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SPECIES Rattus rattus

Author:Linnaeus, 1758.
Citation:Syst. Nat., 10th ed., 1: 61.
Common Name:Roof Rat
Type Locality:Sweden, Uppsala County, Uppsala.
Distribution:Native to Indian Peninsula (Niethammer, 1975) and introduced worldwide in the temperate zone and parts of the tropical and subantarctic zones (Alcover and Gosalbez, 1988; Al-Jumaily, 1998; Amoti et al., 1999; Andreotti et al., 2001; Armitage, 1994; Aulagnier and Thevenot, 1986; Becker, 1978a; Blaaderen, 1992; Corbet and Hill, 1992; Crawford-Cabral, 1998; de Graaff, 1981; de Roguin, 1991; Dieterlen, 1979; Dobigny et al., 2002b; Downs and Wirminghaus, 1997; Duplantier et al., 1991b, 1997; Endepols et al., 2001; Gromov and Erbajeva, 1995; Grubb et al., 1998; Hall, 1981; Harrison and Bates, 1991; Helgen, 2001; Innes, 1990; Johnson, 1962a, b; Key et al., 1998; Kryštufek, 1991; Kryštufek and Vohralík, 2001; Kucheruk, 1994; Lay, 1967; Le Berre, 1990; Mahoney and Richardson, 1988; Meinig, 2000; Mitchell-Jones, et al., 1999; Niethammer, 1975; Osborn and Helmy, 1980; Osgood, 1943; Petrov, 1992; Prakash et al., 1995a, 1995b; Qumsiyeh, 1996; Ranck, 1968; Roberts, 1977, 1997; Smaha, 1996; Stanley et al., 1998, 2000, 2002; Taylor and Horner, 1973; Taylor et al., 1982; Tomich, 1986; Twigg, 1992; Vincent, 2001; Vohralík and Andera, 2000; Watts, 1995j; Yosida, 1980; Yosida et al., 1985). Southernmost limit is the subantarctic Macquarie Isl where R. rattus was introduced by sealers during the 19th century (Pye et al., 1999).
Status:IUCN – Lower Risk (lc).

Rattus rattus species group. Numerous cytogenetic studies focusing on the R. rattus complex, as summarized by Baverstock et al. (1983c), Bekasova and Mezhova (1983), Niethammer (1975), and Yosida (1980), have revealed two basic groups of populations. The Oceanian or European type has 2n = 38 (40 in some), the Asian type is characterized by 2n = 42; the two are also distinguished by biochemical features (Baverstock et al., 1983c) as well as morphological traits (Schwabe, 1979). An ongoing taxonomic study of the Rattus rattus complex by K. Aplin and H. Suzuki and their collaborators, has confirmed that separateness of the 2n = 38 populations (based on samples from four continents, but not yet including Indian samples) from the various East and Southeast Asian populations (Aplin et al., 2003c). Moreover, their studies indicate that the widespread ‘introduced’ populations are genetically all very similar, consistent with progressive lineage restriction as a result of multiple founder effects (K. Aplin, in litt., 2004). Where the Asian type is indigenous, the Oceanian form is restricted to ports or on ships in harbor. Both chromosomal kinds apparently occur together without evidence of interbreeding on the Polynesian island of Fiji (Yosida et al., 1985), but do hybridize in the laboratory (usually producing sterile offspring) and on the South Pacific islands of Chichijima and Eniwetok (with apparent introgression). The biological status of the two kinds is best summarized by Baverstock et al. (1983c:978), who noted that if "the chromosomal, electrophoretic and laboratory hybridization data are considered together, it seems that the 2n = 38 and 2n = 42 forms are best considered as incipient species. Where they meet, they may introgress, become sympatric without interbreeding or one may replace the other depending upon the prevailing biological conditions," a view earlier espoused by Capanna (1974). Rattus rattus is the name for the 2n = 38/40 group, and we list it as a species separate from the 2n = 42 form, for which the oldest name is apparently R. tanezumi (see that account).

Populations on Ceylon are unique among R. rattus in that most highland samples exhibit 2n = 40 ("Ceylonese type"; found nowhere else within the range of the species), lowland samples have 2n = 38, and hybrids (2n = 39) occur in both regions (Yosida et al., 1979). Detailed analyses of chromosomal and biochemical traits have been used to characterize these Ceylonese populations, extent of hybridization in the laboratory and field, and evolutionary origin of the 2n = 40 configuration in context of phylogenetic relationship to typical peninsular Indian R. rattus (Yosida, 1977, 1978b, 1979, 1980; Yosida et al., 1974).

