Daily Rhythms of Body Temperature in Acornys russatus: The Response to Chemical Signals Released by Acomys cahirinus

Two species of spiny mice of the genus Acomys—the golden spiny A. russaturs and the common spiny A. cuhirinus—are syrnpatnc in the and and hot parts of the Rift Valley in Israel. The coexistence of these two species is due to exclusion of A. russatus mice by A. cuhirinus mice from nocturnal activity. The aim of this research was to study if odor signals released by A. cahirinus mice can play a role in the exclusion of A. russatus mice. A. russatus mice with an implanted transmitter recording body temperature (T_b) were kept alone in a metabolic chamber under constant conditions of ambient temperature (27°C) and photoperiod (12 h light: 12 h dark). After 5 days of recording, chemical signals from an A. cuhirinus mouse were added through the air tube going into the metabolic chamber of the A. russatus mice. This treatment caused a shift of ～ 2 h inT_b daily rhythm of the naive tested A. russutus mice, whereas no shift was observed in A. russatus mice that had been kept in the same room with the A. cahirinus mouse before measurements. These results strongly support the idea that chemical signals released by A. cahirinus mice can entrain the T_b rhythms of A. russatus mice. Therefore, it may be assumed that the exclusion of A. russatus mice from nocturnal activity by A. cuhirinus mice could be achieved through the odor released by the latter.     

Interspecific competition and torpor in golden spiny mice: two sides of the energy-acquisition coin

We studied the occurrence of torpor in golden spiny mice in a hot rocky desert near the Dead Sea. In this rodent assemblage, a congener, the nocturnal common spiny mouse, competitively excluded the golden spiny mouse from the nocturnal part of the diel cycle and forced it into diurnal activity; this temporal partitioning allows the two species to partition their prey populations, particularly in summer when the diet of the two species is comprised mainly of arthropods, and largely overlap. We studied the effect of the presence of the common spiny mice at two resource levels (natural food availability and food added ad libitum) on populations of golden spiny mice in four large outdoor enclosures: two with common spiny mice removed and two enclosures with populations of both species. We hypothesized that with interspecific competition and/or reduced resources, golden spiny mice will increase their use of torpor. As we expected, supplemented food reduced the total time spent torpid. In summer, when the different activity periods of the two species results in prey species partitioning, removal of the congener did not affect torpor in the golden spiny mouse. However, in winter, when insect populations are low and the two species of mice overlap in a largely vegetarian diet, removal of the common spiny mouse reduced torpor in golden spiny mice, whether food was supplemented or not. This result suggests that torpor, a mechanism that allows small mammals to sustain periods of low availability of resources or high energetic requirements, may also help them to tolerate periods of enhanced interspecific competition. This may be a significant short-term mechanism that reduces competition and hence increases fitness, in particular of individuals of the subordinate species whose accessibility to resources may be limited.     

A differential response in the reproductive system and energy balance of spiny mice Acomys populations to vasopressin treatment

Increased dietary salinity suppressed reproduction of the xeric adapted golden spiny mouse, Acomys russatus. Testicular and uterine mass were reduced, suppressed spermatogenesis and vaginal closure were observed. The anti-diuretic hormone, vasopressin (VP), was suggested to mediate such effects. However, increased dietary salinity did not affect reproductive status of a mesic adapted population of the common spiny mouse, A. cahirinus. In the present study, the effect of exogenous VP on the reproductive status and energy balance of both males and females of A. russatus and of a mesic population of A. cahirinus was tested. Vasopressin (Sigma, 50 µg/kg) was injected intraperitoneally in three-day intervals for four weeks. In VP-treated A. russatus, spermatogenesis was significantly suppressed while the change in testis mass did not show significant difference. Both control and VP-treated females lost body mass (W_b) significantly and the latter also exhibited a higher energy expenditure compared to their male counterparts. VP did not affect reproductive status in both sexes of A. cahirinus. Also it did not have a significant effect on W_b, energy intake, and energy expenditure in this species. Our results support the idea that VP mediates the effects of increased diet salinity on reproduction in A. russatus. The results also reinforce previous knowledge that different physiological systems could be integrated by a single biochemical signal.     

