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Isothrix bistriatayellow-crowned brush-tailed rat

By Angela ChappaLarrea

Geographic Range

Yellow-crowned bush-tailed rats, Isothrix bistriata, are found in South America’s western sides of the Amazon Basin in Peru, Bolivia, Venezuela, southeastern Colombia, and Brazil. The species is also thought to reside in Eastern Ecuador where it has been photographed on 2 occasions. I. bistriata is the only known species of Isothrix west of the Negro-Madeira rivers axis. (Cadena-Ortiz, et al., 2016; Emmons and Patton, 2015; Fabre, 2016; Patton, et al., 2000; Tirira, 2004)

Habitat

The habitat of yellow-crowned brush-tailed rats is composed of lowland forests with seasonal flooding and within river floodplains. Yellow-crowned brush-tailed rats build their nests in the holes of large trees, especially palms, and live among the canopy. (Emmons and Patton, 2015; Patton, et al., 2000)

Physical Description

Yellow-crowned brush-tailed rats are medium-sized arboreal rodents with a cream-colored patch on the crown of their head, two dark stripes going from forehead to nape of their neck, and a furry tail. Their dark head stripes do not meet behind the ears, marking the difference between I. bistriata and the other Isothrix species. Their body fur is soft and non-spiny, and mostly yellowish-brown with some black hairs grizzled about. Their abdomen is pale yellow and their tails go from rusty golden on the first two thirds of the tail to a dark brown third tip in adults, or a pale yellow termination in juvenile individuals. Their tail hair curls outward, resembling a bottlebrush, and doesn’t cover all tail scales. The mean head and body length is 249 mm, while the mean tail length is 242 mm. With their tail about the same length as their body, the mean tail:body ratio of yellow-crowned brush-tailed rats is about 97%. The specific body weight of I. bistriata has not been reported. However, the mean body weight of their close relatives in the Isothrix genus is 320-570 grams. In other body part measurements, their mean hind foot length ranges from 45-54 mm, their mean ear length ranges from 15-20 mm, and their mean condylo-incisive length is 51 mm. Yellow-crowned brush-tailed rats are often considered adults when cheek teeth are erupted and somewhat worn down. (Emmons and Patton, 2015; Nowak, 1999; Patterson and Velazco, 2008; Patton and Emmons, 1985)

Male yellow-crowned brush-tailed rats have a blunt, short, and wide-grooved phallus. Their baculum is long and narrow. Adult males develop 25 mm midventral chest glands and possess relatively large testes (measuring 24 mm length x 12 mm width) that stay in the abdomen and do not descend to the scrotum. (Emmons and Patton, 2015; Nowak, 1999; Patterson and Velazco, 2008; Patton and Emmons, 1985)

The number of teats in female yellow-crowned brush-tailed rats are three lateral pairs of mammae and one inguinal pair situated by the groin area. Female I. bistriata develop enlarged nipples in adulthood, possibly as a result of sexual maturity and lactation. (Emmons and Patton, 2015; Lacey and Myers, 2005)

The skeletal features most studied on the yellow-crowned brush-tailed are their skull and their teeth. Like other Isothrix species, I. bistriata have a relatively flat, broad cranium with a short, broad rostrum, making them morphologically resemble a squirrel. Their supraorbital ledges extend posteriorly to the parietals, and the interorbital region is broad. Tympanic bullae in I. bistriata are somewhat large, the auditory meatus is near the squamosal bone and is medium-sized, and the auditory tube is short and tilted forward. The mandible of I. bistriata has a strong base composed of well-developed masseter and pterygoid crests. Their masseter and infraorbital arrangement classify I. bistriata as hystricomorphous. (Emmons and Patton, 2015; Patton, et al., 2000; Patton, et al., 2015)

In terms of teeth, like other Isothrix species, I. bistriata has nearly laminate teeth, with maxillary cheekteeth rows being short, small, parallel to the palate, and somewhat tilted back. Dental formula of I. bistriata was not available, but the dental formula of the Echimyidae family is I(1/1), C(0/0), P(1/1), M(3/3) = 20. (Emmons and Patton, 2015; Neves and Pessôa, 2011; Patton, et al., 2000)

