Description
Allobates grillismilis is, as of 2013, the smallest Dendrobates frog in the genus Allobates with a snout-vent length of 13.9 ± 0.8 mm in males and 14.4 ± 0.8 mm in females. The body is robust with a head that is generally wider than long (a ratio of 0.91) and a total head length that is 1/3 of the total body length. The eye is larger than the distance between anterior corner of the eye to the nares. The anterolaterally directed nostrils are located posterolaterally from the tip of the snout and are highly visible from all angles except dorsally. The distance between the nares is 2/5th of the width of the head. The canthus rostralis is initially convex beginning at the snout to the nostrils but straightens out from the nostrils to the eye. The loreal region is perpendicular to the snout. The indistinct tympanum is round and about half the size of the diameter of the eye. Except for the lower anterior edge of the tympanum all other margins are faint. The species has one distinct vocal sac located in the middle and towards the back of the throat that expands into a round shape. On the hands, a tear-drop shaped palmar tubercle can be found with the tip toward the second finger. Oval thenar tubercles, which are approximately a third the size of the palmar tubercle, can be seen from the ventral view of the hand but do not distinctly protrude. Relative finger lengths are 4 < 2 < 1 < 3 with moderately to weakly expanded discs, which have paired scutes, range from 1.2 – 1.7 of the adjacent phalanx. All fingers have round, oval subarticular tubercles but finger four lacks a distal subarticular tubercle. The species lacks carpal and metacarpal ridges, fringes, and webbing on the fingers. Tibia are approximately two-thirds the length of the snout-vent. On the foot, a tubercle-like tarsal keel is present that begins with a strong curve then straightens and flattens toward the metatarsal tubercle. There is a slight thickening of the skin on the outer edge of the foot and no metatarsal fold is present. There are no fringes on the preaxial edges of the foot. Relative toe lengths are 1 < 2 < 5 < 3 < 4 and webbing can only be found at the bases of toes three and four. Discs of toes are moderately expanded, ranging in proportion to the phalanx from 1.4 to 1.9, and also have paired scutes. The skin of the body is smooth overall but can be found with a few small, clear-colored granules toward the posterior end and top of the legs. The cloaca does not have a dermal flap (Simoes et al. 2013).

Allobates grillismilis tadpoles have dorsoventrally flattened bodies with round snouts in the dorsal view. Also from the dorsal view the snout appears flattened anteriorly, but from the side appears anterodorsally flattened from the nostrils to the tip of the snout. Dorsolaterally directed nares are small, closer to the snout than eye, and narrowly spaced. Eyes are also closely spaced and directed dorsolaterally. The oral disc is anteroventral, emarginated laterally, and transversely elliptical. The anterior labium is continuous with the snout and only separated by a shallow depression. Marginal papillae are round or pyramidal and found only on the lateral side of the anterior labium on the outer edges. The posterior labium is free and only has a single row of marginal papillae. Papillae number vary between individuals. Labial tooth rows follow a 2(2)/3(1) formula with anterior rows being equal in length and poster rows being equal in length. The anterior and posterior rows closest to the mouth each have medial gaps. The upper jaw is flat and serrated while the lower jaw is deep, serrated, and V-shaped. Tadpoles have a single sinistral spiracle located posterodorsally and level with the axis of the body when viewed from the side. The vent is free and opens dextrally. The finned tail has deep musculature and is wide along the first third, being widest at the body-tail insertion. The ventral fin begins at the body-tail insertion, but the dorsal fin begins further up the body. The fin is tallest mid-way down the tail (Simoes et al. 2013).

Allobates grillismilis can be differentiated from other Allobates by its habitat preference, smaller snout vent length, advertisement call (see Life History section below), and color patterns. Specifically, A. grillismilis’ lack of red or yellow coloration on the dorsal surface of the legs and lack of marbled black and white on the ventrum differentiates it from A. femoralis, A. hodli, and A. myersi. The lack of a distinct diamond or hourglass mark on the dorsum and brown markings on the head differentiate A. grillismilis from A. brunneus, A. gasconi, A. crombiei, and A. paleovarzensis. Alternatively, the lack of cross-like markings differentiates A. grillismilis from A. olfersioides and A. goianus. Small size and unpigimented throats and ventrums differentiate the species from A. nidicola, A. masniger, and A. vanzolinius. The unpigmented ventrum and lack of a swollen third finger in males further differentiates A. grillismilis from A. fuscellus, A. marchesianus, and A. trilineatus. Preserved A. grillismilis can be easily confused with A. caeruleodactylus, A. conspicuous, A. granti, A. spumaponens, A. subfolionidificans, and A. sumtuosus (Simoes et al. 2013).

