The camas pocket gopher (Thomomys bulbivorus), also known as the camas rat or Willamette Valley gopher, is a rodent and the largest member in the genus Thomomys of the family Geomyidae. First described in 1829, it is endemic to the Willamette Valley of northwestern Oregon in the United States. The herbivorous gopher forages for vegetable and plant matter, which it collects in large, fur-lined, external cheek pouches. Surplus food is hoarded in an extensive system of tunnels. The dull-brown-to-lead-gray coat changes color and texture over the year. The mammal's characteristically large, protuberant incisors are well adapted for use in tunnel construction, particularly in the hard clay soils of the Willamette Valley. The gophers make chattering sounds with their teeth; males and females make purring (or crooning) sounds when they are together, and the young make twittering sounds. Born toothless, blind and hairless, the young grow rapidly before being weaned at about six weeks of age.
Although the camas pocket gopher is fiercely defensive when cornered, it may become tame in captivity. While population trends are generally stable, threats to the species' survival include urbanization, habitat conversion for agricultural use and active attempts at eradication with trapping and poisons. It is prey for raptors and carnivorous mammals, and host to several parasitic arthropods and worms. Scientists believe that the gopher's evolutionary history was disrupted when the Missoula Floods washed over the Willamette Valley at the end of the last ice age. The floods almost completely inundated its geographic range, which may have caused a genetic bottleneck of survivors that repopulated the region after the waters receded.
Taxonomy There are six genera of North American pocket gophers: Cratogeomys, Geomys, Orthogeomys, Pappogeomys, Thomomys, and Zygogeomys. The camas pocket gopher is a smooth-toothed pocket gopher of the genus Thomomys, within the pocket-gopher family Geomyidae. The incisors of gophers in the genus Thomomys have characteristically smooth anterior surfaces, while those of Geomys have two deep grooves per tooth and those of Cratogeomys have a single groove. The camas pocket gopher is a member of the subgenus Megascapheus, established in 1903, at that time for the camas pocket gopher alone. Taxonomists subsequently assigned other gophers to the same subgenus. The name Thomomys derives from the Greek σωρός (heap) + μῦς (mouse), probably describing the mounds of excavated soil produced by the burrowing gopher. Bulbus translates as "bulb" in Latin, and the word for "devour" is voro. Naturalist David Douglas reported that the gopher consumed bulbs of the camas lily, and Vernon Bailey later attributed the lack of camas lilies in areas inhabited by the gopher to the bulbs being eaten. However, naturalist H. M. Wight observed that the gopher ate primarily dandelion greens, and was skeptical that it was a large consumer of bulbs.
Early history
The taxonomy of the camas pocket gopher and its genus, Thomomys, have a convoluted history. According to a review article published by the American Society of Mammalogists in 1987, Johann Friedrich von Brandt was the first to refer to the camas pocket gopher as Thomomys bulbivorus in an 1855 article published by the Imperial Academy of Sciences. In the 1855 article, Brandt refers to Tomomys bulbivora without the "h" and ending with an "a". He writes parenthetically "(man schreibe nicht Thomomys)". The authors of the 1987 review note that they did not see Brandt's actual article, but source the textbook The mammals of North America published in 1981.
Early confusion arose from writings by John Richardson between 1828 and 1839. Although he describes six species in the genus, according to later critics he was unfamiliar with all specimens. Richardson's descriptions of the animals and the figures in the text were also criticized. His 1829 Fauna boreali-americana describes a type specimen of camas pocket gopher obtained from the "banks of the Columbia River, Oregon", the northern limit of the gopher's geographic range. This was probably Portland, at the confluence of the Willamette and Columbia Rivers, the only place on the Columbia where subsequent specimens have been found. The present location of this initial specimen is uncertain; reportedly stored at the Hudson Bay Museum, it could not be located in 1915. When Richardson made his first examination, the specimen was apparently incomplete; although Joel Asaph Allen wrote in 1893 that it consisted only of the skin, Richardson described the skull and facial features in detail.
In Fauna boreali-americana, Richardson assigns the mammal to the now-defunct genus Diplostoma described by Rafinesque in 1817. He named it Diplostoma ? bulbivorum. Illustration-labeling errors in Richardson's book further confounded subsequent taxonomists; the plate was labeled Diplostoma douglasii.
The confusion around the species' taxonomy and identification amplified when naturalist Spencer Fullerton Baird interpreted Richardson's reports. The camas pocket gopher's large size led Baird to conclude that the animal's measurements (reported by Richardson) were an artifact of its taxidermy preparation. Baird was also apparently in error about the location from which the specimen was taken, attributing the name Thomomys bulbivorus to a set of previously collected specimens later known as the California Gopher. This confusion was echoed by subsequent authors. The article on gophers in the 1879 edition of the American Cyclopædia has an illustration captioned "California Gopher (Thomomys bulbivorus)". The ninth edition of the Encyclopædia Britannica (published during the late 19th century) mistakenly reports Thomomys bulbivorus as abundant along the central California coast.
