The Extinction of the Golden Toad (class=SpellE>Bufostyle='font-family:Arial'> periglenes) style='font-family:Arial;font-style:normal;mso-bidi-font-style:italic'>Ð
Symptom of a Worldwide Crisis
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src="Golden%20Toad%20Outline_files/image002.jpg" v:shapes="_x0000_i1025">
style='mso-list:Ignore'>I.
Habitat
style='mso-list:Ignore'>A.
Golden toads occupied a few square miles in the class=SpellE>Monteverde Cloud Forest Reserve in northern w:st="on">Costa Rica
style='mso-list:Ignore'>B.
Habitat occurred at about 2000 m ASL
style='mso-list:Ignore'>C.
Golden toads were thought to live under fallen
leaves and moss
style='mso-list:Ignore'>1.
Sightings of golden toads were limited to about
one week per year, when they came out to breed
style='mso-list:Ignore'>II.
Mating habits
style='mso-list:Ignore'>A.
forstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'> a
week in April every year, thousands of these brilliant toads gathered in pools
in a breeding orgy.
style='mso-list:Ignore'>1.
The golden toad is renowned for its
brilliant color- it is the only known species of toad that is not gray or brown
style='mso-list:Ignore'>2.
Golden toads displayed extreme sexual dimorphismstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>a)
Males- golden
style='mso-list:Ignore'>b)
Females- range from olive to dark brown
or black, spotted with scarlet
style='mso-list:Ignore'>3. Males outnumbered females about 8 to 1
style='mso-list:Ignore'>B.
Mating would occur near temporary water
pools
style='mso-list:Ignore'>1.
Unable to differentiate gender, males
would clasp anything that moves
style='mso-list:Ignore'>a)
Males possessed a special vibration
signal to relay gender, and disengage other males
style='mso-list:Ignore'>b)
Inadvertent coupling with other species
of frogs could occur, lasting for days
style='mso-list:Ignore'>2.
Males would remain attached to females
in amplexus until the female laid eggsstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>a)
Females would lay approx. 200 to 400 eggsstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>b)
After hatching- larvae remain in water
for five weeks before metamorphosis into their terrestrial form
style='mso-list:Ignore'>III.
Decline/Extinction
style='mso-list:Ignore'>A.
Discovered in 1964
style='mso-list:Ignore'>B.
The April breeding frenzy was the only
time that the toads were ever observed
style='mso-list:Ignore'>C.
In 1987, more than 1500 golden toads
were observed during the breeding period
style='mso-list:Ignore'>D.
1988 and 1989- onle
one toad was observed
style='mso-list:Ignore'>1.
The reserve also had several captive
frogs, but they died of unknown causes in the mid 1980Õs.
style='mso-list:Ignore'>2.
Other species of amphibians declined at
this time also
style='mso-list:Ignore'>E.
1992- the
golden toad was pronounced almost certainly extinct, as the last one had been
sighted in 1989.
style='mso-list:Ignore'>IV.
Reasons for decline
style='mso-list:Ignore'>A.
Climactic
style='mso-list:Ignore'>1.
1986-1987 El Nino resulted in the
lowest rainfall on record at Monteverde 2
style='mso-list:Ignore'>2.
Low rainfall could have caused chemical
pollutants to become concentrated in breeding pools
style='mso-list:Ignore'>3.
Changing climate alters the patterns of
temperature, mist, and rainfall, causing cloudbanks to form at increasing
elevations, and compressing the possible range for cloud forests.style='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>B.
Pollutants
style='mso-list:Ignore'>1. For many pesticides, there isnÕt
sufficient data regarding its negative effect on amphibians.style='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>a)
Atrazine is probably the most widely used
herbicide in the world and one of the most common contaminants in ground and
surface waters.
style='mso-list:Ignore'>b)
atrazine induced class=SpellE>hermaphroditism at concentrations of only 0.1 ppb (Hayes et
al. 2002) when administered throughout larval development of African clawed
frogs
style='mso-list:Ignore'>c)
Most water sources in the w:st="on">United States,
including rainwater, have been found to exceed that concentrationstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>d)
This concentration is 30 times less than the US
EPA-mandated drinking water standard.5
style='mso-list:Ignore'>e)
10Ð92%
of male leopard frogs in different regions of the w:st="on">United States show class=SpellE>gonadal abnormalities such as retarded development and class=SpellE>hermaphroditism
style='mso-list:Ignore'>C.
Ultraviolet radiation
style='mso-list:Ignore'>1.
solar ultraviolet (UV) B radiation (of
wavelength 280-320 nm) damage in the declines of R. cascadae
and B. boreas boreas in w:st="on">Oregonstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>2.
Blaustein and Wake
(1995) have recently suggested that UV exposure impairs immune function, making
the larvae more susceptible to infection by the fungus Saprolegnia,
which naturally occurs in lakes and ponds.
style='mso-list:Ignore'>D.
