Akodon orophilus Osgood 1913
Creators: name: Jiménez, Carlos F.
name: Pacheco, Víctor
name: Vivas, Dan
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Muridae
Akodon
Akodon orophilus

description: Akodon orophilus Osgood, 1913
Holotype. FMNH 19724, adult male, skin and skull, collected on 26 May 1912 by W. H. Osgood and M. P. Anderson, original number 4795.
Type locality. "...six miles west of Leimabamba, Peru (in mountains near headwaters of Utcubamba River)...," Osgood, 1913 10:98, 2203 m, approximately 6ºS, 78ºW, Leymebamba, Chachapoyas, Amazonas, Peru (Fig. 1, locality 2).
Emended diagnosis. Akodon orophilus is distinguishable from other members of the A. aerosus species group by the following combination of characters: general coloration uniform olive green, dorsal and ventral pelage not strongly contrasting; contours of posterior edge of nasal smooth, tapering and V-shaped; lacrimals small; zygomatic plate slanted, with the anterior edge sigmoid or slightly convex; antorbital bridge moderately wide; zygomatic notch wide and intermediate in depth; incisive foramina penetrate between first upper molars but comparatively short; diastema intermediate in length; and jaw moderately robust, with delicate capsular projection.
Distribution. The distribution of Akodon orophilus encompasses montane forests of Amazonas Department and northern of San Martín Department east side of Río Marañón (Fig. 1). Elevation range is from 1900 to 2860 m.
Morphological description (Fig. 2). Medium size for the genus, overall color dorsal Olive to Brownish Olive. Fur hairs are gray based with a subterminal light brown pheomelanin bands about 1 mm in length, and reddish brown tips; length of pheomelanin bands vary as their coloration. Each hair averages about 9 mm long. Guard hairs are gray at their bases and black at their tips; and extend 3 or more mm beyond fur hairs. The venter is Olive Gray and slightly paler than the dorsum. Fur hairs are Olive Gray at their bases and buffy on the tips, these tips vary in coloration and in length. Chins have some hairs that are totally white. Eyerings are inconspicuous. Hindfeet are dark and covered with bicolored hairs with black at the base and white tips. Forefeet are slightly paler, covered with bicolored hairs with black or brown bases. Ears are covered by delicate and short hairs. Mystacial vibrissae reach anterior margin of ears, some are white and others are black; the submental and interramal vibrissae (1–4) are white, the first are shorter than the second. One to three dark superciliary vibrissae are present; one of them is the longest. One dark genal-1 (sensu Pacheco 2003) is also present. The ungual tufts on manus and pes are white. Tail is slightly contrasting and relatively long, its length is about 83% of the head-body length. The scales on both sides of the tail are black while the hairs on the dorsal surface are black and on ventral side are white. Dorsal hairs are over 2 or 2.5 scales in length at most.
The cranium has a rounded braincase and is slightly elongated. Profile is flat or slightly domed. Rostrum is arched, long, and narrow. Gnathic process is conspicuous. Nasals are somewhat long, extending anteriorly and posteriorly beyond the premaxillae. The nasals present a slightly pointed to rounded anterior edge, and tapering posterior margin, that extend to level of lacrimals and adopt a V-shaped with uniform margin. The nasals project little beyond the premaxilla. The interorbital region is intermediate in width, hourglass-shaped, and without ridges. The diastema is intermediate in length. Fronto-parietal suture is rounded. Zygomatic notches are moderately wide and somewhat deep with rounded borders, or sometimes slightly squared. Zygomatic arches are slightly robust and convergent anteriorly with thick malar processes. Lacrimals are small. Lambdoid ridges are well developed especially in old animals, and run in dorsoventral direction. The interparietal is reduced.
