Malformed Frogs: The Collapse of Aquatic Ecosystems

2. Malformed Frog Types

two MALFORMED FROG TYPES Die Anatomie ist das Schicksal. (Anatomy is destiny.) SIGMUND FREUD1 In an attempt to organize, and to correlate effect with cause, malformations , whether human, frog, or otherwise, have tended to be divided into types. Malformation types are almost always based on: (1) structures absent or reduced, (2) structures duplicated (or multiplied), and (3) structures present but otherwise abnormal (e.g., eye position, jaw shape, limb shape, skin color, pigment pattern). Definitions of malformed frogs have been provided by Carol Meteyer and her colleagues.2 The team we assembled in 2001 to re-examine the hottest of the Minnesota malformed frog hotspots slightly modified this terminology,3 which is in turn slightly modified and presented in Table 2.1. Note that internal soft tissue features , such as malformed gonads and larynxes (voice box), which are known to occur following exposure to some environmental contaminants (see Chapter 4), and oral deformities in marginal papillae, tooth rows, and jaw sheaths caused by the Batrachochytrium dendrobatidis (chytrid) infections4 are not included here. WHICH ANIMALS TO REPRESENT Collections of malformed frogs have never been done in a sufficiently systematic way to permit meaningful statistical analyses (see discussion in Chapter 5). About all you can really say is that animals of species X with particular malformation Y were collected at wetland Z on day A. Absence of malformation types in collections may or may not reflect 21 their absence in the sampled wetland. Percentages of malformed frogs collected as newly metamorphosed animals (which can and do vary from day to day) may or may not reflect true percentages. Further, percentages of malformed metamorphosed frogs may or may not represent percentages of malformed tadpoles or malformed embryos in that population. 22 malforme d frog type s table 2.1. Classification and definitions of frog abnormalities Type and Location of Abnormality Description Craniofacial Anophthalmia small eye Brachygnathia abnormal shortness of lower jaw Eye discoloration iris pigment discolored or missing Eye displacement eye displaced laterally, medially, cranially, or caudally Microcephaly blunt nose; shortened upper jaw Microphthalmia missing eye Forelimb and Hindlimb Abnormal pigment pigment pattern missing or abnormal Amelia missing limb Taumelia long bone bent back on itself forming > 90° angle Bony expansions distal end of a bone expands into spongy balloon Brachydactyly normal number of metatarsals but abnormal number of phalanges Curved long bone all long bones bend at the site of artery penetration Ectrodactyly complete absence of digit including metatarsal bone Ectromelia missing limb segments (e.g., femur present but rest of limb missing) Hemimelia shortened bone Micromelia entire limb present but all limb elements shortened Polydactyly complete extra digit including metatarsal bone Polymelia complete extra limb Skin webbing band of skin crossing a joint Syndactyly fusion of digits Whole Body Bloated body swelling in the torso and limbs of the animal Note: Data from Meteyer and colleagues.2 What all this really means is that either way radiographs are represented— as a full collection (prohibitively costly, not to mention redundant) or as a highly selected subsample—there is bias. And bias is bias—no matter whether there is a little of it or a lot of it—and to be honest we have to acknowledge it and deal with it. As mentioned above, frog malformations can be categorized simply as parts missing, parts present but abnormal, and parts extra, and that is how I organized this chapter. For each category, the best representatives were chosen. Radiographs were selected that would allow comparisons5 of species, sites, and malformation types. In all, 63 radiographs representing eight species are presented. Many specimens used here were collected from Minnesota by Minnesota Pollution Control Agency field biologists and by Dave Hoppe. Several specimens were collected at one Wisconsin site by Dan Sutherland. Specimens were collected at two California sites by Pieter Johnson, at one southeastern Indiana site by Charles Facemire, at two east-central Indiana sites by Laura Blackburn, and at a National Wildlife Refuge in Alaska by Mari Reeves.6 An historic specimen, collected in Ohio and housed in the Hefner Zoology Museum at Miami University in Oxford, Ohio, was sent to me by Curator Mike Wright. A specimen in the collection at the Field Museum in Chicago was sent to me by Alan Resetar. UNILATERAL AMELIA too few hindlimbs Example 1 Each malformed frog has its own story to tell. The details of the morphologies we see reflect not only the malformation, and...