Introduction

The Golden Spiny Mouse, Acomys russatus, gets its name from the reddish-orange spiny fur that covers it body from head to tail. This coarse, inflexible fur

Guard hair

Guard hairs are the longest, coarsest hairs in a mammal's coat, forming the topcoat . They taper to a point and protect the undercoat from the elements. They are often water repellent and stick out above the rest of the coat...

 is thought to protect it from predation

Predation

In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

. Aside from the golden fur that covers its head and upper parts, its flanks are yellow and its underside is pale. It has gray legs with pale feet and black soles. It is also described as having a small, but distinct white spot under each eye. Often, it is found in the wild missing a part or all of its tail because it is able to shed this as a defense mechanism. However, the it is not known how this is done, how often it can occur, or under what conditions. It lives an average of three years in the wild. It is omnivorous

Omnivore

Omnivores are species that eat both plants and animals as their primary food source...

 and feeds on seeds, desert plants, snails, and insects. Living in desert

Desert

A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...

 regions, it is a xeric animal that obtains water from the plants that it eats and produces very concentrated urine in order to conserve water . A. russatus is naturally nocturnal, but adapts

Adaptation

An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

 to being diurnal when it shares a habitat with A. cahirinus.

Environment

The Golden Spiny mouse thrives in dry, hot deserts and is common in Egypt and much of the Middle East, including Jordan, Israel, Oman, Saudi Arabia, and Yemen. It is limited to these areas because its metabolic rate is much slower than predicted for an animal of its size, so it is unable to maintain a viable body temperature in colder environments where the temperature falls below 18° C and can live in temperatures as high as 42.5°C. A. russatus does not have a thermal neutral zone

Thermal neutral zone

A thermal neutral zone is essentially an endotherm's temperature tolerance range. Within the TNZ the basal rate of heat production is in equilibrium with the rate of heat loss to the external environment...

, but shows lowest oxygen consumption at 30°C. However, one population was found in the high summits of the mountains in southern Sinai where the temperature falls well below this threshold and there is often snow in the winter.

A. russatus is also very good at conserving the little water it gets from its diet of insects and plants. It does this by producing extremely concentrated urine with urea

Urea

Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

 content up to 4800 mM and chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

 concentration up to 1500 mM! This means that it could survive drinking sea water, which is very rare in mammals.

Reproduction

Acomys russatus is an opportunistic breeder that reaches sexual maturity at approximately 58 days of age. There is no mating season for Spiny Mice

Spiny mouse

The term spiny mouse refers to any species of rodent within the genus Acomys. Similar in appearance to mice of the genus Mus, spiny mice are small mammals with bare, scaled tails...

, but rather they continue to breed throughout the year. Each female has an average of 3.5 litters per year with about 34 days between litters. They are viviparous and each gestation period lasts 5-6 weeks and produces 1-5 offspring . Weaning of each litter takes two weeks. When rainfall decreases, the salt concentration in their food sources increases, which negatively impacts reproduction in both males and females..

Flexible Circadian Rhythm

The most frequently studied aspect of Acomys russatus is its apparent ability to switch from nocturnal to diurnal

Diurnal

Diurnal may refer to:* Diurnal cycle, any pattern that recurs daily** Diurnality, the behavior of animals and plants that are active in the daytime* Diurnal motion, the apparent motion of stars around the Earth...

 activity patterns. Specifically, it is naturally nocturnal, but will become diurnal when sharing a habitat with its congener

Congener

Congener has several different meanings depending on the field in which it is used. Colloquially, it is used to mean a person or thing like another, in character or action.-Biology:In biology, congeners are organisms within the same genus...

, another Spiny Mouse species, Acomys cahirinus. Since the two species share food sources, competition

Interspecific competition

Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resource in an ecosystem...

 does not allow for both of them to be active at the same time in the same habitat. Because of its tolerance for higher temperatures and significantly greater ability to conserve water by concentrating its urine, A. russatus is the species that is better suited to become day-active to eliminate this competition. When this occurs, there is a true switch in circadian rhythm

Circadian rhythm

A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

 that affects body systems such as metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 and excretion

Excretion

Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...

. This new rhythm can furthermore adapt to seasonal changes in day length, as with any other diurnal species.

However, it is clear that the species has not completely evolved to be diurnal. In a lab setting where no other species is present, Acomys rusatus immediately adopts nocturnal activity patterns with no transient phase, suggesting that its diurnal behavior is only an adaptation that is made when necessary. Furthermore, it has been found that the Golden Spiny Mouse’s eyes have not evolved to fit a diurnal lifestyle, but rather match the normal pattern of a nocturnal animal. This finding, along with their preference to forage in areas of lower light, such as between and under boulders, further shows that, if not for environmental factors, Golden Spiny Mice would be nocturnal animals.