Golden Toad

The Golden Toad is notable in its genus for being both sexually dichromatic and visually striking (Savage 1966). Male coloration is characteristically bright orange, uniform on the dorsum but sometimes slightly mottled on the venter. Female dorsal pigmentation ranges from greenish-yellow to black and is marked with bright scarlet spots edged in yellow, while the ventral surface is greenish-yellow to flesh colored. Adult female standard length ranges from 47 to 54 mm, while males range from 41 to 48 mm. Other size-based sexually dimorphic traits include a longer, more acute snout in males, and proportionally longer limbs. In both sexes, body surface is relatively smooth with the warts being granular and tipped with small black spines. Supraorbital, postorbital, canthal, and supratympanic external crests are present, which are low and warty. The tympanum is absent, and no vocal sac or slits are present. The iris is black and marked with gold flecks, and set in a horizontally elliptical pupil. Tubercles are not present on the hands and feet, and only the toes are webbed near their base.See photos and film clip of Bufo periglenes at the ARKive site:http://www.arkive.org.uk/species/display.asp?id=17A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio) (http://darnis.inbio.ac.cr/FMPro?-DB=UBIpub.fp3&-lay=WebAll&-Format=/ubi/detail.html&-Op=bw&id=4377&-Find).

The Golden Toad is found in a small area (less than 10 square kilometers) contained in the Monteverde Cloud Forest Preserve in the Cordillera de Tilaran, near Monteverde, Provincia de Puntarenas, Costa Rica. The habitat is undisturbed, elfin cloud forest, consisting of an understory of mosses, ferns, and epiphytes, and a canopy including Didymopanex pittieri, Clusia alata, Oreopanax nubigenum, and Zanthoxylum melanostichum (Jacobson and Vandenberg 1991). The area experiences a distinct dry season, dominated by tradewind-based precipitation rising from the Caribbean basin, and a wet season, characterized by convectional storms from the Pacific lowlands (Crump et al. 1992). Mean annual biotemperature ranges from 12 to 18 degrees Celsius, and rainfall annually is over 4000 mm (Savage 1966). The habitat is characterized by Holdridge (1967) as a lower-montane rain-forest lifezone.

The disappearance of the golden toad is perhaps the most striking case of amphibian decline, not only because its habitat and dispersion ability seem to have been unaffected (Pounds et al. 1997), but also because of the abrupt nature of its decline. The documented story is a good one, beginning with Savage's (1966) preliminary description, spanning through the late 1980's when B. periglenes disappeared, and continuing now with extensive causal analysis. The history of abundance begins with Savage's (1966) initial sighting in 1964, when he noted that "within a radius of 5 meters at least 200 toads were visible." In 1977, Jacobson and Vandenberg (1991) counted 988 individuals in a single day, as compared to a greatest daily count of 85 in 1982. The last significant record came from May 1987, when Crump et al. (1992) observed a total of 1500 adult toads over the duration of the breeding season. This count was reduced to a single toad in both 1988 and 1989 (Pounds and Crump 1994), and none have been found thereafter (Pounds et al. 1997). The extremely limited geographic distribution and fragile status of B. periglenes was internationally recognized when the International Union for the Conservation of Nature (IUCN) listed it as Endangered in 1979. In 1996, the status of the Golden Toad was revised to Critically Endangered, and in 2001, the IUCN declared the Golden Toad formally Extinct.The rapid manner in which this population vanished, from 1500 to none in just a few years, has led to the argument that B. periglenes suffered from a high adult mortality rather than the gradual effects expected from poor juvenile recruitment or unsuccessful breeding (Pounds and Crump 1994). This reasoning, in conjunction with the toad's pristine habitat, have centered causal hypotheses around abiotic factors involving climate change (Pounds et al. 1999). Field studies reported complete egg desiccation in both 1982 (Jacobson and Vandenberg 1991) and in 1987 (Crump et al. 1992). This seems readily explainable by the warming of the pools and the low level of precipitation, which produced drier conditions overall (Pounds and Crump 1994). However, a causal explanation for the disappearance of the adult toads is not as forthright. Certain factors have been ruled out, such as the detrimental effects of Ultraviolet (UV) exposure and pH contamination. Crump et al. (1992) argue that the Golden Toad's fossorial lifestyle and the heavy cloud cover of the montane environment should prevent damaging UV radiation, while their tests of pH change in cloud water, convective and advective precipitation turned up negative. Examining weather data, Pounds and Crump (1994) noted the correlation between the desiccation events and the adult disappearance, and the 1982-1983 and the 1986-1987 El Niño/Southern Oscillation. This led them to propose several climate-based hypotheses: moisture stress, temperature stress, climate-linked epidemic hypothesis (see Pounds et al. 2006), and the climate-linked contaminant pulse hypothesis. Pounds et al. (1999) added support to the climate-induced decline in their careful analysis of precipitation, air temperature, sea surface temperature, and stream flow patterns in relation to tropical anuran, avian, and anoline lizard communities. They concluded, as did Pounds et al. (2006) that it was not simply the effect of the El Niño/Southern Oscillation, but rather a global warming trend in general (this trend remained significant with the El Niño fluctuations included) which crossed a threshold in late 1980's and precipitated a broad tropical anuran decline. This was matched by a decline in anoline lizards, and resulted in significant restructuring of tropical avian communities. However, Lips et al. (2008) reanalyzed the data of Pounds et al. (2006), and argued that the climate-linked epidemic hypothesis was not supported, as did Rohr et al. (2008). Anchukaitis and Evans (2010) reconstructed a century of climatic data for Monteverde, Costa Rica, and suggested that cloud forest ecology changes have been driven by natural variability in the local climate (in particular, extreme dry periods associated with El Niño weather patterns) rather than by anthropogenic climate forcing.

