Talamancan Rice Rat
Encyclopedia
Transandinomys talamancae is a rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
in the genus Transandinomys
Transandinomys
Transandinomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—T. bolivaris and T. talamancae—found in forests from Honduras in Central America south and east to southwestern Ecuador and northwestern Venezuela in northern South America...
that occurs from Costa Rica to southwestern Ecuador and northern Venezuela. Its habitat consists of lowland forests up to 1525 m (5000 ft) above sea level. With a body mass of 38 to 74 g (1.3 to 2.6 oz), it is a medium-sized rice rat
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
. The fur is soft and is reddish to brownish on the upperparts and white to buff on the underparts. The tail is dark brown above and lighter below and the ears and feet are long. The vibrissae (whiskers) are very long. In the skull, the rostrum (front part) is long and the braincase is low. The number of chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s varies from 34 to 54.
The species was first described in 1891 by Joel Asaph Allen
Joel Asaph Allen
Joel Asaph Allen was an American zoologist and ornithologist, born in Springfield, Massachusetts.He studied at Harvard University under Louis Agassiz...
and thereafter a variety of names, now considered synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
s, were applied to local populations. It was lumped into a widespread species "Oryzomys capito" (now Hylaeamys megacephalus) from the 1960s till the 1980s and the current allocation of synonyms dates only from 1998. It was placed in the genus Oryzomys
Oryzomys
Oryzomys is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
until 2006, as Oryzomys talamancae, but is not closely related to the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of that genus and was therefore moved to a separate genus Transandinomys in 2006. It shares this genus with Transandinomys bolivaris, which has even longer vibrissae; the two overlap broadly in distribution and are morphologically similar.
Active during the night, Transandinomys talamancae lives on the ground and eats plants and insects. Males move more and have larger home range
Home range
Home range is the area where an animal lives and travels in. It is closely related to, but not identical with, the concept of "territory".The concept that can be traced back to a publication in 1943 by W. H. Burt, who constructed maps delineating the spatial extent or outside boundary of an...
s than females. It breeds throughout the year, but few individuals survive for more than a year. After a gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
period of about 28 days, two to five young are born, which reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
within two months. A variety of parasites occur on this species. Widespread and common, it is of no conservation concern.
Taxonomy
In 1891, Joel Asaph AllenJoel Asaph Allen
Joel Asaph Allen was an American zoologist and ornithologist, born in Springfield, Massachusetts.He studied at Harvard University under Louis Agassiz...
was the first to scientifically describe Transandinomys talamancae, when he named Oryzomys talamancae from a specimen from Talamanca, Costa Rica. He placed it in the genus Oryzomys
Oryzomys
Oryzomys is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
, then more broadly defined than it is now, and compared it to both the marsh rice rat
Marsh Rice Rat
The marsh rice rat is a semiaquatic North American rodent in the family Cricetidae. It is found mostly in the eastern and southern United States, from New Jersey and Kansas south to Florida and northeasternmost Tamaulipas, Mexico; its range previously extended further west and north, where it may...
(O. palustris) and to O. laticeps
Hylaeamys laticeps
Hylaeamys laticeps, also known as the Atlantic Forest Oryzomys or Large-headed Rice Rat, is a species of rodent in the genus Hylaeamys of family Cricetidae. It occurs in the Atlantic Forest region of southeastern Brazil...
. Several other names that are now recognized as synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of Transandinomys talamancae were introduced in the following years. In 1899, Allen described Oryzomys mollipilosus, O. magdalenae, and O. villosus from Magdalena Department
Magdalena Department
Magdalena is a department of Colombia, located to the north of the country by the Caribbean Sea. The capital of the Magdalena Department is Santa Marta and was named after the Magdalena River...
, Colombia. Oldfield Thomas
Oldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
added O. sylvaticus from Santa Rosa
Santa Rosa, El Oro
Farming center about 10 miles south of Machala, Ecuador. Santa Rosa that is the site for a large new airport to service the southern part of Ecuador.This aerport is operational offering flights to mayor cities in Ecuador like Guayaquil, Quito, Cuenca, and in the near future Peru and...
