EUGENE M. MCCARTHY, PHD GENETICS
Akodon dolores [Dolorous Grass Mouse]
× Akodon molinae (↔) [Molina’s Grass Mouse] CHR. HPF(♂&♀). CON: southern Cordoba, Argentina. These hybrids are more readily obtained when A. molinae is the mother. Lisanti et al. 2001; Merani et al. 1978, 1983; Wittouck et al. 1995.
Akodon molinae [Molina’s Grass Mouse] See: Akodon dolores.
Neotoma albigula [White-throated Woodrat] In Arizona hybridization occurs between three populations, treated as races of Neotoma albigula: near Cavecreek (between albigula and mearnsi), and near Parker and Ehrenberg (between mearnsi and venusta). Hoffmeister 1986 (pp. 409, 410).
Neotoma albigula [White-throated Woodrat]
× Neotoma floridana [Eastern Woodrat] CHR. Parapatric contact zone in north-central Texas. Birney 1976.
× Neotoma micropus [Southern Plains Woodrat] ENHR(w U.S.). A large fraction of the population is hybrid in southeastern Colorado, western Oklahoma, and northwestern Texas. This interbreeding has been demonstrated on the basis of both genetic and morphological data. Hybridization also occurs in northern Mexico (Chihuahua, and possibly Coahuila). Hybridization occurs where semiarid plains of yucca-shortgrass or cactus-shortgrass (habitats preferred by N. micropus) interface with rocky habitats or canyons in association with junipers and yucca (habitats preferred by N. albigula). Anderson 1969; Birney 1976; Braune and Mares 1989; Finley 1958; Huheey 1972; Macêdo and Mares 1988.
Neotoma bryanti [Bryant's Woodrat]
× Neotoma lepida [Desert Woodrat] ENHR(Mexico). BRO: Cedros Island, Baja California Norte. Shurtliff et al. 2013.
Neotoma devia [Arizona Woodrat]
× Neotoma lepida (♂) [Desert Woodrat] CAENHR(southwestern U.S., lower Colorado Valley). Mascarello and Hsu (1976) report captive hybridization. Mascarello (1978, p. 493) says a population in northern Baja California is “genetically intermediate.” These woodrats have been treated as conspecific, but were split by Koop et al. (1985) and Mascarello (1978). N. lepida occurs west and north of the Colorado, N. devia, to the east. The former has 6, 7, or 8 large biarmed chromosomes; the latter, 10, 11, or 12. Hoffmeister 1986 (p. 413).
Neotoma floridana [Eastern Woodrat]
See: Neotoma albigula.
× Neotoma magister [Allegheny Woodrat] NHR(e U.S.). Hybridization occurs in Burke County, North Carolina. Analysis of mtDNA D-loop sequences identiﬁed two specimens as N. floridana, that had been judged to be N. magister based on morphology (cranial measurements and presence of a maxillovomerine notch). These intermediates, then, were probable hybrids. Formerly, floridana and magister were treated as conspecific. Ray 2000.
× Neotoma micropus [Southern Plains Woodrat] CAENHR(central North America). HPF(♂&♀). Adjacent populations of these woodrats approach each other in both qualitative and mensural traits, which suggests extensive gene flow. Patterns of hybridization seem to have been well studied only in western Oklahoma. Contact occurs at interfaces between woodland habitat (preferred by N. floridana) and grassland-yucca-cactus habitat (preferred by N. micopus). Birney 1973, 1976; Birney and Perez 1971; Braune and Mares 1989; Caire et al. 1989; Heist 1970; Mascarello 1978 (p. 492); Spencer 1968; Wiley 1980 (p. 6).
Neotoma fuscipes [Dusky-footed Woodrat]
× Neotoma macrotis [Big-eared Woodrat] NHR. Matocq (2002) elevated woodrat populations in southern and Baja California, formerly treated as subspecies of N. fuscipes, to separate specific status under the name Neotoma macrotis (see Matocq 2002, Fig. 7). However, Matocq’s analysis of morphological and genetic traits did reveal the existence of intermediate individuals (probable hybrids).
