Akodon boliviensis Meyen, 1833

J. Pablo Jayat, Pablo E. Ortiz, Jorge Salazar-Bravo, Ulyses F. J. Pardiñas & Guillermo D’Elía, 2010, The Akodon boliviensis species group (Rodentia: Cricetidae: Sigmodontinae) in Argentina: species limits and distribution, with the description of a new entity, Zootaxa 2409, pp. 1-61 : 20-23

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https://doi.org/ 10.5281/zenodo.293461



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Akodon boliviensis Meyen, 1833


Akodon boliviensis Meyen, 1833

Akodon boliviense Meyen, 1833 . Verhandlungen der Kaiserlichen Leopoldinisch-Carolinischen Akademie der Naturforscher, 16(2):600, pl. 43, fig. 1.

Holotype: no holotype was designated by Meyen.

Type locality: “Auf der Hochebene von Hochperu, in dem Indianer-dorfe Pichu-pichun, auf einer Höhe von 14,000 fuss gefangen.” Pichu-Pichún, 14,000 ft., Chucuito Province, Puno Department, Peru (as clarified by Myers et al. 1990).

Description: Detailed morphological description in Myers et al. (1990). The specimens of northwestern Argentina follow, in general, this description and can be distinguished from the remaining species present in this region by the following combination of characters. Dorsal fur soft and somewhat dense, with dorsal coloration uniform pale brown with an olivaceous tinge and lightly streaked with black hairs. Yellow eyerings well defined. Ears of the same color as dorsum and densely covered with hairs. Coloration of sides similar to or somewhat lighter than dorsum. Venter buffy, clearly contrasting with dorsum. Chin with a small patch of completely white hairs. Inguinal region almost rufous in some individuals. Fore and hind feet of the same general coloration than the venter, with bicolored hairs, brown on base and whitish or pale buff on tip. Tail heavily covered with hairs and bicolored, dark brown dorsally and whitish or pale buffy ventrally.

Skull with rostrum short and relatively broad. Zygomatic notches proportionally broad and deep. Frontal sinuses slightly swollen. Interorbital region slightly divergent with margins in posterior half something squared in adult specimens. Zygomatic arches relatively well developed. Braincase inflated with temporal and lambdoidal crests relatively well developed. Zygomatic plate with anterior margin flat or slightly concave, oriented vertically or slopes gently backward from bottom to top. Most of examined specimens shows a posterior ascending process of alisphenoid projected at least to the squamoso-alisphenoid groove. Incisive foramina extending to the level of the hypoflexus of M1 or surpassed it. Mesopterygoid fossa narrow with straight borders and sides either parallel or gradually diverging posteriorly, and anterior margin rounded or squared. Parapterygoid fossae broader than mesopterygoid fossa, diverging backward and with straight to slightly convex lateral margins. Mandibular ramus delicate with masseteric crest extending slightly behind of the anterior border of m1, although in some individuals it only reaches the level of protoflexid. Capsular projection well developed and generally situated below the sigmoid notch.

Upper incisors generally orthodont. The M1 with procingulum and anteromedian flexus well developed. The anteroloph and mesoloph are always present, the enteroloph is tiny and present only in some specimens. The M2 shows a well developed mesoloph and the M3 is large and complex, with well developed metaflexus and hypoflexus making it distinctively “8”-shaped in most specimens. The m1 presents a well developed procingulum and a penetrating anteromedian flexid. Protostylid and ectostylid are always presents but the second is poorly defined in some individuals. A small mesolophid-mesostylid is present in a few specimens. In m2 most of the examined specimens have an ectostylid, and a mesolophid-mesostylid is present only in a few individuals but always vestigial (the only young specimen and two adults individuals). The m3 is proportionally large (nearly a half of m2), showing a poorly developed anterior cingulid in most specimens.

Karyotype: 2n = 40, FN = 40-42, from Puno and Tacna Departments, Peru ( Gardner & Patton, 1976; Myers et al., 1990).

