Rattus exulans Peale 1848

Rattus exulans Peale 1848, Mammalia, in: Repts. U. S. Expl. Surv., Vol. 8: 47.

Type Locality: Society Isls, Tahiti Isl (France).

Vernacular Names: Pacific Rat.

Synonyms: Rattus aemuli (Thomas 1896); Rattus aitape Troughton 1937; Rattus apicus (Mearns 1905); Rattus basilanus (Hollister 1913); Rattus bocourti (Milne-Edwards 1872); Rattus browni (Alston 1877); Rattus buruensis (J. A. Allen 1911); Rattus calcis (Hollister 1911); Rattus clabatus (Lyon 1906); Rattus concolor (Blyth 1859); Rattus echimyoides (Ramsay 1877); Rattus ephippium (Jentink 1880); Rattus equile Robinson and Kloss 1927; Rattus eurous Miller and Hollister 1921; Rattus gawae Troughton 1845; Rattus hawaiiensis Stone 1917; Rattus huegeli (Thomas 1880); Rattus jessook (Jentink 1879); Rattus lassacquerei Sody 1933; Rattus leucophaetus (Hollister 1913); Rattus luteiventris (J. A. Allen 1910); Rattus malengiensis Sody 1941; Rattus manoquarius Sody 1934; Rattus maorium (Hutton 1870); Rattus mayonicus (Hollister 1913); Rattus melanoderma (Dieterlen 1986); Rattus meringgit Sody 1941; Rattus micronesiensis Tokuda 1933; Rattus negrinus (Thomas 1898); Rattus obscurus (Miller 1900); Rattus ornatulus (Hollister 1913); Rattus otteni Kopstein 1931; Rattus pantarensis (Mearns 1905); Rattus praecelsus Troughton 1937; Rattus pullus (Miller 1901); Rattus querceti (Hollister 1911); Rattus raveni Miller and Hollister 1921; Rattus rennelli Troughton 1945; Rattus schuitemakeri Sody 1933; Rattus solatus Kellogg 1945; Rattus stragulum (Robinson and Kloss 1916); Rattus suffectus Troughton 1937; Rattus surdus (Miller 1903); Rattus tibicen Troughton 1937; Rattus todayensis (Mearns 1905); Rattus vigoratus (Hollister 1913); Rattus vitiensis (Peale 1848); Rattus vulcani (Mearns 1905); Rattus wichmanni (Jentink 1890) .

Distribution: E Bangladesh, C and S Burma, Thailand, Laos, Cambodia, C and S Vietnam, Yongxing Isl in the Xisha Arch (in South China Sea southeast of Hainan Isl between 16E and 18EN; Wang, 2003), E Taiwan and Miyakojima Isl in S Ryukyus (Motokawa et al., 2001 a), Sundaic region (incl. Mentawai Isls, and islands of Enggano, Nias, and Simeulule), Christmas Isl (Gibson-Hill, 1947), Sulawesi, Philippines (Heaney et al., 1998), Moluccas (Flannery, 1995 b), and Nusa Tenggara (Lesser Sunda Isls); New Guinea Region (Taylor et al., 1982; Flannery, 1995 a), SW Pacific Isls (Flannery, 1995 b) Adele and Murray Isls off the coast of NW and NE Australia (not recorded from mainland; Mahoney and Richardson, 1988; Taylor and Horner, 1973; Watts, 1995 h; Watts and Aslin, 1981), Micronesia, New Zealand (Atkinson and Moller, 1990), Polynesia (including Caroline Isls; Buden, 1996 a, 1996 b), Hawaiian Isls (Tomich, 1986), and Easter Isl. Not documented from Andaman or Nicobar Isls (Chaturvedi, 1980; Musser’s research), despite assertion of Wodzicki and Taylor (1984), who otherwise adequately summarized general distribution; details recorded by Musser and Newcomb (1983) and Corbet and Hill (1992). Range also based upon our study of specimens in several museums (also see Matisoo-Smith et al., 1998).

Conservation: IUCN – Lower Risk (lc).

Discussion: Rattus exulans species group. Inadvertent or intentional human introduction or possibly natural rafting is responsible for most of the Pacific insular occurrences (Langdon, 1995; Matisoo-Smith and Robins, 2004; Matisoo-Smith et al., 1998; Roberts, 1991), and for distributions on islands and archipelagos outside of mainland SE Asia, the region where the species may have originated (Musser and Newcomb, 1983). Matisoo-Smith et al. (1998) claimed that R. exulans was among the plant and animal species carried by ancestral Polynesians in their colonizing canoes. They analyzed mtDNA sequences in an array of Polynesian samples, concluding that the sequences "prove to be valuable genetic markers for tracing the migration routes and movement of the first humans entering the remote Pacific" (p. 15149). A subsequent study by Matisoo-Smith and Robins (2004) documents evidence for origins and dispersals of Polynesians derived from mtDNA phylogenies of R. exulans . Standard karyotype (2n = 42, FN = 60) for Philippines, Indomalayan region, Oceania, and Papua New Guinea summarized by Rickart and Musser (1993), and for Taiwan sample by Motokawa et al. (2001 a).

In a significant report on variation in skull size among R. exulans, R. rattus, and R. norvegicus in New Zealand and other Pacific islands, Yoram et al. (1999) documented increase in skull size with latitude for R. exulans but not for the other two. Other relationships between skull size and island area as well as species sympatry are also presented; all aspects bear on understanding insular morphological variation in these species, especially R. exulans, and their taxonomy. Reliability of radiocarbon dating skeletal remains of New Zealand R. exulans discussed by Hedges (2000) and Higham and Petchey (2000), a test between radiocarbon dates and those obtained by Carbon 14 accelerator mass spectrometry using R. exulans reported by Holdaway and Beavan (1999), and possible role of burial contamination or diet in radiocarbon anomalies documented by Beavan-Athfield and Sparks (2001 a, 2001 b; also see references cited there). Reliability of dating techniques bears significantly on first colonization dates of R. exulans to New Zealand. Data presented by Holdaway (1996:226) indicates the Pacific rat was established on both main islands nearly 2000 years ago, much earlier than the time established for human settlement (about 850 years ago) based on unequivocal evidence. Holdaway reasoned that R. exulans was introduced by "transient human visitors, who either left immediately or quickly died out," and noted that for "more than 1,000 years after its arrival, the Pacific rat was the sole exotic predator in New Zealand." Whether R. exulans was spread by human transport or natural rafting throughout the Pacific is a controversial topic, and Langdon’s (1995) discussion of rodent colonization of Easter Isl is relevant in this context (see also Matisoo-Smith and Robins, 2004; Matisoo-Smith et al., 1998).