Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 6

HONDURAS: El Caliche, Cedros; Hatillo; La Piedra de Jesus Sabana Grande; Cementario. GUATEMALA: Lake Atescatempa; 1 mi. S Rabinal, 3450 ft.

[7] United States National Museum (Biol. Surv. Collections).

[8] American Museum of Natural History.

[9] Univ. Michigan, Museum of Zoology.

=Baiomys musculus handleyi= Packard

_Baiomys musculus handleyi_ Packard, Univ. Kansas Publs., Mus. Nat.

Hist., 9:399, December 19, 1958.

_Baiomys musculus musculus_, Goodwin, Bull. Amer. Mus. Nat. Hist., 68(1):39-40, December 12, 1934 (part); Miller and Kellogg, Bull.

U. S. Nat. Mus., 205:512, March 3, 1955 (part).

_Baiomys musculus nigrescens_, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

_Type._--Adult female, skin and skull; No. 275604 U. S. Nat. Mus. (Biol.

Surv. Coll.); Sacapulas, El Quiche, Guatemala; obtained on April 24, 1947, by Charles O. Handley, Jr., original number 991.

_Range._--Known only from the type locality in the valley of the Rio Negro. Zonal range: Part of the Chimaltenangan Province of Smith (1949:235).

_Diagnosis._--Size medium to large for the species; dorsum Wood Brown in some series to Buffy Brown; guard hairs of dorsum black-tipped, color of underhairs Avellaneous; hairs white to base in region of chin, throat, and median venter; in lateral region, hairs Neutral Gray at base; dorsal surfaces of forefeet and hind feet and ankles white; tail white below, brownish above; nasals truncate anteriorly; frontoparietal suture forming an obtuse angle with the suture separating the parietals; alveolar length of upper molar tooth-row and tail long. Average and extreme external and cranial measurements for nine adults from the type locality are as follows: Total length, 121.4 (115-128); length of tail vertebrae, 50.7 (49-54); length of body, 70.8 (66-77); length of hind foot, 15.3 (15-16); occipitonasal length, 19.6 (18.8-20.7); zygomatic breadth, 10.5 (10.2-11.0); postpalatal length, 6.9 (6.4-7.4); least interorbital breadth, 4.0 (3.9-4.0); length of incisive foramina, 4.2 (4.0-4.5); length of rostrum, 7.2 (7.0-7.7); breadth of braincase, 9.8 (9.7-10.2); depth of cranium, 7.1 (6.8-7.2); alveolar length of maxillary tooth-row, 3.5 (3.4-3.6); for photographs of skull, see Plate 1_c_, and Plate 3_c_.

_Comparisons._--From _B. m. nigrescens_, _B. m. handleyi_ differs as follows: everywhere paler; forefeet and hind feet whitish instead of dusky to sooty; hairs of anterior part of face white instead of brown; tail bicolored instead of unicolored; anterior tips of nasals truncate rather than rounded; frontoparietal suture forming obtuse angle with suture separating parietals instead of forming right angle; tail and upper molar tooth-row longer.

From _B. m. grisescens_, _B. m. handleyi_ differs in: slightly paler above and below, primarily as a result of lacking buff-colored hairs; forefeet and hind feet white, not flesh-colored with gray overtones; tail bicolored, not unicolored; anterior tips of nasals truncate rather than flaring; tail and upper molar tooth-row longer.

_Remarks._--_B. m. handleyi_ seems to be restricted to the valley of the Rio Negro, in the region of Sacapulas, Guatemala. Stuart (1954:7) points out that the Rio Negro drops down into a gorge at a place near Sacapulas and flows northward through a deep canyon for approximately 60 kilometers. The Rio Negro, then, flows onto the lowlands of the Yucatan Peninsula. The habitat is xerophytic in the valley of the Rio Negro near Sacapulas. Stuart (_op. cit._:10) suggests that this xerophytic habitat may be continuous to a place to the north of Chixoy, Chiapas, where the vegetation then becomes more mesic. The mesic conditions to the north in Tabasco and Yucatan probably have restricted the movement of pygmy mice to the north. No specimens of this mouse are known from the Yucatan Peninsula or from the State of Tabasco, Mexico. _B. m. handleyi_ intergrades with _B. m. grisescens_ to the south. Specimens from 1 mi. S Rabinal, and those from a second locality 1/2 mi. N and 1 mi. E Salama, Guatemala, are intermediate in color of pelage between _handleyi_ and _grisescens_. Stuart (_op. cit._:5) mentions the continuity of habitat and tributaries from the Salama Basin into the valley of the Rio Negro.

