Rose’s mountain toadlet

Rose's mountain toadlet

Derivation of scientific name

The first part of the genus name Capensibufo  refers to the Cape (capensi-), and the second part (–bufo) was taken from the former genus name Bufo, under which most southern African toads were originally placed before being split up into a number of different genera (none of the southern African toads are Bufo anymore). The species name rosei was given in honour of famous herpetologist, Walter Rose, who found and photographed some of the first known populations of this species.

Common names

Rose’s mountain toadlet, striped mountain toad, Rose’s mountain toad (Eng.); Rose-se-dwergskurwepadda (Afr.).

Introduction

Capensibufo rosei is part of the genus Capensibufo, or Cape mountain toads. This genus is only found in mountainous regions of the southwestern Cape. Rose’s mountain toadlet is endemic to Table Mountain National Park, and is the only known voiceless amphibian in southern Africa (cannot call or even hear). Although formally part of a larger species complex all known as Capensibufo rosei, recent genetic studies show that the mountain toadlets on the Cape Peninsula are a separate species from those found east of False Bay. The C. rosei on the peninsula has declined rapidly since the 1960s, and is currently known from only two populations.

How to recognise Rose’s mountain toadlet

Adult males are typically 18–24 mm in length, while the females are slightly larger, usually 23–26 mm (although historic populations on Table Mountain had larger individuals). The body is short and stocky. The eyes have a golden iris and horizontally elongated pupils.

Dorsal colour varies from a uniform charcoal with black spots, to more colourful individuals with three distinct light bands (one dorsal, and two dorsolateral) on a darker, spotted or blotchy background, with each mottle or spot sometimes outlined in gold. Many individuals also have bright red to brick-red or orange patches along their flanks and on their parotid glands, behind the eyes. Females are generally light in colour. Underneath, they are granular white with varied amounts of charcoal or grey mottling.

The tympanum is absent, and the parotid glands behind the eyes are prominent (and often red or orange in colour). If the animal is hurt, it may produce a toxin from its parotid glands. The skin texture is quite glandular or ‘warty’, but may seem smooth when wet.

Tadpoles are small (~10–20 mm) and uniformly dark grey in colour, with long, muscular tails compared to the body length. Eggs (~3 mm diameter) occur in strings of jelly, with constrictions in the jelly between individual eggs. The eggs and tadpoles generally occur in high densities in shallow, peaty puddles.

Getting around
This species generally does not hop like other toads, but ‘runs’ or crawls, using alternate left and right, back and front legs. It may hop suddenly from a stationary position to initiate an escape, but then continues to run afterwards, often in short bursts.

Rose's mountain toadlet

Communicating

Capensibufo rosei does not utter any mating calls or audible noises; neither can it hear sounds, as it has missing or reduced ear elements. It seems that breeding aggregations may form due to visual or perhaps chemical cues, though this is yet unknown.

Distribution

Rose’s mountain toadlets are only found in two populations, each with a very limited distribution, within Table Mountain National Park in the Western Cape of South Africa.

Habitat

Rose’s mountain toadlet occurs in sandy mountain fynbos heathland, from 60–1 600 m above sea level. They are found in moist or marshy patches, often characterised by a peaty substrate. They appear not to roam very widely, but remain within these marshy areas throughout most of the year. They are active throughout the year, during the day and probably also at night. However, much of their time is spent inside burrows a few centimetres underground (where they may be actively foraging), particularly during the dry season. These burrows are often dug by other animals, such as rodents or molerats.

C. rosei breeds in shallow puddles, in small clearings or among short restios. Although they usually breed inside the core marshy habitat, they may venture out onto clearings or paths to find a suitable breeding site, particularly if their habitat is too heavily vegetated. They have been found breeding on hiking paths, inside animal tracks and even on roads, up to 30 m outside their core marshy habitat.

Food

Capensibufo rosei is a generalist predator, and feeds on insects, spiders and worms. They forage for prey amongst the peat and vegetation in damp areas, and may also forage underground in rodent or molerat burrows.