Historically, three color phases have been considered as subspecies with their own geographic distributions: alexandrinus (grayish brown dorsum, pure white venter), frugivorus (grayish brown dorsum and gray through grayish buff to slate-gray venter), and rattus (ranging from grayish black upperparts merging into slate-gray underparts to completely melanistic coats). Nearly 140 years ago, de L’isle (1865) determined through breeding experiments that all three morphs interbreed freely, can even be found in the same litter, and signal color polymorphism within a single species, not intraspecific geographic variation, results substantiated by subsequent research and observations (Feldman, 1926; Grubb et al., 1998, and references cited therein; Hinton, 1918; Johnson, 1946b, 1962a; Jones and Johnson, 1965; Rosevear, 1969; Tomich, 1968, 1986; Tomich and Kami, 1966; see color plate in Innes, 1990). Prakash et al. (1995a) recorded ecology and distribution of R. rattus alexandrinus from the Aravalli Ranges in Rajasthan, India, could not distinguish differences between what had been called rufescens and the "alexandrinus" color phase of R. rattus, and synonymized the two.

Allocation of five synonyms requires explanation. Musser and Califia (1982) listed keelingensis as a synonym of diardii, which is included in R. tanezumi (see that account); Musser reexamined the holotype and part of the type series collected from Pulau Tikus in the Cocos-Keeling Isls and now realizes they are introduced R. rattus. Both 2n = 42 and 2n = 38 have been attributed to specimens identified as Indian wroughtoni from the Mysore region (Gadi and Sharma, 1983; Lakhotia et al., 1973; Raman and Sharma, 1977); the holotype and paratypes are examples of R. rattus (Corbet, in litt., 2003; Musser’s study of types and material at BMNH), which accords with 2n = 38 recorded for most of the specimens; the individuals with 2n = 42 are likely R. satarae (see that account). Holotypes of Hinton’s (1918) Indian girensis and narbadae and most of the specimens in BMNH identified as these taxa represent R. rattus (Musser’s study of the specimens); material in the BMNH identified by Hinton as arboreus also sample populations of R. rattus.

Several recent studies elucidate regional colonization history, geographic distribution, and systematics of R. rattus: genetic diversity within and between W Mediterranean island populations (Cheylan et al., 1998; Cheylan, 1999); morphometric analysis of population from Congreso Isl, and comparison to nearby Iberian mainland populations (Ventura and López-Fuster, 2000); osteometric analysis of archaeological samples from the XIV and XVIIth centuries on Lavezzi Isl (off the coast of S Corsica), and comparison with recent samples from the island and Corsica (Vigne et al., 1993); analyses of chromosomes and mtDNA restriction patterns comparing samples from islands in the Mediterranean and Atlantic with mainland Europe and Africa (Libois et al., 1996); morphometric study comparing samples from the Azores with a continental sample (Ramalhinho et al., 1996); analysis and interpretation of archaeological samples from medieval (XIIIth Century) Portugal (Morales and Rodriguez, 1997); historical interpretation of presence in Eolian Arch. (Cristaldi and Amori, 1988); genetic and morphological divergence among introduced populations in the Galápagos Arch. (Patton et al., 1975); systematics of Turkish samples based upon chromosomal and morphological traits (Yi—it et al., 1998); assessment and review of swimming ability in context of potential for colonizing tropical oceanic islands (Spennemann and Rapp, 1989); review of Korean population (Jones and Johnson, 1965; Won and Smith, 1999); status and role in Baltic region (Miljutin, 1997, 1998; Timm et al., 1998).

Rattus rattus is unknown in Europe before the Holocene (Kowalski, 2001), and may have reached Mediterranean Europe by pre-Roman times (4000-2300 years BC) along ancient trade routes from India through the Indus Valley and Mesopotamia (Armitage, 1994; Toškan and Kryštufek, in press). The species already occupied (apparently as a commensal) coastal regions of N Israel by the Epipalaeolithic, about 15,000 years ago (Tchernov, 1968, 1996), and so was part of the Levant fauna since just before end of the Pleistocene. There is also a record of R. rattus from a cold interval in middle Pleistocene cave sediments of Turkish Thrace (Santel and Koenigswald, 1998). By the fourth century AD, the roof rat was in Britain and associated with Roman occupation (Armitage, 1994; Yalden, 1999). The earliest known record of R. rattus in the Americas comes from Haiti, at the site of La Navidad, the "first Spanish settlement in the New World, established by Columbus on December 26th, 1492"; by the late 1500s, the species was established along coasts of North, Central, and South America (Armitage, 1993:174-175).

