Tome's spiny rats primary inhabit lowland tropical evergreen forest up to 800m in elevation. They are found in forests ranging from dry to very wet, and inhabit both primary and secondary growth, but have a preference for secondary growth. They tend to inhabit areas with forest gaps, shorter canopies, and higher densities of smaller trees, logs and woody vines, but are overall quite generalized and non-specific in their use of available microhabitat. (Adler, 1996; Adler, 2000; Lambert and Adler, 2000; Reid, 2009; Tomblin and Adler, 1998)
Tome’s spiny rats have stiff fur and narrow flexible spines. Their upper pelage is glossy and chestnut-brown to grey-brown, and their underparts are usually white. Tome's spiny rats have long narrow heads and pointed snouts, naked dark-colored ears, large brown eyes, and very long whiskers. They have bicolored tails, with grey tops and white bottoms. Their tails are not longer than their bodies; a defining characteristic of genus Proechimys is that their tails that are less than 90% of the length of the rat's head and body. The tails of Tome's spiny rats break off frequently, so adult rats may be found without tails (around 8-25% of adults are tailless). Their hind feet are long and narrow with black soles and white tops. Young Tome's spiny rats are typically grey-brown with white underparts. Morphological measurements vary greatly among populations of Tome's spiny rats. Most adults average 300-400 grams, but older individuals have been measured at over 700 grams. Additionally, Tome's spiny rats change in mass throughout the seasons as well; rats have larger body mass in the wet season, when resources are abundant, and have lower mass in the dry season, when resources are limited. Most adults are between 180-270 millimeters long. Ear length ranges from about 23-26 mm, hind foot length ranges from 50-60mm, and tail length ranges from about 160 to 180 mm. The dental formula of Tome's spiny rats is I 1/1, C 0/0, P 1/1, M 3/3. The skull of the Tome's spiny rat is elongate, has distinct, well developed supraorbital and parietal ridges, large bullae, and a long, narrow incisive foramen. The molars of Tome's spiny rats have four counterfolds in M3 and M2, three to four counterfolds in M1, lower premolars with four and lower molars with three counterfolds. Skull length ranges from 58-67 mm and skull width ranges from 28-31 mm. Size and morphology does not differ significantly between the sexes. (Benshoof, et al., 1984; Emmons and Feer, 1990; Gliwicz, 1983; Gliwicz, 1984; Kellog, 1946; McKee and Adler, 2002; Moojen, 1948; Patton, 1987; Thomas, 1911)
Tome's spiny rats have a promiscuous mating system, implied by their widely overlapping home ranges, lack of territoriality, and larger home ranges of sexually active males. There is no evidence of mate defense or territorial behavior in this species. Tome's spiny rats may be facultatively monogamous at low population densities. (Endries and Adler, 2005; Gliwicz, 1984; Seamon and Adler, 1999)
Tone's spiny rats reproduce throughout the year, and may reproduce several times a year. However, reproduction is timed such that most pregnancies line up with the period of lowest food supply (late in the dry season, which generally spans from November-April), and most young are born at the period of peak food supply (the beginning of the rainy season, in May-October). This pattern reflects the need for rich and abundant food during lactation, which is the most energetically costly period for female rodents. The length of reproduction period can vary greatly between populations and regions, from four to 11 months long. The gestation period for Tome's spiny rats is typically about 60 days long. They birth 2-4 offspring per litter, and the average birth weight of newborn rats is 30 grams. (Adler and Beatty, 1997; Adler, 1995; Adler, 1998; Adler, 2000; Gliwicz, 1984; Seamon and Adler, 1999)
Parental investment by Tome's spiny rats is not well studied. After a short gestation period of 60 days, females nurture their young through lactation. Young Tome's spiny rats are likely nested in burrows until they are weaned from their mothers. Young are born at the time of peak food supply, allowing females to meet the energetically costly demands of lactation and ensuring that there will be food available for young once they have been weaned. (Adler and Beatty, 1997; Emmons and Feer, 1990; Gliwicz, 1984)
The median life expectancy of Tome's spiny rats is 6.5-10 months of age, with maximum lifespan ranging from 36 to 53 months. The life expectancy of the Tome's spiny rat is very right-skewed, with most individuals having short lifespans just past the age of first reproduction, with few surviving past 2 years of age. Maximum known lifespans for Tome's spiny rats are 4.4 years in the wild, and 5 years in captivity. (Jones, 1982; Oaks, et al., 2008)
Tome's spiny rats are fossorial and nocturnal. They inhabit subterrenean burrows, which are normally dug near to water in areas with sparse vegetative cover. Many rats inhabit burrows at the bases of palm trees, one of their main food sources. They rest in these burrows throughout the day, and come out to forage at night. Burrows may be inhabited by a single rodent, or may be co-occupied by multiple males and females. Co-occupancy of burrows is relatively common, and there is no evidence of territorial behavior in this species.
