Marmosops noctivagus (Tschudi, 1845)

VOSS, ROBERT S., TARIFA, TERESA & YENSEN, ERIC, 2004, An Introduction to Marmosops (Marsupialia: Didelphidae), with the Description of a New Species from Bolivia and Notes on the Taxonomy and Distribution of Other Bolivian Forms, American Museum Novitates 3466, pp. 1-40 : 27-29

Marmosops noctivagus

This appears to be the appropriate name for the most­frequently collected species of Marmosops in north­central Bolivia (fig. 12); we consider albiventris , dorothea , keaysi, and yungasensis to be synonyms, as explained below. The name noctivagus is based on Peruvian type material that we have not examined, but a series of AMNH specimens from the Andean piedmont (<1000 m) near Tarma in the department of Junín are moreor­less topotypical, and we have a large series of very similar specimens from Loreto. One Bolivian specimen from La Paz ( USNM 579250) and three from Pando ( AMNH 262402–262404) closely resemble this lowland Peruvian material and could be referred to the nominotypical subspecies (M. n. noctivagus ) if a trinomial nomenclature were needed. This material comprises relatively large specimens ( table 9) with dull reddishbrown dorsal fur, mostly self­whitish ventral fur, pale­furred metapodials that do not contrast abruptly in color with the digits, and more­or­less unicolored (all­dark) tails. All of the adult males we examined have welldeveloped gular glands, knobby (not bladelike) lateral carpal tubercles, and pale scrotums with whitish fur and unpigmented skin. Although we have not seen fluid­preserved parous adult females from Bolivia, two Peruvian specimens ( AMNH 272782, 273051) each have 5–1–5 = 11 mammae, of which the anteriormost pair is pectoral. Associated skulls have distinct supraorbital beads (best developed in fully adult individuals; fig. 4B) and lack dorsally visible postorbital constrictions; palatine fenestrae are present, and the auditory bullae are small and conical. The upper canine lacks accessory cusps, and M4 is very wide.

11 Although Anderson (1997: 152–154) reported ‘‘ Marmosops dorothea ’’ and ‘‘ Marmosops noctivagus keaysi ’’ as co­occuring at Chijchijpa in the department of La Paz, all of the specimens in question (at AMNH and MSB) are taxonomically indistinguishable. Anderson’s records of these taxa from Chijchijpa therefore represent alternative identifications (apparently copied from skin labels), not sympatry.

The remaining Bolivian material that we refer to Marmosops noctivagus is from the foothills and lower montane regions of Beni, Cochabamba, and La Paz. The specimens in question include the type material of dorothea and yungasensis, but an older name for the same phenotype is keaysi (from southern Peru; appendix 1). 11 Measurements of representative examples (including relevant type material; table 10) indicate that these highland specimens are about the same size as typical (lowland) noctivagus , but they have (on average) slightly broader interorbital regions, shorter molar rows, and narrower fourth upper molars. In addition, the dorsal fur tends to be slightly longer, the palatal fenestrae to be somewhat larger, and the bullae to be more inflated in highland examples than in lowland specimens. Also, whereas most lowland specimens have more­or­less unicolored (all dark) tails, tails of highland specimens are usually indistinctly bicolored (dark above, pale below) and particolored (paler distally than basally). Despite such elevation­correlated phenotypic variation, cytochrome­ b sequences analyzed by Mustrangi and Patton (1997) and by Patton et al. (2000) indicate only minor divergence (about 3%) among lowland and highland haplotypes of noctivagus ­like Marmosops , including specimens from the Amazonian lowlands of western Brazil (e.g., INPA 2931), the Andean slopes of southeastern Peru (e.g., MVZ 171408), and northern Bolivia (e.g., AMNH 268936). The nominal taxon that Tate (1931) described as albiventris , currently synonymized with M. impavidus , is morphologically indistinguishable from M. noctivagus and has similar mtDNA sequences ( Mustrangi and Patton, 1997). 12

Traditional taxonomic distinctions among forms that we consider conspecific with Marmosops noctivagus are almost entirely based on coat color. Tate (1933: 153–161), for example, described the dorsal fur as ‘‘varying from natal brown... to Mars brown’’ in typical noctivagus , by contrast with ‘‘bone brown... or warm sepia’’ in keaysi and ‘‘pecan brown’’ in dorothea . These chromatic differences are real, but similarities among these nominal taxa in other morphological characters, the existence of intermediate pelage hues in larger series of noctivagus ­like eastern­slope specimens obtained in recent years, and the modest range of mtDNA variation among geographically widespread samples suggest that such color contrasts are not taxonomically significant.

Paradoxically, several holotypes in this complex exhibit atypical craniodental measurements, a factor that may have contributed to the traditional view that these specimens represent distinct taxa. For example, the holotype of keaysi is an exceptionally large male with a very broad interorbit that is not matched by any paratype or topotype that we examined. By contrast, the holotype of dorothea has an unusually narrow interorbit, and the holotype of yungasensis has a conspicuously short molar toothrow. Unfortunately, there are no large series from any locality to serve as a relevant standard by which such morphometric variation might be assessed. Just among the 11 specimens of ‘‘ yungasensis ’’ from Pitiguaya, however, interorbital breadth varies from 5.6 to 6.4 mm, and length of the molar series varies from 6.3 to 7.1 mm. Therefore, none of the exceptional values for these dimensions in table 10 would appear inconsistent with the hypothesis that the taxa represent one geographically variable species.

Most of the specimens that we refer to Marmosops noctivagus were identified by Anderson (1997) as M. dorothea or M. noctivagus keaysi , but some were identified as M. impavidus as explained in the preceding account, and three others ( UMMZ 155829, 156006, 156007) were identified as Gracilinanus agilis unduaviensis .

BOLIVIAN SPECIMENS EXAMINED: Beni, 1 km E La Embocada ( UMMZ 156008, 156013), Rurrenabaque ( AMNH 247651); Cochabamba, Incachaca ( AMNH 38718), Cordillera de Mosetenes ( CBF 7527, 7560, 7573, 7577), Tablas Monte ( AMNH 275451–275458; MSB 70276–70280, 87080); La Paz, 20 km NNE Caranavi ( UMMZ 126680), Chijchijpa ( AMNH 268936, 268937, 275459; MSB 57004, 68333, 68334, 87092, 87110), El Vertigo ( CBF 4003), 13 km SW Ixiamas ( USNM 579250), Kahua ( CBF 3880), La Reserva ( MSB 68335), Pitiguaya ( AMNH 72550, 72558–72562, 72564, 72566; UMMZ 155829, 156006, 156007), Río Solacama ( BMNH 1.2.1.36, 1.6.7.79), Serranía Bella Vista ( AMNH 275460), Ticunhuaya ( AMNH 72567); Pando, Palmira ( AMNH 262402, 262403), Santa Rosa ( AMNH 262404).