Absence of physiographic and biotic barriers in the corridor between these two basins probably allows for some gene flow between _handleyi_ and _grisescens_, and results in populations intermediate in color. To the north and northwest of Sacapulas, the Sierra de los Cuchumatanes rises abruptly and separates the known geographic range of _handleyi_ from that of _nigrescens_ to the north, while to the west the cactus-mesquite habitat of _handleyi_ gives way to the oak-pine timber that, so far as known, does not support _Baiomys_. The difference in elevation and flora seems to restrict gene flow between _handleyi_ and the more northern _nigrescens_. The only evidence of integration between these two subspecies is provided by one specimen from Chanquejelve, Guatemala. That specimen is intermediate in color between the pale _handleyi_ and blackish-brown _nigrescens_.

The subspecies closest, geographically, to _B. m. handleyi_ is _B. m.

nigrescens_, from which _B. m. handleyi_ differs more in color than from any of the other named subspecies, except _B. m. pullus_. There is a close correlation of pallor of mice and the xeric Rio Negro Valley, and the darkness (melanistic color) of mice and the mesic mountains and valleys to the north.

_Specimens examined._--Total 49, from GUATEMALA: type locality, including the type: 12 (U. S. Nat. Mus., Biol. Surv. Coll.), 37 (Amer.

Mus. Nat. Hist.).

=Baiomys musculus infernatis= Hooper

_Baiomys musculus infernatis_ Hooper, Jour. Mamm., 33:96, February 18, 1952; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959.

_Baiomys musculus musculus_, Hooper, Jour. Mamm., 28:50, February 15, 1947 (part).

_Type._--Adult male, skin and skull; No. 91497 Univ. of Michigan, Museum of Zoology; Teot.i.tlan, Oaxaca, Republic of Mexico, obtained on February 24, 1947, by Helmuth O. Wagner, original number 2702.

_Range._--Southeastern Puebla, in the basin drained by the Rio Salado and Rio Quiotepec, into northern Oaxaca. Zonal range: Arid Tropical in a part of the Orizaba-Zempoaltepec Faunal District of the Transverse Volcanic Biotic Province of Moore (1945:218). Occurs from 3100 feet in Oaxaca up to 6000 feet in Puebla.

_Diagnosis._--Size medium for the species; dorsum Drab, terminal parts of individual guard hairs black, Neutral Gray basally, distal parts of underfur Pinkish Buff, proximally Neutral Gray; sides same color as dorsum; hairs in region of throat and chin white to base; venter whitish to Neutral Gray with tinges of Pinkish Buff; dorsal parts of forefeet and hind feet whitish with flesh-colored undertones, ventral parts whitish to dusky-gray; tail bicolored, grayish-brown above, white below; tip of tail not bicolored, instead grayish-brown throughout; ears pale brown, spa.r.s.ely haired; incisive foramina long, not constricted posteriorly. Average and extreme external measurements for 9 adults from the type locality are as follows: total length, 113.9 (106-122); length of tail vertebrae, 44.1 (41-48); length of body, 71.0 (65-79); length of hind foot, 14.8 (13-16); length of ear, 11.9 (11-12). Average and extreme cranial measurements of 7 adults from the type locality are as follows: Occipitonasal length, 20.1 (19.7-20.4); zygomatic breadth, 10.4 (10.2-10.6); postpalatal length, 7.3 (7.0-7.7); least interorbital breadth, 4.2 (4.0-4.4); length of incisive foramina, 4.8 (4.4-5.6); length of rostrum, 7.2 (6.6-7.5); breadth of braincase, 9.6 (9.5-9.8); depth of cranium, 7.4 (7.1-7.6); alveolar length of maxillary tooth-row, 3.3 (3.1-3.4); for photographs of skull, see Plate 1_d_, and Plate 3_d_.

_Comparisons._--For comparisons with _B. m. nigrescens_ and _B. m.

brunneus_, see accounts of those subspecies. From _B. m. pallidus_, _B.

m. infernatis_ differs in: sides, ears, and dorsum paler (less of dark brown); venter whitish gray rather than gray with tinge of buff and brown; forefeet and hind feet paler; tail bicolored, not unicolored; incisive foramina longer and not constricted posteriorly; mastoid process turning dorsally and sickle-shaped at posteriormost point rather than capitate.

_Remarks._--_B. m. infernatis_ resembles _B. m. handleyi_ more than any other subspecies in color of pelage and in external and cranial dimensions. The resemblance in color between _B. m. pallidus_, in certain parts of its range, and _B. m. handleyi_ may have resulted from nearly parallel selective forces that gave rise to two subspecies, widely separated geographically. The same relation obtains between _B.

m. infernatis_ and _B. m. handleyi_. Both inhabit arid river basins. In them, pale soil and low relative humidity are important pa.s.sive factors of selection that give adaptive value to the pale colors of pelage of both _infernatis_ and _handleyi_.