  • Range length
    429 to 546 mm
    16.89 to 21.50 in

Reproduction

The mating systems of yellow-crowned brush-tailed rats have not been reported, however of the close relatives within the Echimyidae family that have been studied, mostly polygynous mating systems are known to happen. Within Echimyidae, mating systems can be considered facultatively promiscuous, polygynous, or monogamous because they depend on density and home range sizes. (Patton, et al., 2015)

Yellow-crowned brush-tailed rats are known to be sexually mature when all cheek teeth have erupted and have started to wear down, however their specific age of sexual maturity has not been studied. Males and female pairs nest in tree holes, with their breeding season thought to continue year round. The average litter size is thought to be small, around one or two offspring, evidenced by the number of placental scars never being more than two. It is thought I. bistriata breed throughout the year. (Patton, et al., 2000; Patton, et al., 2015)

  • Breeding season
    Year-round
  • Range number of offspring
    1 to 2

Parental care in I. bistriata behavior has not been studied. Captured females accompanied by their offspring suggest relatively high parental investment. It is known for some relatives within the Echimyidae family, like genus Kannabateomys to perform biparental care of their young, meaning that both parents cooperate to take care of their young. (Patton, et al., 2000; Patton, et al., 2015)

Lifespan/Longevity

Specific longevity of yellow-crowned brush-tailed rats has not been studied. However, in a Echimyidae family relative, Proechimys semispinosus, lifespan was found to be a minimum of 6.5-10 months and a maximum of 36-53 months. Lifespan limiting factors have not been studied in I. bistriata. (Oaks, et al., 2008)

Behavior

Yellow-crowned brush-tailed rats are arboreal and nocturnal. They are solitary individuals. I. bistriata commonly protrude their heads out during daytime, they appear at the entrance of their tree holes in the afternoon, and come out to forage at night. It is common for all members of the Isothrix genus, including I. bistriata, to be allopatric to their range. (Emmons and Patton, 2015; Patton, et al., 2000; Patton, et al., 2015; Tate, 1931)

Home Range

Home range of yellow-crowned brush-tailed rat individuals has not been documented. However, relatives from the Echimyidae family appear to be minimally territorial, so their home ranges are determined by population density. There also appears to be a difference in territory size between male and female members of the Echimyidae family, with males having relatively larger home ranges, and present fairly extensive home range overlaps within species. I. bistriata is an arboreal species that prefers floodplain areas, so their home range will be limited by the extent of trees located in floodplains. (Adler, 2011; Emmons and Patton, 2015)

Communication and Perception

Communication of yellow-crowned brush-tailed rats has not been studied. There is no information on social communication, potential mate communication, social rank communication, or resource communication found in the literature. There is evidence of chemical communication and signaling in close relatives of the Echimyidae family, such as the spiny rat Trinomys yonenagae and Proechimys semispinosus, by using scent glands near the anus. Scent recognition is thought to be used by spiny rats. However, the presence of scent glands in I. bistriata have not been documented. The olfactory function of the snout of I. bistriata might allow for scent recognition. (Adler, 2011; Manaf, et al., 2011)

Food Habits

Foraging behaviors of I. bistriata have not been studied. However, the general diet of their family Echimyidae is omnivorous and includes mainly fruits, vegetative plant parts, seeds, fungi, and/or arthropods. (Adler and Kestell, 1998; Patton, et al., 2015; Pinotti, et al., 2011)

Predation

There is little available information on predation in yellow-crowned brush-tailed rats. Close relatives, such as the members of the Echimyidae family, are often hunted by humans, smaller primates and spectacled owls Pulsatrix perspicillata, however actual capture and feeding by small primates or spectacled owls on yellow-crowned brush-tailed rats has not been documented. (Patton, et al., 2015)

