Bruno's Casque-Headed Frog
© 2010 Mauro Teixeira Jr (1 of 2)
When the limbs are adpressed towards each other along the body, the elbow and the knee are widely separated. There are no dermal ridges on the arms. The hands have a rudimentary pollex that appears as a blunt, semicircular projection from the first finger. The fingers barely have any webbing. Finger two is much shorter than the fourth finger and the third finger is longer than the fourth by one-disc length. The disc of the third finger is two-thirds the diameter of the tympanum. The fingers have distinct subarticular tubercles (Cochran 1955).
When the hindlimb is adpressed to the body, the heel reaches the anterior edge of the eye. When the hindlimbs are held at right angles to the body, the heels slightly overlap. There are no dermal ridges on the heel or foot. There is a long, blunt inner metatarsal tubercle and a very small outer metatarsal tubercle. The toes are one-fourth webbed. The third toe and the fifth toe are about equal in length. The disc on the fourth toe is about half the diameter of the tympanum. The toes have distinct subarticular tubercles (Cochran 1955).
The body is elongated but stocky. Except for the labia and canthus rostralis, the skin on the head is smooth. The skin is also smooth on the dorsal surface of the body and limbs and nearly as smooth on the throat, chest and sides of the body. The belly and the femur, unlike the rest of the underside area, appear to have a granular texture. There are no skin folds on the chest but there are a pair of lateral vocal sac (Cochran 1955) or a single or paired subgular vocal sacs (Pimental et al. 2009).
At Gosner stages between 32 – 41, tadpole bodies appear triangular from the lateral view and oval in dorsal and ventral views. The tadpoles are large; a single individual at stage 32 measured 35.3 mm in total length and 11.2 mm in body length, individuals in stage 36, 37, 38, and 40 have mean total lengths of 49.0 ± 5.3, 50.6 ± 4.1, 55.5 ± 4.2, and 63.2 ± 9.2 respectively, and body lengths of 14.3 ± 0.2, 16.1 ± 0.8, 17.4 ± 0.5, and 18.9 ± 0.5 (approximately 30% of their total length). Their maximum body height is approximately before the beginning of the dorsal fin. Their greatest body width is at the level of spiracle. The body is 1.7 times higher than wide. In the lateral view, the snout protrudes, but in the dorsal view it is truncated. The nostrils are oval shaped, dorsolaterally located, and nearer to the eyes than to the snout. The nostril openings are anterolaterally directed, marked with a somewhat prominent marginal rim, and the surrounding surface is countersunk. The tadpole’s eyes are on the sides of its head and are located above the midline of the body. The interorbital distance is wider than the internarial distance. They have a single spiracle that is short, sinistral, and positioned at the middle third and below the midline of the body. The tadpole’s body is 2.5 times wider than the oral disc. The oral disc is anteroventral, oval, and has non-emarginated marginal papillae surround most of the oral disc, except for a wide gap at the upper labium. On the upper labium, the papillae are uni- to biserial and on the lower labium they are bi- to triserial. There are scattered submarginal protuberances on the lateral and anterolateral sections, some of them with tooth rows. The labial tooth row formula is 2(2)/5-6(1) with 6 lower tooth rows being more common. The sixth posterior tooth row is moderately fragmented. The jaw sheaths are serrated with the upper jaw appearing extended, slender, and arched, while the lower jaw is narrow. The jaws form a V-open shape. The spiracle’s opening is directed upward and backward. The inner wall of the spiracle appears present as a small ridge. The anal tube is located medially and is connected to the ventral fin by a tiny web. The tail’s caudal musculature narrows off to a sharp flagellum-like tip. The height of the tail is about 4.6 mm higher than body height. The dorsal fin is slightly higher than the ventral fin (0.5 mm). The dorsal fin begins at the middle third of the body. Both of the fins are arched with the maximum caudal height on the anterior third of the tail and have an outline that appears rippled (Wogel et al. 2006).
From other genera of southeast Brazil, adult members of Aparasphenodon can be distinguished from Gastrotheca and Flectonotus by the former lacking a pouch. The lack of opposable fingers and toes differentiates Aparasphenodon from Phyllomedusa. The lack of parasphenoid teeth distinguish Aparasphenodon from Phyllodytes. The bony co-ossified skull with an elongated head distinguishes the focal genus from Hyla and Trachychephalus respectively (Cochran 1955).