, Ecuador in 1900 and O. panamensis from Panama City
Panama City
Panama is the capital and largest city of the Republic of Panama. It has a population of 880,691, with a total metro population of 1,272,672, and it is located at the Pacific entrance of the Panama Canal, in the province of the same name. The city is the political and administrative center of the...
, Panama, in 1901. In the same year, Wirt Robinson and Markus Lyon named Oryzomys medius from near La Guaira
La Guaira
La Guaira is the capital city of the Venezuelan state of Vargas and the country's chief port. It was founded in 1577 as an outlet for Caracas, to the southeast. The town and the port were badly damaged during the December 1999 floods and mudslides that affected much of the region...
, Venezuela. Allen added O. carrikeri from Talamanca, Costa Rica, in 1908.
Edward Alphonso Goldman
Edward Alphonso Goldman
Edward Alphonso Goldman was an American zoologist. He worked extensively in Mexico with Edward William Nelson and described and revised many groups of mammals....
revised North American Oryzomys in 1918. He placed both panamensis and carrikeri as synonyms of Oryzomys talamancae and mentioned O. mollipilosus and O. medius as closely related species. O. talamancae was the only member of its own species group, which Goldman regarded as closest to Oryzomys bombycinus (=Transandinomys bolivaris). In 1960, Philip Hershkovitz
Philip Hershkovitz
Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...
listed talamancae, medius, magdalenae, sylvaticus, and mollipilosus among the many synonyms of "Oryzomys laticeps", a name later replaced by "Oryzomys capito". The species remained lumped under Oryzomys capito until 1983, when Alfred Gardner again listed it as a valid species, an action more fully documented by Guy Musser
Guy Musser
Guy Graham Musser is an American zoologist. His main research field is the subfamily Murinae, in which he has described many new species.Musser was born in Salt Lake City, Utah...
and Marina Williams in 1985. Musser and Williams also found that the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Oryzomys villosus, the affinities of which had been disputed, in fact consisted of a skin of O. talamancae and a skull of the Oryzomys albigularis group (equivalent to the current genus Nephelomys
Nephelomys
Nephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica...
). They restricted the name to the skin, making villosus a synonym of O. talamancae. They also examined the holotypes of panamensis, carrikeri, mollipilosus, medius, and magdalenae and identified them as examples of Oryzomys talamancae. Additionally, they included sylvaticus and Oryzomys castaneus J.A. Allen, 1901, from Ecuador as synonyms, but without examining the holotypes. Musser and colleagues reviewed the group again in 1998 and confirmed that sylvaticus represents Oryzomys talamancae; however, they found that castaneus was in fact an example of Oryzomys bolivaris (the current Transandinomys bolivaris).
In 2006, Marcelo Weksler published a phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
analysis of Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
("rice rats"), the tribe to which Oryzomys is allocated, using morphological data and DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
s from the IRBP
RBP3
Retinol-binding protein 3, interstitial , also known as IRBP is a protein that in humans is encoded by the RBP3 gene. RBP3 orthologs have been identified in most eutherians except tenrecs and armadillos.- Function :...
gene. His results showed species of Oryzomys dispersed across Oryzomyini and suggested that most species in the genus should be allocated to new genera. Oryzomys talamancae was also included; it appeared within "clade B", together with other species formerly associated with Oryzomys capito. Some analyses placed it closest to species now placed in Euryoryzomys
Euryoryzomys
Euryoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes six species, which are distributed in South America. Until 2006, its members were included in the genus Oryzomys, but they are not closely related to the type species of that genus, and therefore they were...
or Nephelomys
Nephelomys
Nephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica...
, but with low support. Later in the same year, he, together with Alexandre Percequillo and Robert Voss, named ten new genera for species previously placed in Oryzomys, including Transandinomys
Transandinomys
Transandinomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—T. bolivaris and T. talamancae—found in forests from Honduras in Central America south and east to southwestern Ecuador and northwestern Venezuela in northern South America...
