General note: As is characteristic of the genus, Telmatobius culeus displays high variability in morphological characters including size, color, external morphology, and even osteology (Benavides 2005). This may be due to considerable phenotypic plasticity in the species. There may be different ecotypes of the species: for instance, one consisting of large frogs found in the deep water and one of small bodied forms that develop more quickly and live in shallower water (Benavides et al. 2002).
Color: Telmatobius culeus has variable coloration ranging from uniform olive brown to brown with white spots. Some have many white spots, such that they appear grey (Garman 1876). Black spots and patches are sometimes present. One depicted individual has black spots over entire dorsal surface (ventrum not shown) (Vellard 1992). The ventral surface of the Lake Titicaca frog ranges from light grey in some populations to bright orange (in the southern ‘T. albiventris’ population) (Vellard 1992). Body color in this species has also been described as dark green (Fontúrbel 2004).
External appearance: The Lake Titicaca Frog has a dorsoventrally compressed (flattened) body and head, with its head nearly as wide as its trunk (Vellard 1992). A prominent feature in this species is baggy skin on the dorsum, sides and the hind legs. In larger individuals there are bilateral dorsolateral folds running from the eye to the groin, creating a large dorsal disc of skin (Parker 1940). This skin may be filled with fluid in life, approximately doubling the animal’s volume (Vellard 1992). Telmatobius culeus has un-webbed fingers, with partially-webbed toes. The tympanum is not visible. In some individuals vomerine teeth are present in two small groups, or on one side only (Garman 1876), but often do not penetrate the oral mucosa (Parker 1940). Telmatobius culeus has a short tongue, which is free posteriorly (Allen 1922). Its skin can be smooth or warty. There is no vocal sac present (Garman 1876).
Body size: Adults are over 130 mm long (snout-vent length) (Vellard 1992), and up to 140 mm (Hutchison et al. 1976). Parker (1940) states a maximum length of 115-134 mm, considering males and females. There may be sexual dimorphism in body size, with the average female length 97.2 mm (N = 17) and an average length in males of 85.2 mm (N = 20) (Parker 1940). Weight in this species can reach 250g (Hutchison et al 1976). The animal may grow much larger than these reported values. Pough et al. (2004) report lengths of up to 250 mm.
Viscera: One of the key features of the internal anatomy of T. culeus is the drastic reduction in the size of the lungs to approximately one third of the size of a ranid frog of equivalent body size (Hutchison et al. 1976; Allen 1922). The lungs have primary alveoli only, likely limiting their respiratory capacity. The lungs do function to some extent—when placed in hypoxic water T. culeus can maintain its metabolic rate using pulmonary respiration alone for several hours (Hutchison et al 1976). Cutaneous respiration likely makes up for reduced pulmonary respiratory capacity. The Lake Titicaca Frog’s skin is highly vascularized, with capillaries nearly reaching the outermost layers of the epidermis (Hutchison et al. 1976). The network of relatively large capillaries is more intricate and extensive than most frogs, according to Allen (1922).
Ontogenetic changes: The extent of toe webbing increases with age (Parker 1940). Juveniles do not display skin bagginess and cannot be distinguished from T. marmoratus (Parker 1940). The requirement for baggy skin would presumably increase as the animal grows, since the surface area to volume ratio would decrease with increasing body volume.
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