Akodon latebricola (Anthony)

VOSS, ROBERT S., 2003, A New Species of Thomasomys (Rodentia: Muridae) from Eastern Ecuador, with Remarks on Mammalian Diversity and Biogeography in the Cordillera Oriental, American Museum Novitates 3421, pp. 1-48 : 21-22

Akodon latebricola (Anthony)

SPECIMENS COLLECTED: 10.6 km (by road) W Papallacta, 12,600 ft (UMMZ 155616); 7.5 km (by road) W Papallacta, 12,000 ft (UMMZ 155607–155615, 155768–155772, 155774); 6.2 km (by road) W Papallacta, 11,700 ft (UMMZ 155773, 155775, 155776); Río Papallacta valley [3–5 km by trail NNW Papallacta], 11,100 ft (UMMZ 155617, 155618).

OTHER MATERIAL: None.

TAXONOMY: Originally described as Microxus latebricola , this species has long been known only from the holotype (AMNH 67506) collected by G.H.H. Tate in 1924 at Hacienda San Francisco, a locality in the Cordillera Oriental east of Ambato ( Anthony, 1924b: 3). A peculiar feature of AMNH 67506 is its intensely black fur, which is quite unlike the normal coloration of any other muroid rodent species known to me. Anthony (1924b) considered and rejected the hypothesis that the holotype was a melanistic mutant, but the rediscovery of this taxon at Papallacta lends support to the opposite conclusion.

Except in pelage color, the Papallacta specimens are qualitatively indistinguishable from the type of latebricola , and measurements of the type fall within the range of morphometric variation in the Papallacta series. By contrast with the unnatural appearance of AMNH 67506, the Papallacta skins are dark grizzled­brown dorsally, and the ventral fur is gray­based with a superficial brownish wash; the ears, feet, and the dorsal surface of the tail are likewise dark brown, but the ventral surface of the tail is covered with long silvery hairs. Because brownish pigmentation is almost universal among the small akodontine rodents that inhabit humid Andean habitats, it is more parsimonious to assume that this is the normal coloration of Akodon latebricola , and that the coloration of the type is not, in point of fact, typical.

This species closely resembles Akodon bogotensis Thomas (1895a) , another eastern­ Andean species that was formerly referred to the genus Microxus . Among other shared similarities, both species differ from typical Akodon by their very small size; possession of a slender, tapering rostrum flanked by very shallow zygomatic notches (versus a shorter, stouter rostrum flanked by deeper zygomatic notches); origin of the superficial masseter from an indistinct tubercle or scar on the anterior margin of the zygomatic plate (versus from a scar posteroventral to the anterior edge of the zygomatic plate); confluence of the buccinator­ masticatory foramen and foramen ovale (versus buccinator masticatory foramen and foramen ovale accessorius separated by a vertical strut of the alisphenoid); proportionately shorter incisive foramina, wider parapterygoid fossae, and more inflated bullae; and highly distinctive molars with opposite (versus alternating) cusps. Although phylogenetic analyses of mitochondrial DNA sequences do not support the separate generic status of Microxus (as represented by the type species mimus Thomas; see Smith and Patton [1993] and references cited therein), sequence data from latebricola and bogotensis have not been analyzed. Despite their current generic classification, these two northern­Andean endemics clearly form a distinct clade that merits nomenclatural recognition. Subtle but consistent craniodental differences (M. Gómez­Laverde, personal commun.) distinguish latebricola from bogotensis and support their current status as valid species.

REMARKS: In a previous list of Papallacta mammals ( Voss, 1988: table 43), I misidentified this material as Microxus bogotensis .

FIELD OBSERVATIONS: The 21 specimens of Akodon latebricola that I collected near Papallacta in 1980 were trapped at elevations ranging from 3380 to 3840 m. Of these, 16 were taken in the shrubby páramo/forest ecotone, 2 in Subalpine Rain Forest, 2 in grassy glades surrounded by Subalpine Rain Forest, and 1 in grassy páramo. All recorded captures were on the ground: 9 in runways under dense bunch grass, 8 among mixed grasses and mossy shrubs, and 4 under moss mats or low herbs. Unlike other murid rodents that I collected near Papallacta (which appear to be strictly nocturnal), several individuals of A. latebricola were captured in broad daylight, between the time when traps were checked just after dawn and when they were rebaited in the late afternoon.