Lone Mountain Tank, Duck Tank, Burro Tank.
2) Dig deep pools prior to rain events on Tornillo Flat. See Newman (1989).
3) Swimming pool lab study. Buy 3-6 plastic swimming kiddy pools and fill with water from hose at K-bar. Place enclosures in kiddy pools. You might have to put some tadpoles outside of the enclosures to graze algae off the enclosures in the kiddy pools.
Equipment
References
| Blaustein, A.R., P.R. Hoffman, D.G. Hokit, J.M. Kiesecker, S.C. Walls, and J.B. Hayes. 1994. UV repair and resistance |
| to solar UV-B in amphibian eggs: A link to population declines? Proc. Natl. Acad. Sci. 91:1791-1795. |
| Blaustein, A.R., J.M. Kiesecker, D.P. Chivers, and R.G. Anthony. 1997. Ambient UV-B radiation causes deformities in |
| amphibian embryos. Proc.Natl. Acad. Sci. 94:13735-13737. |
| Jung, R.E., and C.H. Jagoe. 1995. Effects of low pH and aluminum on body size, swimming performance, and susceptibility |
| to predation of green tree frog (Hyla cinerea) tadpoles. Can. J. Zool. 73:2171-2183. |
| Madronich, S. 1993. UV radiation in the natural and perturbed atmosphere. Pp. 17-61 in: Tevin, M. (Ed.). UV-B |
| radiation and ozone depletion: effects on humans, animals, plants, microorganisms, and materials. Lewis Publishers, |
| Boca Raton, FL. |
| Marvin, C.F. 1941. Psychrometric tables for obtaining the vapor pressure, relative humidity, and temperature of the dew |
| point from readings of the wet- and dry-bulb thermometers. W.B. No. 235, U.S. Department of Commerce, |
| Weather Bureau. |
| Newman, R.A. 1989. Developmental plasticity of Scaphiopus couchii tadpoles in an unpredictable environment. Ecology |
| 70:1775-1787. |
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