The yellow-rumped leaf-eared mouse (''Phyllotis xanthopygus'') otherwise known as the Patagonian leaf-eared mouse is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

in 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 almost 608 species, it is the second-largest family of mammals, and has m ...

and order

Rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

ia. It is the most widespread member of the genus.

Description

''Phyllotis xanthopygus'' is a predominantly greyish brown/sand-colored

New World mouse The New World rats and mice are a group of related rodents found in North and South America. They are extremely diverse in appearance and ecology, ranging in from the tiny ''Baiomys'' to the large ''Kunsia''. They represent one of the few exampl ...

that reaches around 55g in its adulthood. Its thick coat is typically lighter on its underside, most prominent posteriorly, exhibiting

countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and ...

that is typical for many small mammals as it aids in camouflage from predators. True to its name, the Patagonian leaf-eared mouse has broad triangular ears similar to other leaf-eared members that compose the genus

Phyllotis ''Phyllotis'' is a genus of rodent in the family Cricetidae. These mice are commonly confused with '' Auliscomys, Graomys'' and '' Loxodontomys.'' ''.'' In order to tell these genera apart, one must look at the tail. Species in the genus ''Ph ...

. The pelage of ''Phyllotis xanthopygus'' is known to differ seasonally. This example of

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

contributes to its ability to camouflage in a dynamic, seasonal, environment. Blending in with the vegetation and rocky outcrops is an important characteristic as their primary predators are raptors most notably owls, which rely on being able to spot their prey from the air. While not explicitly nocturnal, they are most active at night due to the correlation between light intensity, visibility, and predation risk. The adults of ''P. xanthopygus'' are quite large as far as the genus goes with a body mass of fifty-five grams and large ears that are normally around twenty-seven millimeters long. The throat and chin are a pale buff or a light tan with dull grey underfur. These mice boast a long soft fur with yellow brown guard hairs that are sometimes black tipped with grey bases.

Distribution and habitat

''Phyllotis xanthopygus'' occurs in South America, specifically in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

mountain range in Peru, Argentina, Chile, and Bolivia from sea level to 5,000 m. While the rocky habitat of the Andes provides ample cover from predators, the high elevation environments are limited in food availability therefore restricting reproduction to the warmer months. The highest elevation the yellow-rumped leaf-eared mouse ever was found was at the summit of Volcán

Llullaillaco Llullaillaco () is a dormant stratovolcano at the border of Argentina (Salta Province) and Chile (Antofagasta Region). It lies in the Puna de Atacama, a region of tall volcanic peaks on a high plateau close to the Atacama Desert, one of the dri ...

(6739 m) and this is the highest altitude a mammal was ever found in nature. Its distribution at high altitudes across the Andean plateau has led to plasticity in its

non-shivering thermogenesis Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily (''Sauromatum venosum''), and the giant wate ...

in order to cope with the low temperatures. This thermal acclimation relies on

brown adipose tissue Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat). Brown adipose tissue is found in almost all mammals. Classification of brown fat refers to two distinct cell populations with si ...

and is often induced by ingestion. This adaptation is important for small mammals like ''Phyllotis xanthopygus'' that undergo

torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...

because it accelerates heating during arousal events. There is insufficient research concerning small mammalian populations south of Mendoza Argentina due to the large array of species within Rodentia as well as the continuous discovery of new members.

Diet

Members of

are known for variety in their diets, for ''Phyllotis xanthopygus'' this range includes

herbivory A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

insectivory A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

granivory Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of plants as a main or exclusive food source,Hulme, P.E. and Benkman, C.W. (2002) "Granivory", pp. 132 ...

, and

frugivory A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance an ...

. This variation enables them to be opportunistic feeder: an advantageous trait as it permits quick and unselective foraging in open and vulnerable areas. Their teeth are specialized to accommodate for the diversity in their diet as they have enlarged

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, whe ...

s which are separated from the cheekteeth by a

diastema A diastema (plural diastemata, from Greek διάστημα, space) 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. More colloquially, the condition ...

. The teeth are characterized as aradicular, being that they grow continuously throughout an organism's' lifetime. This results in the incisors resembling a chisel due to rapid wear on the soft

dentin Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...

at the back of the tooth from rubbing against one another. One study that was done with these rodents tested how their behaviors changed based on the amount of light that was allowed in their habitat. The researchers found that the habitats with the least amount of light had the most foraging activity with the mice. This behavior correlates to the rodents avoiding predators by foraging in darker areas. These mice rapidly increase their metabolic heat production in cooler climates by having a high metabolic rate and using non shivering thermogenesis which allows them to acclimate to their seasonal climates better. In order to avoid predation these mice have been known to display an escape behavior due to large shadows rather than small raptor shadows. The males have also been shown to go out foraging at an earlier time than the females do.

References

*Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. pp. 894–1531 ''in'' Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore. *Steppan, S. J. 1996. ''Phyllotis xanthopygus''. Tree of Life

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