The incisive foramina are comparatively short with anterior and posterior borders rounded; the latter is slightly divergent and extends to the protocone of M1. The maxillary septum occupies half or slightly more than half of the incisive foramen length. The anteror-palatal pits are very conspicuous and located at the level of the protocone of M2, while the postero-palatal pits are reduced and located slightly behind the anterior margin of the mesopterygoid fossa or reduced in some specimens. The mesopterygoid fossa is broad and has parallel margins; extends anteriorly to the level of the posterior border of M3 or slightly behind; the anterior margin is rounded, without a noticeable median process; and the breadth is subequal to or narrower than the parapterygoid fossa. Sphenopalatine vacuities are present. Parapterygoid fossa is fenestrated, triangular, and divergent with external margins slightly convex. The auditory bullae are flask-shaped and intermediate in size, with short and broad Eustachian tubes, and with a slight thickening in the dorsal margin in some specimens.
Laterally, the zygomatic plate is somewhat narrow in size and its ventral root is slightly anterior to its dorsal root, therefore inclined backwards from its base; the anterior margin is slightly convex or sigmoid. Antorbital bridge is moderately wide. The posterior ascending process of alisphenoid varies in form and extension but it is always located below the squamoso-alisphenoid groove. The tegmen tympani are in contact or slightly overlapping the posterior processes of the squamosals. The dorsal aperture of the ectotympanic ring is opened or closed. Nasolacrimal foramen is present, its diameter is less than or equals to the size of M2. Oval foramen and the foramen ovale accessorius are approximately the same diameter or less than the length of M3. The optic foramen is equal to or greater than M3 length. Ethmoid foramen is placed dorsal to M3. The carotid circulation is primitive; the sphenofrontal foramen, stapedial foramen, and squamoso-alisphenoid groove are present. Postglenoid foramen is larger than the subsquamosal fenestra and both are rounded; the hamular process of squamosal is thick. Masticatory–buccinator foramen is present and can be divided or not. The sphenopalatine foramen is sometimes hidden by ethmoturbinals and it is smaller than M2 length. The hypoglossal, jugular and stylomastoid foramina are present. Incisors are short, intermediate in length, ungrooved and orthodont, with yellow-orange enamel bands.
The lower jaw is similar to other Akodon species. The rami are somewhat delicate. Coronoid process of mandible is delicate and falciform. Lunar notches are deep and wide. Angular process is slightly robust. The condylar process is moderately long and placed posterior to angular process. Lower incisor alveolus without distinct capsular process. Mandibular and mental foramina are present but reduced.
Teeth morphology resembles other members of Akodon. Upper molars are crested and main cusps are diagonally arranged. The anterolabial and anterolingual conules of M1 are about equal in size and are divided by a well-developed anteromedian flexus. On the labial side, the anteroflexus and paraflexus are present as well as a posteroloph and an anteroloph. Posteroflexus is very shallow. In lingual side, the hypoflexus is present and the protoslyle is absent. Mesoloph and mesostyle are present but conspicuous only in young animals. M2 has a conspicuous cingulum. Protocone, paracone, hypocone, and metacone are present. M2 has also a mesoloph, mesostyle, and a poorly defined posteroloph. M3 has a protocone, paracone, and hypocone; the protocone being the most developed; the posteroflexus and the paraflexus are present, and the hypoflexus is well developed.
In the lower toothrow, the conids are arranged diagonally with metaconid and entoconid anterior to protoconid and hypoconid, respectively. The m1 has a deep anteromedian flexid. Anterolingual conulid is smaller than anterolabial conulid. Protostylid is well developed but the metastylid is absent. Ectostylid and mesostylid are minute, and a posterolophid with a well-defined posteroflexid is present. The main cusps of second lower molar: protoflexid, mesoflexid, hypoflexid, and posteroflexid are present and arranged diagonally. A tiny mesolophid is present while ectostylid and mesostylid are absent. The third lower molar is “8” shaped.
Karyotype. The chromosome number (2n) and fundamental number (FN) of specimens from Amazonas Department are 26 and 40, respectively. The autosomes are composed by three pairs of large to medium metacentrics, four pairs of large to medium-sized submetacentrics, four pairs of small acrocentrics, and another pair of small metacentrics. The sexual pair consists of a large submetacentric X-chromosome and a small mediumsized acrocentric Y-chromosome (Fig. 3). We also report a XY female from Huiquilla (MUSM 36971). The sex of this specimen was confirmed by examination of its reproductive tract.