, which has Oryzomys talamancae (now Transandinomys talamancae) as its type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
. They also included Oryzomys bolivaris, which was not included in Weksler's phylogenetic study, in this new genus. The two species are morphologically similar, but Weksler and colleagues could identify only one synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
(shared-derived trait) for them: very long superciliary vibrissae (vibrissae, or whiskers, above the eyes). Transandinomys is one of about 30 genera in Oryzomyini, a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels in the subfamily Sigmodontinae
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
of family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
, along with hundreds of other species of mainly small rodents.
Several common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s have been proposed for Transandinomys talamancae, including "Talamanca Rice Rat", "Transandean Oryzomys", and "Talamancan Rice Rat".
Description
Transandinomys talamancae is a medium-sized, brightly colored rice rat. It is similar to T. bolivaris and the two are often confused. They are about as large, but in T. talamancae the tail is longer and the hindfeet shorter. Both species share uniquely long vibrissae, with both the mystacial (above the mouth) and superciliary vibrissae extending to or beyond the back margin of the ears when laid back against the head, but those in T. bolivaris are substantially longer. H. alfaroi, a widespread species ranging from Mexico to Ecuador, is also similar. It is smaller and darker, but young adult T. talamancae are similar in color to adult H. alfaroi and often misidentified. Hylaeamys megacephalus, with which T. talamancae was synonymized for some decades, is similar in body size, but is not known to overlap with T. talamancae in range.The fur is short, dense and soft in Transandinomys talamancae; in T. bolivaris, it is longer and even more soft and dense. The color of the upperparts varies from reddish to brownish, becoming lighter towards the sides and the cheeks. The underparts are white to buff, with the bases of the hairs plumbeous (lead-colored). The fur of T. bolivaris is darker: dark brown above and dark gray below. H. megacephalus also has darker fur. Juveniles have thin, gray fur, which is molted into the dark brown subadult fur when the animal is about 35 to 40 days old. This fur is replaced by the bright adult fur at age 49 to 56 days. Juveniles are never blackish as in T. bolivaris. The ears are dark brown, large, and densely covered with very small hairs.
| Country | nNumber of specimens measured. | Head and body | Tail | Hindfoot | Ear |
|---|---|---|---|---|---|
| Panama | 22 | 124.4 (101–136) | 124.7 (110–143) | 29.2 (27–32) | 21.1 (16–25) |
| Colombia | 13 | 135.2 (120–151) | 125.2 (114–140) | 29.5 (27–32) | 19.0 (18–22) |
| Ecuador | 2019 for tail length. | 124 (118–136) | 128.5 (118–137) | 29.1 (28–31) | – |
| Measurements are in millimeters and in the form "average (minimum–maximum)". | |||||
The sparsely haired tail is about as long as the head and body. It is dark brown above and lighter below. In contrast, the tail of H. megacephalus has little to no difference in color between the upper and lower surface. In 2006, Weksler and colleagues noted tail coloration as a difference between the two species of Transandinomys (bicolored in T. talamancae and unicolored in T. bolivaris), but in their 1998 study, Musser and colleagues could not find differences in tail coloration between their Panamanian samples of the two species.
The hindfeet are long and have the three central digits longer than the two outer ones. They are white to pale yellow above, where the foot is covered with hairs, which are longer than in T. bolivaris. The digits of the hindfeet are surrounded by ungual tufts of silvery hair that are longer than the claws themselves. The claws are short and sharp. Parts of the sole are covered by indistinct scales (squamae
Squamae
In some rodents, squamae are small tubercles resembling scales on the sole of the hindfeet. Among oryzomyine rodents, their development is variable; most have well-developed squamae, but in others they are indistinct or entirely absent. Delomys sublineatus and Peromyscus maniculatus also have...
), which are usually entirely absent in T. bolivaris. The pads are moderately large.
The length of the head and body is 105 to 151 mm (4.1 to 5.9 in), tail length 105 to 152 mm (4.1 to 6.0 in), hindfoot length 26 to 32 mm (1.0 to 1.3 in), ear length 17 to 24 mm (0.67 to 0.94 in), and body mass 38 to 74 g (1.3 to 2.6 oz). As in most oryzomyines, females have eight mammae. There are 12 thoracic vertebra with associated ribs, 7 lumbars, and 29 caudals; a pair of supernumerary (additional) ribs is occasionally present.