A possible anti-predator mechanism in relatives of I. bistriata within the Echimyidae family is tail autotomy, or breaking off of the tail, by the spiny rats of the Proechimys semispinosus species. However, this mechanism has not been documented in I. bistriata. (Mckee and Adler, 2002)

Ecosystem Roles

There is little available information on the ecosystem roles of yellow-crowned brush-tailed rats. However, an important ecosystem impact of some of their relatives within the Echimyidae family consist of seed dispersal, like in the case of spiny rats Proechimys semispinosus, due to their frugivorous diet. (Adler and Kestell, 1998)

Economic Importance for Humans: Positive

There is little available information on the positive economic impacts of yellow-crowned brush-tailed rats. However, within the Echimyidae family, various species are often hunted or used as laboratory animals. (Suárez, et al., 1995)

  • Positive Impacts
  • food
  • research and education

Economic Importance for Humans: Negative

Information regarding potential negative economic impacts of yellow-crowned brush-tailed rats on humans has not been documented. Some relatives of I. bistriata in the Echimyidae family are reservoirs of disease. For example, Tome’s spiny rats Proechimys semispinosus carry cutaneous leishmaniasis (Leishmania panamensis and Leishmania chagasi) which can affect humans infected by sand fly hosts. However, parasites or diseases have been studied in I. bistriata. (Travi, et al., 2002)

Other relatives of I. bistriata in the Echimyidae family, under the Rhizomyinae subfamily, affect sugarcane and tapioca crops in Thailand, such as the Atlantic bamboo rat Kannabateomys amblyonyx, however there are no studies on the effects of I. bistriata on crops. (Lekagul and McNeely, 1977)

Conservation Status

Assessed in 2016 as Least Concern by the IUCN. Although Isothrix bistriata is uncommon, due to specimens being found along a wide range within various protected areas, populations are thought to be stable and at low risk of decreasing their size at an alarming rate. (Patton, 2016)

Contributors

Angela ChappaLarrea (author), University of Washington, Laura Prugh (editor), University of Washington, Tanya Dewey (editor), 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

arboreal

Referring to an animal that lives in trees; tree-climbing.

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.

female parental care

parental care is carried out by females

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.

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.

native range

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

nocturnal

active during the night

rainforest

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.

sexual

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

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

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

young precocial

young are relatively well-developed when born

References

Adler, G., D. Kestell. 1998. Fates of Neotropical Tree Seeds Influenced by Spiny Rats (Proechimys semispinosus). Biotropica, 30 (4): 677-681. Accessed May 12, 2021 at http://www.jstor.org/stable/2388839.

Adler, G. 2011. Spacing patterns and social mating systems of echimyid rodents. Journal of Mammalogy, 91, 1: 31-38. Accessed June 04, 2021 at https://doi.org/10.1644/09-MAMM-S-395.1.

Cadena-Ortiz, H., B. Alexis, J. Brito. 2016. New records of Isothrix (Wagner 1845) (Rodentia: Echimyidae) from Ecuador. Mammalia, 80 (6): 663-666. Accessed May 12, 2021 at https://doi.org/10.1515/mammalia-2015-0161.

Emmons, L., J. Patton. 2015. Mammals of South America. Chicago: The University of Chicago Press.

Fabre, P. 2016. Handbook of Mammals of the World. Barcelona: Lynx Editions.

Lacey, E., P. Myers. 2005. Mammalian Diversification: From Chromosomes to Phylogeography (A Celebration of the Career of James L. Patton). UC Publications in Zoology, 133: 247-310. Accessed May 12, 2021 at https://escholarship.org/uc/item/31r875b5.

Lekagul, B., J. McNeely. 1977. Mammals of Thailand. Bangkok, Thailand: Association for the Conservation of Wildlife.

Manaf, P., L. de Brito-Giratana, E. Oliveira. 2011. Evidence of chemical communication in the spiny rat Trinomys yonenagae (Echimyidae): Anal scent gland and social interactions. Canadian Journal of Zoology, 81, 7: 1138-1143. Accessed June 05, 2021 at https://doi.org/10.1139/z03-095.