The Golden Toad is a fossorial species, which remains hidden underground throughout the year, emerging only for a short breeding season. During the onset of the wet season (March to June), B. periglenes breeds explosively in shallow pools or depressions (depth up to 0.1 m), particularly those formed by tree roots (Jacobson and Vandenberg 1991). They are gregarious during breeding, and because of a heavily male-biased sex ratio, females become a limiting resource. Intense male agonistic behavior has been observed, both between lone males and against pairs in amplexus (Jacobson and Vandenberg 1991). However, competition seems to manifest mainly as scramble competition for females, as attacking pairs in amplexus seemed to have little effect and no female choice seems to be operating (Jacobson and Vandenberg 1991). Females deposit two to four hundred large eggs at a time, and tadpoles require five weeks to metamorphose (Crump et al. 1992). It has been noted that a prolonged time may be taken for mating, as one pair remained in amplexus 25 hours after their initial marking (Jacobson and Vandenberg 1991). Jacobson and Vandenberg (1991) describe two call types, one as a release call (usually in combination with body vibrations) and characterized as a low intensity trill, and another which was not linked to any physical interactions (only one male issued the call while in amplexus). Records and personal observations of B. periglenes document its abundance from 1971 to 1987, after which it abruptly disappeared (with 1,500 individuals recorded in 1987, five individuals found in 1988 and one in 1989; Pounds and Crump 1994), and it has not been seen since (Pounds et al. 1997).

The golden toad is most important to the scientific world. They give us the opportunity to study rare and beautiful species up close and personal. They also strengthen the scientific community's resolution to find out why amphibians are decreasing globally.

The golden toad is an extreme example of a sexually dimorphic amphibian. The males possess a very striking orange coloration. The females are black with scarlet blotches edged in yellow. The females range in length from 42 -- 56 mm while the males are 39 -- 48 mm. The striking physical differences between male and female cannot be determined until adulthood. Juveniles tend to be unsexable since they carry similar characteristics and body size (Jacobson, 1991).

Other Physical Features: ectothermic ; bilateral symmetry

The golden toad occupies a wet, montane area of the forest in northern Costa Rica. The elevation of this habitat ranges from 2000 -- 2100 meters (Jacobson, 1991).

The golden toad once occupied a small area of 4 km2 of elfin cloud forest on the Cordillera de Tilaran in northern Costa Rica. This area is now known as the Monteverde Cloud Forest Preserve (Pounds, 1996).

There are little information regarding this species' food habits since they have been primarily observed during the breeding season and live very secretive lives within the forests. Judging by size, many would agree that they feed on smaller invertebrates (Jacobson, 1991).