Clarifications
Although Baird and Elliott Coues were involved in early assessments of the genus, according to Allen neither ever saw a specimen of the camas pocket gopher (T. bulbivorus). Allen obtained and examined two large adults (male and female) collected in Beaverton, Oregon, in May 1890 which were considerably larger and darker than previously examined specimens. Skull features and white markings around the mouth and anus also differed. His findings and the specimen-collection location helped identify the camas pocket gopher as a species separate from California gophers. The California specimens were classified by Eydoux and Gervais as Oryctomys bottae, now known as Thomomys bottae (Botta's pocket gopher). They were found near Monterey, California, over south of the now-recognized range of the Camas pocket gopher.
The distribution of Elliot's "great pocket gopher" (as it was known) extended along the California coast "north of San Francisco." James Audubon and John Bachman reassessed the taxonomy on the camas pocket gopher in the late 1800s. They referred it as the "camas rat". They reclassified the gopher as Pseudostoma borealis. They rejected Diplostoma as a genus, and assigned Diplostoma bulbivorum as synonymous with P. borealis. They attributed any differences described by Richardson to artifact, from a specimen that was "twisted and disfigured" in preparation. Based on observations of taxidermy specimens in Europe, they suggested that Townsend's pocket gopher (Geomys (Thomomys) townsendii) belonged to the same species. In 1875, the camas pocket gopher was reported as a sub-species of the northern pocket gopher (Thomomys talpoides),. During the 1920s H. M. Wight referred to it colloquially as the "Willamette Valley gopher".
Current phylogeny In 2008, a team of biologists from the University of California, Berkeley and Harvard University published multilocus phylogenetic analysis results of the genus Thomomys. The camas pocket gopher was found to be well separated from other taxa in the subgenus Megascapheus. These findings suggested that the camas pocket gopher was a sister to the other taxa in the subgenus, but the relationships between those other animals was less clear. Only one camas pocket gopher was included in this study, which limited the ability to distinguish features such as monophyly. The following cladogram was presented showing the placement of the camas pocket gopher among its closest relatives:
Patterns of genetic variation in the camas pocket gopher have been studied. Although there are no subspecies, there is substantial genetic diversity within the species. Its genetic patterns are consistent with limited inbreeding within specific populations. This is similar to patterns described in Botta's pocket gopher and the southern pocket gopher, both of which are members of the same genus. However, it contrasts with patterns noted in Baird's pocket gopher and the plains pocket gopher, members of a separate genus, Geomys, which showed a higher degree of inbreeding.
The species' genetic diversity is similar to that of other pocket gophers occupying a larger geographic range and diversity of habitat. Compared to Townsend's pocket gopher, which is distributed across a much larger area, but less diverse habitat, it is more genetically heterogeneous. Although there is considerable differentiation between separate populations of camas pocket gophers, their genetic variability does not affect the mammal's appearance. Study of the effects of genetic change over time revealed a pattern affected by a cataclysmic event across the species' entire geographic area about 13,000 years ago. Such an event would cause a population bottleneck, leading to scattered, isolated populations.
Description
The camas pocket gopher is, by a small margin, the largest member of its genus (Thomomys). The fur is a dull brown above and dark, leaden gray beneath. There are often patches of white on the chin, throat and around the anus, and it has blackish ear and nose markings. The external ear is a thickened rim of tissue. During the summer, the gopher's coat is short and coarse; winter pelage is longer and furrier. The coat of the young is similar to the adult summer coat, but with more sparsely distributed fur; the abdominal skin may be visible.
Like other gophers, it has small eyes and ears and a nearly hairless tail. Its shoulders are broader than its hips. It is pentadactyl, with five claws on each foot. The claws on its forefeet are longer than those on its hind feet, and its middle claws are longest. The front claws of the camas pocket gopher are short and weak relative to its size. It employs plantigrade locomotion. The male is larger than the female, measuring an average in length. A large male weighs about . One male specimen was long and weighed . Females are about long. The tail measures in the male and in the female. An adult male's hind feet measure , and an average female's hind feet measure . There are four mammary glands: two in the inguinal region and two in the pectoral region, each supplying a pair of nipples. Morphologically, it most closely resembles Botta's pocket gopher; differentiation can be made based on the concavity of the inner surface of the pterygoids, small claws, more uniform fur coloring and exoccipital groove of the camas pocket gopher.
Skull and dentition
The skull of the camas pocket gopher is sturdily proportioned. The camas pocket gopher and other smooth-toothed pocket gophers with robust snouts are included in the subgenus Megascapheus. Male skulls measure in length across the base and if the incisors are included. The short, wide skull has a relatively short nasal passage. In width, the skull measures across the nasal passages, across the mastoids and at the zygomatic arches. The external auditory meatus is broad and open, although the auditory bullae are confined.