Rosenberg's treefrog (Hypsiboas rosenbergi), also known as Rosenberg's gladiator frog or Rosenberg's gladiator treefrog, is a species of frog in the family of tree frogs (Hylidae) and genus of gladiator frogs (Boana) found in Costa Rica, Panama, Colombia, Trinidad and Tobago and north-western Ecuador. Its scientific name is a testimony to Mr. W. F. H. Rosenberg who collected the type series, and its common name refers to the aggressiveness of males of the species.
Description The size of H. rosenbergi varies based on the population that they belong to, with individuals from the Costa Rican population being smaller in size than those from the Panamanian population. In the Panamanian population, males of H. rosenbergi measure on average 83 mm (3.3 in) in snout–vent length and females 86 mm (3.4 in). Females also tend to be heavier than males. It has partly webbed fingers and entirely webbed toes and large disks on both fingers and toes. Its skin is granulated with small warts, and yellowish, greyish, or reddish in colour, with brown or blackish marbling or spots. It also has dark worm-like markings across the dorsal surfaces of the body and limbs, with gray-white undersurfaces and a pigmented area that covers near the throat. Males tend to have more pigmented throats than females, a feature which is likely a result of hormonal control due to more pigmented individuals calling more often. Females, on the other hand, tend to contain more yellow dorsal colors than males. In addition, the female's body wall in front of its groin is nearly transparent, a feature that allows its black eggs to be easily seen. H. rosenbergi has a pale yellow lower jaw with similar black worm-like markings as seen on the dorsal surface, and its eyes have a bronze/golden iris with black around it. However, most of their color fades to light gray or tan during the day, and most of the patterns visible also disappear. H. rosenbergi males have prepollical spines on their hands that consist of pointed spines with scythe-shaped features. The prepollical spines are used in combat and contribute to its alternative name "Rosenberg's gladiator frog". Females also possess these spines, though they are very small, and only males have control over its position and the ability to retract its fleshy sheath to reveal the scythe-shaped parts for combat.
Habitat and distribution H. rosenbergi inhabits primary and secondary forest, as well as in heavily altered areas such as small strips of trees in pastureland. The species has been recorded from Panama to Costa Rica. However, it is unknown if the species is discontinuous throughout this distribution or if the three disjunct ranges that have been found in south-central Panama or extended over the Panamanian canal zone over Colombia to Ecuador represent failure to make collections of the species. At its largest, the distribution of H. rosenbergi may stretch from central Panama to western Ecuador. It is sympatric with H. boans and sometimes H. pugnax, and co-occur with both of these species in the headwaters of Rio Sinu and in Parque Nacional Natural de Katios in the northern Choco region of Colombia.
Conservation It is considered an adaptable species that is not facing any significant threats. H. rosenbergi has been found in Piedras Blancas National Park and Corcovado National Park in Costa Rica, providing it with protected habitat to alleviate concerns of habitat loss.
Diet Individuals of H. rosenbergi eat arthropods that are found close to the ground. Known and suspected insect prey reach their peak abundance during the wet season. Reproductively mature frogs do not grow during the breeding season, this is due to increased energy expenditure rather than food shortage. Females allocate energy towards growing eggs, and males allocate energy towards advertising for mates, building nests, and defending territory – all of which simultaneously detracts from hunting time. During the breeding season, females tend to hunt for food around the forest canopy, while males find food at lower elevations.
Reproduction and life-cycle Females of H. rosenbergi lay clutches approximately once every 25 days, with an average clutch size of around two thousand eggs. These eggs have a dark animal pole and yellow-white vegetal pole surrounded by two clear capsules, and are laid singly onto the surface of the water where they spread to form a monolayer. The offspring form tail buds around 40 hours after fertilization, which then grow rapidly until 150 hours after fertilization, after which the tail bud lengthened more slowly. In addition, the offspring start hatching from the eggs around 40 hours after fertilization, followed by swimming motions around 85 hours after fertilization, and active swimming by 140 hours after fertilization. The tadpoles had large filamentous gills. Tadpoles of H. rosenbergi undergo metamorphosis at a size of 21mm SVL, approximately 40 days after fertilization, resulting in extremely large fat bodies and visibly undifferentiated gonads. These froglets are covered with many small dark spots and have much less webbing in the fingers and toes as compared to adult frogs. After metamorphosis, the froglets leave the water. Individuals of this species can reach sexual maturity in one year. Reproduction in H. rosenbergi is influenced by both social and environmental factors. Females of the species have been found to be influenced by the social cue of the current chorus size in moderating their reproductive activity, while males have been found to be influenced both by same day precipitation (with heavy rainfall decreasing activity) and previous day chorus size.
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