Drymoreomys
   HOME

TheInfoList



OR:

''Drymoreomys'' is a
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
in the tribe
Oryzomyini Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of S ...
that lives in the Atlantic Forest of Brazil. The single species, ''D. albimaculatus'', is known only from the states of
São Paulo São Paulo (; ; Portuguese for 'Paul the Apostle, Saint Paul') is the capital of the São Paulo (state), state of São Paulo, as well as the List of cities in Brazil by population, most populous city in Brazil, the List of largest cities in the ...
and Santa Catarina and was not named until 2011. It lives in the humid forest on the eastern slopes of the
Serra do Mar The Serra do Mar (; ) is a system of mountain ranges and escarpments in Southeast Region, Brazil, Southeastern Brazil. Geography The Serra do Mar runs parallel to the Atlantic Ocean coast from the state of Espírito Santo to southern Santa Ca ...
and perhaps reproduces year-round. Although its range is relatively large and includes some
protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural or cultural values. Protected areas are those areas in which human presence or the exploitation of natural resources (e.g. firewood ...
s, it is patchy and threatened, and the discoverers recommend that the animal be considered "
Near Threatened A near-threatened species is a species which has been Conservation status, categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to Endangered species, endangerment in the ne ...
" on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
. Within Oryzomyini, ''Drymoreomys'' appears to be most closely related to '' Eremoryzomys'' from the
Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
of Peru, a biogeographically unusual relationship, in that the two populations are widely separated and each is adapted to an arid or a moist environment. With a body mass of , ''Drymoreomys'' is a medium-sized rodent with long fur that is orange to reddish- buff above and grayish with several white patches below. The pads on the hindfeet are very well developed and there is brown fur on the upper sides of the feet. The tail is brown above and below. The front part of the skull is relatively long and the ridges on the
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
are weak. The
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 sep ...
is short, with its back margin between the third
molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
. Several traits of the genitals are not seen in any other oryzomyine rodent.


Taxonomy

''Drymoreomys'' was first recorded in 1992 by Meika Mustrangi in the state of
São Paulo São Paulo (; ; Portuguese for 'Paul the Apostle, Saint Paul') is the capital of the São Paulo (state), state of São Paulo, as well as the List of cities in Brazil by population, most populous city in Brazil, the List of largest cities in the ...
. The animal was not, however, formally described until 2011, when Alexandre Percequillo and colleagues named it as a new genus and species within the tribe
Oryzomyini Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of S ...
: ''Drymoreomys albimaculatus''. The generic name, ''Drymoreomys'', combines the Greek ''δρυμός'' (''drymos''), meaning "forest", ''ὄρειος'' (''oreios''), meaning "mountain-dwelling", and ''μῦς'' (''mys''), meaning "mouse". The name refers to the animal's occurrence in mountain forest. The
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
, ''albimaculatus'', derives from the Latin ''albus'', meaning "white", and ''maculatus'', meaning "spotted", a reference to the spots of white in the animal's fur. Percequillo and colleagues found little geographic variation among samples of ''Drymoreomys'', although a few traits differ in frequency between populations from the states of São Paulo and Santa Catarina. According to a
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analysis of evidence from
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
, the
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics * Nuclear space *Nuclear ...
gene IRBP, and the
mitochondrial A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...
gene cytochrome ''b'', ''Drymoreomys albimaculatus'' is most closely related to ''
Eremoryzomys polius ''Eremoryzomys polius'', also known as the gray rice rat or the Marañon oryzomys,Musser and Carleton, 2005, p. 1153 is a rodent species in the tribe Oryzomyini of the family Cricetidae. Discovered in 1912 and first described in 1913 by Wilf ...
'', an oryzomyine from northern Peru and the only species in the genus ''Eremoryzomys''. Together, ''Drymoreomys'' and ''Eremoryzomys'' are part of Marcelo Weksler's clade D, one of four main
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s within Oryzomyini. Some subsequent studies did not support a relationship between the ''Drymoreomys–Eremoryzomys''
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
and the rest of clade D, but this is probably due to saturation of the
phylogenetic signal In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
in mitochondrial data. Oryzomyini includes well over a hundred species distributed mainly in South America, including nearby islands such as the
Galápagos Islands The Galápagos Islands () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...
and some of the
Antilles The Antilles is an archipelago bordered by the Caribbean Sea to the south and west, the Gulf of Mexico to the northwest, and the Atlantic Ocean to the north and east. The Antillean islands are divided into two smaller groupings: the Greater An ...
. It is one of several tribes recognized within the subfamily
Sigmodontinae The rodent subfamily Sigmodontinae 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 ...
, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae is the largest subfamily of the family
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At over 870 species, it is either the largest or second-largest family ...
, other members of which include
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of lo ...
s,
lemming A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also inclu ...
s,
hamster Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera. They have become established as popular small pets. The best-known species of hamster is the golden or Syrian ...
s, and deermice, all mainly from Eurasia and North America.


