Lagostomus maximus (Desmarest, 1817)

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Chinchillidae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 462-481 : 477

1.

Plains Viscacha

Lagostomus maximus

French: Viscache des plaines / German: Viscacha / Spanish: Vizcacha de llanura

Other common names: Argentine Plains Viscacha

Taxonomy. Dipus maximus Desmarest, 1817 ,

type locality not given. Restricted by A. Cabrera in 1961 to southern Corrientes Province, Argentina.

Three subspecies recognized.

Subspecies and Distribution.

L.m.maximusDesmarest,1817—CArgentina.

L.m.inmollisThomas,1910—SEBolivia,S&WParaguay,andNCArgentina.

L. m. petilidens Hollister, 1914 — S Argentina (S Buenos Aires, La Pampa, and Rio Negro provinces).

Descriptive notes. Head-body 531-615 mm (males) and 395-562 mm (females), tail 154-205 mm (males) and 135-173 mm (females; measurements to tip of longest hair on tail), ear 50-65 mm (males) and 52-59 mm (females), hindfoot 118-136 mm (males) and 104-118 mm (females); weight 5.8-8 kg (males) and 3.5-5 kg (females). Mean weights of adult Plains Viscachas in semiarid grasslands of San Luis Province, Argentina, are lower: 5-9 kg (males) and 3-4 kg (females). The Plains Viscacha looks like an enormous chinchilla with a massive head, males in particular. It is among the most sexually dimorphic rodents. Head is remarkable by its rather large eyes, dark and coarse vibrissae (absent in females), and external nasal folds (to prevent earth entering nostrils). Both sexes have striking white markings on cheeks (more contrasted in males), above eyes, and at bases of moderately furred ears. Furred tail is short, proportionally much shorter than on other chinchillids. Hair is longest dorsally. Hindfeet are long and well developed, having three fingers with strong claws (digits one and five are missing); forefeet are shorter, with four long fingers with small thick claws for digging; specialized humeri also reflect digging ability. Front fingers have small terminal toe pads and strong hairs like combs. General color varies from silver-gray to brown-gray, with some sky-blue, and is darker on dorsum and whitish on venter and inside legs. Skull of the Plains Viscacha is flat, with broad frontals that bear triangularshaped postorbital processes and heavy parasagittal ridging for muscle attachment. Rostrum appears robust, but nasals are relatively long and narrow. Jugal is deep and thick, extending upward to meet expanded lacrimal, and has moderately developed post-orbital process. Floor of large infraorbital foramen has deep groove bordered by lateral flange for nerve passage. Tympanic portion of bulla is expanded ventrally; mastoid portion is not inflated and, while visible when viewed from behind,is not visible on dorsal surface of cranium. Paroccipital processes are long, vertical, and extend well below and free from contact with small bullae. Incisive foramina are short, occupying less than one-half the length of diastema. Palate is strongly constricted anteriorly. Dental formula of the Plains ViscachaisI1/1,C0/0,P1/1,M 3/3 (x2) = 20, with constantly growing teeth. Upper incisors are distinctly proodont, with weakly pigmented enamel, and are covered with faint longitudinal grooves. Each maxillary cheektooth has only two straight and rather thick laminae, except M? that has three, with the last plate essentially lacking a posteriorly directed heel. All mandibular teeth have two laminae. Mandible is thick and stout, with a reduced angular process thatflares laterally, a low but conspicuous coronoid process, and well-developed ridge lateral to condyle for attachment of posterior masseter muscle. Chromosome number is 56, with 110 chromosomal arms. Molecular genetic distance (mtDNA sequences of cytochromeb gene) between the Plains Viscacha and all species of Chinchillinae is very large at 182% (16-2-19-7%).

Habitat. Lowland habitats of dry thornscrub in Bolivia, Paraguay, and north-central Argentina; subtropical, humid grasslands in north-eastern Argentina; semiarid grasslands of central Argentina; and desert scrub in its south-western distribution. Annual precipitation in habitats occupied by Plains Viscachas varies from more than 1000 mm in north-eastern Argentina to less than 300 mm in west-central Argentina; predictability also varies annually.

Food and Feeding. The Plains Viscacha is strictly herbivorous; it eats a wide variety of plant species, mainly grasses in central Argentina, but also 27 herbaceous species, eleven shrub species, and occasionally seeds, fruits, and barks in dry scrub habitats. By intense and selective grazing and clipping, Plains Viscachas alter species composition, cover, and vegetation structure around their burrows, called vizcacheras, usually increasing amount of bare ground. Groups of up to 30 individuals may forage together. Adult males forage with females and young in winter but alone during the rest of the year. Between foraging bouts, individuals return to their natal vizcachera. On nights with no wind, feeding may last until after sunrise. Individuals spend more time feeding and less time at vizcacheras in winter than in other seasons, reversing the pattern in other seasons. Female Plains Viscachas nurse young inside vizcacheras for 2-3 months in spring, spending large amounts of time between foraging bouts during summer. Coprophagy has been observed.

Breeding. The Plains Viscacha reproduces seasonally, with most females breeding in austral autumn and young born in spring. Females have a vaginal closure membrane and a copulatory plug. Estrous cycle lasts c.40 days, hyper-ovulating 200-800 ova, followed by delayed implantation of up to five blastocysts in each uterine horn. Gestation is ¢.154 days, and young at birth are large and precocial. Average litter size is c.1-9 young. Lactation from two lateral pairs of thoracic mammae lasts 2-3 months. Females first conceive at a mean age of 214 days and give birth at ¢.368 days. Males reach sexual maturity at 12-16 months and exhibit a well-defined seasonal reproductive cycle. Testicular and epididymal masses and serum testosterone peak during mating in autumn when 91% of males are fertile. Males have a filiform penis and no sacculus urethralis— a trait that is unique among hystricomorph rodents. Gonadal activity decreases in winter. Longevity is estimated at 7-8 years.