Variation. We report some morphological variation within populations of Akodon orophilus from Amazonas Department. The specimens from Huiquilla have molars with slightly higher crown compared to other Amazonas populations. This character could be related to diet. The populations from Hierba Buena and Puca Tambo are darker than other populations from Amazonas Department. This coloration is usually associated to environmental wetter conditions (Gogler’s rule). The darker coloration of individuals from Puca Tambo was used by Osgood (1913) to distinguish A. o. orientalis from A. o. orophilus; however, such coloration might also be associated to the moisture level. We failed to find additional discrete morphological differences between the presumed populations of A. o. orientalis and A. orophilus proper. Then, we supported the placement of orientalis as a synonym of orophilus by Musser and Carleton (1993, 2005).
Comparisons (Fig. 4, Table 1). Although no other species of Akodon is currently known to be sympatric with Akodon orophilus s. s., we compare it with four other species from the aerosus group (sensu Smith & Patton 2007) that are distributed in Peruvian montane forests: A. aerosus, A. mollis, A. surdus, and A. torques.
Akodon orophilus is distinguishable from A. mollis by its darker dorsal pelage coloration; longer tail; larger nasal and premaxillary bones, producing a more noticeable rostral tube; shallower zygomatic notch; a more tapered posterior border of the nasal, thinner incisors, almost inconspicuous capsular projection, small lacrimals, and convex anterior borders of the zygomatic plates. In addition, the karyotype of A. orophilus (2n = 26, FN = 40) differs from the diploid number of A. mollis: 2n = 22 from Ancash, or 2n = 36-38 from Piura (Patton & Smith 1992).
Akodon orophilus may be distinguishable from A. aerosus by its paler coloration, smaller body size and skull dimensions. A. orophilus has narrower, longer rostrum, and narrower zygomatic plate with its convex anterior border and deeper zygomatic notch, tapered posterior border of nasal. Thinner zygomatic arch, thinner hamular process of squamosal, smaller oval foramen, smaller lacrimal, smaller median lacerate foramen, shorter parapterygoid plate, less rounded fronto-parietal suture, narrower interorbital region, and narrower braincase. Also, the antorbital bridge and malar process are narrower than in A. aerosus. Also, the toothrow is shorter and the jaw is delicate with inconspicuous capsular projection. A. aerosus also differs from A. orophilus in karyotype, based on the three known diploid numbers of A. aerosus: 2n = 22 from Cusco, and 2n = 40 from Ayacucho Department (Gardner & Patton 1976). The population of A. aerosus baliolus from Puno with 2n = 38 (Patton et al. 1990) was recently elevated to full species by Pacheco et al. (2011).
Akodon orophilus can be distinguished from A. surdus by a paler coloration, more dense fur, shorter claws, longer tails, and paler and narrower feet. Cranially, A. orophilus has narrower and shorter nasals with less tapering posterior borders, narrower braincase, shallower zygomatic notch narrower and less expanded antorbital bridge, longer rostrum, smaller lacrimal, less inflated nasolacrimal capsule. Zygomatic plate slope more slanted backward from the base, narrower zygomatic plate, thinner zygomatic arch, hamular process of squamosal, and malar process. The incisive foramen and mesopterygoid fossa are narrower, the parapterygoid fossa and the molar toothrow are shorter and the jaw is delicate. The karyotype of A. surdus is unknown.
Finally, Akodon orophilus, compared to A. torques, has paler coloration, shorter tail, shorter rostrum; nasal less tapering to the posterior tip; smaller lacrimals; broader zygomatic plate; inconspicuous masseteric tubercle, and larger oval foramen. The nasals project little beyond premaxillae. More robust zygomatic arch, thicker hamular process of squamosal, and broader malar process, fronto-parietal suture is more rounded. A. torques has three known karyotypic variants: 2n = 22 and 2n = 24, each from a different, but adjacent geographic area from Cusco department (Patton et al. 1990), and the variant 2n = 26 from Ayacucho department (Hsu & Benirshcke 1976).