Development - Life Cycle: metamorphosis

Unfortunately, the golden toad is a reproductively vulnerable species. They are classified as having a "narrow window of time" in order to breed. During the rainy season, just the right amount of rain must fall in order to have a successful year. If the rains are too heavy, the larva might flow onto the forest floor and be stranded. However, if the rains are too light, the larvae will desiccate. During 1987, there was a major population crash in the golden toads. Due to erratic weather, the pools dried up before the larva had matured. Out of potential 30,000 toads, only 29 had survived. Since then, only a few scattered individuals had been found up until 1991 when no toads were reported. Finding out why this happened is a mystery. Some say that global warming caused the erratic weather that destroyed the reproductive efforts of the golden toad. Others say it was deforestation around the preserve that killed many of the adults when they left the reproductive area. Finally, some say that the toads are simply hiding out until the conditions are right to reproduce. Overall, no one can say for sure and only time will tell. Until then, their reproductive area is still protected if and when they return (Harding, 1993).

IUCN Red List of Threatened Species: extinct

The golden toad appears to use visual rather than vocal recognition used by most other toads. It only gives two types of calls, the release call and another call given by a male in amplexus. The frequency and duration of these calls could only be heard over a few meters. The calls could not even be heard on rainy days. It is suggested that the bright coloration and diurnal activities of this toad facilitated visual rather than acoustical identification (Jacobson, 1991).

The golden toad is an explosive breeder during the months of April through June in which there is a heavy rainy season. The toads gather in enormous numbers around small, temporary pools and other water-filled depressions that are located within the forest. During this time, the competition between males for females is quite fierce. The males generally outnumber the females by an 8:1 ratio. It is at this time that males will mate with almost any moving object and molest other pairs that were in amplexus. Males also exhibited a behavior known as "toad balls" in which 4-10 males would clasp each other. However, a successful mating would produce around 200 to 400 eggs. The large diameter of the eggs is around 3.0 mm (Jacobson, 1991) The larval forms are all unsexable because of the same size and color. They remain in the pool and take up to 5 weeks to metamorphose (Harding, 1993).

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)

Very little is known of the natural history of this species (2). It is active in the day, and breeding is confined to a short space of time between April and June during the rainy season (2). Huge numbers of golden toads once gathered at temporary pools of water, and as the males outnumbered females by 8:1, competition for females was fierce. Once a male forms a bond with a female, the pair are said to be in 'amplexus'; the male clasps the female tightly with his forearms around her back until they mate. During this time the male may face harassment from non-paired males trying to gain access to the female (2). Females produce 200 to 400 eggs, after hatching the larvae remain in the pool for about five weeks before metamorphosis into the terrestrial form occurs. It is thought that this toad feeds on small invertebrates, and may live underground at certain times of the year (2).

The probable extinction of the golden toad reflects the current worldwide decline in amphibian populations. The more subtle effects of human activities on the world's ecosystems such as the build-up of pollutants, the decrease in atmospheric ozone, and changing weather patterns are beginning to take their toll. Amphibians may be our first and only early warning that these effects are starting to reach catastrophic levels (6), and may be the first sign of impending ecosystem crashes (7). In 1991, the Species Survival Commission of the IUCN established the Declining Amphibian Populations Task Force (DAPTF), which later merged into the Amphibian Specialist Group, which aims to raise money and promote research into the global amphibian decline (6).

The golden toad has not been seen since 1989, and is believed to be extinct (1). This toad displays extreme sexual dimorphism; males are a brilliant orange colour but females are dark and mottled with yellow-edged red blotches. Females also tend to be slightly larger than males. In juveniles, however, the sexes cannot be determined as they are very similar (2).

The golden toad inhabits wet montane forest at 2,000 to 2,100 metres above sea level (2).

This species was known from a small area of undisturbed montane cloud forest in northern Costa Rica, Central America. This region has been designated as the Monteverde Cloud Forest Reserve (2).

Classified as Extinct (EX) on the IUCN Red List (1), and listed on Appendix I of CITES (3).

The population of golden toads underwent a massive crash in 1987 (2). A few individuals were found up until 1989, but the species has not been seen since then (2). Twenty out of 50 species of frogs and toads (anurans) occurring within a 30 kilometres squared area in Monteverde disappeared after synchronous population crashes in 1987, and have shown no sign of recovery (4). The area is pristine and free of direct human influences (5), a number of reasons have been proposed to explain the decline, including fungal disease, and climatic changes (4) (7).