Neotoma lepida [Desert Woodrat]
See: Neotoma bryanti, N. devia.
× Neotoma macrotis [Big-eared Woodrat] NHR(southwestern U.S.). Mearns (1907, p. 489) writes, “I have examined specimens that were intermediate in characters, both external and cranial, between Neotoma fuscipes macrotis and N. intermedia. They were found in leaf nests in oak trees, and I am disposed to consider them as hybrids between the two species.” Today, intermedia is usually treated as a subspecies of N. lepida, and macrotis has been elevated to species status (see Neotoma fuscipes × N. macrotis).
Neotoma macrotis [Big-eared Woodrat] See: Neotoma fuscipes; N. lepida.
Neotoma magister [Allegheny Woodrat] See: Neotoma floridana.
Neotoma mexicana [Mexican Woodrat] In Arizona (Graham Mountains) probable hybrids occur between two populations (mexicana, pinetorum) treated as races of N. mexicana. Hoffmeister 1986 (p. 428).
Neotoma micropus [Southern Plains Woodrat] See: Neotoma albigula; N. floridana.
Ochrotomys nuttalli [Golden Mouse] Five populations (aureolus, flammeus, floridanus, lisae, nuttalli), treated as races of this mouse, have hybrid zones where they interface. At least two (aureolus, nuttalli) were formerly treated as separate species. Linzey and Packard 1977.
Onychomys leucogaster [Northern Grasshopper Mouse]
× Onychomys torridus(↔ usu. ♀) [Southern Grasshopper Mouse] CHR. HPF(♀♀). In captivity 27% of mixed matings produced offspring. F₁ hybrids are lighter than O. leucogaster and heavier than O. torridus. Hybrids produced from backcrosses to O. torridus are morphologically indistinguishable from O. torridus, and males are partially fertile. In areas of sympatry (southwestern U.S., northern Mexico) these mice form altitudinal contact zones (leucogaster occurs above torridus). According to Pinter, natural hybrids would be hard to identify as such and might therefore have escaped attention. It is possible she says (p. 580), that “workers actually have collected hybrids or backcross offspring, yet assigned them to one of the two known species of grasshopper mice in the absence of obvious distinguishing characteristics.” Pinter 1971.
Peromyscus attwateri [Texas Deer Mouse]
× Peromyscus boylii [Brush Deer Mouse] NHR? Parapatric contact zone in western Texas. Osgood (1909) concluded that specimens with intermediate coloration were hybrids, but Lee et al. (1972) suggest that no reliable judgment can be made of the basis of such evidence.
× Peromyscus truei [Piñon Mouse] Hoffmeister (1981, p. 4) notes that a population comanche, has been treated as a race of both P. boylii and P. truei, and as a separate species. Normally such a history of treatment would suggest comanche as a PHP of crossing between boylii and truei. However, Schmidly (2004, p. 397) says Choate examined all available comanche specimens and concluded that they were all P. attwateri. Since, however, the specimens in question come from a region where attwateri and truei come into contact (northern Texas), it seems likely that comanche actually is a PHP of crossing between attwateri and truei.
× Peromyscus gossypinus [Cotton Deer Mouse] Parapatric contact zone (northern Texas, southern Oklahoma). No hybrids as yet reported. Schmidly 2004.
Peromyscus boylii [Brush Deer Mouse] See: Peromyscus attwateri.
Note: Peromyscus comanche is not listed by Duff and Lawson (2004).
Peromyscus comanche [Tule Deer Mouse]
× Peromyscus nasutus [Northern Rock Deer Mouse] CHR. HPF. Parapatric contact zone in northern Texas (see Hall and Kelson 1959, p. 643). Several male hybrids produced no spermatozoa, but at least one successfully backcrossed to P. comanche. These taxa were formerly lumped. Blair 1943a; Tamsitt 1958.
× Peromyscus truei [Piñon Rock Deer Mouse] CHR. DRS. These taxa are now usually lumped, but Tamsitt (1958, 1960) says their hybrids produce defective spermatozoa.