Population sizes and dynamics of Tome's spiny rats are highly variable. In general, island populations have much higher densities, more stable populations, larger individuals and lower reproductive rates compared to mainland populations. Densities, reproductive rates and survivorship can vary greatly between different island populations and mainland populations. Densities on island populations can range from 12 individuals per hectare up to 50 individuals per hectare. Mainland populations are much more dispersed, with an average of 6 individuals per hectare. Population densities also fluctuate on a seasonal basis, with densities being highest in the wet season and lowest in the dry season. Mainland populations follow a pattern with distinct phases in population density: numbers decrease in the dry season, increase during the first half of the rainy season when resources are abundant, and decrease in the second half of the rainy season.
Tome's spiny rats overlap in range with Hoplomys gymnurus, the armored rat, and both species exploit the same food resources and experience the same seasonal limitations. The species are likely able to persist sympatrically because they have different microhabitat preferences; the armored rat is found mainly in undisturbed forests along streams with wet, rocky microhabitats, whereas Tome's spiny rats are distributed generally throughout the habitat with no specific microhabitat preference. Additionally, Tome's spiny rats exhibit dominant behavior over armored rats. Levels of aggression in Tome's spiny rats increase during the dry season, when resources are more scarce. (Adler, 1995; Adler, 1996; Adler, 2000; Dupre, et al., 2015; Endries and Adler, 2005; Fleming, 1971; Gliwicz, 1984; McKee and Adler, 2002; Seamon and Adler, 1999; Shargal, et al., 1999; Tomblin and Adler, 1998)
Tome's spiny rats generally have very large home ranges which overlap extensively with one another; total range overlap varies from 300 to 5700 square meters, and core home range overlap varies from zero to 180 square meters. Total home range sizes vary from 180 to 2375 square meters, with core ranges varying from 40 to 470 square meters. Average home range sizes are larger in the rainy season (average of 1260 square meters) than the dry season (average of 740 square meters), and there is greater range overlap in the rainy season. The home ranges of males are marginally larger than those of females. (Endries and Adler, 2005; Seamon and Adler, 1999)
Communication and perception in Tome's spiny rats is not well understood. These rats have large eyes which are likely important for seeing at night, as they are nocturnal. A related species, Trinomys yonenagae, uses chemical signalling via anal glands for recognition of individuals, so scent recognition may be used in spiny rats as well. (Emmons and Feer, 1990; Manaf, et al., 2003; Patton, 1987)
Tome's spiny rats are primarily frugivorous, and fruit abundance is the main factor in determining their population density. Tome's spiny rats consume a very broad array of fruits and seeds; in a captive study, they consumed virtually all of the 97 species of forest fruits offered to them. They have a preference for consuming fruits with larger seeds, including plants in the palm family (f. Arecaceae) such as black palm (Astrocaryum standleyanum) and wine palm (Attalea butyracea). They are also known to consume the fruits of the large-seeded tree species Dipteryx oleifera. They may also scatterhoard their seeds. Tome's spiny rats are not primarily seed-eaters, as they leave behind viable seeds from most of the fruit they eat. Although fruits are the most important part of the diet of Tome's spiny rats, they are also mycophagous. They are known to consistently consume arbuscular mycorrhizal fungi, but their population densities are less dependent on this food source. Fungi are likely to be more important in supplementing the rodents’ diets when fruit and seeds are more scarce, or may have importance in providing essential nutrients not found in fruit and seeds. (Adler and Beatty, 1997; Adler, 1995; Carvajal and Adler, 2008; Dittel, et al., 2015; Mangan and Adler, 1999)
The role of Tome's spiny rat as a prey species is not well understood, but they are likely an important prey species to neotropical forest predators as they are the most abundant neotropical rodent. The common oppossum (Didelphis marsupialis) is a known predator of Tome's spiny rats, and other potential predators include the gray four-eyed oppossum (Philander opossum), the brown four-eyed opossum (Metachirus nudicaudatus), the white-nosed coati (Nasua narica), the spectacled owl (Pulsatrix perspicillata) the mottled owl (Strix virgata), and several large snakes including the species Boa constrictor, Bothrops asper, Mastigodryas melanolomus, and Spilotes pullatus.