Natural history. Akodon orophilus has been found in simpatry with six species of rodents from montane forests of Amazonas Department: with Thomasomys notatus, T. ischyrus, and Nephelomys albigularis in Leymebamba; with Microryzomys minutus, T. ischyrus, and N. albigularis in Huiquilla; and with Microryzomys altissimus and Hylaeamys yunganus in Hierba Buena. These mice have also been taken in highland grasslands known locally as "jalca" with M. minutus.
Compared with other rodents, this mouse is very common especially in areas with corn and potatoes crops. It represented ca. 46 % of the captured animals during a twelve-night trapping survey in Amazonas department in July and August 2007. Three out of six females collected in the dry season were pregnant. Additional data about the ecology of these rodents are unknown.
Populations from Amazonas might be associated with the Chachapoyan physiographic province established by Young (1992).
Remarks. Akodon orophilus includes specimens from Amazonas Department identified as Akodon mollis by Myers et al. (1990).
Akodon josemariarguedas i, sp. nov.
Holotype. MUSM 22754, adult male, body in alcohol and skull removed, collected on 23 September 2005 by María Peralta, original number 237.
Type locality. Galloganán, Ambo, Huánuco, Peru, 3420 m. 10º 09' S, 76º 08' W (Fig. 1, locality 2).
Diagnosis. Akodon josemariarguedasi can be distinguished from congeners by the following combination of characters: dorsal pelage coloration uniformly Brownish Olive, strongly contrasting with Smoke Gray to whitish abdominal region; fur hairs with paler gray-based; tail dark and moderately countershaded; posterior end of nasal blunt with serrated contour; lacrimals large; zygomatic plate with the anterior margin less slanting and convex in its anteromedial area or straight; antorbital bridge moderately wide; zygomatic notch somewhat deep; palate narrow; maxillary toothrow somewhat short; mandible delicate with thin and large condylar process; and deeper lunar notch. The nasal projects distinctly behind of the premaxilla. An internal fossetus between paracone and protocone of M1 is present.
Paratypes. Three specimens collected at the type locality in September 2005: males MUSM 22749 and MUSM 22753 and female MUSM 22759; all consisting of skull and skins.
Etymology. The specific name josemariarguedasi is given in honor of the Peruvian writer José María Arguedas (1911–1969) for dedicating his life to understanding the Andean people, their culture and folklore.
Distribution. This rodent is found in four localities of Huánuco Department, south of Río Huallaga (Fig. 1).
Habitat. Akodon josemariarguedasi is known from mountain cloud forest of Huánuco Department between 2900 to 3800 m.
Morphological description (Fig. 5). Overall color with marked distinction between dorsum and venter; dorsal surface is Brownish Olive in contrast with venter that varies from Smoke Gray to whitish. Fur hairs project up to approximately 11 mm long. The pheomelanin bands are 1–1.5 mm long. Guard hairs extend by approximately 3–4 mm beyond the fur hairs. Tail is moderately countershaded; with dorsal black hairs extend to 2 or 2.5 ring-scales and ventral hairs almost totally white and extend the distance of 3 ring-scales, it averages about 86% of the length of the head plus body. Eyerings are inconspicuous. Hindfeet and forefeet are covered by almost black hairs. Digits of manus and pes are covered by white hairs.