Description


External morphology

''Drymoreomys albimaculatus'' is a medium-sized, long-tailed, short-eared, short-footed rodent. It is quite distinct from other oryzomyines and has a number of unique traits. In 11 adults from Parque Natural Municipal Nascentes do Garcia in Santa Catarina, head and body length was , tail length was , hindfoot length was , ear length was , and body mass was . The fur is long and dense and consists of thin, short, woolly underfur and long, thick overfur. Overall, the fur of the upperparts is orange to reddish- buff. In the closely related ''Eremoryzomys'', the upperparts are grayish. The hairs of the underfur, which are long, are grayish for most of their length and orange or brown at the tip. In the overfur, the cover hairs (which form the main body of the fur), are long and brown at the tip, with an orange band below the tip, and the longer, sparse
guard hair Guard hair or overhair is the outer layer of hair of most mammals, which overlay the fur. Guard hairs are long and coarse and protect the rest of the pelage (fur) from abrasion and frequently from moisture. They are visible on the surface of the ...
s are red to dark brown in the half closest to the tip and are long. The sides are reddish brown. On the underparts, the hairs are grayish at the base and white at the tip, except on the throat, chest, and (in some specimens) groin, where the hairs are entirely white—a trait unique among the oryzomyines. In overall appearance, the underparts are grayish, with white spots where the hairs are completely white. The small, rounded ears are covered with dense golden hairs on the outer and with reddish brown hairs on the inner surface. The mystacial vibrissae (whiskers on the upper lip) are long, usually extending a little beyond the ears when laid back against the head, but the superciliary vibrissae (whiskers above the eyes) are short and do not extend beyond the ears. The upper surface on the forefeet is covered with brown fur, and there is white or silvery fur on the digits. Ungual tufts (fur around the bases of the claws) are present on the second through fourth digits. On the short, fairly broad hindfeet, the upper side is covered densely with silvery to white hairs near the tips of the feet and toes, and with brown fur otherwise. No other oryzomyine has such brown fur on its hindfeet. The second through fourth digits have long silvery-white ungual tufts, but those on the first digit are short. On the sole, the pads are very large. Among oryzomyines, only '' Oecomys'' and the extinct '' Megalomys'' have similarly large pads between their digits. There is a dense cover of short brown hairs on both the upper and lower sides of the tail. Unlike in ''Eremoryzomys'', the tail is the same color above and below. The tail ends in a tuft, an unusual feature among oryzomyines.


