Hotspot of tadpole abnormality in suburban south-west Florida

Abstract

A high concentration of Cuban treefrog (Osteopilus septentrionalis) tadpoles displaying morphological abnormalities was discovered in an untreated swimming pool in Bonita Springs, Florida. This find initiated a 4-year survey (2012-2015) of surrounding roadside drainage ditches that had been treated with insecticide for mosquito control. The study was extended to the populations of Ave Maria, Florida, and Everglades National Park. The core data set of 36,550 tadpoles from the swimming pool and ditches contained 25,136 abnormal tadpoles, an abnormality average of 68.8 %, well above the 5 % minimum definition for a hotspot. The frogs from Ave Maria and the Everglades National park were 0 % abnormal. The type of tadpole abnormality differed between the suburban treated roadside drainage ditches versus the untreated swimming pool, although the same abnormalities were found in both the suburban treated and untreated water. In the untreated swimming pool, 70.1 % of tadpoles displayed abnormalities such as bent tails, abnormal limbs, and disfigured or absent mouthparts. Larvae in the untreated swimming pool metamorphosed en masse despite abnormalities. The high frequency of abnormal metamorph abnormalities found were: kyphosis, scoliosis, microcephaly, and forelimb abnormalities. In the treated roadside drainage ditches, Gosner stage 16-25 tadpoles could not undergo metamorphosis and experienced mass mortality. The abnormalities found at Gosner stage 16 of the embryo were in the head and body. Tadpoles at Gosner stages 19-25 failed to develop gills, were bloated, had growth retardation, and mouthpart abnormalities. The older Gosner stage 25-41 tadpole populations in the ditches showed bloating, lumps, emaciation, and growth retardation. A brief synopsis of O. septentrionalis treefrog biology is also given, including breeding congregations, average 8 hour time to hatching, and 19 days metamorphosis.