Braincase is slightly globular, dorsal profile of the cranium is relatively flat. Rostrum is long, slightly arched and narrow; gnathic process is relatively conspicuous surpassing the anterior face of incisors. Nasals are relatively narrow and long, extending well beyond the premaxilla-frontal sutures. Posterior tips of nasal are blunt with irregular outline while anterior margins are rounded. Supraorbital edges are smooth and rounded. The nasals project distinctly behind to the premaxillae. Fronto-parietal suture is slightly U or V-shaped. Zygomatic notches are somewhat narrow, moderately deep, with rounded edges. Lacrimals are large. Zygomatic arches are relatively thick, anteriorly convergent and slightly expanded laterally with thick malar processes and the hamular process of squamosal is thick. Antorbital bridge is moderately wide. Lambdoid crest is well developed and interparietal is reduced. Ventrally, the incisive foramina are relatively long and narrow, extending between protocones of M1 with rounded anterior and posterior edges. Palate is narrow and short or slightly long with shallow palatal groove. Maxillary septum occupies more than half of incisive foramen. Antero-palate pits are very conspicuous placed at level of protocones of M2 while postero-palate pits are inconspicuous and situated at the same level of the anterior margin of mesopterygoid fossa or slightly backward. Mesopterygoid fossa has rounded anterior margin and subequal in breadth to parapterygoid fossa or narrower. Parapterygoid fossa is triangular in shape, the outward edges are convex with small perforations and slightly excavated. The bullae are medium-size with short and broad Eustachian tubes.
In lateral view, the zygomatic plates are relatively narrow, slightly inclined and its anterior edges more convex in the anteromedial parts or straight. The posterior ascending process of alisphenoid is always located under the squamoso-alisphenoid groove. Tympanic ring can be opened or closed. The oval foramen is mediumsized. The accessory foramen ovale diameter is greater than or equal to M3 length, optic foramen is larger or subequal to M3 length. Ethmoid foramen is placed dorsal to M3. Carotid circulation is primitive (pattern 1). Postglenoid foramina are larger than the subsquamosal foramina, both with rounded margins. The masticatorybuccinator foramen is not divided. Sphenopalatine foramen length is lesser than M2 length and almost completely hidden by ethmoturbinal.
Incisors are slightly broad and usually orthodont or proodont. The lower jaw is typical for the genus with slender and delicate rami. Capsular projection is inconspicuous, placed behind of sigmoid notch. The condyloid process is long and extends beyond the posterior margin of angular process. Lunar notch is narrow and relatively deep.
In general dental morphology is similar to other Akodon taxa, except for an internal fossetus present between paracone and protocone of M1 and a deeper metaflexus.
Karyotype. 2n = 22, FN = 40, from Huánuco Department, Peru. Both sexual chromosomes are acrocentric (Pacheco et al. 2012). In that report, the authors assigned this karyotype to Akodon orophilus.
Comparisons (Table 1). Akodon josemariarguedasi is compared with five members of the Akodon aerosus group that inhabit the Peruvian montane forest where this new species is found: A. aerosus, A. orophilus, A. mollis, A. surdus, and A. torques.
Akodon josemariarguedasi can be distinguished from A. mollis by a more contrasting overall tinge and paler ventral pelage, longer tails, longer nasals. The zygomatic notches are shallower, interorbital region is broader and the incisive foramen is longer. The nasal projects distinctly behind of the premaxilla. The jaw is delicate with inconspicuous capsular projection.
Akodon josemariarguedasi is distinguishable from A. aerosus by its paler ventral color, smaller and less robust skull. The nasal is narrower, projecting distinctly behind of the premaxilla. The zygomatic plates are clearly narrower and less vertical with convex anterior border, deeper zygomatic notch, and narrower interorbital region. The foramen oval is smaller and upper molar toothrow is shorter. In addition, the antorbital bridge and the malar process are thinner. The jaw is delicate and the capsular projection is indistinct.
Akodon josemariarguedasi can be distinguished from A. surdus by a paler and more countershaded coloration, shorter claws and longer tails. Cranially, the braincase is narrower in A. josemariarguedasi. Its nasals are narrower with less tapering posterior border, the zygomatic notches are shallower and the zygomatic plates are narrower and less convex. The interorbital region, the incisive foramen and the mesopterygoid fossa are narrower. The hamular process of squamosal is thinner. The mandible is delicate with inconspicuous capsular projection.