Skull

In the skull, the rostrum (front part) is relatively long. The
nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery * ...
and
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
ry bones extend in front of the
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s, forming a rostral tube, which is shared among oryzomyines only with '' Handleyomys''. The zygomatic notch (a notch formed by a projection at the front of the
zygomatic plate In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the ...
, a bony plate at the side of the skull) is shallow. The interorbital region (between the eyes) is narrow and long, with the narrowest part towards the front. The crests on the
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
and interorbital region are weakly developed. ''Eremoryzomys'' has larger crests on its interorbital region. The incisive foramina (openings in the front part of the
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 sep ...
) are long, sometimes extending to between the first
molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
(M1). The bony palate is broad and short, with the posterior margin between the third molars (M3). '' Nephelomys levipes'' is the only other oryzomyine with such a short palate, although that of ''Eremoryzomys polius'' is only slightly longer. The posterolateral palatal pits (openings in the back part of the palate near the M3) vary from small to fairly large and are located in slight fossas (depressions). In ''Eremoryzomys'', these fossas are deeper. The roof of the mesopterygoid fossa, the opening behind the palate, is completely closed or contains small sphenopalatine vacuities. The vacuities are much larger in ''Eremoryzomys''. The alisphenoid strut, a piece of bone that separates two
foramina In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, arter ...
(openings), is present in all ''Drymoreomys'' specimens examined, except in one juvenile specimen. The
mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
(lower jaw) is long and low. The coronoid process, the frontmost of the three main processes (projections) at the back of the jawbone, is large and about as high as the
condyloid process The condyloid process or condylar process is the process on the human and other mammalian species' mandibles that ends in a condyle, the mandibular condyle. It is thicker than the coronoid process of the mandible and consists of two portions: the ...
behind it. The angular process, below the condyloid, is fairly short and does not extend further backwards than the condyloid. There is no noticeable capsular process (a raising at the back of the jaw that houses the root of the lower incisor).


Dentition

The upper incisors are opisthodont (with the cutting surface oriented backwards) and have orange to yellow enamel. The upper molar rows are either almost parallel or slightly convergent with each other toward the front. ''
Holochilus ''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus ...
'' and ''
Lundomys ''Lundomys molitor'', also known as Lund's amphibious ratMusser and Carleton, 2005, p. 1124 or the greater marsh rat, is a semiaquatic rat species from southeastern South America. Its distribution is now restricted to Uruguay and nearby Ri ...
'' are the only other oryzomyines with non-parallel molar rows. The valleys between the cusps of the upper molars extending from the inner and outer sides overlap slightly across the midlines of the teeth. The molars are high-cusped, almost
hypsodont Hypsodont is a pattern of dentition characterized by with high crowns, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritty, fibrous material. The oppos ...
. On M1, the anterocone (the front cusp) is divided into two cuspules on the lingual (inner, towards the tongue) and labial (outer, towards the lips) sides of the teeth. The mesoloph, a crest near the middle of the labial side of the tooth, is long and well developed on each of the three upper molars. On the lower molars (m1 to m3), the cusps on the labial side are located slightly in front of their lingual counterparts. The anteroconid, the front cusp on the m1, is divided in two. The m1, m2, and usually m3 have a mesolophid, a crest corresponding to the mesoloph but located on the lingual side. Each of the lower molars has two roots.


Other anatomy

There are 12 ribs and 19
thoracolumbar Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
(chest and abdomen), four sacral, and 36 to 38 caudal (tail) vertebrae. There are three digits at the tip of the penis, of which the central one is the largest. The two lateral digits are not supported by mounds of the
baculum The baculum (: bacula), also known as the penis bone, penile bone, ''os penis'', ''os genitale'', or ''os priapi'', is a bone in the penis of many placental mammals. It is not present in humans, but is present in the penises of some primates, ...
(penis bone). There is only one
spine Spine or spinal may refer to: Science Biology * Spinal column, also known as the backbone * Dendritic spine, a small membranous protrusion from a neuron's dendrite * Thorns, spines, and prickles, needle-like structures in plants * Spine (zoology), ...
on the
papilla Papilla (Latin, 'nipple') or papillae may refer to: In animals * Papilla (fish anatomy), in the mouth of fish * Papilla (worms), small bumps on the surface of certain worms * Basilar papilla, a sensory organ of lizards, amphibians and fish * ...
(nipple-like projection) on the upper side of the penis. On the urethral process, located in the crater at the end of the penis, a fleshy process at the side, the lateral
lobule In anatomy, a lobe is a clear anatomical division or extension of an organ (as seen for example in the brain, lung, liver, or kidney) that can be determined without the use of a microscope at the gross anatomy level. This is in contrast to the mu ...
, is present. The preputial glands (glands in front of the genitals) are large. The lack of lateral bacular mounds, presence of a lateral lobule, and size of the preputial glands are all unique traits among the oryzomyines.


