Morphological Abnormality Patterns in a California Amphibian Community

Increasing reports of amphibian limb malformations from many parts of North America have prompted investigations into the potential causes of these abnormalities and their implications for amphibian populations. Over a two-year period, we monitored the frequency and composition of morphological abnormalities in four amphibian species (Hyla regilla, Taricha torosa, Bufo boreas, and Rana catesbeiana) from two California ponds. The frequency of abnormalities differed significantly by species, life-history stage, pond, and season. Generally, the frequency and severity of abnormalities were greater in the amphibians from Frog Pond over those from Hidden Pond, and in larval stages over emerging and adult amphibians. Larvae of T. torosa exhibited the highest rate of abnormalities, ranging from 15-50%, followed by larval and metamorphic H. regilla (10-25%), and finally by metamorphic B. boreas and R. catesbeiana, both of which had rates of less than five percent. Within each species, the composition of abnormalities was strongly consistent between years, ponds, and early life-history stages. We recorded the most severe malformations in H. regilla, and more than 60% of the abnormalities in treefrogs involved extra hindlimbs, femoral projections, and skin webbings. Similarly severe, the abnormalities of R. catesbeiana were dominated by extra and missing hind- and forelimbs. In B. boreas and T. torosa, the most common morphological abnormalities were missing limbs and digits, which accounted for approximately 75% and 95%, respectively, of their total abnormalities. Potential causes of the observed abnormalities, including infection by the trematode Ribeiroia, and the conservation significance of amphibian malformations are discussed.