Amphibian deformities

46 Pages·2014·5.83 MB·English

by  Martin Ouellet

E C OTOX I C O L $.@$',',',,,.
OF AMPffiIBIAN$.....
AND REPTILE$.".'''.
,
Edited by
Donald W. Si,peiLg,
Greg Linder
,
Christine A.
ii.l:!l
CHnpren I I
Amphibion Deformities: Current Stote of
Knowledg"
Martin Ouellet
Isolated cases of amphibian deformities have been reported in scientific literature
for nearly 300 years. vallisneri (1733b, 1733c) recorded the occurrence of a frog with
an additional limb, first described in 1706. In this particular frog, the fifth limb was
located in the right pelvic region and the left hindlimb was polydactylous with seven
toes (see Appendix). The specimen was caught in Scandiano, a little town located in
the region of Emilia-Romagna in northern Italy. In lT40,DeSuperville mentioned a
frog with a supernumerary limb at the level of the right shoulder. This case and two
others (published in 1783 by Guettard, and 1816 by otto) were cited by Geoftoy
Saint-Hilaire (1836b) in the third volume of his classic treatise on monstrosities in
humans and animals. Virey (1819) and Geoftoy Saint-Hilaire (1832) also cited
instances of polydactyly in frogs and salamanders, respectively. Dum6ril (1g65a)
reviewed early observations of deformed anurans, most of them carrying supernu-
merary limb structures, and described in detaii 10 cases that were known to him,
although at least 17 extraJegged frogs had in fact been documented by 1g65 (Taruffi
1880; Ercolani 1881). Taruffi (1880) presented a good historic review, tabulating 32
observations of polymelous anurans by year of publication from 1706 until 1g7b. In
North America, the first described abnormal amphibian was a five-leg ged Rana
pipiens thought to be found in Rochester, New York, around 1850 (fingsley 1gg1).
More contemporary reviews of supernumerary Iimbs and other deformities in
amphibians are those of Bateson (1894), Gemmill (1906), Przibram (1921),
Woitkewitsch (1959), Van Valen (1974), Vizotto et al. (1977), and Dubois 11979).
Past records of polymelous frogs found in Japan were recently presented by Takeishi
(1996). A well-illustrated atlas of anuran deformities was produced by Rostand
(1958). An atlas of developmental abnormalities also exists for xez opus laevis
embryos raised under laboratory conditions (Bantle et al. 1gg1). A general review of
color abnormalities in free-living anurans such as albinism, melanism, black eyes,
and blue frogs is given by Dubois (1979). Although most of these reports refer to
individual cases of deformed amphibians, the recent literature concentrates more
on the description of mass occurrences of deformities in particular populations. It is
E.olilttolopt oI Amphibant and Rtptila.Don ld W. Sp.rling et rl-, editos. 6t7
O 2000 Society of Environmen tal Toricology and Chemisrry (SmAC). ISBN l-8806I I.2E-7
618
Ecotoxicology of Amphibions ond Reptiles
impossible to know how many of the historic mentions were part of population Ievel
phenomena.
Morphological abnormalities and injuries occur normally at low frequencies in wild
populations of amphibians, ranging fro m 0 to 2o/o (Rostand 1g4gb; Dubois and
Vachard 1969; Koskela 1974; Dubois 1979; Semlitsch et al. 1981; Borkin and Pikulik
1986;Luis and Biez 1987; Meyer-Rochow and Asashima 1988;Read and Tyler 1994;
Marvin and Hutchison 1997). For example, 451 cases (1.0%) of clinodactyly,
ectrodactyly, and polydactyly were recorded in a sample of 44,000 addt Bufo bufo
examined from two regions of France (Rostand 1949b). Meyer-Rochow and
Asashima (1988) reported 2.4% or 335 cases of external deformities (ectrodactyly,
polydactyly, polymely, abnormal webbing of toes, and tailprojections) for a total of
13,815 adult Cynops pynhogasler newts from Japan. Of 4737 frogs examined from
different age classes, eight cases (0.2%) of unilateral anophthalmia were found in
populations of Rana esculenta complex (Dubois 1979). In his standard table for
staging anuran embryos and larvae, Gosner (1960) mentioned that aberrant mouth
parts were common in some samples (see also Griliitsch and Grillitsch 1989).
However, this is not the phenomenon of concern. It is only when frequencies of
abnormalities grossly exceed the baseline level that there is any reason to be
alarmed. Recently, an increasing number of populations where frequencies of
deformities were abnormally high (> 5%) have been described in parts ofNorth
America, Europe, and Asia. Up to 85% of the individuals from a given population
can show external abnormalities (Rostand 1959, 1971; Rostand and Darr6 1968;
Mizgireuv et al. 1984; Flindt 1985; Vershinin 1989, 1995b; Sessions and Ruth 1990;
Veith and Viertel 1993; Bohl 1997; Flax and Borkin 1997; Ouellet et al. 1997;
Burkhart et al. 1998; Helgen et al. 1998; Johnson et al. 1999). Many factors have
been proposed or shown to cause developmental abnormalities in amphibians, but
further studies will be necessary to explain the exact mechanisms and developmen-
tal pathways involved. The ecological significance ofseveral ofthese factors also
remains to be proven. Whatever the actual causes of such deformities, the biggest
challenge that remains is to determine if their origins are natural or anthropogenic.
The apparent global decline of amphibians and the consequent growth of interest in
monitoring amphibian populations have stimulated numerous studies around the
world (Kuzmin et al. 1995; Green 1997; Lannoo 1998). Are amphibian deformities
more common simply because of increased surveillance, or are they recent and
widespread phenomena? fue deformities related to the worldwide decline of
amphibian populations? fue natural causes responsible, or are we ourselves
contributing to ecosystem degradation, with possible relevance to human health?
To better appreciate the difficutty and complexity of answering these questions, I
have reviewed the existing literature on amphibian deformities up to early 1999.
Almost exclusively, peer-reviewed and published material has been considered. I
have standardized the technical terms used to describe these abnormalities (see
I 1: Amphibion deformities: Curreni slote of knowledge 619
Appendix). The terms abnormalities, anomalies, malformations, malformities, and
monstrosities were used interchangeably in the literature to refer to cases of am-
phibian deformities. I focused on all external deformities involving the eyes, head,
limbs, mouth, oral cavity, snout, and tail. Accounts of color mutations, diseases,
neoplasms, and internal abnormalities were not included in this review. I had
multiple objectives. First, I reviewed the reports of deformed frogs, toads, newts,
and salamanders in the wild to seek generalities of species sensitivity and geo-
graphic distribution. Second, the possible causes and hypotheses used to explain
deformities were explored and analyzed. Third, I also examined the implications of
developmental abnormalities with regard to amphibian population declines,
ecosystem degradation, and human-health concerns. Finally, I conclude with
recommendations and suggestions for future research on amphibian deformities.
Species Sensitivity ond Geogrophic Distribution
A total of 67 different species of anurans and 26 species of salamanders with
deformities have been documented (Tables I1-1 and 11-2). Many of the accounts are
purely descriptive without any analysis. One hundred and forty-one reports out of a
total of 202 (69.8%) refer to deformities in fewer than 10 individuals per species at
particular sites (Figure I[-1), and many of these describe only a single case. At the
other extreme, 17 situations (8.4%) have deformity occurrences at one or more sites
greater than 100 individuals per species. Some reports may refer to the same
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Numhr of deformed amphibians
Figure 11-1 Numbers of published reports describing numbers of deformed amphibians
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