Peromyscus crinitus [Canyon Mouse] Two populations (auripectus, pergracilis), treated as races of P. crinitus, hybridize in northern Arizona (w end of Grand Canyon). Hoffmeister 1986 (Map 5.76 and p. 349).
Peromyscus difficilis [Zacatecan Deer Mouse]
× Peromyscus nasutus [Northern Rock Deer Mouse] Parapatric contact zone (n Mexico). No hybrids as yet reported. Hall and Kelson 1959 (p. 643).
Peromyscus eremicus [Cactus Deer Mouse]
× Peromyscus interparietalis (↔) [San Lorenzo Deer Mouse] CHR. HPF(♂&♀). DRS. Heterotic hybrids. These taxa were recently lumped. Brand and Ryckman 1969; Lawlor 1971.
Peromyscus gossypinus [Cotton Deer Mouse]
See also: Peromyscus attwateri.
× Peromyscus leucopus (↔) [White-footed Deer Mouse] CAENHR. HPF(♂&♀). CON: broad overlap in Mississippi Valley. In regions where these mice come into contact gossypinus is generally restricted to lowlands and leucopus occurs at higher elevations. Natural hybridization occurs in most areas of contact. Barko and Feldhamer 2002; Blair 1943b, 1951; Bradshaw 1965, 1968; Dice 1937, 1940a, 1940b; Foreman 1966; Howard 1950; Howell 1921 (p. 50); Lovecky et al. 1979; McCarley 1954a, 1954b, 1963, 1964; St. Romain 1974.
× Peromyscus maniculatus (♀) [North American Deer Mouse] CHR. CON: southeastern U.S. Maddock and Dawson (1974, p. 625) say that in artificial insemination experiments only a single hybrid embryo implanted (although some others showed normal cleavage). The reciprocal cross was not attempted.
Peromyscus interparietalis [San Lorenzo Deer Mouse] See: Peromyscus collatus; P. eremicus.
Peromyscus keeni [Northwestern Deer Mouse]
× Peromyscus maniculatus [North American Deer Mouse] CHR. CON: northwestern North America. HPF. The reported cross was “Peromyscus maniculatus oreas” × “P. m. gracilis,” but oreas is a synonym of keeni. Liu 1954 (see also: Zheng et al. 2003).
Note: There are hybrid zones between various cytotypes of Peromyscus leucopus. Morzunov et al. 1998; Nelson et al. 1987; Schmidt (C. A.) 1999; Stangl 1986; Stangl and Baker 1984; van den Bussche et al. 1993.
Peromyscus leucopus [White-footed Deer Mouse]
See also: Peromyscus gossypinus.
× Peromyscus maniculatus (♀) [North American Deer Mouse] CANHR. CON: U.S., Mexico. Maddock and Dawson (p. 625) mention unconfirmed reports of adult natural hybrids. They also say that, within 15 days of artificial insemination, development is usually arrested, but that hybrids are sometimes born alive. Chang et al. 1969; Dawson et al. 1972; Maddock and Dawson 1974.
Note: Peromyscus maniculatusis probably the most widespread and abundant mammal native to North America. Two populations are treated as subspecies, maniculatus, a large, long-tailed, big-eared woodland form and the other, bairdii, a much smaller, short-tailed (much less than half as long), small-eared field, or prairie form. Morphologically intermediate populations exist in Wisconsin and Michigan. Internet Citations: BOBP.
Peromyscus maniculatus [North American Deer Mouse]
See also: Peromyscus keeni.
× Mesocricetus auratus [Golden Hamster] Insemination of a P. maniculatus female with M. auratus sperm produced two instances of first cleavage. Maddock and Dawson (1974, pp. 630-631) say that in one of these cases “a regular two-cell stage was observed, and each blastomere indicated regular organization of a mitotic apparatus for the second division.” In another mouse, probable sperm penetration of an ovum was seen.