Karyotype

The
karyotype A karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is discerned by de ...
of ''Drymoreomys albimaculatus'' is 2n=62, FN=62: the animal has 62
chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...
s, and 29 pairs of
autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes ...
s (non-sex chromosomes) are
acrocentric The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
(with one arm so short as to be almost invisible) and one small pair is metacentric (with two equally long arms). Both sex chromosomes are
submetacentric The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
(with one arm noticeably longer than the other), and X is larger than Y. Blocks of
heterochromatin Heterochromatin is a tightly packed form of DNA or '' condensed DNA'', which comes in multiple varieties. These varieties lie on a continuum between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a rol ...
are present on all autosomes and the long arm of Y. Telomeric sequences are found near the
centromere The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fiber ...
s of the sex chromosomes. Aspects of this karyotype—with a high number of mostly acrocentric chromosomes and the presence of heterochromatin on the Y chromosome—are consistent with the pattern seen in other oryzomyines. However, no other oryzomyine has exactly the same karyotype as ''D. albimaculatus''. Other species in clade D have fewer chromosomes, down to 16 in '' Nectomys palmipes'', although the karyotype of ''Eremoryzomys polius'' is unknown. This suggests an evolutionary trend of decreasing chromosome number within the clade.


Distribution and ecology

''Drymoreomys albimaculatus'' occurs in the Atlantic Forest on the eastern slopes of the
Serra do Mar The Serra do Mar (; ) is a system of mountain ranges and escarpments in Southeast Region, Brazil, Southeastern Brazil. Geography The Serra do Mar runs parallel to the Atlantic Ocean coast from the state of Espírito Santo to southern Santa Ca ...
in the Brazilian states of São Paulo and Santa Catarina, at above sea level. It has not been found in the intervening state of Paraná, but is likely to occur there. The biogeographical pattern indicated by the relationship between ''Drymoreomys'' and the Andean ''Eremoryzomys'' is unusual. While there are some similar cases of relationships between Andean and Atlantic Forest animals, these involve inhabitants of humid forests in the Andes; ''Eremoryzomys'', by contrast, lives in an arid area. ''Drymoreomys albimaculatus'' appears to be a specialist of dense, moist,
montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...
and premontane forest. It has been found in disturbed and
secondary forest A secondary forest (or second-growth forest) is a forest or woodland area which has regenerated through largely natural processes after human-caused Disturbance (ecology), disturbances, such as Logging, timber harvest or agriculture clearing, or ...
s as well as in pristine forest, but probably needs contiguous forest to survive. Reproductive activity has been observed in females in June, November, and December and in males in December, suggesting that the species breeds year-round. Although some of its morphological traits, such as the very large pads, are suggestive of
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
(tree-dwelling) habits, most specimens were collected in pitfall traps on the ground.


Conservation status

The range of ''Drymoreomys albimaculatus'' is relatively large and the species occurs in several
protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural or cultural values. Protected areas are those areas in which human presence or the exploitation of natural resources (e.g. firewood ...
s, but it has only been found in seven localities and its habitat is threatened by deforestation and fragmentation. Therefore, Percequillo and colleagues suggest that the species be assessed as "
Near Threatened A near-threatened species is a species which has been Conservation status, categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to Endangered species, endangerment in the ne ...
" under the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
criteria.


References


Literature cited

* * * * * * * {{Featured article Oryzomyini Rodents of Brazil Endemic mammals of Brazil Fauna of the Atlantic Forest Mammals described in 2011 Taxa named by Alexandre Reis Percequillo Taxa named by Marcelo Weksler Taxa named by Leonora Pires Costa Monotypic rodent genera