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Akodon philipmyersiMyers' grass mouse

By Tanya Dewey

Geographic Range

Akodon philipmyersi is known only from the Northern Campos biome in the southern portions of Misiones province, northern Argentina. This area is bordered, to the northeast, by the Atlantic forests of Brazil and, to the southwest, by Ibera wetland areas. (Pardiñas, et al., 2005)

Habitat

Akodon philipmyersi has been found only in habitats characterized as Northern Campos in Argentina. This habitat type is made up of tall grasslands that are typically near wooded areas. Individuals were captured in areas with tall grasses (2 meters or more). This is a unique habitat type with a limited distribution, making up only 0.7% of Argentinean landcover. Endemicity in Northern Campos habitats seems to be high, indicating that it is an important habitat to target for protection measures. (Pardiñas, et al., 2005)

Physical Description

Myers' grass mice are typical of the genus Akodon. They are small, stout-bodied, short-limbed mice with relatively short tails. Akodon philipmyersi head and body length averages 93 mm and tail lengh 58 mm (40% of head and body length). The hind foot averages 17 mm long, without the claw, and ear length averages 12 mm. Average weight is 23 grams. The pelage is soft and somewhat long (10 mm dorsally). The dorsal pelage has agouti at the hair tips and is grayish on the hair bases. The venter is creamy, with grey on the distal 2 mm of the hairs, giving the venter a grayish appearance. The feet are covered with whitish fur and the tail is well-furred and distinctly scaled. The upper incisors are slightly opisodont and orange pigmented. (Nowak, 1991; Pardiñas, et al., 2005)

Akodon philipmyersi is distinguished from other Akodon species by the following characters: condyloincisive length less than 24 mm, zygomatic breadth less than 13 mm, maxillary toothrow length less than 24 mm, a short rostrum - with the incisive foramen length measuring 5.6 mm on average, short and wide nasals, narrow zygomatic plate, wide mesopterygoid fossa with a median palatine process on the anterior border, an interorbital constriction between 4.3 and 4.6 mm wide, medium-sized auditory bullae, a diploid number of 2n=36, and a number of molecular synapomorphies from the mitochondrial cytochrome b gene. (Pardiñas, et al., 2005)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    23 g
    0.81 oz
  • Average length
    93 mm
    3.66 in

Reproduction

There is no specific evidence relevant to mating systems in A. philipmyersi. Similarly, little is known about mating systems in other Akodon species. (Nowak, 1991; Pardiñas, et al., 2005)

Very little is known about reproduction in this newly described species. Reproductive condition was recorded for 12 individuals captured. Of these, 10 were reproductively active at the end of the summer season (March). Pregnant females had 3 or fewer embryos. Other Akodon species seem to have two litters per year of 3 to 4 young from August to May, although breeding seasons may vary. Akodon azarae, a related species, reproduce seasonally, giving birth to an average of 4.6 young per litter after a gestation period of 22.7 days. Delayed implantation may occur in A. azarae and sexual maturity occurred usually at 2 months. (Nowak, 1991)

  • Breeding interval
    Akodon philipmyersi probably gives birth to two litters per year.
  • Breeding season
    Breeding is likely to occur during the summer months.
  • Range number of offspring
    3 (high)

There is no specific evidence regarding parental investment in this species. As mammals, females nurse and care for their young until they are weaned. Other Akodon species wean their young at 14 to 15 days old. (Nowak, 1991; Pardiñas, et al., 2005)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Lifespan/Longevity

Nothing is known about lifespan in A. philipmyersi. It is likely that these rodents have relatively short lives, from 12 to 18 months in the wild. (Pardiñas, et al., 2005)

Behavior

All known specimens of A. philipmyersi were captured at night or recovered from owl pellets. Other aspects of the life history of these mice remain to be studied. Akodon is a diverse genus, and natural history may vary substantially. Other Akodon species make small burrows including globular nests. (Pardiñas, et al., 2005)

Home Range

Home range is unknown in A. philipmyersi. Abrothrix olivaceus individuals have home ranges that average 54 meters and population densities averaging 30 to 97 per hectare, varying seasonally. (Nowak, 1991)

Communication and Perception

Communication and perception have not been studied in this recently described species. Like most small, sigmodontine rodents, they are likely to rely extensively on hearing and olfaction in navigating the environment and in communicating with conspecifics. Their nocturnal habits also suggest that these modes of perception may be especially important.

Food Habits

There is no specific evidence concerning the food habits of A. philipmyersi. The related species, Akodon azarae, is reported to be mainly herbivorous, but takes animal prey opportunistically. (Pardiñas, et al., 2005)

Predation

Akodon philipmyersi was discovered during analysis of barn owl (Tyto alba) pellets and was found to represent a major proportion of barn owl prey in Northern Campos grasslands. They represented 30.7% of 182 prey items in one locality and 23% of 149 prey items in another locality. Other predators of A. philipmyersi are unknown. Although specific anti-predator adaptations are unknown in these grass mice, it is likely that they use their cryptic coloration, secretive, nocturnal habits, and vigilance to decrease their risk of predation. (Pardiñas, et al., 2005)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Myers' grass mice are likely to be primary consumers and act as important prey for larger predators, such as owls. (Pardiñas, et al., 2005)

Economic Importance for Humans: Positive

There are no known positive effects of Akodon philipmyersi for humans, aside from their role as members of healthy, natural ecosystems. (Pardiñas, et al., 2005)

Economic Importance for Humans: Negative

There are no known negative impacts of Akodon philipmyersi. (Pardiñas, et al., 2005)

Conservation Status

Akodon philipmyersi is a recently described species and its conservation status has not been extensively reviewed. It is the only known mammalian endemic species of the Northern Campos grasslands. This rare habitat has been extensively converted to agriculture, especially yerba mate, tea, introduced tree plantations (Pinus and Eucalyptus), and cattle grazing. Several, large mammalian species have already been extirpated in this region (Blastocerus dichotomus, Myrmecophaga tridactyla, Panthera onca, Ozotoceros bezoarticus, and Pteronura brasiliensis). Northern Campos grasslands represent an area where northern and southern faunas mix, elevating biodiversity in this region. All A. philipmyersi individuals were captured in Northern Campos grassland areas, suggesting that they do not inhabit areas in the region converted to agriculture. With only 0.4% of Northern Campos grasslands protected, A. philipmyersi may be especially vulnerable to the effects of additional habitat destruction. (Pardiñas, et al., 2005)

Other Comments

Akodon philipmyersi was named in honor of Dr. Philip Myers for his contributions to the understanding of Akodon systematics and ecology. Dr. Myers is also the founder and director of the Animal Diversity Web. (Pardiñas, et al., 2005)

Contributors

Tanya Dewey (author), Animal Diversity Web.

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

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

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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.

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

seasonal breeding

breeding is confined to a particular season

sexual

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

tactile

uses touch to communicate

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.

References

Nowak, R. 1991. Walker's Mammals of the World. Baltimore, Maryland: The Johns Hopkins University Press.

Pardiñas, U., G. D'Elía, S. Cirignoli, P. Suarez. 2005. A new species of Akodon (Rodentia, Cricetidae) from the Northern Campos grasslands of Argentina. Journal of Mammalogy, 86: 462-474.

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