AMPHIBIAWEB
Aubria subsigillata
family: Pyxicephalidae
subfamily: Pyxicephalinae

© 2011 Greg F.M. Jongsma (1 of 8)
Conservation Status (definitions)
IUCN (Red List) Status Least Concern (LC)
CITES
Other International Status None
National Status None
Regional Status None

Country distribution from AmphibiaWeb's database: Cameroon, Congo, Congo, the Democratic Republic of the, Gabon, Ghana

 

View distribution map using BerkeleyMapper.

   

From the Encyclopedia of Life account:

Etymology

Auguste Duméril, who first described the species as Rana subsigillata in 1856, called it “Grenouille tachetée en dessous,” or “Frog with the speckled underside.” The specific epithet subsigillata comes from Latin sub, under, and sigillatus, ornamented with small marks (Ohler and Kazadi 1990).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Taxonomic Notes

There is still some dispute about whether Aubria subsigillata and Aubria occidentalis comprise one or multiple species (Perret 1994, Ohler 1996, Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Summary

Aubria subsigillata is a large, stocky frog with a dark brown back and a relatively small but visible tympanum. The underside is speckled white over a brown background, although in older individuals the throat may be almost entirely white while only the posterior portion of the underside retains the speckled pattern. Distinct yellow-brown glands are present on the underside of the thigh at the midpoint of the femur in all individuals, even juveniles and sub-adults. Snout-vent length is 65-95 mm and females are typically significantly larger than males. It is generally difficult to tell the sexes apart, though, as male secondary sex characteristics such as vocal sacs and nuptial pads are absent. However, compared with males, females may have relatively shorter eyes, and femoral glands closer to the base of the thigh.


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Distribution

Aubria subsigillata ranges from southwestern Cameroon through mainland Equatorial Guinea to southwestern Gabon. It occurs on the island of Bioko (Equatorial Guinea) (Amiet et al. 2004). Jackson et al. (2007) have collected A. subsigillata as far east as the northeastern part of the Republic of the Congo. The contact zone between this species and the more recently described Aubria masako and A. occidentalis is poorly understood and requires further investigation. It is possible that this species ranges as far west as Nigeria. An old record from Angola is shown by Perret (1996) to belong to a very different, undescribed species (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Osteology

The osteology of the skull has been thoroughly described by Procter (1919). The skull is “strongly ossified, rather depressed, and broader than long, the general shape being typically frog-like. The interorbital portion of the brain-case is slender. Seen in profile, the cranium slopes upwards from the nasal region to a point in line with the posterior orbital borders, from which there is an abrupt decline to the foramen magnum."

In terms of membrane bones, “The nasals are large, well-developed triangular bones, and somewhat rugose. They meet each other in the median line almost throughout their length, which is nearly two-thirds that of the fronto-parietals. Anteriorly each is obtusely pointed; posteriorly they form short oblique sutures with the anterior borders of the fronto-parietals, exposing in the centre a minute diamond shaped area of the ethmoid. The distal ends do not reach the maxilla proper, although they rest upon the maxillary processes in conjunction with the palatine cartilages. The vomers are oblique, presenting an acute angle backwards and inwards, where they approach the proximal ends of the palatines, and the parasphenoid. Anteriorly they are deeply notched, the anterior processes reaching the maxillae. These bones overlie the subnasal laminae and the adjoining border of the ethmoid. The vomerine teeth are arranged in a simple line of four, springing from a prominent ridge on the outer oblique edge of each bone. The fronto-parietals are strongly ossified, and somewhat rugose on the anterior surface. The sagittal suture commences almost at their anterior extremities, but does not persist beyond a third of their length. Their combined width, anteriorly, is about a quarter of their length. At the postero-inner corner of the orbit they form small sharp projections, and then reach double the width. Posteriorly there is a slight sagittal crest, with two oblique lateral wings which form the commencement of the mastoid processes. The parasphenoid is of the usual dagger shape, but rather more shapely than that of [Rana] temporaria, and has an extremely tapering point. The lateral limbs of this bone are partially hidden beneath the superimposed inner limbs of the pterygoids."