Tome's spiny rats have spines that are adapted from their guard hairs, which likely act as predator defense. Tome's spiny rats exhibit tail autonomy, which is a very unique trait among rodents. Autonomy of appendages is quite common in many invertebrate groups as an antipredator defense, but true autonomy is exceedingly rare in mammals, present in approximately 30 species of rodents across eight families. Mammals cannot regenerate their tails, so they may function only once as an antipredator defense. Rates of tail loss in populations of rats vary between 8% to up to 25%. Rates of tail loss are lower on smaller islands; as tail loss is hypothesized to be an anti-predation mechanism, lower rates may be a result of fewer predators on smaller islands. (Adler, 1996; McKee and Adler, 2002; Patton, 1987; Shargal, et al., 1999)
Tome's spiny rats are often the most abundant rodent in lowland tropical forests, and are thought to be the most widespread rodent throughout much of Central America and northwestern South America. These rats serve as important dispersers of tropical plant seeds due to their broad frugivorous diet and their scatterhoarding tendencies. Additionally, Tome's spiny rats are not primarily seed eaters; the majority of large seeds removed by the rats are not actually consumed and are still viable after the rats dispose of them. Tome's spiny rats disperse seeds an average of five meters from where they are collected, but many seeds are also deposited more than 10 meters from where they are collected. Due to their preference for fruits with larger seeds, Tome's spiny rats may be particularly important for the dispersal of large-seeded species that other rodents are not capable of eating, such as the fruits of black palm (Astrocaryum standleyanum). Seed removal rates are higher among island populations than mainland populations due to the higher population densities on islands. Tome's spiny rats may also have a role in the dispersal of arbuscular mycorrhizal fungal spores which are necessary for the growth of many tropical plants, as these spores are found in 77% of Tome's spiny rat feces. The Tome's spiny rat’s preference for association with treefall gaps and young forest indicate it may be a very important species for the regeneration of trees in disturbed area via dispersal of mycorrhizal fungi and seeds. Tome's spiny rats are used as hosts by the larvae of botflies (Cuterebra). Prevalence is quite low, averaging around 5%, but varying by population (between 2-8%). Botfly prevalence is not dependent on rat population density, and prevalence in Tome's spiny rats is highest in the dry season. Tome's spiny rats are also a reservoir host for the parasitic trypanosome Leishmania, although they are only weakly infective to sand flies, the intermediate hosts of Leishmania, so they may not be an important reservoir for this parasite. However, because they are often the most abundant lowland forest rodent in their range, they may be a very important reservoir on a population or region-wide scale. Tome's spiny rats may also be a reservoir host for Trypanosoma cruzi. Tome's spiny rats have also been found infected as an intermediate host with the tapeworm species Echinococcus oligarthrus. (Adler, 1995; Adler, et al., 2003; Carvajal and Adler, 2008; D'Alessandro, et al., 1981; Dittel, et al., 2015; Hoch and Adler, 1997; Lambert and Adler, 2000; Mangan and Adler, 1999; Travi, et al., 1994; Travi, et al., 2002)
The meat of Tome's spiny rats is commonly consumed by rural Afro-Colombian communities; rodents are trapped locally but the meat is not frequently sold in markets. Tome's spiny rat meat is a good source of protein and is not associated with the transmission of any diseases. Additionally, due to their consumption of seeds and mycorrhizal fungi, as well as their preference for microhabitats with treefall gaps and younger forest, Tome's spiny rats may have an important role in the regeneration of disturbed forest through seed and fungi dispersal. This species also serves as an important model species of tropical rodent for studies on rodent reproduction, population dynamics and seed dispersal. (Adler and Beatty, 1997; Adler, 1995; Adler, 1996; Asprilla-Perea, et al., 2012; Mangan and Adler, 1999)
Tome's spiny rats are a reservoir of cutaneous leishmaniasis, and can be found naturally infected with multiple species of Leishmania. Tome's spiny rats carrying Leishmania are only weakly infective to sand flies, the intermediate hosts of Leishmania; however, because they are often the most abundant lowland forest rodent in their range, they may be a very important reservoir on a population or region-wide scale. Tome's spiny rats may also be reservoirs of Trypanosoma cruzi, the causative agent of Chagas Disease in humans. (Travi, et al., 1994; Travi, et al., 2002)
Laura Eliuk (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
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.
uses smells or other chemicals to communicate
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.
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
having the capacity to move from one place to another.
an animal that mainly eats fungus
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
places a food item in a special place to be eaten later. Also called "hoarding"
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
young are relatively well-developed when born
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