Rattus rattus, not the Asian R. tanezumi, also occurs on Madagascar (Duplantier et al., 2003; Musser’s research). The species may have accompanied the first human immigrants to Madagascar about 2000 years ago with speculated transport through Zanzibar and Comoros islands to Madagascar, the same sea route used by Arab traders that facilitated the introduction of Suncus murinus (Duplantier and Duchemin, 2003; Hutterer and Tranier, 1990). Rattus rattus presently occurs everywhere on Madagascar, ". . . homes, fields, and forests, from sea level up to elevations of more than 2400 m" (Duplantier and Duchemin, 2003:1191). Its distribution over the island and along altitudinal transects, as well as associations with different forest formations and anthropogenic habitats has been extensively documented by recent faunal surveys (Carleton and Goodman, 2000; Goodman et al., 1996a, b; Goodman and Carleton, 1996, 1998; Stephenson, 1995). Relationship between the introduced R. rattus and nesomyine rodents, tenrecs and small-bodied lemurs in the context of protecting that endemic and unique assemblage (particularly competition between nesomyines and R. rattus, and possible elimination of the former by the introduced murine) is explicitly addressed by Goodman (1995) and Ramanamanjato and Ganzhorn (2001). Rattus rattus, not any of the native nesomyines, is also a reservoir for plague, which has been present in Madagascar for at least a century, and is restricted to two foci above 800 m (Duplantier et al., 2003).

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    aequicaudalis (Hodgson, 1845)
    aethiops (Philippi, 1900)
    albiventer (Jentink, 1909)
    albiventris (Jentink, 1909)
    albus (Fitzinger, 1867)
    alexandrino-rattus (Fatio, 1902)
    alexandrinus (É. Geoffroy, 1803)
    alexandrinus (Desmarest, 1819)
    arboreus (Horsfield, 1851)
    arboricola (Gould, 1863)
    asiaticus (Gray, 1837)
    ater (Fitzinger, 1867)
    ater (Millais, 1905)
    atratus (Miller, 1902)
    atridorsum (Miller, 1903)
    auratus (Grandidier, 1899)
    beccarii (Peters and Doria, 1881)
    brahminicus (Lloyd, 1909)
    brookei (Crew, 1923)
    caeruleus (Lesson, 1842)
    caledonicus (Wagner, 1842)
    ceylonus (Kelaart, 1850)
    chionogaster (Cabrera, 1921)
    chionogaster (Lönnberg and Mjoberg, 1916)
    coquimbensis (Philippi, 1900)
    crassipes (Blyth, 1859)
    cyaneus (Philippi, 1895)
    doboensis (de Beaufort, 1911)
    domesticus (Fitzinger, 1857)
    doriae (Trouessart, 1897)
    erythronotus (Temminck, 1844)
    flavescens (Elliot, 1839)
    flavigaster (Heuglin, 1861)
    flaviventris (Brants, 1827)
    frugivorus (Rafinesque, 1814)
    fuliginosus (Bonaparte, 1833)
    fulvaster (Fitzinger, 1867)
    fuscus (Fitzinger, 1857)
    galapagoensis (Waterhouse, 1830)
    girensis Hinton, 1918
    griseocaeruleus (Higgins and Petterd, 1883)
    indicus (É. Geoffroy, 1803)
    infralineatus (Blylth, 1863)
    insularis (Waterhouse, 1838)
    intermedius (Ninni, 1882)
    jacobiae (Waterhouse, 1838)
    jujensis (Lönnberg, 1916)
    jurassicus (Burg, 1921)
    kandianus (Kelaart, 1850)
    kandiyanus (Kelaart, 1887)
    keelingensis Tate, 1950
    kelaarti (Wroughton, 1915)
    kijabius (J. A. Allen, 1909)
    latipes (Bennett, 1835)
    leucogaster (Pictet, 1841)
    longicaudus Mori, 1937
    muansae (Matschie, 1911)
    narbadae Hinton, 1918
    nemoralis (Selys Longchamps, 1841)
    nericola Cabrera, 1921
    novaezelandiae (Buller, 1871)
    osorninus (Philippi, 1900)
    personatus (Krefft, 1867)
    picteti (Schinz, 1845)
    rattiformis (Matschie, 1915)
    rattoides (Pictet and Pictet, 1844)
    rufescens (Gray, 1837)
    ruthenus Ognev and Stroganov, 1936
    saltuum (Philippi, 1900)
    samharensis (Heuglin, 1877)
    setosus (Lund, 1841)
    siculae (Lesson, 1827)
    subcaeruleus (Lesson, 1842)
    subrufus (Philippi, 1900)
    sueirensis Cabrera, 1921
    sylvestris (Pictet, 1841)
    tectorum (Savi, 1825)
    tetragonurus (Kelaart, 1850)
    tettensis (Peters, 1852)
    tompsoni (Ramsay, 1881)
    variabilis (Higgins and Petterd, 1883)
    varius (Fitzinger, 1867)
    wroughtoni Hinton, 1919

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