× Peromyscus melanotis (♂) [Black-eared Deer Mouse] CHR. ENHI. CON: southwestern U.S. HPF(♂&♀). The fact that there has been uncertainty whether certain variable populations in southern Arizona should be assigned to one or the other of these taxa (Bowers et al. 1973), suggests that they are intermediate. They are therefore PHPs of this cross. In a small-scale experiment, Clark (1966) obtained viable progeny from one of two caged pairs.
× Peromyscus oreas (♀) [Columbian Deer Mouse] CHR. CON: northwestern U.S. (Puget Sound region). Hogan et al. (1993) lumped P. oreas under P. keeni. Liu 1950.
× Peromyscus polionotus (↔) [Oldfield Deer Mouse | Beach Mouse] CHR. HPF(♂&♀). CON: southeastern U.S. (northern Alabama, northern Georgia, northwestern S. Carolina). Dawson et al. (1982, p. 1) say that when P. polionotus female sare caged for six months or longer with P. maniculatus males, only about 5% of mated pairs produce offspring that survive to weaning, due to substantial fetal and maternal mortality, compared with 50-75% for the reciprocal cross or for pure parental matings. At birth, hybrids from P. maniculatus mothers are about twice the size of the reciprocal hybrid (the placenta is six times as large). Displaying edema and eczema, they suffer from high pre-weening mortality, unlike hybrids from the reciprocal cross (Dawson 1966). With the cross in either direction, hybrids are partially fertile in both sexes. Mature F₁ hybrids with Peromyscus maniculatus mothers are smaller on average even than P. polionotus, the smaller parental form. F₁ hybrids from the reciprocal cross are generally larger than P. maniculatus. Similar size differences are seen in the reciprocal crosses of lion (Panthera leo) and tiger (Panthera tigris). In the F₁ generation, males are less fertile than females, but F₂ generations have been produced. Dawson (1965, p. 54) says, “Backcrosses and crosses between the F₁ gave higher fertility in general than did the interspecific crosses.” Maddock and Dawson found that 62% of P. maniculatus ova artificially inseminated with P. polionotus sperm were fertilized (compared with 81% fertile for P. maniculatus inter se inseminated controls). Bell and Dawson 1983; Bell et al. 1983; Blair and Howard 1944; Camp 1960; Chang et al. 1969; Cowling et al. 1994; Dawson 1963, 1969, 1965, 1966, 1971, 1982; Dawson et al. 1982, 1983, 1993; Dice 1933, 1940b; Dice and Blossom 1937; Duselis and Vrana 2007, 2010; Finlay 1970; Finlay and Dawson 1970; Fukuda et al. 1979; Hertwig 1936; Liu 1953a, 1953b†; Loschiavo et al. 2006; Maddock and Chang 1979; Maddock and Dawson 1974; Moore 1965; Rogers and Dawson 1970; Sumner 1930, 1932; Vrana 1999; Vrana et al. 1998, 2000, 2001; Watson 1942; Wiley et al. 2008; Zechner et al. 2004.
× Podomys floridanus [Florida Mouse] Attempted artificial insemination of P. maniculatus females failed to produce hybrids. Maddock and Dawson 1974.
× Oryzomys palustris [Marsh Rice Rat] Insemination of a P. maniculatus female with O. palustris sperm produced a regular two-cell embryo. Maddock and Dawson 1974 (p. 630).
× Sigmodon hispidus [Hispid Cotton Rat] Insemination of a P. maniculatus femalewith S. hispidus sperm produced a regular two-cell embryo. Maddock and Dawson 1974 (p. 630).
Peromyscus melanotis [Black-eared Deer Mouse] See: Peromyscus maniculatus.
Peromyscus nasutus [Northern Rock Deer Mouse]
See also: Peromyscus comanche; P. difficilis.