Specimens from 6-1/2 mi. SW Izucar de Matemores, and 1 mi. SSW Tilapa, Puebla, are intergrades between _B. m. infernatis_ and _B. m.

pallidus_. These specimens are intermediate in color and cranial characters between the aforementioned subspecies but possess more of the pale brown overtones seen in paratypes of _pallidus_, and are best referred to that subspecies.

_Specimens examined_ (All in Univ. Michigan, Mus. Zool.).--Total 18, all from the Republic of Mexico and distributed as follows: PUEBLA, Tepanaco, 6000 ft., 3, Tehuacan, 5400 ft., 3. OAXACA: Type locality, 3100 ft., 12 (including the type).

_Marginal records._--See specimens examined.

=Baiomys musculus musculus= (Merriam)

_Sitomys musculus_ Merriam, Proc. Biol. Soc. Washington, 7:170, September 29, 1892; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:135, January 15, 1909.

_Baiomys musculus_ [= _musculus_], Mearns, Bull. U. S. Nat. Mus., 56:381, April 13, 1907; Hooper, Jour. Mamm., 36:29, May 26, 1955.

_Peromyscus musculus_ [_musculus_], J. A. Allen and Chapman, Bull.

Amer. Mus. Nat. Hist., 9:203, June 16, 1897; Elliot, Field Columb.

Mus. Publ., 105(4):135, July 1, 1905; Osgood, N. Amer. Fauna, 28:257, April 17, 1909 (part).

[_Peromyscus_] _musculus_, Trouessart, Cat. Mamm., 1:518, 1898.

[_Peromyscus_] _musculus_ [_musculus_], Elliot, Field Columb. Mus.

Publ., 95(4):175, July 15, 1904.

_Baiomys musculus musculus_, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat.

Mus., 178:258, March 6, 1942; Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Hooper, Jour. Mamm., 28:50, February 15, 1947 (part); Hall and Villa-R., Univ. Kansas Publs., Mus. Nat. Hist., 1:460, December 27, 1949 (part); Hall and Villa-R., a.n.a.l. del Inst.

Biol., 21:196, September 28, 1950 (part); Goldman, Smith. Miscl.

Coll., 115:336, July 31, 1951 (part); Miller and Kellogg, Bull.

U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hooper, Occas.

Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

_B._ [_aiomys_] _m._ [_usculus_] _musculus_, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:400; December 19, 1958.

_Baiomys taylori allex_, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

_Type._--Adult female, skin and skull; No. 33437/45460 U. S. Nat. Mus.

(Biol. Surv. Coll.); Colima (City), Colima, Republic of Mexico, obtained on March 9, 1892, by E. W. Nelson, original number 2055.

_Range._--Southwestern Nayarit and northwestern Jalisco, south into Colima, thence eastward into Michoacan. Zonal range: part of arid Lower Tropical Subzone of Goldman (1951:330); approximates part of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Colima up to 5800 feet in Jalisco.

_Diagnosis._--Size large for the species; dorsum Olive-Brown in darkest series to Buffy Brown with tones of Fawn Color in the palest series; guard hairs of dorsum black-tipped, gray basally (in some specimens, guard hairs gray-tipped with subterminal black band, and gray base); underfur of dorsum black-tipped with subterminal band of fawn to buff, Neutral Gray basally; face and head paler than back because of greater number of fawn-colored and buff-colored hairs; hairs on throat and chin white to base; venter and flanks Pale Olive-Buff in palest series to Gray (Pale Gull Gray) in darkest series; individual hairs of venter tipped with white to buff, basally Gray (Dark Gull Gray); forefeet and hind feet white to gray with flesh-colored undertones; tail faintly bicolored, individual hairs above black, below white; nasals flared anteriorly; zygoma and zygomatic plate thick. Average and extreme external and cranial measurements for 8 adults from Armeria, Colima, are as follows: total length, 125.5 (115-135); length of tail vertebrae, 47.5 (42-54); length of body, 75.6 (68-81); length of hind foot, 16.5 (16-17); occipitonasal length, 20.3 (19.8-20.7); zygomatic breadth, 10.7 (10.3-11.1); postpalatal length, 7.4 (7.1-7.7); least interorbital breadth, 4.0 (3.9-4.1); length of incisive foramina, 4.3 (4.1-4.5); length of rostrum, 7.3 (6.9-7.6); breadth of braincase, 9.8 (9.4-10.0); depth of cranium, 7.1 (6.7-7.2); alveolar length of maxillary tooth-row, 3.4 (3.3-3.6); for photographs of skull, see Plate 1_e_, and Plate 3_e_.