Skull and teeth
The skull has a long rostrum (front part), broad interorbital regionInterorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups....
(between the eyes), and low braincase. It differs from that of T. bolivaris in various proportions, which are more apparent in adults than in juveniles. The skull of H. megacephalus is distinctly larger. The zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
is broad and includes a well-developed zygomatic notch at its front. Its back margin is level with the front of the first upper molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
. The zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
(cheekbone) is heavy. The nasal
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
and premaxillary bones extend about as far backward. The interorbital region is narrowest toward the front and shows weak beading at its margins; T. bolivaris is similar, but has stronger beading and H. megacephalus entirely lacks the beading. The parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
is usually limited to the roof of the braincase and does not extend to its side, as it does in most T. bolivaris. The interparietal bone, part of the roof of the braincase, is large.
The incisive foramina (openings in the front part of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
) are short and do not reach between the first molars; they are longer in H. alfaroi. The bony palate is long and extends beyond the end of the molar row and the back margin of the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry bones. The posterolateral palatal pits
Posterolateral palatal pits
In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...
, which perforate the palate near the third molars, are small, and may or may not be recessed into a fossa
Fossa (anatomy)
In anatomical terminology, fossa has come to mean a depression or hollow, in general, in a bone. Other parts of the body may be involved, for example, the antecubital fossa...
. The sphenopalatine vacuities
Sphenopalatine vacuities
In rodents, sphenopalatine vacuities are perforations of the roof of the mesopterygoid fossa, the open space behind the palate, in between the parapterygoid fossae. They may perforate the presphenoid or basisphenoid bone...
(openings in the roof of the mesopterygoid fossa, behind the palate) are also small, as are the auditory bulla
Auditory bulla
The auditory bulla is a hollow bony structure on the ventral, posterior portion of the skull of placental mammals that encloses parts of the middle and inner ear. In most species, it is formed by the tympanic part of the temporal bone.In extant primates, the structure is found in tarsiers,...
e. As in most oryzomyines, the subsquamosal fenestra
Subsquamosal fenestra
In some rodents, the subsquamosal fenestra is an opening between two parts of the squamosal bone, at the back of the skull. It can be seen in lateral view. Most Oryzomyini have the fenestra, but some species, including those in the genera Nectomys, Sigmodontomys, and Melanomys among others, lack...
, an opening at the back of the skull, is present. The pattern of grooves and foramina
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
(openings) in the skull indicates that the circulation of the arteries of the head in T. talamancae follows the primitive pattern, as in most similar species but unlike in Hylaeamys
Hylaeamys
Hylaeamys is a genus of South American oryzomyine rodents found principally in humid forested areas east of the Andes. The species in this genus have historically been placed in Oryzomys. They are most closely related to Euryoryzomys, Transandinomys, Nephelomys, Oecomys, and Handleyomys, and most...
.
The mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(lower jaw) is less robust than in T. bolivaris. The coronoid process
Coronoid process of the mandible
The mandible's coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size....
(a process
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
in the back part of the bone) is small and the capsular process
Capsular process
In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial side of the mandible as a raising in the bone...
, which houses the root of the lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
, are small. The mental foramen
Mental foramen
The mental foramen is one of two holes located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals.- Variations :...
, located in the diastema
Diastema (dentistry)
Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:...
between the lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
and the first molar, opens towards the side, as usual in oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, do not join into a single crest and extend forward to below the first molar.
The upper incisor is opisthodont, with the cutting edge oriented backward. As usual in oryzomyines, the molars are brachydont
Brachydont
Brachydont is a type of dentition characterized by low-crowned teeth, as opposed to high-crowned, hypsodont teeth. Human teeth are brachydont.-External links:*http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/tooth_diversity.html...
