Orthogeomys grandisgiant pocket gopher

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Geographic Range

Members of the genus Orthogeomys are restricted to Central America and Mexico. The species Orthogeomys grandis is found on the south Pacific Slope of Mexico to southeastern Honduras. (Nowak, 1997; Reid, 1997; Woods, 1990)

Habitat

A fossorial species, O. grandis inhabit evergreen, deciduous, forests in tropical lowlands and mountain valleys as well as agricultural areas. Their elevational range extends from sea level to 3,000 meters.

The gophers prefer areas that are conducive to digging with soil that is neither too rocky, too hard, too steep, nor too moist. Species in the genus Orthogeomys spend most of their time in shallow tunnels typically 10-30 cm below the surface. (Nowak, 1997; Reid, 1997; Woods, 1990)

  • Range elevation
    0 to 3,000 m
    0.00 to ft

Physical Description

Orthogeomys grandis is the largest species of pocket gophers in the family Geomyidae. The animals are uniformly reddish brown to black in color with pale, sparsely furred undersides. The bodies of the gophers are covered with sensitive vibrissae. Individual head and body measurements range from 225 mm to 285 mm and tail measurements range from 85mm to 135 mm. Individuals typically weighs around 830 grams. In general, males tend be slightly larger than females as females stop growing as soon as they become sexually mature whereas males grow continuously throughout their lives.

Pocket gophers in the genus Orthogeomys have thick, stocky bodies with nearly indistinguishable necks. Their short, naked tails are highly vascularized and very sensitive. As a result, tails are used as a tactile organs and aid the gophers in finding their way through their underground burrows. Their tails may also serve to regulate the animal's body temperature, dissipating body heat when burrows become too warm.

Well suited to their underground lifestyle, their eyes and ears are small. Lids tightly seal their eyes and a protective flap covers their auditory canals. Well-developed lacrimal glands produce a think fluid that keeps their corneas free of dirt. Their lips can be closed behind their large incisors enabling the gophers to chew away at dirt while digging without getting any in their mouths.

There are two long, external, fur-lined pockets that extend from the facial region of the gophers to their shoulders and are used for the transport of food. The pouches can be turned inside-out for cleaning and pulled right side in with a specialized muscle. Their forearms are specialized for digging as are their five robust claws. The flexibility and thickness of the skin around their heads and throats of the gophers is thought to be advantageous for fighting.

Pocket gophers have massive, angular, flat skulls with wide zygomatic arches; excellent modifications for their fossorial life. They have a total of 20 hypsodont teeth with greatly reduced enamel. Their dental formula is 1/1, 0/0, 1/1, 3/3. Their dumbbell shaped premolars are the largest grinding teeth. Their upper incisors each have one center groove, a feature that distinguishes them from other gophers in the family Geomyidae.

The range of O. grandis overlaps the range of O. hispidus, a species that tends to be smaller and redder in color. Both species have a groove in their upper incisors, though the groove in O. hispidus is narrower, more shallow and more offset than the groove in O. grandis.

There is no information regarding the basal metabolic rate of O. grandis, though in general, fossorial rodents tend to have low basal rates of metabolism, high conductances, and high ranges of thermoneutrality. (Freye, 1975; McNab, 1966; Nelson and Goldman, 1930; Nowak, 1997; Reid, 1997; Woods, 1990)

  • Sexual Dimorphism
  • male larger
  • Average mass
    830 g
    29.25 oz
  • Range length
    225 to 285 mm
    8.86 to 11.22 in

Reproduction

Orthogeomys grandis is a polygamous species with around four females to each male. Otherwise solitary, pocket gophers become much more social during the reproductive period. Because it is thought that O. grandis mates year round, it can be inferred that, in general, individuals of this species are more tolerant of each other than other members in the genus and family. As a result of this tendency, it is suggested that this species is also less territorial than other closely related species. Little is known about how O. grandis raises its young. (Woods, 1990)

Orthogeomys grandis is rarely seen above the surface and as a result its behavior is poorly studied. It is thought, however, that the milder climatic zone in which the species lives allows the gophers to reproduce nearly year round. Most species of pocket gophers reach sexual maturity at about one year, though O. grandis is thought to reproduce at as early as three months. The specific gestation period is unknown though is thought to be relatively short compared to those of similar species, which average about 20 days. Females have at least one litter per year and typically have two young per birth but may have more. Newborn pocket gophers in the genus are underdeveloped and weight about 0.2 oz. Their teeth and eyes are not fully formed at birth. Species in the genus wean their young after about 40 days and the young generally leave their parents lodge after about 60 days. Information specific to O. grandis is unavailable. (Nowak, 1997; Woods, 1990)