Mckee, R., G. Adler. 2002. Tail Autotomy in the Central American Spiny Rat, Proechimys semispinosus. Studies on Neotropical Fauna and Environment, 37, 3: 181-185. Accessed June 05, 2021 at https://doi.org/10.1076/snfe.37.3.181.8568.

Neves, A., L. Pessôa. 2011. Morphological distinction of species of Thrichomys (Rodentia: Echimyidae) through ontogeny of cranial and dental characters. Zootaxa, 2804: 15-24. Accessed June 04, 2021 at https://doi.org/10.11646/zootaxa.2804.1.2.

Nowak, R. 1999. Walker's Mammals of the World, 6th Edition. Baltimore: Johns Hopkins University Press.

Oaks, J., J. Daul, G. Adler. 2008. Life Span of a Tropical Forest Rodent, Proechimys semispinosus. Journal of Mammalogy, 89, 4: 904-908. Accessed June 04, 2021 at https://doi.org/10.1644/07-MAMM-A-045.1.

Patterson, B., P. Velazco. 2008. Phylogeny of the rodent genus Isothrix (Hystricognathi, Echimyidae) and its diversification in Amazonia and the Eastern Andes. Journal of Mammalian Evolution, 15: 181-201. Accessed May 12, 2021 at https://drive.google.com/file/d/0BxXh3ddQptWXeS1ldDB4QTNKYk0/view.

Patton, J. 2016. "Isothrix bistriata" (On-line). The IUCN Red List of Threatened Species. Accessed May 12, 2021 at https://dx.doi.org/10.2305/IUCN.UK.2016-2.RLTS.T90386297A22211362.en.

Patton, J., M. da Silva, J. Malcolm. 2000. Mammals of the Rio Jurua and the Evolutionary and Ecological Diversification of Amazonia. Bulletin of the American Museum of Natural History, 224: 178-186. Accessed May 12, 2021 at http://digitallibrary.amnh.org/handle/2246/1593.

Patton, J., L. Emmons. 1985. A review of the genus Isothrix (Rodentia, Echimyidae). American Museum novitates, 2817: 1-14. Accessed May 12, 2021 at http://digitallibrary.amnh.org/handle/2246/5225.

Patton, J., U. Pardiñas, G. D’Elía. 2015. Mammals of South America, Volume 2. Chicago: The University of Chicago Press. Accessed May 12, 2021 at DOI: 10.7208/chicago/9780226169606.001.0001.

Pinotti, B., L. Naxara, R. Pardini. 2011. Diet and food selection by small mammals in an old-growth Atlantic forest of south-eastern Brazil. Studies on Neotropical Fauna and Environment, 46 (1): 1-9. Accessed May 12, 2021 at https://doi.org/10.1080/01650521.2010.535250.

Suárez, E., J. Stallings, L. Suárez. 1995. Small-mammal hunting by two ethnic groups in north-western Ecuador. Oryx, 29 (1): 35-42. Accessed May 12, 2021 at https://doi.org/10.1017/S0030605300020858.

Tate, G. 1931. Random Observations on Habits of South American Mammals. Journal of Mammalogy, 12 (3): 248-256. Accessed May 12, 2021 at https://doi.org/10.2307/1373874.

Tirira, D. 2004. Nombres de los mamíferos del Ecuador. Ecuador: Ediciones Murciélago Blanco. Accessed May 12, 2021 at https://www.researchgate.net/publication/313023888_Nombres_de_los_mamiferos_del_Ecuador.

Travi, B., A. Arteaga, A. Léon, G. Adler. 2002.

Susceptibility of Spiny Rats (Proechimys semispinosus) to Leishmania (Viannia) panamensis and Leishmania (Leishmania) chagasi.
. Memórias do Instituto Oswaldo Cruz, 97: 887-892. Accessed June 05, 2021 at https://doi.org/10.1590/s0074-02762002000600025.

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