As for cartilage-replacement bones, “the ethmoid, as compared to that of [Rana] temporaria, is elongated…[up to] almost one-half the length of the entire skull. Anteriorly it is trilobate, or fleur-de-lys-shaped; dorsally this portion is overlain by the nasals, and ventrally the central lobe is partially obscured by the vomers and the proximal ends of the palatines. The main tubular portion of this bone, which reaches almost to the optic foramen, is covered by the fronto-parietals, but is visible on the ventral side through the semi-transparent parasphenoid. As already stated, only a minute diamond-shaped area of the ethmoid is exposed to view on the dorsal surface, where it is bounded by the postero-median notch between the nasals anteriorly, and by the antero-median notch between the fronto-parietals posteriorly. In the antero-inner corner of the orbit the ethmoid is pierced on each side by a small foramen for the orbito-nasal nerve."

"The prootics. – The dorsal surface of each is largely covered by the inner branch of the squamosal, and its inner borders underlie the fronto-parietals. In the anterior wall below the flange of the fronto-parietals is the foramen for the fifth and seventh cranial nerves. The prootic forms the roof and anterior wall of the auditory capsule. The exoccipitals meet each other in the median line both dorsally and ventrally. The prootic-exoccipital suture proceeds along the crest of the mastoid process; the fronto-parietal-exoccipital suture is difficult to trace. Ventrally the anterior borders of these bones are bounded by the parasphenoid. The exoccipital condyles are well developed, and are visible from three aspects; at the base of each are two foramina, the upper minute and the lower larger and internally divided; these give exit to the ninth and tenth cranial nerves. The nasal cartilages consist of a roundly-pointed nasal roof above and a trifid sub-nasal lamina below. Small triangular praerhinals are attached to the septum nasi. The palatine cartilages extend from the ethmoid to the maxillae, and are not peculiar in any way. Owing to the thickness of the fronto-parietals and the extreme delicacy of the chondrocranium, I have not satisfied myself as to the size and exact positions of the fontanelles. It is clear, however, that there is a large median fontanelle, the anterior portion of which is bordered by the ethmoid, which at this point has a slightly bilobular tongue-shaped area carved out of it. The posterior wall of the otic capsule is cartilaginous; it is bounded by the parasphenoid below and by the prootic above. The columella auris is strongly developed. The inter- and medio-stapedial portions are not unusual in any way; the extra-stapedial section is strongly developed and has a fan-shaped terminal of considerable size, which is applied in an inverted position to the tympanic membrane. The squamosal, at the junction of the interior limb with its stem, forms a deep arch over this delicate cartilage, and also gives support to the annulus tympanicus, which is somewhat funnel-shaped, broader than deep, and slightly notched above."

As for the maxillary arch, “the palatines are straight, semi-transparent bones, placed at right angles to the axis of the skull. They do not meet each other. The squamosals differ widely from those of Rana (sensu stricto). They are enormously developed. The zygomatic branch, slightly rugose, forms a suture with the maxilla which is prolonged forward to the naso-palatine bar. This process tapers considerably at its anterior end, and is about half the length of the entire skull [processes measured from their junction with the shaft of the bone, not from the right angle from where they join each other]; the suture is about four-fifths of this length. The inner limb, just over one-third the length of the zygomatic, with which it forms a right angle, is superimposed on the prootic, of which but a small border is exposed on each side. The posterior limb, or stem, of this bone is somewhat oblique, flat, and rounded at its distal end; it is applied to the pterygoid and the quadrate cartilage. The pterygoids are the most remarkable bones in the skull. The inner processes overlap the lateral processes of the parasphenoid almost to their junction with the blade-like portion. At the junction of the anterior and posterior limbs, and opposite the root of the interior limb, is a large rounded process, which, when the skull is in its natural position, is directed outwards and downwards; when the jaws are closed the outer face of this process is presented to the coronary process of the angulo-splenial, which it resembles in size and shape. This process seems to be very rare in the Anura, and until now has remained unnoticed. The quadrate cartilage projects in two strong condyles, well beyond the extremities of the pterygoid, squamosal, and quadratojugal bones. It is of massive build, and in the specimen figured strongly ossified. The praemaxillae have rather long processes. Ventrally, at the suture which they form with each other, there is a shallow oval pit. The maxillae are wide, strong, and slightly rugose. Ventrally, and close to the sutures which they form with the praemaxillae, are round shallow concavities. Posteriorly each is slightly bifid, the inner border of the inner limb completing the squamoso-maxillary suture, and the outer and longer branch forming a wedge-shaped suture with the quadrato-jugal. The quadrato-jugal is a small short bone; its suture with the maxilla is very difficult to trace in old specimens."

