|
Eligmodontia morgani Allen, 1901, is a sigmodontine rodent commonly known as the western Patagonian laucha. A small, delicate, arid-adapted rodent, it is 1 of 7 currently recognized species in the genus Eligmodontia. The species occurs in the semiarid steppe habitat of western Patagonia of Argentina and Chile. E. morgani is listed as “Least Concern” by the International Union for Conservation of Nature and Natural Resources. NOMENCLATURAL NOTES. The species' description was “based on a large series of specimens collected at or near Cape Fairweather” (Allen 1901:410); Allen (1905:53) later clarified the locality as “Basaltic Cañons, 50 miles southeast of Lake Buenos Aires, Patagonia,” Santa Cruz Province, Argentina, noting that the locality was given as Arroyo Else on the labels and in the original description. Eligmodontia morgani pamparum was described by Thomas (1913:572) with a type locality of “Peru Station F. C. P., about 200 kilometres N. W. of Bahia Blanca,” La Pampa Province, Argentina. The locality is outside of the currently recognized range of E. morgani and near that of E. elegans (a synonym of E. typus). E. morgani had been recognized as a synonym of E. elegans (Gyldenstolpe 1932) and E. typus typus (Hershkovitz 1962). Based on morphology, E. morgani pamparum is recognized as a synonym of E. typus (Thomas 1929). The holotype of E. morgani is deposited in the mammal collection of the American Museum of Natural History (AMNH 27689). Our use of literature in preparing this monograph is based on our work in clarifying the distribution and systematics of Eligmodontia (Mares et al. 2017) and that of others. Literature in which the species of Eligmodontia could not be determined was not included. The etymology of the genus name is derived from eligma (Greek), meaning curling or winding, and odous (Greek), meaning tooth, which are references to the occlusional pattern of the molars (Palmer 1904; Braun and Mares 1995). The specific epithet was chosen to honor Mr. J. Pierrepont Morgan, who supported the Princeton Patagonian Expedition during which the type specimen was collected (Allen 1901). E. morgani also is known as Morgan's gerbil mouse (Wilson and Cole 2017); the silky desert mouse (Tiranti 1997); laucha sedosa (Argentina—Díaz and Ojeda 2017); ratita de pie sedoso del sur (Chile—Pedreros and Valenzuela 2017); Patagonia or southern silky-footed mouse and ratita patagonica de piel sedosa (Chile—Kelt 1994); and laucha sedosa de Patagonia (Chile—Mann 1978). DIAGNOSIS Species of the genus Eligmodontia (bolsonensis [highland gerbil mouse], dunaris, hirtipes, moreni [monte laucha], morgani [western Patagonian laucha], puerulus [Altiplano laucha], and typus [eastern Patagonian laucha]) are distinguishable from other species of phyllotine rodents by their elongated hind feet; the fusion of plantar pads 2, 3, and 4 on the hind feet; absence of the hypothenar pad; and the hair in the pectoral region being entirely white from base to tip (Hershkovitz 1962; Steppan 1995). Eligmodontia morgani differs from E. bolsonensis in coloration of the dorsum and venter (brownish or grayish with hairs of the venter gray basally versus yellowish brown with hairs of the venter immaculate white with white bases), tail color (dark dorsally and whitish ventrally versus whitish both dorsally and ventrally), and by having more densely haired soles of hind feet (versus soles that are relatively hairless or lightly haired—Mares et al. 2017). E. morgani is larger than (total length average 166.36 mm versus 139.5 mm) and has more densely haired hind feet than the Chilean endemic E. dunaris (Spotorno et al. 2017). E. morgani differs from E. hirtipes in coloration of the dorsum (brownish or grayish versus sandy buff), venter (whitish hairs with gray bases versus immaculate white with white bases), and tail (dark dorsally and whitish ventrally versus whitish both dorsally and ventrally—Thomas 1902); the karyotype also differs, being diploid number (2n) = 50, fundamental number (FN) = 48 in E. hirtipes (Lanzone and Ojeda 2017) and 2n = 32–34, FN = 32 in E. morgani. E. morgani differs from E. moreni in having more densely haired soles of hind feet (versus soles that are relatively hairless or lightly haired), pelage coloration (brownish or grayish with hairs of the venter gray basally versus brownish yellow with hairs of the venter immaculate white with white bases), and absence of a tail tuft (Thomas 1896); the karyotype also differs, being 2n = 52, FN = 50 in E. moreni (Lanzone and Ojeda 2017). E. morgani differs from E. puerulus in length of the tail (generally ≥ length of the head and body versus generally < length of the head and body) and width of the band on the dorsum of the tail (broad versus thin—Osgood 1943; Mann 1978); the karyotype also differs, being 2n = 32–34, FN = 48 in E. puerulus (Lanzone and Ojeda 2017). E. morgani is slightly smaller (166.36 mm, range = 146–197 mm) than E. typus (175.84 mm, range = 146–197 mm) and has a shorter (69–90 mm versus 77–104 mm), more well haired, bicolored tail, more densely haired soles of hind feet, and shorter ears (14–19 mm versus 16–22 mm—Pearson 1995; Sikes et al. 1997); the karyotype also differs, being 2n = 43–44, FN = 44 in