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 ab normalities and their implications for amphibian populations. Over a two-ye ar period, we monitored the frequency and composition of morphological abno rmalities in four amphibian species (Hyla regilla, Taricha torosa, Bufo bor eas, and Rana catesbeiana) from two California ponds. The frequency of abno rmalities 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 lan,a l 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 a nd R. catesbeiana, both of which had rates of less than five percent. Withi n each species, the composition of abnormalities was strongly consistent be tween years, ponds, and early life-history stages. We recorded the most sev ere 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 wore dominated by ex tra and missing hind- and forelimbs. In B. boreas and T torosa, the most co mmon morphological abnormalities were missing limbs and digits, which accou nted for approximately 75% and 95%, respectively., of their total abnormali ties. Potential causes of the observed abnormalities, including infection b y the trematode Ribeiroia, and the conservation significance of amphibian m alformations are discussed.