Genetic diversity refers to genetic variations within a population or species of a given organism and it has been shown to offer the amphibians protection against environmental adversaries. Research has shown that the wood frogs (Rana sylvatica) that have a lower genetic diversity are more susceptible to the negative effects of ultraviolet- B radiation than those having a higher genetic diversity. In the experiment done, frogs eggs and larvae were exposed to three different conditions that included; unfiltered sunlight, sunlight filtered through a UV-B blocking filter (Mylar), and through a UV-B transmittin known as acetate. The findings showed a negative relationship between genetic diversity and egg mortality, larval mortality, and defog filter city rates. It showed that the UV-B radiation causes an increase in egg and larval mortality rates and it also increased the number of deformities in amphibians.
Amphibians have been shown to be declining in numbers across the globe and the reason for this could be as a result of loss of genetic diversity among these amphibians. The reasons for this loss is as a result of habitat fragmentation because many of the amphibians are highly philopatric, have short natal distances due to their small sizes, experience low dispersal across habitats because they require moist habitats, and, lastly, the amphibian populations undergo fluctuations from year to year which gradually leads to loss of genetic diversity.
The amphibians are getting exposed to increased amounts of radiation (280-320 nm wavelength) that are reaching the earth’s surface due to the depletion of the ozone layer. The global increase in UV-B radiation has made researchers hypothesize it as the reason behind the global decline in the population of amphibians. Some research done in trying to explain the reason behind the declining numbers of amphibians has shown a level of synergism between the UV-B and diseases, low PH, and harmful chemicals. This study though is trying to show the synergism between the UV-B and low genetic diversity as possible proof of the hypothesis that the UV-B could be the possible cause of declining amphibian populations.
The hypothesis for this research was that the genetically diversified amphibians exhibit a higher resistance to the UV-B than the less genetically diversified ones. The hypothesis was tested on the wood frogs (Rana sylvatica). Wood frogs were collected from twelve amphibian populations; their genetic diversity was then analyzed after which they were subjected to three different UV-B treatments discussed above. The eggs were collected from the woodlots that interspersed the row crop agricultural fields. The distance between one population of wood frog population to the next was measured as 441m between two woodlots. The genetic structure of the wood frog population was then analyzed using Randomly Amplified DNA markers (RAPD).
Genetical diversity estimates for 12 populations of wood frogs were obtained in 12 separate island woodlots. The eggs were collected from the ponds and about thirty of them per pond, a maximum of 25 egg masses from each pond were sampled. The eggs from each egg mass were then placed in a separate plastic container with pond water and then transported to the laboratory where they were grown under controlled laboratory conditions. Three eggs from each egg mass were maintained in order to counteract possible problems that could occur during DNA extraction. The eggs were then subjected to Mylar, acetate and direct sunlight treatments. The UV-B measurements of the experimental room was about 25-285µ W/cm2 and the Mylar filters blocked 90% of the UV-B while the acetate filters blocked about 36% of the UV-B.
Most mortality occurred at the larval stage and 186 tadpoles were deformed, 4 of them showed signs of edema, 181 had axial malformations and 1 had both axial malformation and edema. Exclusion of the sun treatment resulted in lowered mean larval mortality and deformity rates and a slightly increased egg mortality rates.
The data indicates that a synergistic interaction between the UV-B and the genetical diversity amphibians can influence amphibians’ fitness. The findings of the research were that UV-B has a significant effect on the survival of wood frogs; under the UV-B transmitting filter (acetate), the mean larval mortality rate was 8 times higher and mean deformity rates was about 10 times higher than under the UV-B blocking Mylar. The study also showed that the egg mortality was not really affected by UV-B treatment. The study also provides evidence to support the hypothesis that genetic diversity alone affects egg mortality, larval mortality and deformity rates in wood frogs.
From this study, one can confidently conclude that the interaction between the UV-B and the genetical diversity has a significant influence on the survival of the wood frogs. The UV-B radiation affects the larval mortality rates and increases the deformity rates but does not affect egg mortality in any significant way.