(low-crowned) and bunodont (with the cusps higher than the connecting crests). The first upper molar is narrower than in T. bolivaris. As in this species, but unlike in many other rice rats, including H. alfaroi and E. nitidus, the mesoflexus on the second upper molar, which separates the paracone
Paracone
An atmospheric reentry or spaceflight mission abort concept using an inflatable cone.A notable feature of the paracone concept is that it facilitates an abort throughout the entire flight profile....
(one of the main cusps) from the mesoloph (an accessory crest), is not divided in two by an enamel bridge. The hypoflexid on the second lower molar, the main valley between the cusps, is very long, extending more than halfway across the tooth; in this trait, the species is again similar to T. bolivaris but unlike H. alfaroi. Each of the upper molars has three roots (two at the labial, or outer, side and one at the lingual, or inner, side) and each of the lowers has two (one at the front and one at the back); T. talamancae lacks the additional small roots that are present in various other oryzomyines, including species of Euryoryzomys, Nephelomys, and Handleyomys.
Male reproductive anatomy
As is characteristic of Sigmodontinae, Transandinomys talamancae has a complex penis, with the distal (far) end of the baculumBaculum
The baculum is a bone found in the penis of most mammals. It is absent in humans, but present in other primates, such as the gorilla and chimpanzee.The bone aids in sexual intercourse.-Purpose:...
(penis bone) ending in a structure consisting of three digits. As in most oryzomyines, the central digit is larger than the two at the sides. The outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue.
Some features of the accessory glands in the male genital region vary among oryzomyines. In Transandinomys talamancae, a single pair of preputial gland
Preputial gland
Preputial glands are exocrine glands that are located in front of the genitals of some mammals and produce pheromones. The preputial glands of female animals are sometimes called clitoral glands....
s is present at the penis. As is usual for sigmodontines, there are two pairs of ventral prostate
Prostate
The prostate is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals....
glands and a single pair of anterior and dorsal prostate glands. Part of the end of the vesicular gland is irregularly folded, not smooth as in most oryzomyines.
Karyotype
The karyotypeKaryotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
in T. talamancae is variable. Samples from two different localities in Venezuela have 34 chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s and a fundamental number of 64 chromosomal arms (2n = 34, FN = 64). Four specimens from another Venezuelan locality each have a different karyotype, with the number of chromosomes ranging from 40 to 42 and the fundamental number from 66 to perhaps 67. The autosome
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
s (non-sex chromosomes) of the 2n = 34 karyotype all have two major arms, but the 2n = 40–42 karyotypes include several acrocentric autosomes, which only have one major arm. The 2n = 34 karyotype includes two large submetacentric pairs, which have two long arms but one distinctly longer than the other, and one pair of subtelocentric chromosomes, with a long and a much shorter arm, but the 2n = 40–42 karyotypes lack the submetacentrics and have another pair of subtelocentrics. Both Robertsonian translocation
Robertsonian translocation
Robertsonian translocation is a common form of chromosomal rearrangement that in humans occurs in the five acrocentric chromosome pairs, namely 13, 14, 15, 21, and 22. Other translocations occur but do not lead to a viable fetus. They are named after the American biologist William Rees Brebner...
s (fusions of the long arm of one chromosome with the long arm of another and the short arm of the one with the short arm of the other) and pericentric inversions (reversals of part of a chromosome that includes the centromere
Centromere
A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...
) are needed to explain the difference between the two groups. Musser and colleagues, in discussing these karyotypes, assumed that the 2n = 40–42 sample was from within a hybrid zone
Hybrid zone
A hybrid zone exists where the ranges of two interbreeding species meet. For a hybrid zone to be stable, the offspring produced by the cross have to be less fit than members of the parent species, although this condition does not need to be met in the very first hybrid generation...
between two karyotypic morphs.
