Meteyer C U, Loeffler I K, Fallon J F, Converse K A, Green E, Helgen J C, Kersten S, Levey R, Eaton-Poole L, Burkhart J G
United States Geological Survey, Biological Resource Division, National Wildlife Health Center, Madison, Wisconsin 53711, USA.
Teratology. 2000 Sep;62(3):151-71. doi: 10.1002/1096-9926(200009)62:3<151::AID-TERA3>3.0.CO;2-2.
Reports of malformed frogs have increased throughout the North American continent in recent years. Most of the observed malformations have involved the hind limbs. The goal of this study was to accurately characterize the hind limb malformations in wild frogs as an important step toward understanding the possible etiologies.
During 1997 and 1998, 182 recently metamorphosed northern leopard frogs (Rana pipiens) were collected from Minnesota, Vermont, and Maine. Malformed hind limbs were present in 157 (86%) of these frogs, which underwent necropsy and radiographic evaluation at the National Wildlife Health Center. These malformations are described in detail and classified into four major categories: (1) no limb (amelia); (2) multiple limbs or limb elements (polymelia, polydactyly, polyphalangy); (3) reduced limb segments or elements (phocomelia, ectromelia, ectrodactyly, and brachydactyly; and (4) distally complete but malformed limb (bone rotations, bridging, skin webbing, and micromelia).
Amelia and reduced segments and/or elements were the most common finding. Frogs with bilateral hind limb malformations were not common, and in only eight of these 22 frogs were the malformations symmetrical. Malformations of a given type tended to occur in frogs collected from the same site, but the types of malformations varied widely among all three states, and between study sites within Minnesota.
Clustering of malformation type suggests that developmental events may produce a variety of phenotypes depending on the timing, sequence, and severity of the environmental insult. Hind limb malformations in free-living frogs transcend current mechanistic explanations of tetrapod limb development.
近年来，北美大陆各地关于畸形青蛙的报道有所增加。大多数观察到的畸形涉及后肢。本研究的目的是准确描述野生青蛙的后肢畸形，这是朝着了解可能病因迈出的重要一步。
1997年至1998年期间，从明尼苏达州、佛蒙特州和缅因州收集了182只刚变态的北美豹蛙（Rana pipiens）。其中157只（86%）存在后肢畸形，这些青蛙在国家野生动物健康中心接受了尸检和放射学评估。详细描述了这些畸形，并将其分为四大类：（1）无肢体（无肢畸形）；（2）多肢体或肢体元件（多肢畸形、多指畸形、多指骨畸形）；（3）肢体节段或元件减少（短肢畸形、缺肢畸形、缺指畸形和短指畸形）；（4）远端完整但畸形的肢体（骨旋转、桥接、皮肤蹼状和短肢畸形）。
无肢畸形和节段及/或元件减少是最常见的发现。双侧后肢畸形的青蛙并不常见，在这22只青蛙中只有8只畸形是对称的。特定类型的畸形往往发生在从同一地点收集的青蛙中，但畸形类型在所有三个州以及明尼苏达州内的研究地点之间差异很大。
畸形类型的聚集表明，发育事件可能根据环境损伤的时间、顺序和严重程度产生多种表型。自由生活青蛙的后肢畸形超越了目前对四足动物肢体发育的机制解释。