Unlike other members of the genus Aparasphenodon, A. brunoi is venomous. The frog produces toxins through skin secretions and injects them from small spines protruding from the skull. A similar species, Corythomantis greening (Greening’s Frog), is also venomous, but lacks the irregular dark brown patches found on the body of A. brunoi (Jared et al. 2015). Morphological differences between adult A. brunoi and other members of Aparasphenodon include a straight, prominent, and elevated canthus rostralis that distinguishes it from A. arapapa, A. pomba, and A. venezolanus; a deeply concave loreal region that distinguishes it from A. arapapa and A. pomba; a prenasal bone that distinguishes it from A. pomba; and a brown to dark red iris that distinguishes it from the dark brown of A. bokermanni, bright red of A. pomba, and grayish with dark vermiculations of A. venzolanus (Pimental et al. 2009, Assis et al. 2013). Additionally, the spotted dorsal patterning in A. brunoi distinguishes it from the uniform dorsal coloration in A. arapapa and A. bokermmani and the reticulated patterning of A. pomba (Cochran 1955, Pimental et al. 2009, Assis et al. 2013). And lastly, the nuptial pads in A. venzolanus have multiple dark-colored projections that are distinctly different from A. brunoi (Blotto et al. 2020).
In 2006, there were only three species of Aparasphenodon: A. bokermanni, A. brunoi, and A. venezolanus. At that time, tadpoles of A. bokermanni and A. venezolanus were not known (Wogel et al. 2006). When A. arapapa and A. pomba were described in 2009 and 2013 respectively, their tadpoles were also unknown (Pimental et al. 2009, Assis et al. 2013). However, Lourenço-de-Moraes et al. (2013) later described and compared A. arapapa larvae with A. brunoi, finding that A. brunoi has a larger size at Gosner stage 40 (63.2 mm vs. 49.9 mm), laterally arranged eyes, antroventral oral disc (vs. dorsal), fewer lower labial tooth rows (2 vs. 5 - 6), a triserial lower lip (vs. uniserial), and a diagnostic tail flagellum.
From other casque-headed treefrog genera (Argenteohyla siemersi siemersi, A.s. pedersoni, Osteocephalus buckleyi, O. elkejungingerae, O. taurinus, O. verruciger, Trachycephalus jordani, and T. nigromaculatus) at Gosner stage 40, A. brunoi is markedly larger. Trachycephalus jordani has a larger total tail height, however, A. brunoi has a larger mean tail musculature and dorsal fin height. The anteroventrally positioned oral disc in A. brunoi distinguishes it from the ventrally positioned discs in Ar. s. siemersi, Ar.s. pedersoni, O. buckleyi, O. elkejungingerae, and O. taurinus. The arrangement of marginal papillae, with uni- to biserial papillae on the upper labium and bi- to triserial on the lower labium in A. burnoi differentiate it from Ar. s. siemersi, Ar.s. pedersoni, O. buckleyi, O. elkejungingerae, O. verruciger, and Trachycephalus jordani. A labial tooth row formula of 2(2)/5-6(1) in A. brunoi can be similar to O. elkejungingerae, and O. verruciger, however, the formula is dependent on developmental stage and/or variable in these species. Nostrils positioned closer to the eyes in A. brunoi differentiates it from T. jordoni, which have nostrils positioned closer to the snout, and from Ar. s. pedersoni, O. buckleyi, and O. verruciger, which have nostrils that are equidistant from the eyes and snout. Laterally located eyes differentiate A. brunoi from the dorsolaterally positioned eyes of Ar. s. siemersi, Ar.s. pedersoni, O. buckleyi, O. elkejungingerae, O. taurinus, and O. verruciger . The position of the spiracle below the midline of the body differentiate A. brunoi from O. elkejungingerae and O. taurinus, which have spiracles at the midline of the body. The mid-tail origin of the fin in A. brunoi differentiates it from all the Osteocephalus species. Lastly, the flagellum-like tail tip differentiates A. brunoi from all of these tadpoles except T. jordani (Wogel et al. 2006).
