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AMPHIBIAN DECLINE, ULTRAVIOLET RADIATION AND LOCAL POPULATION ADAPTATION
Hansen, L J. AMPHIBIAN DECLINE, ULTRAVIOLET RADIATION AND LOCAL POPULATION ADAPTATION. Presented at Audobon Society Local Chapter Meeting, Pensacola, FL, Feb. 22, 2001.
Amphibian population declines have been noted on both local and global scales. Causes for these declines are unknown although many hypotheses have been offered. In areas adjacent to human development, loss of habitat is a fairly well accepted cause. However in isolated, seemingly pristine high elevation locations the causes are less certain. Suggested causes include pesticide drift from agricultural areas, globally cycled metals that can collect at high elevation locations, other anthropogenic contaminants (such as polychlorinated biphenyls), global warming, increased ultraviolet B (UVB) radiation due to stratospheric ozone depletion, and introduced species competition and predation. The potential role of environmental contaminants or an anthropogenically altered habitat (i.e. ozone depletion, global warming) points to the need to integrate conservation biology and ecotoxicology in assesing causes of amphibian declines. In order to explore the role of UVB radiation on native amphibian species, a series of laboratory and field experiments were undertaken. The first examined the difference between high and low elevation populations of the Pacific tree frog (Hyla regilla) to various intensities of UVB radiation in a solar simulator. Examination of hatching success, survival to limb bud formation, growth and development endpoints at a single temperature, indicated that the low elevation population was the more sensitive of the two, as would be predicted if high elevation populations have adapted to increased UVB. These experiments further demonstrated that hatching success is not the most sensitive indicator of effect in H.regilla, and that post-hatching growth and development effects are more influenced by UVB. Based on this observed lack of embryonic mortality in the first experiment, the second experiment examined the role of egg mass jelly in protecting two species of anurans (H. regilla and Bufo canorus ) from UVB radiation. This determined that jelly does not protect these developing embryos from UVB radiation and is not a factor in the adaptation of H. regilla to UVB. The third experiment examined the tolerance of B. canorus, a high elevation species believed to be declining, to UVB radiation and found this species to be extremely tolerant to all experimental doses including those almost twice current natural exposures. Finally a series of reciprocal transplant field experiments, using H. regilla as a model species, led to the development of a field enclosure suitable for studying developing embryos through premetamorphosis, characterization of a number of sites for metal and pesticide residues, and allowed for observation of high elevation H. regilla breeding habits.