SEX and LIFE CYCLES
Sex:

Breeding occurs from late July to August, sometimes until early September during high rainfall years. Males form dense breeding aggregations in small, ephemeral puddles with a peaty substrate. Hundreds of males can aggregate in a single puddle during breeding. Females enter the breeding puddles only to lay her eggs, which are externally fertilised by males, then leave the breeding puddle as soon as spawning is completed. Many males may try to enter in amplexus with a female simultaneously, which sometimes results in her drowning.

Each female lays around 100 large eggs (3–4 mm in diameter) in one continuous string of jelly. The jelly is thick around each individual egg, and thin in between eggs. At the end of breeding, the breeding puddles may contain so many eggs that the egg mass protrudes above the water surface. The tadpoles hatch in a matter of weeks, and the breeding puddle soon becomes a thick mass of dark, wriggling tadpoles. If the puddle is larger or there are fewer tadpoles in it, the tadpoles will often form a dense swarm or cluster along the edge of the puddle.

Metamorphosis is usually complete within 7–9 weeks, and the tiny, 4 mm long juvenile toadlets will spend some time in the moist soil around the breeding puddle before dispersing into the surrounding vegetation. Juveniles appear to take two years before reaching sexual maturity. Adult longevity is not known, but some evidence suggests that Rose’s mountain toadlets may live up to ten years.

Rose's mountain toadlet

Family life

Rose’s mountain toadlets are most likely not highly social animals, though they may live in high densities. They probably spend most of the year foraging solo. Interactions between individuals outside of the breeding season are not known, although much intra-sexual competition takes place between males at the breeding site. Furthermore, tadpoles and metamorphs will often swarm together whilst inside the breeding puddle.

THE BIG PICTURE

Friends and Foes

Although reptiles, rodents, small birds and even spiders or centipedes may compete for food and resources with Capensibufo rosei (as they too feed on insects), its closest competitors are probably other amphibians. However, because C. rosei appears to be the most common amphibian where it is found, intraspecific competition is probably more prevalent than competition with other animals.

Rodents and other burrowing animals provide C. rosei with shelter and a hidden foraging habitat. Hence co-existing with these species may be essential to its survival.

Not many animals are known to prey on C. rosei, although the eggs, tadpoles and young metamorphs may occasionally be eaten by mongoose, and even by ants! Likely candidates for natural enemies include snakes, birds, mongoose, centipedes, rodents or even larger amphibians, such as the Cape river frog, which has been known to eat smaller frogs. However, it appears that predator-induced mortality is very low in this species, while energy expensive breeding costs is most likely the main cause of death, particularly in high rainfall years when the breeding season is extended.

Smart Strategies

Rose’s mountain toadlets opportunistically use burrows and tunnels dug by other animals, such as rodents, to hide from predators and gain shelter during hot, dry conditions. They also shelter inside these burrows during a fire, and are hence well-adapted to survive even the hottest dry-season fires in the fynbos. Furthermore, these burrows may be a perfect underground foraging habitat for them.

When hurt and threatened, Rose’s mountain toadlets produce a toxin from their parotid glands, which may act as a fierce predator deterrent. This is most likely why predation pressure on this species seems to be so low.

They are also very successful breeders, providing their tadpoles with a lot of yolk in order to develop fast before the puddles dry up, despite living in a nutrient-poor system with little food for tadpoles.

Poorer world without me

Like many other amphibians, this species is a ferocious insect predator, and contributes by reducing pest and disease vector populations substantially. Amphibians in general are also a very important prey species for many other animals, such as birds, mammals and snakes, although Rose’s mountain toadlets may largely avoid being eaten with their chemical defences.

Rose’s mountain toadlet is a valuable species in and of itself. It is not only rare, beautiful and endemic, but it is biologically unique because it is one of the world’s few voiceless frog species, and the only one in southern Africa.