In live adult specimens, the dorsum of A. brunoi has a main base color that is reddish-brown to burnt chocolate. On the head the bony ridges are a lighter color and appear more metallic than the rest of the body. There appear to be an abundant number of black spots along the sides, with fewer appearing near the mid-vertebrae region. Smaller black spots appear along the outside of the tibia and forearm. There is a black oval-shaped spot on the top of the head between the eyes and a non-uniform dark spot behind each of the nostrils. The wrists and upper part of the finger disks are dark brown in color, with the hands and the toes close in color but a lighter shade. Specimens preserved in alcohol have a color that appears bleached to pale pink on the dorsal parts, turning to an earthy clay color on the head and ventral parts. A cinnamon brown color appears in the armpit and the groin areas (Cochran 1955).
In life, the dorsal and lateral surfaces of the tadpole body and tail are brown in color. There is a bright cream stripe that begins at the snout and extends to the anterior margin of the eyes. The ventral surfaces range from blue to violet with dark brown spots that also continue on to the first third of the tail. The remaining two thirds of the tail is crossed by dark brown transverse. In preservative, cream facial stripes and the dark brown ventral spots fade while the coiled intestines become more visible (Wogel et al. 2006).
Sexual dimorphism is apparent in this species. There are three identifiable morphological differences that have been designated as the most important characters of the two sexes: females have longer tibia, eye widths, and snout-vent lengths than males (Mesquita et al. 2004).
Tadpoles vary in their labial tooth formula and in how their vent tube attaches to the ventral fin. In stages 32 and 37, some individuals had five instead of six lower labial tooth rows. Additionally, in some individuals, the vent tube is attached to the tail fin by both walls rather than just at the medial portion (Wogel et al. 2006).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Aparasphenodon brunoi is nocturnal, with all individuals restricted to bromeliads during daylight hours. These frogs are excellent climbers and spend most of their active time clinging to tree trunks and vines. Activity peaks during the rainy season from October to March and all but ceases by the dry months of July and September (Gomez-Mesa et al. 2017).
Males call at night from perches between the forest edge and the nearest source of water. The advertisement call consists of a quiet initial note followed by a series of up to eight louder notes. Advertisement calls lasted from 34 to 1363 milliseconds. The duration of rests between calls was 0.7 to 452.1 seconds. Each note contained a rapid series of 4 to 26 pulses with 136.4 to 394.7 pulses per second. Most calls ranged in frequency from 861.3 to 1894.9 Hz. Additionally, another call was recorded composed of a single note, again with multiple pulses. Frogs sometimes gave this call after an advertisement call and sometimes used it alone. The purpose of this call is unknown (Freire et al. 2019).
Knowledge of A. brunoi reproductive behavior is limited. Although A. brunoi retreats inside bromeliads for shelter during the day, it does not depend on these plants for reproduction. Instead, they probably lay eggs in pools that form on sand during the rainy season on Brazil’s coastal plains. Most females lay their eggs at the beginning of the rainy season to ensure that the larvae have enough time to develop before their sandy pools dry up (Teixeira et al. 2002). Females put forth a high reproductive effort, producing about 900 oocytes each breeding season. Aparasphenodon brunoi’s relatively large size for a tree frog probably helps females sustain the production of this high number of oocytes (Gomez-Mesa et al. 2017).
Aparasphenodon brunoi is an arthropod generalist that consumes insects of allochthonous bromeliads, and it may hunt for insects outside of bromeliad microhabitats. Stomach contents of juveniles include cockroaches, termites, grasshoppers, locusts and crickets, cicadas, aphids, planthoppers, leafhoppers, shield bugs, ants, butterfly and moth larvae, insect remains, millipedes, centipedes, spiders, shed skin, and vegetable remains (Teixeira et al. 2002).
There has been some evidence that suggests A. brunoi may opportunistically prey on fellow anurans. In July 2016, a female A. brunoi specimen with a snout-vent length of 81.7 mm was collected from a bromeliad plant in Parque Nacional da Restinga de Jurubatiba, Brazil. This frog was the first known A. brunoi specimen to have consumed vertebrate prey, which was later determined to be an anuran of the Scinax genus (Carmo and Woitovicz-Cardoso 2018).
As of 2002, there was no information available on the natural predators of A. brunoi (Texiera et al. 2002). Likewise, the hypothesized use of the frog’s venomous casque to fend off predators has never actually been observed in the field or experimentally (de Andrade and Abe 1997). Many individuals have been observed to lie completely still when collected from their hiding places (Teixeira et al. 2002). Aparasphenodon brunoi’s first line of defense against predators therefore seems to be playing dead.