The karyotype of an Ecuadorean sample from north of the Gulf of Guayaquil
Gulf of Guayaquil
The Gulf of Guayaquil is a large body of water of the Pacific Ocean in western South America. Its northern limit is the city of Salinas, in Ecuador, and its southern limit is Punta Pariñas, in Peru.The gulf takes its name from the city of Guayaquil...
is similar to that of Venezuelan animals at 2n = 36, FN = 60; it includes four acrocentric and two subtelocentric pairs and no submetacentrics. In contrast, a sample from south of the Gulf had 2n = 54, FN = 60, including 23 pairs of acrocentrics and four pairs of metacentrics (with two equally long arms). Musser and colleagues termed the difference between the two Ecuadorian forms "impressive" and noted that further research was needed to understand the karyotypic differentiation within the species more fully. Both T. bolivaris and H. alfaroi have more chromosomes and arms, at 2n = 58, FN = 80 and 2n = 60–62, FN = 100–104 respectively. Hylaeamys megacephalus has 2n = 54, FN = 58–62 and the similar Hylaeamys perenensis has 2n = 52, FN = 62; these karyotypes resemble that of southern Ecuadorean T. talamancae.
Distribution and habitat
The distribution of Transandinomys talamancae extends from northwestern Costa Rica south and east to northern Venezuela and southwestern Ecuador, up to 1525 m (5000 ft) above sea level. It is a forest species and occurs in both evergreenEvergreen forest
An temperate evergreen forest is a forest consisting entirely or mainly of evergreen trees that retain green foliage all year round. Such forests exist in the tropics primarily as broadleaf evergreens, and in temperate and boreal latitudes primarily as coniferous evergreens.-Tropical evergreen...
and deciduous forest. Although its distribution broadly overlaps that of T. bolivaris, it is more widely distributed in South America because of its greater tolerance of dry forest habitats.
Transandinomys talamancae reaches the northern limit of its range in Costa Rica, but except for one record from the far northwest (in Guanacaste Province
Guanacaste Province
Guanacaste is a province of Costa Rica located in the northwestern part of the country, along the coast of the Pacific Ocean. To the north it borders Nicaragua. To the east is the Alajuela Province, and to the southeast is the Puntarenas Province. It is the most sparsely populated of all the...
near the southern margin of Lake Nicaragua
Lake Nicaragua
Lake Nicaragua or Cocibolca or Granada or is a vast freshwater lake in Nicaragua of tectonic origin. With an area of , it is the largest lake in Central America, the 19th largest lake in the world and the 9th largest in the Americas. It is slightly smaller than Lake Titicaca. With an elevation...
), it is known only from the southeastern third of the country. In contrast, T. bolivaris and H. alfaroi occur further north, into Honduras and Mexico respectively. It occurs throughout Panama at low elevations. Along the Pacific coast in Colombia and Ecuador, it is found on the coastal plain and the adjacent foothills of the Andes. The southernmost known record is in far southwestern Ecuador, but the species may well range into nearby Peru.
It also occurs throughout northern Colombia at low elevations and into western Venezuela west of Lake Maracaibo
Lake Maracaibo
Lake Maracaibo is a large brackish bay in Venezuela at . It is connected to the Gulf of Venezuela by Tablazo Strait at the northern end, and fed by numerous rivers, the largest being the Catatumbo. It is commonly considered a lake rather than a bay or lagoon, and at 13,210 km² it would be the...
and at the foot of the western part of the Venezuelan Coastal Range
Venezuelan Coastal Range
The Venezuelan Coastal Range is a mountain range that runs along the central and eastern portions of Venezuela's northern coast...
east to Guatopo National Park. Hylaeamys megacephalus occurs further to the east in the eastern portion of the coastal range, separated by the coastal Eastern Caribbean Dry Zone. There is a record from the Orinoco Delta of northeastern Venezuela, well within the range of Hylaeamys megacephalus, but Musser and colleagues suggest that this is based on mislabeled specimens. The species has also been found on the narrow strip between the Llanos
Llanos
The Llanos is a vast tropical grassland plain situated to the east of the Andes in Colombia and Venezuela, in northwestern South America. It is an ecoregion of the Flooded grasslands and savannas Biome....
and the Andes (Cordillera Oriental and Cordillera de Mérida
Cordillera de Mérida
The Cordillera de Mérida is a series of mountain ranges, or massif, in northwestern Venezuela. The Cordillera de Mérida is a northeastern extension of the Andes Mountains. The ranges run southwest–northeast between the Venezuelan–Colombian border and the Venezuelan coastal range...