Activity patterns. The Plains Viscacha is nocturnal and active throughout the year, emerging from burrows shortly before dusk. Groups of up to 30 individuals forage together. Adult males forage with females and young in winter but alone during the rest of the year. Seasonal changes in activity budgets of males are associated with increases in conflicts among males, vigilance for intruding males, and territorial displays. Females remain their natal home ranges, but males typically disperse although they may continue to reside in their natal home ranges when environmental conditions are poor. Groups frequently coalesce and change membership during the night. Complete turnover of adult males is typical every year, with resident males replaced by immigrants from other colonies. Residents repeatedly chase intruders. Fights occur occasionally, with bipedal wrestling, biting of hindquarters and throat, rolling, and kicking. Aggression among neighbors is rare. Grooming was observed among all sex and age classes within a group and consisted of nibbling on face, neck, and back and rubbing cheeks. Mutual grooming is common. Plains Viscachas—most frequently adult males—emit loud, two-syllable “pi-chung,” anti-predator calls, which are interspersed with whinnies, grunts, squeaks, and foot stamping. These calls are similar to those used in response to male intruders. During aggressive encounters,tail is arched, and hairs are erected. Adult Plains Viscachas collect bones, stones, and sticks and pile them at entrances of vizcacheras. Adult males urinate on sticks and rub their cheeks on them; females do not show these behaviors. Tail is used as a third leg when an individualsits on its haunches. Plains Viscachas dig with their forefeet, and soil is pushed out with the nose or kicked backward by hindlegs.

Movements, Home range and Social organization. The Plains Viscacha is colonial and builds a communal vizcachera, where 1-3 adult males, 2—4 times as many females, and young live together throughout the year. Number of burrows is 18-93, with satellite burrows scattered among them. Satellite burrows are seldom used except to escape high-risk situations in winter; they serve as residences and display sites for adult males during the breeding season from spring to autumn. An individual Plains Viscacha generally entersits own vizcachera rather than a satellite or another principal vizcachera, unless there is extreme danger. All individuals from a single vizcachera share a common home range, averaging 1-3 ha in central Argentina, with a minimal overlap between adjacent vizcacheras. Principal vizcacheras and their associated satellites are aggregated in patches called “vizcacherales.” Individuals may forage at considerable distances beyond boundaries of home ranges. A. C. Llanos and J. A. Crespo in 1952 reported that Plains Viscachas forage up to 400 m from their vizcacheras. Boundaries are not defended, but all members of a group will defend their vizcacheras from intruders of either sex or age class. They also have frequent cooperative behaviors such as grooming and anti-predator calls. A call may be repeated continually for several minutes, is contagious among males at neighboring vizcacheras, and results in a general run to their home burrow. The Plains Viscacha is a good and speedy runner (up to 40 km/h) and can jump up to 3 m. When startled by a minor threat, adult females and occasionally juveniles give a single syllable “wank.” A group responds by looking around but does not run for cover. When under severe stress, individuals emit a “scream” that results in conspecifics running to that individual. Members of a group have access to all burrows in vizcacheras, and all members use a communal dust bath. There are no clear dominance hierarchies among males or females. Two or more resident adult males often sit in close proximity to each other near a burrow entrance, occupy the same underground chamber even during the mating season, and forage together. Males disperse, but when environmental conditions are poor, they may remain in their natal vizcachera up to 27 months. During a population decline in semiarid scrub in La Pampa Province, adult females and juveniles abandoned their resident vizcachera when number of individuals became very low and moved as a group to the closest vizcachera. Predators of Plains Viscachas include the Puma (Puma concolor), Geoffroy’s Cat (Leopardus geoffroyr), the Crab-eating Fox (Cerdocyon thous), the Pampas Fox (Lycalopex gymnocercus), the Lesser Grison (Galictis cwja), the great horned owl (Bubo virginianus), the crowned solitary eagle (Harpyhaliaetus coronatus), and the boa constrictor (Boa constrictor).

Status and Conservation. Classified as Least Concern on The IUCN Red List. With increases in cattle grazing, overall distribution of the Plains Viscacha has increased, although many local populations have been eliminated because they damage pastures and provide meat and pelts to local farmers and hunters. More than 370,000 skins of Plains Viscachas were exported in 1976-1979 through Buenos Aires, Argentina.

Bibliography. Barquez et al. (2006), Branch (1993a, 1993b, 1993c), Branch et al. (1993, 1994), Cabrera (1961), Cabrera & Yepes (1960), Canevari & Vaccaro (2007), Diaz & Ojeda (2000), George & Weir (1974), Jackson etal. (1996), Llanos & Crespo (1952), Morgan & Alvarez (2013), Mufoz-Pedreros & Gil (2009), Parera (2002), Redford & Eisenberg (1992), Spotorno & Patton (2015), Spotorno et al. (2004), Walker (1968), Weir (1974), Wiegmann (1835), Woods & Kilpatrick (2005).

Figures

1. Plains Viscacha (Lagostomus maximus), 2. Chilean Chinchilla (Chinchilla lanigera), 3. Short-tailed Chinchilla (Chinchilla chinchilla), 4. Ecuadorean Mountain Viscacha (Lagidium ahuacaense), 5. Common Mountain Viscacha (Lagidium viscacia), 6. Wolffsohn’s Mountain Viscacha (Lagidium wolffsohni)

Subspecies and Distribution. L.m.maximusDesmarest,1817—CArgentina. L.m.inmollisThomas,1910—SEBolivia,S&WParaguay,andNCArgentina. L. m. petilidens Hollister, 1914 — S Argentina (S Buenos Aires, La Pampa, and Rio Negro provinces).