Aparasphenodon brunoi and C. greeningi produce a sticky secretion and flex their heads when threatened. In C. greeningi, this is followed by the frog jabbing and rubbing the spines of its head into the threat. The secretions from these two frog species (and potentially other species) contain proteolytic and fibrinolytic enzymes, as well as nontoxic hyaluronidase enzymes. While the hyaluronidase enzymes themselves are innocuous, they assist the proteolytic and fibrinolytic enzymes by breaking down the skin barrier and making it easier for the toxins to spread. The species differ in that C. greeningi has additional, augmented glands that promote a greater amount of venom secretion. Aparasphenodon brunoi secretes less venom by volume, but makes up for this deficit with more lethal venom, which is 25 times more lethal than the Brazilian pitvipers of the genus Bothrops (Jared et al. 2015). However, it has not been observed if A. brunoi behaves in the same way (de Andrade and Abe 1997).
Both A. brunoi and C. greeningi share phragmotic behavior; they move their bodies backwards into holes and use their heads as a lid (Jared et al. 2007). Frogs in restinga also use the axil part of the plant to defend itself against predators (Teixeira et al. 2002).
Evidence suggests that individual frogs select shelters (i.e. specific tree nooks or plants) based on their own unique size. These behaviors not only protect A. brunoi from predators, but also limit evaporation and water loss in the arid environments where they live. Similar mannerisms were also confirmed in C. greeningi, which has a comparable lifestyle and habitat range as A. brunoi (Jared et al. 2005). It appears that these behaviors may also influence predation tactics, as A. brunoi has been observed to be a sit-and-wait predator that employs opportunistic predation tactics (Teixeira et al. 2017).
Trends and Threats
The Brazilian Atlantic forest has been deforested due to agriculture and logging over the past three centuries. Remaining forest is composed mostly of small fragments smaller than 1000 hectares (ha) and within 1000 meters of a forest edge. Resort communities are increasing along the Brazilian coastal plains. The growth of these communities and other housing developments, the removal of native plants such as bromeliads to sell to horticulturalists, and the introduction of nonnative plants have degraded or destroyed much of the restinga habitat. For example, restingas once covered almost the entire coast of the state of Rio de Janeiro but now exist as twenty-one scattered patches (Rocha et al. 2007, Pimenta et al. 2009). Further findings have shown that animal residency and ecosystem function have decreased after two decades of fragmentation (Haddad et al. 2015). The frog may also have low abundance due to predation and low tadpole survival (Teixeira et al. 2002).
Possible reasons for amphibian decline
General habitat alteration and loss
Between 2013 and 2020, Aparasphenodon included five species, whose monophyly was assumed based on the presence of a prenasal bone. Pimental et al. (2009) questioned the diagnostic value of this trait as it was also found in Triprion. In 2020, Maximum Likelihood and Parsimony analyses of five mitochondrial genes (12S, 16S, ND1, COI, and CytB), six nuclear genes (POMC, RAG-1, RHOD, SIAH, TNS3, TYR), morphology, and behavior of 85 species of casque-headed treefrogs found that A. brunoi was sister to A. arapapa, however, Aparasphenodon was otherwise nonmonophyletic. Indeed, the next most closely related clade includes, A. bokermanni, A. pomba, an undescribed Aparasphenodon, Ar. siemersi, Corythomatis galeata, and Nyctimantis rugiceps. These findings also suggest that A. arapapa, A. bokermanni, A. burnoi, and A. pomba should be transferred to the monotypic genus Nyctimantis, while A. venezolanus should be redesignated as Trachycephalus venezolanus (Blotta et al. 2020).
The genus name stems from “apara-”, meaning “one who comes and goes”; “spheno-”, used to denote things that are “wedge-like” in shape; and the suffix “-odon”, from the Greek word for tooth (odon).
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Originally submitted by: Marc A. Mains, Emma M. Jaworski, Katelyn M. Prince, Kristina L. Aare (first posted 2020-12-15)
Comments by: Michelle S. Koo (updated 2021-07-08)
Edited by: Ann T. Chang (2021-07-08)
Species Account Citation: AmphibiaWeb 2021 Aparasphenodon brunoi: Bruno's Casque-Headed Frog <https://amphibiaweb.org/species/676> University of California, Berkeley, CA, USA. Accessed Sep 24, 2021.
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Citation: AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 24 Sep 2021.
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