) in eastern Colombia and northwestern Venezuela. The unforested Llanos separate these areas from Hylaeamys populations. Hylaeamys perenensis does, however, occur further south along the eastern foothills of the Cordillera Oriental in Colombia and it is possible that the two overlap in this area.
Ecology and behavior
Transandinomys talamancae is a common, even abundant species. Its ecology was studied by Theodore Fleming in the Panama Canal ZonePanama Canal Zone
The Panama Canal Zone was a unorganized U.S. territory located within the Republic of Panama, consisting of the Panama Canal and an area generally extending 5 miles on each side of the centerline, but excluding Panama City and Colón, which otherwise would have been partly within the limits of...
. It lives on the ground and is active during the night. The animal uses nests that are located above the ground and occasionally enters burrows also used by the pocket mouse Liomys adspersus. Its diet is omnivorous, including both plant material such as seeds and fruits and adult and larval insects.
Males tend to move over longer distances than females. The average home range size in Fleming's study was 1.33 hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
s (3.3 acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...
s); males had larger home ranges on average. Specimens that were once captured tended to be captured more frequently than those that had never been captured. Fleming estimated that population densities reached peaks of up to 4.3 per ha (1.7 per acre) late in the rainy season (October–November), but dropped to near zero around June; however, these figures may well be underestimates. In central Venezuela, population densities vary from 5.5 to 9.6 per ha (2.2 to 3.8 per acre).
In Panama, it breeds year-round without apparent seasonal variability. According to Omar Linares's Mamíferos de Venezuela (Mammals of Venezuela), reproductive activity is highest in June–July and December. In the laboratory, the gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
is 28 days; Linares reports that it is 20 to 30 days in the wild. Females produce an average of six litters per year and there are two to five (average 3.92) young per litter, so that a single female may produce about 24 young per year; this is likely an overestimate because most females would not live for a full year. Larger females may have larger litters. Animals become sexually mature when less than two months old; in Fleming's study, some females in juvenile fur, probably less than 50 days old, were already pregnant. The oldest specimen Fleming observed was nine months old; he estimated that animals were unlikely to live for more than a year in the wild and that the mean age at death was 2.9 months.
Ten species of mites (Gigantolaelaps aitkeni, Gigantolaelaps gilmorei, Gigantolaelaps oudemansi, Gigantolaelaps wolffsohni, Haemolaelaps glasgowi, Laelaps dearmasi, Laelaps pilifer, Laelaps thori, Mysolaelaps parvispinosus, and Paraspeleognathopsis cricetidarum), thirteen chiggers (Aitkenius cunctatus, Ascoschoengastia dyscrita, Eutrombicula alfreddugesi, Eutrombicula goeldii, Intercutestrix tryssa, Leptotrombidium panamensis, Myxacarus oscillatus, Pseudoschoengastia abditiva, Pseudoschoengastia bulbifera, Trombicula dunni, and Trombicula keenani), and four fleas (Jellisonia sp., Polygenis roberti, Polygenis klagesi, and Polygenis dunni) have been found on T. talamancae in Panama. G. aitkeni has also been found on this species in Colombia. In addition, the sucking lice Hoplopleura nesoryzomydis and Hoplopleura oryzomydis
Hoplopleura oryzomydis
Hoplopleura oryzomydis is a sucking louse that is known from the southern United States, Nicaragua, Panama, and Venezuela. It is known from several oryzomyine rodents: the marsh rice rat , O. couesi, Handleyomys alfaroi, Transandinomys talamancae, Melanomys caliginosus, and Sigmodontomys...
occur on T. talamancae.
Conservation status
A widespread and common species, Transandinomys talamancae is listed as "Least ConcernLeast Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" by the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
. It occurs in numerous protected area
Protected area
Protected areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the enabling laws of each country or the regulations of the international...
s and tolerates disturbed habitats well, and no important threats are known.
Literature cited
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