Southern grasshopper mouse

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Southern grasshopper mouse
Southern grasshopper mouse.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Neotominae
Genus: Onychomys
Species:
O. torridus
Binomial name
Onychomys torridus
(Coues, 1874)

The southern grasshopper mouse or scorpion mouse (Onychomys torridus) is a species of predatory rodent in the family Cricetidae, [2] native to Mexico and the states of Arizona, California, Nevada, New Mexico, and Utah in the United States. [1] Notable for its resistance to venom, it routinely preys on the highly venomous Arizona bark scorpion.

Contents

Description

The southern grasshopper mouse is a robust, small, nocturnal species that typically forms monogamous pairs. [3] They have a short tail, growing to a total length of 120 to 163 mm (4.7 to 6.4 in). The head, back and sides are pinkish- or grayish-brown while the underparts are white, the two colors being distinctly separated. The tail is club-shaped, short and broad, the anterior part being the same color as the body and the tip being white. [4]

Biology

The southern grasshopper mouse feeds almost entirely on arthropods, such as beetles, grasshoppers and scorpions. In addition to arthropods, it is known to prey upon the little pocket mouse (Perognathus longimembris) and the western harvest mouse (Reithrodontomys megalotis). [4]

In the arid regions inhabited by the southern grasshopper mouse, the Arizona bark scorpion is plentiful and avoided by most predators because of the very painful sting it can inflict. The grasshopper mouse can feed on this scorpion with impunity even when the scorpion stings it repeatedly in the face. [5] Researchers have found that a neural mechanism is involved that blocks the sending of pain messages to the brain. This mouse can normally feel pain from other sources, but can be temporarily insensitive to these stimuli after a dose of venom from a bark scorpion. [5] [6] This pain modulation is activated soon after the scorpion sting; the mouse does briefly feel pain from the sting, but the scorpion venom binds to the transmembrane channel otNav1.8. [7] Specifically, the venom binds to a glutamic acid residue located within the channel protein, [7] thus preventing neuron action potentials from firing and acting as a type of temporary anesthetic and pain reliever for the mouse. When this glutamic acid was replaced with hydrophilic glutamine residue, the venom did not bind with the protein, and the pain modulation ability was lost. [7]

Females are able to produce several litters in a year, but their reproductive life does not usually last into their second year. The average litter size is 2.6 (range 1 to 5), produced after an average gestation period of 29 days. The young are born naked, with pink translucent skin. One day later the pigment is developing on the dorsal surface and by day ten, hairs 3 millimetres (0.12 in) long are present on the back. The eyes open on day 15 and solid food is being consumed by day 19. The females give birth to their first litter when four or five months old. [4]

Ecology

Southern grasshopper mice are unique among other North American rodents in the family Cricetidae in that their diet consists mostly of arthropods. [4] They are usually found in areas with lower population densities. [4] Several studies have demonstrated that the reproductive attributes of this species allows them to be naturally maintained at lower population densities. [4] Females tend to be sexually active only during one breeding season, which is due to their rapid reproductive aging following their first year. [4] Moreover, males' unique pauses in their testicular activity during the breeding season might also contribute to the lower population densities in which they live. [4]

The natural habitat of southern grasshopper mice include hot, arid valleys, and scrub deserts. A male and female along with their offspring occupy a larger home range for burrowing compared to males and females alone. [4] On average, males have a home range of 7.8 acres, while females occupy an area of 5.9 acres. [4] They tend to maintain a specific place of residency for a longer period of time compared to other mammals. [4] The home ranges between southern grasshopper mice are not too far from each other, with an average maximum distance of 118.4± 8.0 meters. [4] However, adult males tend to be very territorial and their efficient spacing is facilitated by vocalizations they make at night. [4]

In a study done by Denise H. Frank and Edward J. Heske, the home range of southern grasshopper mice in the Chihuahuan Desert were observed. [3] The home range of males during the non-breeding season were found to be smaller than those held by males during the breeding season. [3] In contrast, there was not a significant difference between the home ranges of females during the breeding and non-breeding seasons. [3] Male ranges during the reproductive season were some two to three times larger than those of adult females during the reproductive season. [3]

There are no currently known conservation issues associated with southern grasshopper mice, largely due to its wide distribution and tolerance for disturbances caused by arthropods. [8] However, some disturbances have been observed in their low density populations. [8] Many more population studies will need to be performed in order to gain further insight into the conservation status of this species. [8]

Predatory behavior

Southern grasshopper mice are a predatory, and very aggressive rodent species. [9] In a study done by Richard McCarty and Charles H. Southwick, these grasshopper mice were deprived of food and their predatory behavior against laboratory mice and crickets was observed. [9] After 48 hours of food deprivation, southern grasshopper mice spent more time eating crickets than the laboratory food they were provided. [9] Live crickets were preferred to deceased specimens, which might suggest that prey movement might be a catalyst and cue for predatory attack. [9] There was no gender related difference in how much time the mice spent feeding on crickets. [9]

Highly aggressive behaviors were displayed towards laboratory mice in the same study, such as biting the back and tail of their prey. [9] After two days of being around the laboratory mice, six of the 43 male grasshopper mice and 22 of the 45 females grasshopper mice killed and ate certain parts of the laboratory mice. [9] This difference in predatory behavior between the male and female grasshopper mice was significant. [9] In their study, both McCarty and Southwick concluded that food deprivation and the type of prey affected the intensity and aggressiveness of the predatory attacks observed by southern grasshopper mice. [9]

