Transandinomys Bolivaris

''Transandinomys bolivaris'', also known as the long-whiskered rice rat, is a rodent in the family Cricetidae. It is found in humid forest from northeastern Honduras to western Ecuador, up to above sea level. Since it was first described in 1901 from Ecuador, six scientific names have been introduced for it, but their common identity was not documented until 1998 and the species has long been known under the name ''Oryzomys bombycinus'', described from Panama in 1912. The name ''Oryzomys bolivaris'' was used before it was moved to the new genus ''Transandinomys'' with ''Transandinomys talamancae'' (formerly ''Oryzomys talamancae'') in 2006.

It is a medium-sized rice rat distinguished by its very long vibrissae (whiskers)—those above the eyes are up to long. The fur, which is soft and dense, is usually dark brown above and light gray below; it is darker in juveniles. The feet are long and the tail is about as long as the head and body. The skull is narrow and has a broad interorbital region (between the eyes). The species generally lives on the ground. Although it is rare, its conservation status is thought to be secure.

Taxonomy

In 1901, Joel Asaph Allen described four new species of rice rat in the genus ''Oryzomys'': three from Ecuador and the Peruvian '' Oryzomys perenensis''. The three Ecuadorian species–''Oryzomys bolivaris'' from Porvenir, Bolívar Province; ''Oryzomys castaneus'' from San Javier, Esmeraldas Province; and ''Oryzomys rivularis'' from Río Verde, Pichincha Province—were each based on a single specimen collected in 1899 or 1900. He distinguished the three on the basis of coloration, size, and relative tail length.Musser et al., 1998, p. 273 Philip Hershkovitz listed all three among the many synonyms of "'' Oryzomys laticeps''" (currently more narrowly defined as ''Hylaeamys laticeps'') in a 1960 paper.Hershkovitz, 1960, p. 544

Edward Alphonso Goldman described ''Oryzomys bombycinus'' in 1912 from four specimens from Panama. He compared it to '' Oryzomys talamancae'' and placed it with the "''Oryzomys laticeps'' group".Goldman, 1912, pp. 6–7 Three years later, he described ''Oryzomys nitidus alleni'' from Costa Rica as a subspecies of '' Oryzomys nitidus'', without mentioning ''bombycinus''. He revised ''Oryzomys'' of North America in 1918 and recognized ''Oryzomys bombycinus'' as the only member of its own group, with ''alleni'' as a subspecies distinguished by the proportions of the skull. He also mentioned that the group occurred in Ecuador and indicated that ''O. bombycinus'' probably reached Colombia. Goldman considered the group to be similar to ''O. talamancae'', but suggested that ''bombycinus'' and ''alleni'' might only be subspecies of ''O. nitidus''. In 1939, Oliver Pearson added a third subspecies, ''O. b. orinus'', from eastern Panama, and in 1966 the species was first recorded from Colombia.Pine, 1971, p. 592 Ronald Pine reviewed ''Oryzomys bombycinus'' in 1971, when 59 specimens of it were known, and first recorded the species from Nicaragua and Ecuador.Pine, 1971, p. 590 He kept the three described subspecies—''alleni'' from Nicaragua to western Panama, ''bombycinus'' from central Panama, and ''orinus'' from eastern Panama to Ecuador.Pine, 1971, fig. 1

Alfred Gardner and James Patton suggested in 1976 that Allen's ''O. rivularis'' may be the same species as ''O. bombycinus''. They considered ''O. bolivaris'' as probably the same as ''O. nitidus'' and listed ''castaneus'' as a synonym of ''O. capito'' (equivalent to modern ''Hylaeamys megacephalus'' and closely related species plus ''Transandinomys talamancae''). In 1984, Benshoof and colleagues reported the first record of ''Oryzomys bombycinus'' from Honduras.Benshoof et al., 1984, p. 512 Guy Musser and Marina Williams reviewed ''O. talamancae'' in 1985 and included ''O. castaneus'' as one of its synonyms, though without having examined the holotype.Musser and Williams, 1985, p. 14 In the 1993 second edition of ''Mammal Species of the World'', Musser and Michael Carleton used the name ''Oryzomys bolivaris'' for the species previously known as ''O. bombycinus'', and in 1998, Musser and colleagues fully documented the allocation of the names ''bolivaris'', ''castaneus'', ''rivularis'', ''bombycinus'', ''alleni'', and ''orinus'' to the same species, ''Oryzomys bolivaris''. They noted its similarity to ''O. talamancae'', but did not attempt to determine phylogenetic relationships among the species they discussed.Musser et al., 1998, p. 323 In their limited material, they found geographic variation within the species inconsequential and they recognized no subspecies.

