Andrea and Joe return to the boat from Gaulin Reef in San Salvador, Bahamas. See other beautiful phenomena from the Bahamas.
Picture of a couple of the now-extinct Golden Toad (guess which one is the male)
A.Golden toads occupied a few square miles in the Monteverde Cloud Forest
Reserve in northern Costa Rica
B.Habitat occurred at about 2000 m ASL
C.Golden toads were thought to live under fallen leaves and moss
1.Sightings of golden toads were limited to about one week per year, when they came out to breed
A.for a week in April every year, thousands of these brilliant toads gathered in pools in a breeding orgy.
1.The golden toad is renowned for its brilliant color- it is the only known species of toad that is not gray or brown
2.Golden toads displayed extreme sexual dimorphism
b)Females- range from olive to dark brown or black, spotted with scarlet
3.Males outnumbered females about 8 to 1
B.Mating would occur near temporary water pools
1.Unable to differentiate gender, males would clasp anything that moves
a)Males possessed a special vibration signal to relay gender, and disengage other males
b)Inadvertent coupling with other species of frogs could occur, lasting for days
2.Males would remain attached to females in amplexus until the female laid eggs
a)Females would lay approx. 200 to 400 eggs
b)After hatching- larvae remain in water for five weeks before metamorphosis into their terrestrial form
A.Discovered in 1964
B.The April breeding frenzy was the only time that the toads were ever observed
C.In 1987, more than 1500 golden toads were observed during the breeding period
D.1988 and 1989- onle one toad was observed
1.The reserve also had several captive frogs, but they died of unknown causes in the mid 1980’s.
2.Other species of amphibians declined at this time also
E.1992- the golden toad was pronounced almost certainly extinct, as the last one had been sighted in 1989.
IV.Reasons for decline
1.1986-1987 El Nino resulted in the lowest rainfall on record at Monteverde
2.Low rainfall could have caused chemical pollutants to become concentrated in breeding pools
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.
1.For many pesticides, there isn’t sufficient data regarding its negative effect on amphibians.
a)Atrazine is probably the most widely used herbicide in the world and one of the most common contaminants in ground and surface waters.
b)atrazine induced hermaphroditism at concentrations of only 0.1 ppb (Hayes et al. 2002) when administered throughout larval development of African clawed frogs
c)Most water sources in the United States, including rainwater, have been found to exceed that concentration
d)This concentration is 30 times less than the US EPA-mandated drinking water standard.
e)10–92% of male leopard frogs in different regions of the United States show gonadal abnormalities such as retarded development and hermaphroditism
1.solar ultraviolet (UV) B radiation (of wavelength 280-320 nm) damage in the declines of R. cascadae and B. boreas boreas in Oregon
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.
D.Fungal skin infections
1.The underlying cause of the decline of many amphibians could be due to a fungal disease known as chytridiomycosis.
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).
b)Diagnosis is usually only possible through examination of a freshly preserved carcass under an electron microscope.
c)The result of this type of infection is skin damage, leading to skin thickening and eventual suffocation and/or dehydration
V.Reasons for Concern
A.Frogs and toads are extremely sensitive indicators of environmental changes
1.Uptake of oxygen and water through their skin can increase concentrations of pollutants
2.The life cycle of frogs and toads exposes them to water and airborne contaminants
B.Tadpoles eat aquatic plants
C.Adults eat potentially disease-carrying insects
D.Amphibians are a vital part of the food web for many other species of animals
E.The Costa Rican government has adopted a policy towards sustainable 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.
F.Research at Costa Rica’s 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).
G.In 1993 the banana sector accounted for 57% of all pesticides sales, despite occupying less than 10% of Costa Rica’s agricultural area.
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
VI.Implications for amphibians worldwide
A.According to the IUCN Red List of Threatened Species, at least 1,856 amphibian species are threatened with extinction, representing 32 percent of all species.
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.
Sarkar, Sahotra (1996). Ecological Theory and Anuran Declines. Bioscience, 46 (3), 199-208.
Pounds JA, Crump ML. (1994). Amphibian declines and climate disturbance: the case of the golden toad and the harlequin frog. Conservation Biology, 8, 72-85.
Blaustein AR, Wake DB, Sousa WP. (1994). Amphibian declines: judging stability, persistence, and susceptibility of populations to local and global extinctions. Conservation Biology, 8, 60-71.
Daszak, P., Cunningham, A.A. & Hyatt, A.D. “Amphibian Chytridiomycosis and Emerging Infectious Diseases of Wildlife.” Accessed via the web address http://www.vet.uga.edu/ivcvm/2000/Daszak/Daszak.htm Viewed March 25, 2005.
Hayes, T., Haston, K., Tsui, M., Hoang, C.H., and Vonk, A. “Atrazine-Induced Hermaphroditism at 0.1 ppb in American Leopard Frogs (Rana pipiens): Laboratory and Field Evidence.” Environmental Health Perspectives, 111 (4).
Agne, S. and Waibel, H. (1997). “Pesticide Policy in Costa Rica.” Pesticides News 36, 8-10.
Fogden, Michael and Patricia (1984). "All That Glitters May be Toads." Natural History, 93 (5), 46-51.
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