  • Breeding interval
    Orthogeomys grandis breed at least once a year.
  • Breeding season
    Orthogeomys grandis are thought to mate year-round.
  • Range number of offspring
    2 to 10
  • Average age at sexual or reproductive maturity (female)
    3 months
  • Average age at sexual or reproductive maturity (male)
    3 months

Little is known about the parental investment of O. grandis, however, young are born underdeveloped and therefore probably rely extensively on one or both parents for the first 20 days or so until their eyes and ears open, like other species in the genus. (Woods, 1990)

Lifespan/Longevity

Animals in the genus rarely live longer than two years in the wild, though the specific lifespan of O. grandis is unknown. The species does not survive well in captivity because it becomes aggressive. If placed with other individuals, the animals will fight viciously, usually resulting in the death of the smaller gopher. (Nowak, 1997; Woods, 1990)

  • Average lifespan
    Status: wild
    2 years

Behavior

Pocket gophers dig two kinds of tunnels: long, winding, shallow tunnels are constructed to obtain food, while deep tunnels are constructed for shelter and storage. Deeper tunnels are fairly complex with chambers for nests, food storage, and fecal deposits. Burrows are often extensive and are usually marked above ground by a series of mounds of earth, the entrances of which are often closed with dirt, allowing the gophers to survive flooding and heavy rainfall and predation by snakes.

The animals dig with their foreclaws and upper incisors which are used to loosen soil and cut roots. When a considerable amount of loose earth has been accumulated it is held between the chest and forearms and pushed to the surface. Inside the burrows, nesting and living chambers are cushioned with dried grasses while other chambers are left bare, presumably for storing food.

When the gophers walk on hard ground they must draw their claws in so that they are essentially walking on the outer rims of the soles of their feet. On softer ground the animals can walk normally, using their feet as shovels. Inside their burrows, pocket gophers can run backwards almost as fast as they can run forward. They may make special use of their tail when moving backwards so that the tip is in contact with the ground, serving as a tactile organ.

The animals collect large supplies of food in their cheek pouches transferring their loads to their storage rooms under ground. The gophers accomplish this by pressing their pouches from back to front with their fore feet.

It is generally noted that species in this genus tend to be solitary and extremely territorial. Orthogeomys grandis, however is thought to be more tolerant of company because it mates year round.

Orthogeomys grandis does not hibernate and is more active at night than during the day. (Freye, 1975; Nowak, 1997; Woods, 1990)

Home Range

Little is known regarding the size of the home-range of O. grandis. A species in the same genus, O. heterodus, has been observed to have a home range that averages 325 square meters for males and 233 square meters for females, though it is uncertain whether O. grandis exhibits similar behavior. (Bonino, 1994; Bonino, 1994)

Communication and Perception

Little is known about the vocal expressions of pocket gophers. In captivity, it has been reported that species in the genus Orthogeomys sometimes emit shrieks and crying sounds and frequently rattle their teeth. It has also been observed that when an animal produces a clicking sound with its teeth another animal may sometimes respond in a similar manner. Other forms of communication are unknown.

Pocket gophers perceive their environment primarily through the use of their sensitive, vascularized tail and vibrissae that cover their entire body. Their senses of sight and hearing are poorly developed- an adaptation to their nocturnal, subterranean lifestyle. (Freye, 1975; Nowak, 1997; Woods, 1990)

Food Habits

Giant pocket gophers are herbivores, with a diet that consists of a wide variety of plant matter, especially roots, turnips, nuts, tubers, seeds, corn, grasses, wheat, barley, rye, and oats. At night O. grandis emerges to search for food above ground as well as roots just below the surface.

Pocket gophers have several adaptations related to their food habits. Cheek pouches primarily serve as a means for transporting food to their underground storage chambers. The same structure that allows gophers to close their mouths behind their incisors to prevent ingesting dirt also allows them to gnaw at roots and stems that are too big for their mouth cavities. They are also able to store quite a bit internally. Pocket gophers have large appendices and the quantity of food that can be stored in the stomachs, appendices, and small intestines of pocket gophers on average is more than 21 percent of the total weight of the animals. (Freye, 1975; Nowak, 1997; Woods, 1990)

  • Plant Foods
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit

Predation

Predators of O. grandis are unknown, but other species in the family Geomyidae are preyed upon by weasels, badgers, skunks, hawks, owls, and snakes. (Nowak, 1997; Woods, 1990)

Ecosystem Roles

The burrowing activity of pocket gophers has a noticeable impact on the landscape as subsoil is brought to the surface and deposited as mounds near the entrance of burrows. The mounds of O. grandis have been observed as being up to 60 cm high. In effect, this activity serves to aerate the soil. Pocket gophers also disperse plant seeds and roots as a result of their food caching, contributing to the distribution of plants.