As for the mandibular arch, “Meckel’s cartilage, where it articulates with the quadrate, ends in a prominent down-curved knob. The angulo-splenial leaves much of Meckel’s cartilage exposed to view; its coronary process is well developed, and, as before stated, lies face to face with the peculiarly similar process of the pterygoid, from which it is only separated by the elevator temporalis muscle. The dentary at its distal end is raised into a slight tooth-like projection, which, when the jaws are closed, fits into the shallow pit at the anterior end of the maxilla which I have already mentioned. The mento-meckelian bone forms a similar but larger projection which fits into the median pit situated across the praemaxillo-praemaxillary suture." Finally, “the hyoid apparatus, though differing slightly from that of [Rana] temporaria, is not peculiar in any way” (Procter 1919).

In summary, the most relevant features of the skull of Aubria subsigillata are its prolonged squamoso-maxillary suture, the fourth pterygoid process, and a pitted pattern on the nasals, the dorsal plane of the fronto-parietals, the zygomatic processes of the squamosals, and the maxillae. Some dermal bones also overlap markedly, in particular, “the interior branch of the pterygoid on the transverse limb of the parasphenoid,” “the interior limb of the squamosal on the prootic,” and “the nasals and fronto-parietals almost entirely obscuring the ethmoid” (Procter 1919).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Morphology

The original description by Duméril (1856) is incomplete, so the following section is adapted from a thorough redescription by Ohler and Kazadi (1990).

The holotype (specimen 1566 at the Muséum national d’Histoire naturelle, Paris) is an adult male with snout-vent length (SVL) 77.8 mm, collected in Gabon by Charles-Eugène Aubry-Lecomte.

Description of the holotype. – The head is longer (32.0 mm) than it is wide (28.4 mm). The snout is rounded and longer (13.7 mm) than the eye (9.5 mm), projecting in front of the buccal opening. The canthus rostralis is rounded and the loreal region is concave. The distance between the nostrils (5.9 mm) is greater than the interorbital distance (3.5 mm), which is less than half the width of the upper eyelid (7.3 mm). The nostrils are closer to the eye (7.4 mm) than the end of the snout (7.7 mm), with their openings somewhat rounded with two small dermal outgrowths on the external border. The tympanum is rounded, with diameter (4.9 mm) about half of the diameter of the eye (9.5 mm) and less than its distance to the eye (6.4 mm). The pineal ocellus is absent. Vomerine teeth are present at the level of the internal side of the choanae in two rows each containing four teeth. The angle between these rows is approximately 100° opening anteriorly, with the distance between their posterior ends equal to their length. Maxillary teeth are well developed. Three points at the end of the lower jaw correspond to cavities in the upper jaw. The tongue is oval and elongated, with a deep indentation in its free posterior part. A weak supratympanic fold runs from the eye to the shoulder. The forearm is slightly longer and wider than the rest of the arm. The fingers are robust, with digit II the shortest, digit I slightly longer than IV, and digit III the longest. The tips of the digits are rounded and not enlarged. There is a dermal crest on the internal edge of digits II and III. There is a terminal bead at the level of the distal joint in dorsal position on each digit. Sub-articular tubercles are rounded and moderately developed. Metacarpal tubercles are elongated. Just one elongated palmar tubercle is present but it is little developed.