Rose's mountain toadlet

People & I

To our knowledge, people have not had many interactions with Rose’s mountain toadlets. They are not dangerous to man, and are not utilised as a resource, although many adults were collected and sold as museum specimens in the 1900s.

Conservation status and what the future holds

Capensibufo rosei is currently listed as Vulnerable on the IUCN Red List, with the listed threats including infestation by alien vegetation and urbanisation. However, this species listing currently includes the former Capensibufo rosei east of False Bay, which no longer form part of the species C. rosei. Once the taxonomy of the former C. rosei species complex is formalised, it is likely that the Capensibufo rosei on the Peninsula will be listed as Critically Endangered, because of the rapid reduction in subpopulations over recent decades, with only two current subpopulations known for the species.

Rose’s mountain toadlets are currently protected by various stakeholders. Their habitat is protected by SANParks, and the two known subpopulations are being monitored by SANBI to ensure their continued survival, and to understand drivers of population success (or failure). Public access to areas where they breed is restricted during the breeding season, to prevent human disturbance of the short-lived and fragile breeding aggregations, eggs and tadpoles.

It is currently thought that a lack of regular enough fires and grazing animals, which both cause disturbance in the vegetation, may the primary driver of their decline. The toadlets need this kind of disturbance to form the clearings in which they breed – otherwise the habitat becomes too heavily bush-encroached to breed in. In the absence of such disturbances or clearings, these toads have had to rely on hiking paths or even roads, to find suitable clearings to breed in.

Public support for planned management fires within Table Mountain National Park is sorely needed, as many areas are far behind the 13–18 year fire schedule that is necessary to maintain a healthy fynbos ecosystem. A lack of planned management fires also causes a build-up of fuel load, which increases the risk of widespread fires that can burn out of control, such as the recent fires experienced across large parts of the park in 2015.

Rose's mountain toadlet

Relatives

Currently, there are only two species in the genus Capensibufo, namely Rose’s mountain toadlet (C. rosei) and Tradouw’s mountain toadlet (C. tradouwi). However, after recent phylogenetic work, each of these will be split into a number of species and subspecies.

For all those who wonder what the difference between frogs and toads are, let me clear it up: toads are only one family, Bufonidae, within the larger order of frogs (Order: Anura). Other members of the family Bufonidae in South Africa are the typical toads, Amietophrynus; the pygmy toads, Pyontinophrynus; Van Dijk’s toads, Vandijkophrynus; and the monotypic red toad, Schismaderma (carens is the only species in this genus). Toads generally have short legs and rough, thick skins, while frogs generally have longer legs and smooth skins covered in mucus.

References and further reading

  • Becker, F.S. 2014. Searching for answers to a silent decline: first estimates of survival and recruitment for the Critically Endangered Rose’s mountain toadlet, Capensibufo rosei. University of Cape Town (unpubl.).
  • Cressey, E.R., Measey, G.J. & Tolley, K.A. 2014. Fading out of view: the enigmatic decline of Rose’s mountain toad, Capensibufo rosei. Oryx: 1–8.
  • Du Preez, L.H., Carruthers, V. & Burger, M. 2009. A complete guide to the frogs of southern Africa. Struik Nature, Cape Town.
  • Measey, G.J. 2011. Ensuring a future for South Africa’s frogs: a strategy for conservation research. SANBI Biodiversity Series 19: 1–92. South African National Biodiversity Institute, Pretoria.
  • Tolley, K.A., De Villiers, A.L., Cherry, M.I. & Measey, G.J. 2010. Isolation and high genetic diversity in dwarf mountain toads (Capensibufo) from South Africa. Biological Journal of the Linnean Society 100: 822–834.

Author

Francois Becker

SANBI – Molecular Ecology

December 2015

Official Common Name

Rose’s mountain toadlet

Scientific Name and Classification:

Kingdom

Animalia

Class

Amphibia

Order

Anura

Family

Bufonidae

Genus

Capensibufo

Species

C. rosei (Hewitt, 1926)

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