Eligmodontia dunaris, Spotorno & Zuleta & Walker & Manriquez & Valladares & Marin, 2013

Spotorno, Angel E., Zuleta, Carlos, Walker, Laura I., Manriquez, German, Valladares, Pablo & Marin, Juan C., 2013, A small, new gerbil-mouse Eligmodontia (Rodentia: Cricetidae) from dunes at the coasts and deserts of north-central Chile: molecular, chromosomic, and morphological analyses, Zootaxa 3683 (4), pp. 377-394 : 385-388

Eligmodontia dunaris , new species

Holotype. MNHN 1546 , adult male, 15.3 g, collected by C. Zuleta R. in May 2011 (original LCM number 4599), skull (Fig, 6A, B, and C), dried skin and skeleton, and soft tissues in ethanol.

Type locality. CHILE: Coquimbo Region: comuna La Higuera, Sector Playa Los Choros (29°14’ S; 71°18’ W, 15 masl), 55 km N of La Serena city ( Fig. 1 and 7B ), in the coastal transitional desert of central Chile .

Distribution. Restricted to semidesertic habitats south of the plant free Atacama Desert in north-central Chile, from the coastal dunes of the type locality at Playa Los Choros, Coquimbo Region ( Fig. 7B ), through the central plains 30 and 55 km south of Copiapó city, Atacama Region, and reaching the coasts of Copiapó, Atacama Region at Playa Rodillo, 1.5 km N of the Caldera port. Additionally, one living specimen identified by external characters was observed at a burrow entrance in sandy soil, captured and released alive at Bahia Salado, 55 km S of Caldera (two photographs taken by Mr. Alvaro Sepulveda T.; not shown)

Etymology. The specific name designates the preferred dunarian habitat of this new mammal species.

Diagnosis. A member of the genus Eligmodontia , distinguishable from all the other species of the genus by its pygmy adult body size (total length ranging 126-152 mm, Table 2) and weight (range 9.4-15.5 g), as well as by the following combination of characters: small hind foot not larger than 20 mm (range 17-20 mm, Table 2), very light dorsum yellowish brownish gray; whitish immaculate venter; tail without a pencil and whitish dorsally and ventrally slightly differentiated; length of tail slightly shorter than length of head and body; slightly darkish band present extending from nose to between the ears ( Fig. 7A ); ears with external short hairs rather homogenously light gray except a terminal fine dark line; greatest skull length generally 19.9-21.7 mm; length of maxillary toothrow generally 3.4-3.6 mm; length of nasals 8-8.3 mm; anterior border of zygomatic plate slightly concave ( Fig. 6C ); rounded bullae and eustachian tubes poorly developed; moderately developed knobs at frontoparietal suture; braincase less inflated with auditory bullae barely visible in dorsal view ( Fig. 6A ).

Measurements of holotype. External measurements (in mm): total body length, 75; length of tail, 73; length of hind foot, 19; length of ear, 16. Weight: 15.3 g. Cranial measurements (in mm): greatest length of skull, 21.81; width of braincase, 12.38; diastema, 4.6; nasal foramen, 4.2; palatal bridge, 3.9; bullar length less tube, 3.6; length of maxillary toothrow, 3.8; length of nasals, 8.9.

Description. The smallest body size among the species of the genus. Pelage is short, silky and lax. Coloration of the dorsum is light yellow brownish gray, usually darker in coastal or young specimens; venter is white; tail has no pencil and is usually whitish dorsally and ventrally with slight differentiation; tail length a little shorter than length of head and body. Ears of median size usually have whitish pre-auricular tufts reaching the proximal region, with terminally homogenous short light hairs. Color transition from dorsum to venter is sharp. Fore and hind feet are covered with white hairs ( Fig. 7A ). Hind feet are elongated; plantar pads D2-4 fused forming a large pad, with hypothenar pad absent.

Skull is delicate, with rostrum rather short and eyes rather large, giving a juvenile appearance ( Fig. 7A ). Nasals not extending beyond premaxillary-frontal suture ( Fig. 6A ). Incisive foramina short, the posterior margin just reaching M1 ( Fig. 6B ). Palate long, extending beyond the posterior plane of M3. Posterolateral palatal pits anterior to mesopterygoid fossa. Small bullae not very inflated, with eustachian tubes short, not reaching the posterior edge of parapterygoid processes.

Upper incisors opistodont, ungrooved, and pigmented orange in front. Maxillary toothrows slightly posteriorly convergent. Primary cusps of molars alternate. M1 with anteriomedian flexus absent ( Fig. 6I ). M2 with hypoflexus and metaflexus open and lophs and styles absent. M3 with hypoflexus present. m1 with well-developed procingulum; m2 with anterolophid absent; m3 with hypoflexid present.