Abandoned pocket gopher burrows are used by a wide variety of animals including salamanders, toads, lizards, snakes, mice, moles, weasels, and rabbits. While this data is available as a generalization for the entire family, specific species that inhabit the burrows of O. grandis are unknown.

Pocket gophers carry various external and internal parasites. Specifically, chewing lice, Geomydoecus, are known to parasitize O. grandis. (Jones and Genoways, 1988; Nowak, 1997; Page, 1996; Sudman and Hafner, 1992; Woods, 1990)

Mutualist Species
  • salamanders, toads, lizards, snakes, mice, moles, weasels, and rabbits
Commensal/Parasitic Species
  • chewing louse, Geomydoecus

Economic Importance for Humans: Positive

Humans may benefit from the plant dispersal activity of pocket gophers, but the primary benefit of O. grandis is that they are occasionally hunted for food by locals in Mexico and Central America, where some natives consider their meat a delicacy. (Freye, 1975; Nowak, 1997)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Orthogeomys grandis are common agricultural pests. They cause damage to coffee bushes by gnawing off the roots and likely damage a variety of crops in similar ways. During the growing season, the gophers are poisoned with ricin. In Mexico, the animals are killed by professional gopher catchers, or "tuceros," who use traps, snares, spears, and slingshots to capture or kill the gophers. (Nowak, 1997; Woods, 1990)

  • Negative Impacts
  • crop pest

Conservation Status

Orthogeomys grandis is considered a common species and is not listed on the IUCN Red List or in CITES appendices.

Other Comments

Name facts: Giant pocket gophers are called taltuzas or tuzas in Mexico. The family name Geomyidae is derived from the Greek “ge” (earth) and “mys” (mouse).

There are nine other species in the genus Orthogeomys and three subgenera, Orthogeomys, Heterogeomys, and Macrogeomys, all of which are located in Mexico, Central America, and Costa Rica. Mitochondrial DNA sequences indicate that Orthogeomys is only distantly related to the other two subgenera. Within the subgenus Orthogeomys there is only one other species, O. cuniculus.

Fossils of Orthogeomys date back to the Early Miocene. The slight difference in the skull of the extant members of the genus supports the theory that the species recently diverged from the stem group or adapted to their habits in similar ways without additional changes after an early, rapid period of evolutionary change. (Nowak, 1997; Sudman and Hafner, 1992; Woods, 1990)

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Lauren Ris (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

polygynous

having more than one female as a mate at one time

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

soil aeration

digs and breaks up soil so air and water can get in

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Bonino, N. 1994. Home-range, use of habitat and daily activity of the gopher Orthogeomys Heterodus (Rodentia, Geomyidae) in a Costa Rican horticultural zone. Revista de Biologia Tropical, 42 /1-2: 297-303.

Freye, H. 1975. Sciurids or squirrel-like rodents. Pp. 268-272 in H Grzimek, ed. Grzimek Animal Life Encyclopedia, Vol. 11/2, 2 Edition. New York: Van Nostrand Reinhold Company.

Jones, J., H. Genoways. 1988. American Pocket Gophers of the Subgenus Orthogenomys Rodential Geomyidae. Journal of Medical Entomology, 25/5: 331-335.

McNab, B. 1966. The Metabolism of Fossorial Rodents: A Study of Convergence. Ecology, 47/5: 712-733.

Nelson, E., E. Goldman. 1930. The Pocket Gophers of the Genus Orthogeomys. Journal of Mammalogy, 11: 155-159.

Nowak, R. 1997. "Walker's Mammals of the World" (On-line). Taltuzas. Accessed March 22, 2004 at http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.geomyidae.orthogeomys.html.

Page, R. 1996. Temporal Congruence Revisited: Comparison of Mitochondrial DNA sequence divergence in cospeciating pocket gophers and their chewing lice. Systematic Biology, 45: 151-167.

Reid, F. 1997. A Field Guide to the Mammals of Central America and Southeast Mexico. New York: Oxford University Press.

Sudman, P., M. Hafner. 1992. Phylogenetic relationships among Middle American pocket gophers (Genus Orthogeomys) based on mitochondrial DNA sequences. Molecular Phylogenetics and Evolution, 1/1: 17-25.

Woods, C. 1990. Pocket Rodents. Pp. 131-138 in S Parker, ed. Grzimek's Encyclopedia of Mammals, Vol. 3, English Edition. New York: McGraw-Hill.