Variation: In the few known specimens from northwestern Argentina most variation is age-dependent. Pelage color of young specimens is slightly darker than that of adults. Young individuals also present a shorter and more delicate rostrum, narrower zygomatic notch, less swollen frontal sinuses, broader interorbital region and more inflated braincase. Moreover, the incisive foramina and the mesopterygoid fossa are narrower and the parapterygoid fossae not as deeply excavated. Some variable characters unrelated with age include the general coloration, with some individuals more richly colored; eye ring, development of the hamular process of the squamosal (i.e., tympanic hook in Myers et al., 1990) and the shape of anterior margin of the mesopterygoid fossa. Representatives of this species in northwestern Argentina are morphometricly indistinguishable from those of Peru and Bolivia although they are slightly smaller in some measurements (e.g. CIL, RL) and slightly larger in others (e.g. IOC, IFL, RW 2). Nine specimens coming from Abra de Cienaga Negra and one from Azul Cuesta show subtle morphologic and morphometric differences respect to the specimens from Rodeo Pampa and Pampa Verde (whose haplotypes were more closely related to that of a Peruvian specimen MVZ 171607). These specimens are more richly colored, have a broader interorbital constriction ( IOC) and rostral width ( RW 2), and a thiner zygomatic plate (ZP).

Comparisons: Akodon boliviensis is a medium sized species within the boliviensis group and is, on average, larger than A. caenosus for most of the analyzed measurements ( Table 1 View TABLE 1 ). Nevertheless, only braincase breadth (BB), mid rostral width ( RW 2) and molars series ( MTRL and MdTRL) were statistically different according to the N HSD test ( Table 2 View TABLE 2 ). The PCA analysis indicates some overlap between these species ( Fig 2 View FIGURE 2 ) but the DA misclassified only one of the specimens of A. boliviensis as A. caenosus . In general, the coloration of A. boliviensis is somewhat paler than A. caenosus and the ears are more densely furred. Cranial traits such as a more developed zygomatic notches and a proportionally narrower interobital region distinguish A. boliviensis . Contrary to that observed in A. boliviensis , only in few studied specimens of A. caenosus in northwestern Argentina the posterior ascending process of the alisphenoid extend to the squamoso-alisphenoid groove. As Myers et al. (1990) recognized, the shape of M3 and the thickness of the hamular process of squamosal also differentiate both species. However, A. caenosus shows a great variability in these traits. Additionally, these species show a relatively high average percentage (7.0%) of genetic divergence ( Table 12 View TABLE 12 ). The examined skins of Akodon boliviensis are very similar to those of specimens of Akodon spegazzinii from high altitude localities, sharing similar hue and color patterns. However, A. boliviensis is on average smaller than A. spegazzinii for most morphometric measurements ( Table 1 View TABLE 1 ) with the N HSD test indicating significative differences in seven of these measurements ( Table 2 View TABLE 2 ). In this sense, A. boliviensis presents a more delicate skull, with shorter rostrum and molar series, narrower braincase, narrower and more shallow zygomatic notches and less flared zygomatic arches. The PCA analysis indicates some overlap ( Fig 2 View FIGURE 2 ) but the DA was efficient in separating these species, with only two misclassified specimens. The genetic distance between these taxa is relatively small (2.8%).

The striking morphometric and coloration pattern differences between A. boliviensis and A. sylvanus preclude confusing these species. Akodon boliviensis is conspicuously paler, with a drabby brown color, whereas A. sylvanus is dark brown with a strong olivaceous tinge. The contrast between dorsum and venter is more conspicuous in A. boliviensis . In addition, this species shows a more developed eyering and white spot on the chin. The skull of A. boliviensis is clearly more slender, with a shorter and more delicate rostrum, and narrower braincase, interorbital region and mesopterygoid fossa. The molars in A. boliviensis are smaller and clearly less hypsodont. The morphometric differences between these species are notorious with practically no overlap in PCA and none misclassified specimens in DA ( Tables 1 View TABLE 1 , 2 View TABLE 2 and figure 2). The average percentange of genetic divergence between these species is 4.9 %.

The comparison between A. boliviensis and the new species will be addressed under the treatment of the latter.

