A REVIEW OF THE GENUS MINYOBATES

Ángela M. Suárez-Mayorga

The poison frog genus Minyobates was first described by Myers (1987) to clarify in part the taxonomic arrangement of Silverstone (1975, 1976) for the aposematic Dendrobatids. Notable characteristics, according the original description, can be summarized as follows:

1 Absence of alkaloids of the histrionicotoxin or 3,5 disubstituted indolizidine classes

2 Very small size: 12 - 19.5mm Snout vent length (SVL) 

3 Finger discs expanded 

4 Tadpoles with oral disc laterally indented, 2/3 teeth rows 

5 Cephalic amplexus 

6 Tadpoles deposited in leaf axils or bromeliads

Of these characteristics, none are exclusive to Minyobates, but are shared as follows:

Characteristics 1 and 5 are present in Colostethus. It is possible that characteristic 1 in Minyobates is due to synapomorphic loss instead of plesiomorphic absence (Myers et al., 1995). At least one species of Minyobates does not show cephalic amplexus (Suarez Mayorga, in prep.).

Characteristics 2 and 3 are shared with some Dendrobates and the remaining characters are present in many other groups of frogs, so careful consideration should be given when considering this genus.

At present, nine species have been described, all of them from northern South America and adjacent Central America. A further two Colombian species remain undescribed with another now being described (J. Lynch, pers. com.). Five of those species are restricted to relatively small areas, basically in the Andes of Colombia while only two are strictly non-Colombian (Ecuador and Venezuela). Since 1992, all the species included in Minyobates are listed in CITES Appendix II, but at this time this is being re-evaluated. Because we know little about this interesting group of frogs, here I want to present an overview of the species, mainly based on published information:

Minyobates abditus (Myers & Daly, 1976) 
Known only from the type locality, on the Amazonian side of the Andes in Ecuador at 1700m elevation. The habitat seems to be related to preserved montane forest, described by the original authors as Lower Montane Rain Forest. It could be distinguished from all the other Minyobates by their dark colour above and below with only axilar and inguinal orange markings.

Minyobates altobueyensis (Silverstone, 1975) 
[Golden poison arrow frog] 
Restricted to the top of Serrania del Baudó, Chocó, Colombia, near 1000m above sea level. It lives in secondary forest with an abundance of aroids and ferns. It is easily separated by its bright yellow overall colour, mottled with black on the dorsum. From Silverstone's description, tadpoles seem to be released individually in aroid axils.

Minyobates bombetes (Myers & Daly, 1980) 
[Rubí poison-arrow frog] 
Lives in patches of preserved forest, between 1300 and 2000m on the Cordillera Central and Cordillera Occidental of Colombia. Besides this montane distribution it is reported on the Pacific side of Cordillera Occidental, in a very arid zone known as Cañón del Dagua. It is the only species with dorso-lateral red stripes over a black or dark brown dorsum. As in M. altobueyensis, tadpoles are deposited into individual axils (tanks), especially of epiphytic bromeliads. Males display an elaborate courtship that ends in a prolonged mating similar to that of some Dendrobates of the quinquevittatus group (personal observation).

Minyobates fulguritus (Silverstone, 1975) 
[Yellow-bellied poison-arrow frog] 
This ranges from Panamá to middle Valle del Cauca on the Pacific coast of Colombia, mainly in the Holdridge's Tropical Wet Forest (sensu Silverstone, 1975). It's a very small species, adults attaining a maximum of 16.5 mm SVL. The dorsum is black with dorso-lateral and oblique lateral metallic green lines, the ventor yellow-green and sometimes spotted with black. A clutch of three developing eggs was observed and tadpoles were simultaneously carried on the male's back. (personal observations).

Minyobates minutus (Shreve, 1935) 
[Blue-bellied poison-arrow frog] 
Widely distributed from central Panamá to the south of the pacific coast of Colombia, up to 1100m. It is often found on the leaf litter in association with dense forest. The species can be recognized by its chocolate dorsum with orange dorso-lateral stripes/mottled and dark ventor. In spite of their small size (up to 15.5 mm SVL), females of this species can contain 1 or 2 eggs in each ovary, each one of 3 to 4 mm diameter (Silverstone, 1975).

Minyobates opisthomelas (Boulenger, 1899) 
[Andean poison arrow frog] 
Occupies forests on the north of Cordillera Occidental and Cordillera Central in Colombia, at 1100 - 2200m. According to Silverstone (1975) the species could be found only in forest enclaves where bromeliads are abundant. Under this name more than one species could be identified (J. Lynch, per. com.). The dorsum is entirely red and the ventor is usually brown, sometimes spotted with red.

Minyobates steyemarki (Rivero, 1971) 
[Demonic poison-arrow frog] 
Restricted to Cerro Yapacana, Venezuela, on the Amazonian side of the Andes (1200m). This site was described to be "messy and irregular" by the original collector. It' s the only species with an entire purple-red coloration. Presence of cephalic amplexus is reported for this species and, based on it, Myers (1987) proposed this character to diagnose Minyobates.

Minyobates viridis (Myers & Daly, 1976) 
[Green poison-arrow frog] 
Widely distributed along the south-western flank of the Cordillera Occidental in Colombia, from 100 to 1200m elevation. The majority of collected specimens were found in montane forest, but the species is present in lowland forest and disturbed areas (Myers & Daly, 1976). Is a very small green Minyobates, which separates it from all the other species.

Minyobates virolinensis (Ruiz & Ramirez, 1992) 
[Red poison arrow frog] 
One of the few species of Minyobates found on the eastern slopes of the Andes, only in Colombia. It is always associated with primary moist forest. This species is very similar to M. opisthomelas in colouration, habitat, and behaviour. Larvae are deposited in terrestrial or epiphytic plants, with tanks usually containing more than one tadpole.

Ángela M. Suárez-Mayorga Biologist. Amphibian Lab, Instituto de Ciencias Naturales, Universidad Nacional de Colombia, A.A. 7495, Santafé de Bogotá, Colombia.

The author would like to thank John Lynch for his assistance and review of this paper.

The above article first appeared in Swedish in Pilgiftaren, the Newsletter of the Swedish Dendrobatid Group.