There is no sexual dimorphism in A. grillismiliswith regards to color. In life, the dorsum is a solid tan brown with dark brown coloration along the sides. The dorsum can also be spotted in the posterior with the same coloration as the lateral region. The iris is black speckled gold with a pupil ring. The vocal sac is white to translucent in males when inflated and can be speckled with brown along the chin and anterior margin of the sac. A faint dorsolateral can be found in most individuals and a diffuse white, iridescent ventrolateral line can be found running the length of the frog along the lower margin of the flanks, which are brown. Towards the abdomen, pale iridescent marbling can be found on a background of light brown or gray. The dorsal side of the upper arms are light brown to tan, with some individuals having some darker blotches, and white where the arms meet the body. The ventral side of the upper arms is white or translucent, similarly to the throat area. The dorsal and lateral sides of the forearms are patterned with blotches or transverse bars of dark brown color. The ventral side is of the forearm and onto the hand are dark brown with light spots. Fingers are light brown with darker spots on the dorsal side and evenly dark brown on the ventral side. The upper legs near the vent is dark brown and flanked by pale cream paraclocal marks, which has interrupted or solid brown bars on the distal edge that extend to the inner lateral side of the thighs. The dorsal surface of the thighs and shanks is pale brown to tan and marked with transverse bars and irregular spots. Like the arms, the ventral surfaces of the legs match the gular region but has dark brown marbling on the edges. The feet, like the hands are light brown with darker spots on top and evenly dark brown on the ventral side. Toes are also dark brown but have a lighter pattern. Disc scutes on both the fingers and toes are iridescent white. When preserved the body’s dorsal side is a uniform brown, becoming darker near the eyes. The ventral side is also a darker brown. Patterning on the dorsum includes a pale dorsolateral stripe with diffused inner edge. The ventrolateral strip remains a visible bright white as is marbling on the ventrolateral region. Throat, gular and pectoral regions, abdomen, and ventral side of the thighs are all white to translucent. There is some spotting on the chin. The arms are pale brown from above with some darker spotting. The hands have pale areas while fingers are light brown with pale scutes on the discs. Immediately surrounding the vent, the color is a dark brown that is further surrounded by an uncolored band. The paracloacal mark remains solid dark brown leading to the brown lateral and dorsal surface of the thigh and shank. The dorsal surfaces of the legs retain their darker patterning. Ventral surfaces of the legs are white to translucent with dark brown marbling found along the edges and around the knee. Dorsal coloration of the outer feet is paler in color than the thighs and shank, darkening and becoming patterned as it moves to the inner surfaces. Ventral surface of the feet are dark brown and discs are pale (Simoes et al. 2013).

Tadpole coloration in life is translucent bodies spotted with iridescent gold speckles. The medial region of the body is red to pink. Internal organs and blood vessels are visible through the skin. In formaldehyde, the body becomes gray-brown, lightening in color on the tail. Brown spots are spread through the dorsal and lateral surfaces. Skin is still translucent, tail musculature is cream and fins are translucent with brown spotting (Simoes et al. 2013).

Patterning on paracloacal region, thighs, and shanks are variable. The dorsolateral line is also variable in presences or absences. Skin texture can range from smooth to granular. There are size differences between males found in Borba, Nova Olinda do Norte, and Maués, with latter being slightly larger. Maués also has individuals with a great head length to head width ratio (1.08). Female are significantly larger than males at all sites where both sexes were collected. Lastly, there are regional call variations (see Life History; Simoes et al. 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Brazil

View distribution map in BerkeleyMapper.

Allobates grillismilis can be only be found in forests of the northwestern Madeira-Tapajos interfluve of Brazil that do not experience long-term seasonal flooding. From detailed field surveys, it is believed that the species is geographically restricted to the right bank of the Madeira River and east to the area between the Aripuanã River and Municipality of Maués.

Life History, Abundance, Activity, and Special Behaviors
Allobates grillismilis males call from elevated positions such as tree roots, logs, vertical vines, termite nests, or leaves from 3 - 48 cm from the ground. Calls consist of 3 - 15 short tonal notes separated by short breaks. Tonal notes have similar duration with four to seven notes lasting a total duration of 0.178 ± 0.035 seconds. Call frequency was 6497.6 ± 35.9 Hz. Calls duration and frequency vary from locality to locality, with Nova Olinda Do Norte having longer calls (0.227 ± 0.053 second) with low peak frequencies (6219.9 ± 153.9 Hz) and Maués having shorter calls (0.149 ± 0.011 second) with even lower peak frequencies (5964.7 ± 96.3 Hz). Frequency modulation is similar in the first, central, and last pulses with high first pulses that become lower with the central and last pulse (Simoes et al. 2013).

During courtship, females move towards calling males, who change calling patterns when females are in visual distance. Males then move to terrestrial nests, consisting of both flat and curled leaves. Interested females follow males into the nest where males continue to call, using both call types, without body contact. Males then leave the nest and move around their territory, sometimes followed by the female, before returning to the nest where cephalic amplexus occurs for approximately a minute. Immediately after amplexus males return to their calling site and begin calling again. Females remain in the nests for approximately 20 minutes where they deposit 6-13 eggs. All tadpoles used to describe the species were collected from males’ backs, indicating male parental care (Simoes et al. 2013).

Trends and Threats
Because this species is so recently described there are currently no known threats or trends. However, the species authorities note that this is a cryptic species with a restricted range and suggest conservation measures be taken locally to ensure locally adapted species are not lost.

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Habitat fragmentation

Comments
The species authority is Simoes P.I., Sturaro M.J., Peloso P.L.V., Lima A.P. 2013. A new diminutive species of Allobates Zimmermann and Zimmermann, 1988 (Anera, Aromabatidae) from the northwestern Rio Madeira - Rio Tapajos interfluve, Amazonas, Brazil. Zootaxa 3609: 251-273.

The species epithet, grillismilis, comes from the latin, grilli, meaning cricket and similis, meaning similar because this species’ call sounds like a cricket.

Although Allobates grillismilis has the smallest body size (as of 2013), its snout-vent range overlaps with several other species.

References

Simoes P.I., Sturaro M.J., Peloso P.L.V., Lima A.P. (2013). ''A new diminutive species of Allobates Zimmermann and Zimmermann, 1988 (Anera, Aromabatidae) from the northwestern Rio Madeira - Rio Tapajos interfluve, Amazonas, Brazil.'' Zootaxa, 3609, 251-273.

Species Account Citation: AmphibiaWeb 2014 Allobates grillisimilis <https://amphibiaweb.org/species/7968> University of California, Berkeley, CA, USA. Accessed Oct 3, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 3 Oct 2024.

AmphibiaWeb's policy on data use.