Distribution: In northwestern Argentina A. boliviensis is restricted to northernmost Salta Province, mainly above 2500 m ( Jayat et al. 2006). All known records come from the Zenta and Santa Victoria ranges. Thus, it is likely that the species probably reaches adjacent Jujuy province due to the continuity of habitats along these mountain ranges ( Fig. 6 View FIGURE 6 ).

Habitat: We captured most specimens in highland grasslands, both in upper forest/humid grassland ecotones as well as in drier grasslands more typical of Andean environments. Most of the collecting localities are characterized by grasslands interspersed with rocky outcrops, although in Pampa Verde (locality 6 on figure 6) the humid grasslands are adjacent to alder ( Alnus acuminata ) forest along humid ravines.

Natural history: Four individuals captured in winter (July and August) were molting with only one of them with reproductive activity signs. All specimens caught in spring (nine specimens collected in November) showed reproductive activity and were molting. Other sigmodontine species registered in northwestern Argentina alongside A. boliviensis include Akodon caenosus , Akodon budini Thomas , Necromys lactens Thomas , N. amoenus Thomas , Oligoryzomys cf. O. flavescens (Waterhouse) , Oxymycterus paramensis Thomas , Phyllotis osilae J. A. Allen and P. xanthopygus (Waterhouse) .

Comments: Cabrera (1961) considered A. spegazzinii and A. tucumanensis as subspecies of A. boliviensis , and A. alterus as a synonym of A. boliviensis tucumanensis , a position followed by many authors through the 1980s (e.g. Apfelbaum & Reig 1989; Barquez et al. 1980; Mares et al. 1981; Ojeda & Mares 1989). In the first revision of these small Andean forms, Myers et al. (1990) defined the Akodon boliviensis group, characterized the morphological and distributional boundaries of A. boliviensis , and considered A. spegazzinii as a valid species (with two subspecies A. s. spegazzinii and A. s. tucumanensis ).

Jayat et al. (2006) erroneously cited A. boliviensis for Escoipe, in central Salta province. This record was based on one specimen (JPJ 69) whose morphometric characteristics were similar to those of A. boliviensis ; however, our molecular studies indicate that this and other small specimens caught in the same locality are referable to A. spegazzinii .

Díaz (1999) and Díaz & Barquez (2007) referred one specimen (MMD 395) from Miyuyoc, at 3700 m, Jujuy province to Akodon alterus . We did not examine this specimen, but based on the latitudinal position and characteristics of the reported locality where the specimen was trapped, we note that it may represent another record of A. boliviensis .

TABLE 12. Average percentage of observerd sequence divergence within and between seven species of the Akodon boliviensis species group. Standard error estimates are shown between parentheses and were obtained by a bootstrap procedure (500 replicates) in MEGA 4. Positions containing missing data were excluded only in pairwise sequence comparisons. Intraspecific values for A. lutescens and A. subfuscus were not calculated because a single sequence was available for each species.

Species intra- specific A. boliviensis A. lutescens interspecific A. caenosus A. polopi n. sp. A. spegazzinii A. subfuscus
A. boliviensis 1.7 (0.3)            
A. lutescens -- -- 7.0 (0.8)          
A. caenosus 1.0 (0.2) 7.0 (0.8) 3.5 (0.6)        
A. polopi n. sp. 0.2 (0.1) 5.0 (0.7) 7.0 (0.8) 6.2 (0.7)      
A. spegazzinii 1.2 (0.2) 2.8 (0.5) 7.6 (0.9) 7.7 (0.8) 5.5 (0.7)      
A. subfuscus -- -- 8.3 (0.9) 5.1 (0.8) 4.7 (0.7) 8.0 (0.9)   8.5 (0.9)  
A. sylvanus 0.3 (0.2) 4.9 (0.7) 7.0 (0.9) 6.7 (0.8) 4.7 (0.7)   4.9 (0.7) 8.1 (1.0)

Colecao de Culturas de Fungos do Instituto Oswaldo Cruz


Museum of Vertebrate Zoology, University of California Berkeley