Akodon josemariarguedasi is distinguished from A. torques by paler ventral coloration. Body pelage pattern distinctly countershaded. Cranially, the posterior margin of the nasal of A. josemariarguedasi is blunt, serrated and less tapering. The zygomatic plate is less sloped and broader. Zygomatic arches are more robust. The malar process and the hamular process of squamosal are ticker and the fronto-parietal suture is more rounded. Upper incisors are shorter than A. torques.
Akodon josemariarguedasi differs from A. orophilus by its contrasting coloration pattern with paler abdominal region. The posterior margin of the nasal is blunt and serrated, the maxillary septum is thin. Lacrimals are large, and the nasal projects distinctly behind the premaxillae. The palate is narrower. The jaw is delicate, the condylar process is longer and thinner (Fig. 6).
Natural history. Akodon josemariarguedasi co-occurs with the sigmodontines Thomasomys kalinowskii, T. incanus, Microryzomys minutus, M. altissimus, and Oligoryzomys sp. Noblecilla & Pacheco (2012) analyzed the diet composition of 37 individuals of Akodon josemariarguedasi (reported as A. orophilus) characterizing as insectivorous. They consume mainly adult beetles (90%) and other items such as plant materials (seeds and other plant structures) and fruits.
Remarks. Akodon josemariarguedasi apparently includes specimens from Palca (Junín) that were first allocated to Akodon mollis by Patton et al. (1989), Myers et al. (1990), and Smith & Patton (1991). Later, Patton & Smith (1992) reidentified the specimens as A. torques; but finally Smith & Patton (1993; 1999; 2007) corrected them to A. orophilus. We observed by photos of one specimen from Palca (MVZ 173057) shares some skull features with the new taxon; however a depth and comprehensive examination is necessary.
Morphologic analyses. A principal component analysis of 19 characters found that the first four principal components explained 63.6% of the variance. Although, this value is relatively low; the projections of specimens between the 1st principal component (PC 1) and 2nd principal component (PC 2), and between PC 1 and 3rd principal component (PC 3) clearly showed no or minimal overlap between A. orophilus and A. josemariarguedasi (Fig. 7), supporting the existence of two species. Variables with the heaviest load on PC 1 were condylomolar length (CML), zygomatic breadth (ZB) and breadth of rostrum (BR). On PC 2 space, individuals are separated primarily by diastema length (DL) and length of incisive foramina (LIF). PC 3 separated individuals by the breath of zygomatic plate (BZP) whereas PC 4 separated by the breadth of first upper molar (BM1) (Table 2).
The discriminant analysis showed high percentages of correct classifications, 100% for A. orophilus and 100% for A. josemariarguedasi with values of Wilk’s Lambda near zero (0.09) and high value of the canonical correlation (0.95), indicating a large difference between both species. Moreover, univariate analyses of each character between A. orophilus and A. josemariarguedasi found significant differences in 14 of the external and cranial dimensions (Table 3).
Karyological analysis. Akodon josemariarguedasi (reported as A. orophilus by Pacheco et al. 2012) differs from A. orophilus in the number of chromosomes and the morphology of the pair sexual. A. josemariarguedasi has 22 chromosomes whereas A. orophilus has 26. The X and Y are acrocentric in A. josemariarguedasi while the X is s ubmetacentric in A. orophilus. In addition, the Y chromosomes are different in their length. The Y chromosome of A. josemariarguedasi has a two third the length of the X chromosome, whereas the Y chromosome is half the length of the X chromosome in A. orophilus. We highlighted that the karyotype of Akodon orophilus strongly resembles the karyotype of A. torques from Yuraccyacu (Hsu & Benirschke 1973), except for the Y chromosome which is acrocentric in A. orophilus and submetacentric in A. torques.
description: Published as part of Jiménez, Carlos F., Pacheco, Víctor & Vivas, Dan, 2013, An introduction to the systematics of Akodon orophilus Osgood, 1913 (Rodentia: Cricetidae) with the description of a new species, pp. 223-242 in Zootaxa 3669 (3) on pages 226-238, DOI: 10.11646/zootaxa.3669.3.2, http://zenodo.org/record/283898