In 2006, Marcelo Weksler published a phylogenetic analysis of Oryzomyini ("rice rats"), the tribe to which ''Oryzomys'' is allocated, using morphological and DNA sequence data. His results showed species of ''Oryzomys'' dispersed across Oryzomyini and suggested that most species in the genus should be allocated to new genera. Later in the same year, he, together with Alexandre Percequillo and Robert Voss, named ten new genera for these species, including ''Transandinomys'', which has ''Oryzomys talamancae'' (now ''Transandinomys talamancae'') as its type species. They also included ''Oryzomys bolivaris'' in ''Transandinomys'', so that it is now named ''Transandinomys bolivaris'', although it had not been included in Weksler's phylogenetic study. The two species are morphologically similar, but they could identify only one synapomorphy (shared-derived trait) for them: very long superciliary vibrissae (whiskers above the eyes).Weksler et al., 2006, p. 26 ''Transandinomys'' is one of about 30 genera in Oryzomyini, a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.

Various authors have used the common name "long-whiskered rice rat" for this species, but several other names have been proposed. In 1918, Goldman named ''O. bombycinus bombycinus'' the "Long-Haired Rice Rat"Goldman, 1918, p. 77 and ''O. b. alleni'' the "Allen Rice Rat".Goldman, 1918, p. 78 Musser and Carleton, writing in the 2005 third edition of ''Mammal Species of the World'', used "Long-whiskered Oryzomys",Musser and Carleton, 2005, p. 1146 the 2009 IUCN Red List gave "Bolivar Rice Rat", and Thomas Lee and colleagues used "Long-whiskered Trans-Andean Rice Rat" in 2010.Lee et al., 2010, p. 10

Description

''Transandinomys bolivaris'' is a medium-sized rice rat with very long superciliary vibrissae (more than long and extending well beyond the ears when laid back against the head).Tirira, 2007, p. 199; Reid, 2009, p. 208 According to Fiona Reid's ''Mammals of Southeastern Mexico & Central America'', it is distinguishable from any similarly sized rice rats by the length of these whiskers;Reid, 2009, p. 208 ''T. talamancae'' also has long superciliary vibrissae, but not as long as in ''T. bolivaris''. In both species, the mystacial vibrissae (above the mouth) are also long and extend beyond the ears when laid back, but they are again much longer in ''T. bolivaris''. The vibrissae are mostly dark, but translucent at the tips. ''Handleyomys alfaroi'', a rice rat with which young ''T. bolivaris'' are often confused, is much smaller. In ''T. bolivaris'', the cheeks may be light gray, buff, or reddish. The ears are dark brown to black and are sparsely haired.Musser et al., 1998, p. 121

The fur, which is soft, dense, and thick,Musser et al., 1998, p. 123 is dark brown to gray on the upperparts, grading to black on the midback and yellowish brown on the sides. The underparts are sharply different in color. There, the hairs are dark gray at their bases and white at the tips, so that the fur appears grayish white. The fur is shorter and darker than in ''T. talamancae''Musser et al., 1998, p. 128 and softer and thicker than in ''H. alfaroi''.Musser et al., 1998, p. 143 Young animals have darker, finer, and softer fur. Pine separated the subspecies ''alleni'' and ''orinus'' on the basis of their darker fur, but Musser and colleagues could not confirm this pattern and found paler and darker specimens within the same geographical regions.Musser et al., 1998, p. 148

The tail appears naked and is shorter than or about as long as the head and body; it is longer in ''T. talamancae''.Musser et al., 1998, p. 427 Its coloration is variable; it is dark brown above and at the sides and light brown and often white to a greater or smaller extent below, and in some specimens the tail has the same color above and below. The scales on the tail are smaller than in ''T. talamancae''.Musser et al., 1998, p. 129

The forearms are dark gray. The forefeet are unpigmented and ungual tufts of white hairs surround the equally unpigmented claws. The animal has long, narrow hindfeet, longer than in ''T. talamancae'', with usually smooth soles (lacking squamae, which are present in ''T. talamancae''). The three middle digits are much longer than the outer two. Six pads are present on the sole. The upper surface and the sides of the hindfeet are white and appear naked, although short, white hairs are present;Musser et al., 1998, p. 124 these hairs are longer in ''T. talamancae''.Musser et al., 1998, p. 131 Ungual tufts of long, white or gray hairs are present around the claws, which are short and lack pigment.

Head and body length is , tail length , hindfoot length , ear length , and body mass . Females have four pairs of mammae, as usual in oryzomyines. Like most rice rats, ''T. bolivaris'' has twelve thoracic (chest) and seven lumbar vertebrae. A study in Costa Rica found that there are 58 chromosomes, including many that are large and have two arms, and the fundamental number of arms is 80 (2n = 58, FN = 80), a highly differentiated karyotype. The karyotype of ''T. talamancae'' is variable, but has fewer chromosomes (34 to 54) and major arms (60 to 67).Musser et al., 1998, table 13 ''H. alfaroi'' has more chromosomes (60 to 62) and major arms (100 to 104).