× Peromyscus truei (↔) [Piñon Deer Mouse] CHR. HPF(♀♀). CON: southwestern U.S., northwestern Mexico. Hybrids produce abnormal spermatozoa. Moree (1948) says mixed matings result in a reduction of about 85% in litters per mating, 42% in young per litter, and 91% in young per mating. Some male hybrids may be partially fertile—Moree (1946) says that, depending on the particular individual examined, spermatogenesis in hybrids forms a graded continuum between the two extremes of termination in pachytene and normal completion of meiosis. Although no natural hybrids are explicitly reported, Hall and Kelson (1959, p. 642) say nasutus and truei “are difficult to distinguish.” Under such circumstances, hybrids, too, would be hard to identify. Blair 1943b; Dice 1940b, 1952; Dice and Liebe 1937; Moree 1946, 1948.
Peromyscus oreas [Columbian Deer Mouse] See: Peromyscus maniculatus.
Peromyscus polionotus [Oldfield Deer Mouse | Beach Mouse] See: Peromyscus maniculatus.
Peromyscus truei [Piñon Deer Mouse] See: Peromyscusattwateri; P. comanche; P. nasutus. Probable hybrids between two populations (nevadensis, truei), treated as races of P. truei, occur in northwestern Arizona (Mojave Co.). Hoffmeister 1986 (p. 371).
Peromyscus yucatanicus [Yucatán Deer Mouse] On the Yucatan Peninsula (southern Mexico) there is a broad hybrid zone between two populations (badius, yucatanicus) treated as races of P. yucatanicus. Lawlor 1965; Young and Jones 1983.
Phyllotis darwini [Darwin’s Leaf-eared Mouse]
× Phyllotis magister (↔) [Master Leaf-eared Mouse] CHR. DRS. HPF. Walker et al. (1999) say that in hybrids "Usually, only one member of parental homologous chromosomes showed AgNOR+; nevertheless, both homeologous chromosomes were active in many hybrid cells." They suggest that the fact that both NORs were active in many cells suggests that the parents in this cross are closely related.
× Phyllotis xanthopygus (↔) [Yellow-rumped Leaf-eared Mouse] CANHR(e Chile). LFH. Probable hybrids have been reported from Paiguano. A population (vaccarum) of eastern Chile and western Argentina was formerly treated as a race of P. darwini, but now as one of P. xanthopygus (e.g., Kramer et al. 1999; Stepan 1998). This change followed suggestions of Walker et al. (1984) who found that hybrids from P. xanthopygus dams were less viable and occurred in lower mean litter sizes than did the offspring produced from pure matings. Walker et al. examined the testes of three hybrids and found spermatozoa were absent. They also examined the ovaries of two hybrids from vaccarum dams and found they contained no germinal or follicular cells. They detail the histology of these hybrid testes and ovaries. The small scale of their study does not, however, allow one safely to conclude all hybrids are sterile. Pairings of darwini males with xanthopygus females resulted in increased litter sizes and rates of aggression in comparison with the reciprocal cross. Walker et al. (1998) found that active NORs were mainly from darwini chromosomes. Osgood 1943 (p. 205); Pearson 1958 (p. 419); Spotorno and Walker 1983; Walker et al. 1984; 1998.
Phyllotis magister [Master Leaf-eared Mouse] See: Phyllotis darwini
Phyllotis xanthopygus [Yellow-rumped Leaf-eared Mouse] See: Phyllotis darwini
Podomys floridanus [Florida Mouse] See: Peromyscus maniculatus
Oryzomys palustris [Marsh Rice Rat] See: Peromyscus maniculatus.
Reithrodontomys longicauda [Sonoma Harvest-mouse]
× Reithrodontomys megalotis [Western Harvest-mouse] Long PCZ in California. Reithrodontomyslongicauda, Baird 1858 was reclassified as a subspecies of R. megalotis after natural hybridization between the two was reported. Other former common names of R. longicauda are Long-tailed Harvest-mouse and Chiricahua Harvest-mouse. Mearns 1907 (p. 456)
Sigmodon hispidus [Hispid Cotton Rat] See: Peromyscus maniculatus. Two populations (hispidus, texianus), treated as races of S. hispidus, have a narrow hybrid zone in eastern Texas. Pugh and McKnight 2005.
By the same author: Handbook of Avian Hybrids of the World, Oxford University Press (2006).
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