Comparisons. This rare species has the smallest adult body size among all the species of the genus, as well as among all terrestrial mammals of Chile. Eligmodontia hirtipes may be distinguished by the following: larger body size ( Table 2); hind foot always larger than 20 mm, dorsum usually darker, with an external almost blackish terminal wide band at the ears, particularly in juveniles; larger and oblong well-inflated bullae with posterior border almost reaching the anterior border of the foramen magnum; palatal width always larger than 2.6 mm (intermolar in Table 2); larger incisive foramen (> 4.6 mm); posterior border of nasals extends beyond the plane of anterior border of optical foramen; antorbital foramen more rounded and anteriorly convergent; anterior border of zygomatic plate usually straight, not concave; and posterior upper border of optic foramen rather smooth. Eligmodontia puerulus is distinguished by the following external characters: larger body size (81.3± 4.1 mm), tail length (76.7±3.1), hindfoot (24.3± 0.8 mm) and ear length (17± 1.5 mm)(n=19).

Natural history. Reproductively active individuals were captured in June, September and February-March. In July 2011, a 14 g female from Los Choros gave birth to four newborns after three weeks at the laboratory. In August 2011, another 14 g female from Los Choros gave birth to three 2.1 g newborns at the laboratory. Wild females weighing 13, 13 and 14 g were pregnant with 5, 2, and 4 small embryos in September and March. Males weighing 13 and 16 g had testes of 7x4 and 5x 4 mm. The stomach of one field specimen at Los Choros contained pieces of herbs, grains and insects; six young males and five females in the lab ate grains from commercial bird foods as well as cat food. This suggests a granivorous/omnivorous diet. Small mammal species reported or observed in the same habitat of the holotype included the ubiquitous sigmodontine rodent Abrothrix olivaceous , the caviomorph Spalacopus cyanus , and the gray fox Lycalopex griseus .

Habitat. The type locality is a sand dune belt of 16 km in length and 0.5 km in width ( Fig. 7c ). Four grids placed at the northern dunes with 50 standard Sherman-like traps set 10 m apart, and active during three consecutive nights, captured only two E. dunaris first, and four specimens six years later. Rains are scarce and irregular over time ( Armesto et al. 1993); they occur in winter (from May to August), with an annual mean of 90 mm. There are dry years with less than 22 mm, and wet ones with more than 175 mm. Additional moisture is provided by local fog and rain. The plant cover is a xerophytic low matorral, with scarce small shrubs and herbs ( Fig. 7C ), semi-dry most of the year. Plant cover was 43.9 % at the holotype site, mainly Cristaria glaucophylla (13.4%), Tetragonia maritima (8.1%), Frankenia chilensis (6.5%) and Nolana divaricata (5.9%). Another similar grid set at the southern dunes (29° 16´S – 71° 18´W, 20 masl) captured a single individual only. The plant cover here was similar (35%), with F. chilensis (7.6%), C. glaucophylla (6.2%) and Chorizanthe frankenioides (6.0%). Two additional grids set at the plain sites ~ 300 m from the sea border (top of Fig. 7B ) resulted in no captures, a result repeated at two other similar grids set later at the other nearby habitats of Los Choros coastal desert. The two sites south of Copiapó (27°28’ S; 70°29’ W) were semi-desertic sandy plains at the border of a recently completed desert bloom with abundant but ephemeral flowers, seeds and insects. Such a desert bloom is an occasional local event produced during rainy years ( Jaksic 2001).

Figures

FIGURE 1. Map of southern South America showing localities for previously (numbered) and presently studied Eligmodontia specimens (modified from Mares et al. 2008). Below species names are modal diploid chromosome numbers/FN. New northcentral Chile Eligmodontia sites are marked with an X. Map of the infertile Atacama Desert in dark gray (from Latorre 2002).

FIGURE 6. Eligmodontia dunaris MNHN 1546 (holotype): dorsal (A), ventral (B) and lateral (C) views of skull. Occlusal view of upper (F) and lower molars (I) of paratype LCM 3377. Similar views of E. puerulus LCM 1993 (D and G) and E. hirtipes LCM 1748 (E and H) are included for comparisons.

FIGURE 7. (A) Eligmodontia dunaris MNHN 1547, paratype (Photo A. Spotorno). (B) Habitat at Playa Los Choros dunes, type locality (Photo C. Zuleta); intensive trapping at the plain belt (top, below sea border) failed to capture any Eligmodontia. (C) Eligmodontia dunaris captured and released alive at Caldera, Atacama, showing bipedal posture (Photo E. Valenzuela by permission).