The hind legs are short and robust. The heels do not touch when the thighs are placed at a right angle relative to the axis of the body. The leg (30.0 mm) is slightly shorter than the thigh (34.9 mm) or the foot, measured from the proximal edge of the internal metatarsal tubercle to the tip of toe IV (38.2 mm). Toe IV is the longest, with toe III longer than toe V. Toe tips are rounded but not enlarged. There is a terminal bead at the level of the distal joint in dorsal position on each toe. Webbing is moderately developed, up to the proximal edge of the distal sub-articular tubercle of toe IV, and curving in between toes III and IV and between toes IV and V midway between the proximal and intermediate sub-articular tubercles. There is no dermal fringe anywhere on the toes. Sub-articular tubercles are well developed and elongated. Internal metatarsal tubercles are short (2.4 mm) but very prominent, less than half the length of toe I (8.4 mm). There is no external metatarsal tubercle. There is a light tarsal fold from the metatarsal tubercle to the tibio-tarsal joint. The skin on the dorsal surface has miniscule roughnesses, but maintains a smooth aspect. The skin on the sides of the stomach is folded. There is no latero-dorsal fold. A round gland is present on each thigh at two-fifths of the distance between the anus and the knee, of diameter (5.2 mm) larger than that of the tympanum (4.9 mm). There is a heap of glandular cells under the base of each arm. No male secondary sex characteristics are visible.

The color of the dorsal surface is blackish brown, with the ventral surface dirty beige and grey-brown, with a regular design of light round spots on a dark network on the chest and belly. Under the thighs, the tibias, and the feet, there are lighter spots placed in a more irregular manner on a dark background, and there is no marked pattern on the throat.

Specimens determined to be Aubria subsigillata vary in the possession of sub-brachial glands that are not always prominent. Femoral glands are always distinct under the thighs, even in juveniles and sub-adults. A medio-dorsal line has never been observed in this species. The reticulated ventral design is usually very clear on adult specimens. Certain ventral regions can lack this design, but no marked relation between this phenomenon and the age or sex of specimens could be determined. The pineal ocellus is present in almost all specimens but it is absent in the holotype. The medial palmar tubercle, which is also absent in the holotype, is present in most specimens but it is often short and poorly developed.


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Size

This species is generally large. Adult males range in snout-vent length from 65.1-87.6 mm, and adult females are larger with snout-vent lengths of 76.0-95.0 mm (Ohler and Kazadi 1990). Two specimens at Harvard University's Museum of Comparative Zoology have snout-vent lengths of 82 mm and 66 mm (Dietterich, unpublished results).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Diagnostic Description

This is a large species (adult males: SVL 65.1-87.6 mm, n = 13; adult females: SVL 76.0-95.0 mm, n = 9). The distance from the nostrils to the end of the snout is short (64-88‰ of the SVL), and the distance between the nostrils is important (61-74‰ of the SVL). The diameter of the tympanum is relatively small (62-84‰ of the SVL). Round glands are present under the thighs in males, females, and juveniles. The back is uniformly brown without a medio-dorsal line. The throat, chest, and belly have round whitish spots surrounded by a dark brown network in specimens of varying sizes (Ohler and Kazadi 1990, translated/adapted by Dietterich (2010)), although this pattern may disappear from the throat area in adult specimens (Ohler 1996).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Comparisons

Aubria subsigillata can be differentiated from its close relative A. masako by the location of femoral glands, foot webbing, and skin coloration. In particular, the femoral glands of A. subsigillata are located midway between the knee and the cloaca on the ventral side of the thigh, whereas in A. masako they are closer to the knee and located more posteriorly. The feet of A. subsigillata are more webbed (I 1 – 2 II 1 – 2 III 1 – 2.5 IV 2.5 – 1 V) than those of A. masako (I 1½ - 2 II 1 – 2½ III 2 – 3 IV 2½ - 1 V). As for skin coloration, the dorsum of A. subsigillata is more uniformly colored than that of A. masako and lacks a mid-dorsal line; additionally, A. masako may have warts but the skin of A. subsigillata is smooth. Ventral coloration develops differently in the two species as well: the mottled pattern of A. subsigillata disappears first on the throat whereas in A. masako it disappears first on the vent (Ohler 1996).