Fungal
skin infections
style='mso-list:Ignore'>1. The
underlying cause of the decline of many amphibians could be due to a fungal
disease known as chytridiomycosis.style='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>a)
Initial
diagnosis is difficult - occasional abnormal epidermal sloughing and
ulceration, or hemorrhage in the skin were the only gross lesions encountered
and these were rare (Fig. 1).4
style='mso-list:Ignore'>b)
Diagnosis
is usually only possible through examination of a freshly preserved carcass
under an electron microscope.
style='mso-list:Ignore'>c) The
result of this type of infection is skin damage, leading to skin thickening and
eventual suffocation and/or dehydration
style='mso-list:Ignore'>V.
Reasons
for Concern
style='mso-list:Ignore'>A.
Frogs
and toads are extremely sensitive indicators of environmental changesstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>1. Uptake
of oxygen and water through their skin can increase concentrations of
pollutants
style='mso-list:Ignore'>2.
The
life cycle of frogs and toads exposes them to water and airborne contaminantsstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>B.
Tadpoles
eat aquatic plants
style='mso-list:Ignore'>C.
Adults
eat potentially disease-carrying insects
style='mso-list:Ignore'>D.
Amphibians
are a vital part of the food web for many other species of animalsstyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>E.
The
Costa Rican government has adopted a policy towards sustainable class=GramE>agriculture which includes the promotion of Integrated Pest
Management (IPM) and non-chemical crop protection. At the same time, pesticides
remain exempt from taxes and duties, which inevitably increases
their use. 6
style='mso-list:Ignore'>F.
Research
at Costa RicaÕs National University shows that in 1993 about 18% of all
pesticide imports (by volume) were in the World Health Organisation
toxicity classification categories Ia, extremely
hazardous, or Ib, highly hazardous(2). 6style='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>G.
In class=GramE>1993 the banana sector accounted for 57% of all pesticides
sales, despite occupying less than 10% of w:st="on">Costa RicaÕs agricultural area.style='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>H.
a case of massive sterilization of approximately
1,500 workers in Costa Rica,
due to the exposure to a toxic pesticide called DBCP, applied in large
commercial banana plantations
style='mso-list:Ignore'>VI.
Implications for amphibians worldwidestyle='mso-bidi-font-size:10.0pt;mso-bidi-font-family:Arial;color:black'>
style='mso-list:Ignore'>A. According
to the IUCN Red List of Threatened Species, at least 1,856 amphibian species class=GramE>are threatened with extinction, representing 32 percent of
all species.
style='mso-list:Ignore'>B.
This is considerably higher than the comparable
figures for birds (12 %) and mammals (23%), the only other groups for which
comprehensive global assessments have been completed. style='mso-tab-count:2'>
Working Bibliography
Sarkar, class=SpellE>Sahotra (1996). Ecological Theory and
Anuran Declines. Biosciencestyle='font-family:Arial;mso-bidi-font-family:"Times New Roman";font-style:
normal;mso-bidi-font-style:italic'>, 46style='font-family:Arial;mso-bidi-font-family:"Times New Roman";font-style:
normal;mso-bidi-font-style:italic'> (3), 199-208.
Pounds JA, Crump ML. (1994). class=GramE>Amphibian declines and climate disturbance: the case of the style='font-family:Arial;mso-bidi-font-family:"Times New Roman";mso-bidi-font-weight:
bold;font-style:normal;mso-bidi-font-style:italic'>goldenstyle='mso-bidi-font-style:normal'> toad and the harlequin frog.
Conservation Biology, style='mso-bidi-font-style:normal'>8, 72-85.
class=GramE>Blaustein w:st="on">AR, Wake DB, Sousa
WP. (1994). Amphibian declines: judging stability, persistence, and
susceptibility of populations to local and global extinctions. style='mso-bidi-font-style:normal'>Conservation Biology, 8, 60-71.
Daszak, P., Cunningham, A.A. & Hyatt, A.D. ÒAmphibian Chytridiomycosis and Emerging
Infectious Diseases of Wildlife.Ó Accessed via the web address href="http://www.vet.uga.edu/ivcvm/2000/Daszak/Daszak.htm">http://www.vet.uga.edu/ivcvm/2000/Daszak/Daszak.htmstyle='mso-spacerun:yes'> Viewed March 25, 2005.
Hayes, T., class=SpellE>Haston, K., Tsui, M., Hoang,
C.H., and Vonk, A. Òclass=articletitle>Atrazine-Induced Hermaphroditism
at 0.1 ppb in American Leopard Frogs (Rana class=SpellE>pipiens): Laboratory and Field Evidence.Ó class=GramE>Environmental
Health Perspectives, 111 (4).class=medium-normal>
Agneclass=GramE>, S. and Waibel, H. (1997). class=GramE>ÒPesticide Policy in w:st="on">Costa Rica.Ó style='mso-bidi-font-style:normal'>Pesticides News 36, 8-10.class=medium-normal>
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