Brain and body size relation

Relative brain size tends to vary with food preferences. [10] Brain size is usually smallest in folivores, larger in both granivores and insectivores, and largest in generalists. [10] Measurements of cranial volume of museum specimens of southern grasshopper mouse have shown that on average, females were heavier and longer than males, but their cranial volume was about 3% less than that of males. [10] However, this was not a significant difference. [10] This pattern of brain-body relationship can also be seen in northern grasshopper mice. [10] Moreover, the tail length of southern grasshopper mice made up an average of 33.9% of its body length. [10] Their tail length measures an average of 4.58 ± 0.36 cm in females, and 4.50 ± 0.39 cm in males. [10] Average tail length does not vary greatly between the sexes. [10]

On average, female southern grasshopper mice are able to deal with a larger body size without increasing their brain size, when compared to males. [10] There is still not enough evidence to explain the difference in body size and brain between males and females. [10] It is possible that there are different demands on both sexes, which might contribute to this difference. [10] These studies were also only done in the laboratory, and there might be sex-specific stresses in their natural habitat that influence brain growth. [10] However, sexual dimorphism is quite common and has been observed in the central nervous system of other mammals. [10]

Related Research Articles

<span class="mw-page-title-main">Scorpion</span> Predatory order of arachnids

Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always ending with a stinger. The evolutionary history of scorpions goes back 435 million years. They mainly live in deserts but have adapted to a wide range of environmental conditions, and can be found on all continents except Antarctica. There are over 2,500 described species, with 22 extant (living) families recognized to date. Their taxonomy is being revised to account for 21st-century genomic studies.

<span class="mw-page-title-main">Chelicerata</span> Subphylum of arthropods

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids, as well as a number of extinct lineages, such as the eurypterids and chasmataspidids.

<span class="mw-page-title-main">Solifugae</span> Order of spider-like animals

Solifugae is an order of animals in the class Arachnida known variously as camel spiders, wind scorpions, sun spiders, or solifuges. The order includes more than 1,000 described species in about 147 genera. Despite the common names, they are neither true scorpions, nor true spiders. Most species of Solifugae live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of 12–15 cm (5–6 in), including legs. A number of urban legends exaggerate the size and speed of the Solifugae, and their potential danger to humans, which is negligible.

<span class="mw-page-title-main">House mouse</span> Species of mammal

The house mouse is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus Mus. Although a wild animal, the house mouse has benefited significantly from associating with human habitation to the point that truly wild populations are significantly less common than the semi-tame populations near human activity.

<span class="mw-page-title-main">Emperor scorpion</span> Species of scorpion

The emperor scorpion, Pandinus imperator, is a species of scorpion native to rainforests and savannas in West Africa. It is one of the largest scorpions in the world and lives for 6–8 years. Its body is black, but like other scorpions it glows pastel green or blue under ultraviolet light. It is a popular species in the pet trade, and is protected by CITES to prevent over-collecting that might affect the species' survival.

<span class="mw-page-title-main">Arizona bark scorpion</span> Species of scorpion

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<span class="mw-page-title-main">Neotominae</span> Subfamily of mammals

The Neotominae are a subfamily of the family Cricetidae. They consist of four tribes, 16 genera, and many species of New World rats and mice, predominantly found in North America. Among them are the well-known deer mice, white-footed mice, packrats, and grasshopper mice.

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<span class="mw-page-title-main">Algerian mouse</span> Species of rodent

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<span class="mw-page-title-main">Grasshopper mouse</span> Genus of rodents

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Hemiscorpius lepturus is a species of scorpion in the family Hemiscorpiidae. It is found in deserts of the Middle East, especially in southern Iraq and Iran. These scorpions have long, thin tails and wide bodies and grow to 8 cm in males and 5.5 cm in females, allowing them to live in tight rock crevices. They are fairly solitary creatures. H. lepturus has mainly been studied to discover the components and effects of its venom, which is highly lethal and is responsible for most deaths due to scorpion sting in the Iran area. H. lepturus is the only scorpion not in the family Buthidae that is potentially lethal to humans; the Buthidae family is the largest and most abundant family of scorpions, containing many highly venomous species.

References

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  2. Musser, G.G.; Carleton, M.D. (2005). "Superfamily Muroidea". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 1061. ISBN   978-0-8018-8221-0. OCLC   62265494.
  3. 1 2 3 4 5 Frank, D. H., & Heske, E. J. (1992). Seasonal changes in space use patterns in the southern grasshopper mouse, Onychomys torridus torridus. Journal of Mammalogy, 73(2), 292-298.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 McCarty, Richard (1975). "Onychomys torridus". Mammalian Species (59): 1–5. doi:10.2307/3503863. JSTOR   3503863. S2CID   253905384.
  5. 1 2 Wade, Lizzie (24 October 2013). "Mouse impervious to scorpion's sting". Science . Retrieved 16 September 2014.
  6. Reardon, S. (1 November 2013). "Zoologger: Mouse eats scorpions and howls at the moon". NewScientist .
  7. 1 2 3 Thompson, Bemjamin (Spring 2018). "The Grasshopper Mouse and Bark Scorpion: Evolutionary Biology Meets Pain Modulation and Selective Receptor Inactivation" (PDF). Journal of Undergraduate Neuroscience Education . p. R51-R53. Retrieved 9 May 2020.
  8. 1 2 3 Guevara-Carrizales, A. A., Escobar-Flores, J., & Martínez-Gallardo, R. (2012). Marginal record of the southern grasshopper mouse Onychomys torridus in Baja California, México. Western North American Naturalist, 72(3), 416-417.
  9. 1 2 3 4 5 6 7 8 9 McCarty, R., & Southwick, C. H. (1981). Food deprivation: Effects on the predatory behavior of southern grasshopper mice (Onychomys torridus).Aggressive Behavior, 7(2), 123-130.
  10. 1 2 3 4 5 6 7 8 9 10 11 12 13 Mann, M. D., & Towe, A. L. (2003). Brain-body size relations in grasshopper mice. Brain, behavior and evolution, 62(1), 13-18.