The difference between Aubria subsigillata and A. occidentalis is harder to determine because there is still some disagreement about these species’ identities and the boundaries between them. Perret (1994) argues that they can be distinguished by the position of the femoral gland (in the middle of the femur in A. occidentalis, closer to the knee in A. subsigillata) and possibly by the sound of their calls, but Ohler (1996) claims they are the same species. Amiet (2004) agrees with Perret (1994) that A. occidentalis and A. subsigillata are different species, but does not specify how to differentiate them.


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Habitat and Ecology

It lives in swamps or along small streams in lowland rainforest, gallery forest and degraded secondary habitats (farm bush) in the forest zone. It breeds in still-water pools and marshes (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Associations

Aubria subsigillata is unusual among frogs in that its adult diet consists primarily of small fish, in particular Epiplatys that leap out of the water to escape predators or to look for different surroundings. They may also eat smaller amphibians and arthropods (Knoepffler 1976, Channing 2001, Rödel et al. 2005).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Population Biology

Little information is available on its abundance (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Activity and Special Behaviors

This species is nocturnal, becoming active from just after dark until approximately 1:00 a.m. During the day, it burrows down in the mud to depths of 50 cm or more, leaving inconspicuous holes (Knoepffler 1976).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Metamorphosis

Metamorphosis has not been thoroughly studied in this species, but it usually occurs when the tadpole is about 24 days old (Knoepffler 1976).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Advertisement Call

Males sing in swamps, floating on the surface of relatively deep regions. Their call is “a muffled cry like the sound of a timpani” (Perret 1966, translated by Dietterich 2010).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Reproduction

Since these frogs are nocturnal and burrow during the day, they are difficult to observe, but the eggs are numerous, laid in strings, and of the Bufo type (Knoepffler 1976). There is evidence that males might guard their tadpoles in the water but this has yet to be properly documented (Ohler and Kazadi 1990).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Tadpole morphology

Tadpoles are dark in color and frequently aggregate into ball-shaped schools (Knoepffler 1976). The tail (23 mm) is slightly longer than the body (16 mm). The keterodont rows formula is 2:4+4/3 (Ohler 1996). Schiøtz (1963) gave a more thorough description in Danish.


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Evolution

According to Ohler’s review of the genus Aubria (1996), Aubria subsigillata is sister to A. masako. The genus Aubria, in turn, is sister to Pyxicephalus in the subfamily Pyxicephalinae, which is sister to the subfamily Dicroglossinae. Ohler and Kazadi (1990) hypothesized that, since Pyxicephalus appears more derived than Aubria, it either evolved from Aubria, or otherwise Aubria evolved from it in via paedomorphosis. Ecological evidence suggests that Pyxicephalus was the more derived clade (Ohler and Kazadi 1990), but Ohler (1996) suggests that in fact Aubria is more derived than Pyxicephalus, which would imply some paedomorphic events in Aubria’s evolutionary history.


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

IUCN Red List Category and Justification of Conservation Status

The IUCN Red List (2004) categorizes this species as Least Concern in view of its relatively wide distribution, tolerance of a degree of habitat modification, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Trends

Populations of this species are believed to be stable (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Threats

It is an adaptable species that is not likely to be facing any significant threats (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/

Conservation Actions and Management

It presumably occurs in several protected areas (Amiet et al. 2004).


Author: Dietterich, Lee
License: http://creativecommons.org/licenses/by-nc/3.0/