Skull and teeth

The skull is relatively long and has a long, narrow rostrum (front region), broad interorbital region (between the eyes) and narrow braincase with almost vertically oriented walls at the sides and behind. It differs from that of ''T. talamancae'' in various proportions. Although the subspecies previously recognized in "''Oryzomys bombycinus''" have been separated by small differences in skull features, Pine rejected these on the basis of his much larger samples.Musser et al., 1998, p. 145 Musser and colleagues agreed, but noted that Colombian animals appeared to have larger skulls.Musser et al., 1998, p. 146 The zygomatic plates are broad and the zygomatic arches (cheekbones) behind them are nearly parallel to each other. The margins of the interorbital region contain prominent beads, which extend to the braincase as temporal ridges; these are usually less well-developed in ''T. talamancae''.Musser et al., 1998, p. 135 Unlike in ''T. talamancae'' and ''H. alfaroi'', the parietal bone is usually limited to the roof of the braincase and does not extend to the sides.

The incisive foramina, which perforate the front part of the palate, do not extend between the molars. The palate ends beyond the third molars and is perforated by posterolateral palatal pits there. Behind it, the roof of the mesopterygoid fossa is perforated by poorly developed sphenopalatine vacuities. The auditory bullae, which house the inner ear, are large. Usually, the mastoid bone lacks openings (fenestrae), which are present in ''T. talamancae''. The pattern of the arteries in the head is primitive, as indicated by the condition of various foramina (openings) and grooves in the skull.

The mandible (lower jaw) looks chunky and has a long condyloid process at its back; that of ''T. talamancae'' is more slender.Musser et al., 1998, p. 140 The capsular process, a projection at the back of the jaw which houses the root of the lower incisor, is poorly developed.Musser et al., 1998, p. 125

The incisors are large and ungrooved. Their enamel is orange, but paler on the lowers. The orientation of the upper incisors is opisthodont, with the cutting edge oriented backwards. The molars are brachydont (low-crowned) and have two rows of main cusps separated by deep valleys and complemented by a network of crests and smaller cusps. The first upper molar is broader than in ''T. talamancae''. As in this species, but unlike in many other rice rats, including ''H. alfaroi'', the mesoflexus on the second upper molar, which separates the paracone (an accessory crest), is not divided in two by an enamel bridge. The hypoflexid on the second lower molar, the main valley between the cusps, is very long, extending more than halfway across the tooth; in this trait, it is similar to ''T. talamancae'' but unlike ''H. alfaroi''. Each of the upper molars has three roots (two on the outer and one on the inner side) and each of the lowers has two (one at the front and another at the back).

Distribution, ecology, and behavior

''Transandinomys bolivaris'' is an uncommon species. Its known distribution extends from northeastern Honduras, on the Caribbean seaboard, through eastern Nicaragua, Costa Rica, and Panama, into coastal western Colombia and northwestern and west-central Ecuador. It has been found near sea level and the upper altitudinal records are at nearly in Panama and in Ecuador. This distribution coincides with that of the humid Transandean forest.Musser et al., 1998, p. 113 It generally occurs in areas with mean temperatures above and annual rainfall of ,Musser et al., 1998, p. 116 prefers mid-elevation forests (), and often occurs near water. The actual range of this species may be expected to extend further north and west, perhaps into Veracruz, southern Mexico, and western Venezuela, where it has not yet been recorded.Musser et al., 1998, p. 119 Omar Linares mentioned a possible record from the Lake Maracaibo region of northwestern Venezuela in 1998. Its range is similar to that of various other rainforest animals, including the semiplumbeous hawk (''Leucopternis semiplumbeus''), the rice rats ''Sigmodontomys alfari'' and '' S. aphrastus'', the spiny rats ''Proechimys semispinosus'' and ''Hoplomys gymnurus'', and the opossum ''Marmosa zeledoni''. ''T. talamancae'' and ''H. alfaroi'' are often found in the same localities as ''T. bolivaris'', but also occur in other areas.

Little is known of its biology.Tirira, 2007, p. 200 The species mainly lives on the ground, but some young animals have been taken in vegetation, up to above the ground. It is usually captured "under logs, around the roots of large trees, or among rocks along streams." Two females with four embryos each have been caught in Panama in June, one with two in Nicaragua in September, and one with four in Costa Rica in December.Reid and Langtimm, 1993, p. 93 A very young specimen was trapped in Costa Rica in March. One pregnant female was herself still in juvenile fur.Pine, 1971, p. 595 Four species of mites have been found on ''T. bolivaris'' in Panama ('' Gigantolaelaps gilmorei'', '' G. oudemansi'', '' Laelaps pilifer'', and '' Haemolaelaps glasgowi''), two chiggers ('' Leptotrombidium panamensis'' and '' Pseudoschoengastia bulbifera''), and two fleas ('' Polygenis roberti'' and '' Polygenis klagesi'').Tipton and Méndez, 1966, p. 323

Conservation status

The 2009 IUCN Red List lists ''T. bolivaris'' as "Least Concern", as it is a widely distributed species with a presumably large population that is found in numerous protected areas. However, habitat destruction by deforestation may pose a threat.

Notes

References

Literature cited

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Transandinomys
Rodents of Central America
Rodents of South America
Mammals of Colombia
Mammals of Ecuador
Mammals described in 1901
Taxa named by Joel Asaph Allen
Taxonomy articles created by Polbot