A desert octodontid rodent, Tympanoctomys barrerae, uses modified hairs for stripping epidermal tissue from leaves of halophytic plants

Abstract

Desert rodents that consume halophytic plants must have adaptations for coping with the high salt content of the leaves. A kidney capable of excreting very concentrated urine is one method. Another is removal of the hypersaline epidermis by means of chisel-like incisors prior to ingestion of the leaves. Tympanoctomys barrerae has evolved a unique refinement of the latter adaptation. It possesses two bundles of stiffened hairs on either side of the palate just caudal to the incisors. The bundles vibrate against the lower incisors, removing the epidermis from the leaves. The efficiency of the operation is significantly greater than with the use of incisors alone. Such a device has not been described in any other mammal. The facial muscles associated with the lips, the cheek vibrissae, and the oral cavity are described in T. barrerae and the nonhalophilic octodontid Octomys mimax. M. buccinatorius pars intermaxillaris is the only muscle in direct contact with the bristle bundles. Other anatomical features found in T. barrerae that may be associated with this feeding device are: 1) a much enlarged and mobile lower labial pad operated by Mm. buccinatorius pars orbicularis oris, pars longitudinalis profunda, and mandibularis cranialis profunda; 2) two oral glands not described in other rodents; and 3) a shortened tongue. Although, taken as a whole, this epidermal stripping device is unique to T. barrerae, most of its features have evolved by modification of structures present in the facial region of more generalized rodents.

Geographical distribution and ecological diversification of South American octodontid rodents

“…The uplift of the central Andes and Pampean Mountains had marked ecological consequences enhancing the xeric conditions of the northern Monte Desert through a rain shadow effect (Ortiz‐Jaureguizar & Cladera, ; Veblen et al ., ). Thus, divergence at the generic level has been accompanied by specialization for desert existence of the member species of clade I through marked changes in morphology, diet, physiology and behavior (Ojeda et al ., , ; Mares et al ., ; Díaz & Ojeda, ; Giannoni et al ., ; Berman, ; Ebensperger et al ., ). Whereas Octomys developed saxicolous life habits, with narrow geographic distribution and specialization for life and burrowing in rock formations of the Monte desert (Ebensperger et al ., ; Sobrero et al ., ), its sister genera (i.e.…”

Octomys mimax (Rodentia: Octodontidae)

“…Octomys mimax is strictly herbivorous (Berman 2003;Mares 1973;Mares et al 1997;Ojeda et al 1999;Ojeda and Tabeni 2009;Orlog and Lucero 1981;Oyarce 2005;Redford and Eisenberg 1992). Main food items consumed include leaves, fruits, seeds, and pods (Oyarce 2005).…”

“…There is a dense concentration of vibrissae in the oral cavity, along the midline of the palate just caudal to the incisors (Berman 2003). Vibrissae are about 3 mm long and are in contact with the facial muscle bucccinatorius pars intermaxillaris (Berman 2003).…”

“…Vibrissae are about 3 mm long and are in contact with the facial muscle bucccinatorius pars intermaxillaris (Berman 2003). The closely related species T. barrerae has specialized oral vibrissae that are used to strip salt-laden epidermis from leaves of halophytes that the species eats, but function of vibrissae in O. mimax is not known, because the species does not eat halophytes (Berman 2003). Berman (2003) suggests that in O. mimax vibrissae may have a tactile function and sense the position of food in the oral cavity.…”

Evolution of the Largest Mammalian Genome

“…Species of Tympanoctomys and Pipanacoctomys also have a highly specialized ecophysiology that allows them to feed on hypersaline vegetation from the saltbush plant Atriplex (Diaz et al 2000; Berman 2003; Ojeda et al 1999; Torres-Mura et al 1989; Giannoni et al 2000; Ojeda et al 1996; Mares et al 1997). This is an exceedingly rare adaptation in mammals that allows them to survive in arid habitats of Argentina’s Monte and Patagonian Deserts.…”