E. typus (Lanzone and Ojeda 2017). GERAL CHARACTERS Eligmodontia morgani is a relatively small, delicate phyllotine rodent with large ears (Fig. 1). Fur is long, soft, and silky. Dorsal color is dull ochraceous gray. Sides are paler and buffier than dorsum, passing into a well-defined pale yellowish lateral line. Venter is pure white. Ears are dusky brown externally, pale buffy-gray internally. The tail is well haired, sharply to moderately bicolored, dark brown above and grayish white below with a tip that lacks a conspicuous tuft. Tail length is nearly equal to the length of the head and body. Hind legs and hind feet are elongated and well haired. Hypothenar pad is absent, whereas plantar pads 2, 3, and 4 are fused. Toes 1 and 5 on the hind feet are reduced. Soles of hind feet are well haired. FORM AND FUNCTION Dental formula of Eligmodontia morgani is i 1/1, c 0/0, p 0/0, m 3/3, total 16 (Hershkovitz 1962). Upper incisors are opisthodont and ungrooved. Primary cusps are alternate, and the anteromedian flexus of M1 is absent or reduced to a shallow groove. Mesolophs–lophids (including mesostyle–stylids) and anterostyle–stylids are absent. Molars are bilevel crested and molar rows are parallel or slightly convergent posteriorly (Hershkovitz 1962). The glans penis is short (mean length = 3.8 mm; mean diameter = 2.1 mm; n = 3) compared to other phyllotine rodents examined, lacks hooks on the lateral mounds, has relatively large recurved spines on the dorsal papilla and urethral flap, and has epidermal spines that are largest in the basal portion of the glans (Hooper and Musser 1964). The baculum is wide basally, the proximal margin convex and slightly emarginate, with a distinct terminal head, and lacks a keel; the medial digit is cone-shaped and the lateral digits are horn-shaped (Hooper and Musser 1964). Mean measurements (mm) of the baculum were: total length, 3.8; length of proximal bone, 2.8; length of medial digit, 1.0; length of lateral digit, 0.9 (n = 3—Hooper and Musser 1964). Male accessory glands include the following (mm; length): 1 pair of large lateral preputials, 9.5; 1 pair of smaller medial preputials, 2.5; 1 pair of bulbourethrals, 4.5; 1 pair of dorsal prostates, 3.0; 1 pair of lateral ventral prostates, 3.0; 1 pair of medial ventral prostates, 6.0; 1 pair of anterior prostates, 6.0; 1 pair of vesiculars, 9.0; and 1 pair of ampullary glands, 1.5 (Voss and Linzey 1981). The unilocular–hemiglandular stomach is single chambered with a spacious corpus lined with cornified epithelium and an antrum lined with glandular epithelium; the bordering fold is an approximate line that bisects the stomach from the incisura angularis to the greater curvature (Carleton 1973). The specimens examined by Carleton (stomach morphology—1973) and Voss and Linzey (male accessory gland morphology—1981) represent 4 formalin-fixed specimens that were collected in Neuquén, Argentina, and were identified as E. typus, the only species in the genus at the time of their collection. No specific locality was given and no measurements were taken prior to fixation. Approximate measurements given after fixation were total length, 140–160 mm, and length of tail, 72–78 mm. The specimens appear to be E. morgani but are badly faded (P. Myers, in litt.) ONTOGENY AND REPRODUCTION The reproductive season of Eligmodontia morgani in Argentina is documented to begin in October, spring in the Southern Hemisphere, and continues through late April (autumn), with the males and females returning to nonbreeding condition by May (Pearson et al. 1987). In Chile, the breeding season is documented from December through April (Kelt 1994). Breeding males (length of testes > 5.5 mm) are ed for October–January and April (Argentina—Pearson et al. 1987) and males with scrotal testes were captured in December and April in Chile (Kelt 1994). Pregnant females where captured between October and April (Greer 1965; Pearson et al. 1987; Kelt 1994; Saba and de Lamo 1994) and lactating females were captured in October, January, and February (Pearson et al. 1987; Saba and de Lamo 1994). In Argentina, the number of fetuses ranged from 3 to 9 with a mean of 5.90 (Pearson et al. 1987; Saba and de Lamo 1994). Females with 6 and 8 embryos have been ed in Chile (Greer 1965). A “loose,” but significant, positive correlation (r = /0.55) was found between age and number of fetuses (Pearson et al. 1987). Progression of tooth wear was used to determine relative ages, a wearing away of 0.10 mm of molar cusps took approximately 6 weeks, and for each additional 6 weeks of age, mean number of fetuses increased by 0.66 (Pearson et al. 1987). Juveniles appear in the population in January and their proportion increases through May (Pearson et al. 1987). Juveniles of both sexes reach sexual maturity at 6–8 weeks of age; females born in midspring were pregnant or lactating by the start of summer (mid-January—Pearson et al. 1987). Most individuals born in the spring do not survive the breeding season; however, individuals that overwinter breed at the beginning of the new breeding season but are unlikely to survive through the summer (Pearson et al. 1987). 网站原创范文除特殊说明外一切图文作品权归所有；未经官方授权谢绝任何用途转载或刊发于媒体。如发生侵犯作品权现象，英语论文题目，英语论文，保留一切法学追诉权。() |