Friend or foe? Disparate plant–animal interactions of two congeneric rodents

Food and water resources are limiting factors for animals in desert ecosystems. Fleshy fruits are a rare water source in deserts and when available they tend to attract a wide variety of organisms. Here we show that two congeneric rodent species, Acomys cahirinus and A. russatus, employ different fruit eating strategies that result in either dispersal or predation of the small seeds of the desert plant Ochradenus baccatus. The nocturnal A. cahirinus leaves intact seeds when consuming O. baccatus fruits and thus, acts mainly as a seed disperser; whereas the diurnal A. russatus consumes the whole fruit and digests the seeds and thus, acts mainly as a seed predator. Acomys russatus is subjected to the toxic products of the glucosinolates-myrosinase system found in O. baccatus fruits. Acomys cahirinus avoids the toxic compounds by consuming the pulp only, which contains glucosinolates but not the seeds that contain the enzyme that activates them. We suggest that the behavioral responses exhibited by A. russatus are the result of physiological adaptations to whole fruit consumption that are absent in A. cahirinus. Our results shed new light on the ecological divergence of the two congeneric species.     

Spatial and temporal patterns of coexistence between competing <Emphasis Type="Italic">Aedes</Emphasis> mosquitoes in urban Florida

Understanding mechanisms fostering coexistence between invasive and resident species is important in predicting ecological, economic, or health impacts of invasive species. The mosquito Aedes aegypti coexists at some urban sites in southeastern United States with invasive Aedes albopictus, which is often superior in interspecific competition. We tested predictions for three hypotheses of species coexistence: seasonal condition-specific competition, aggregation among individual water-filled containers, and colonization–competition tradeoff across spatially partitioned habitat patches (cemeteries) that have high densities of containers. We measured spatial and temporal patterns of abundance for both species among water-filled resident cemetery vases and experimentally positioned standard cemetery vases and ovitraps in metropolitan Tampa, Florida. Consistent with the seasonal condition-specific competition hypothesis, abundances of both species in resident and standard cemetery vases were higher early in the wet season (June) versus late in the wet season (September), but the proportional increase of A. albopictus was greater than that of A. aegypti, presumably due to higher dry-season egg mortality and strong wet-season competitive superiority of larval A. albopictus. Spatial partitioning was not evident among cemeteries, a result inconsistent with the colonization-competition tradeoff hypothesis, but both species were highly independently aggregated among standard cemetery vases and ovitraps, which is consistent with the aggregation hypothesis. Densities of A. aegypti but not A. albopictus differed among land use categories, with A. aegypti more abundant in ovitraps in residential areas compared to industrial and commercial areas. Spatial partitioning among land use types probably results from effects of land use on conditions in both terrestrial and aquatic-container environments. These results suggest that both temporal and spatial variation may contribute to local coexistence between these Aedes in urban areas.     

Social and life history correlates of litter size in captive colonies of precocial spiny mice (<Emphasis Type="Italic">Acomys</Emphasis>)

Litter size is an important component of life history contributing to reproductive success in many animals. Among muroid rodents, spiny mice of the genus Acomys are exceptional because they produce large precocial offspring after a long gestation. We analyzed data on 1,809 litters from laboratory colonies of spiny mice from the cahirinus-dimidiatus group: Acomys cahirinus, Acomys cilicicus, Acomys sp. (Iran), and Acomys dimidiatus. Generalized mixed-effect models revealed that litter size increased with maternal body weight and/or number of immature females present in the family group. Thus, both maternal body reserves and presence of immature descendants demonstrating previous reproductive success enhance further reproduction in this social rodent.     

Telemetric field studies of body temperature and activity rhythms of Acomys russatus and A. cahirinus in the Judean Desert of Israel

Two species of the genus Acomys coexist in arid zones of southern Israel. Acomys russatus is distributed in extremely arid areas, while A. cahirinus is common in both Mediterranean and arid regions. Individuals of both species from a rodent community in the Ein Gedi Nature Reserve were implanted with temperature-sensitive transmitters. Body temperature (T _b) rhythms were recorded in free-ranging mice at four different seasons of the year. A. cahirinus (30–45 g) showed a nocturnal rhythm of T _b throughout the year. In the activity phase during the night T _b increased to 38.2°C. During the day T _b decreased to 34°C. This species displayed this pattern in summer also when ambient temperatures rose above T _b. The T _b of A. russatus (45–65 g) varied between 34.8 and 41°C during the hot season, showing a bimodal temperature rhythm with maximal values in the morning and in the evening. Measurements of activity in this species showed inactivity during the hottest period of a summer day. In winter A. russatus showed no clearly detectable diurnal or ultradian rhythm in T _b, which remained constant between narrow limits of 35.2 and 36.8°C. Received: 21 December 1998 / Accepted: 15 March 1999     

Characterization of social behavior in the spiny mouse,Acomys cahirinus

While there are many species that are commonly used for the study of mammalian social behavior, there remains a need for lab-suitable organisms that are appropriate for examining sociality specifically in non-reproductive contexts (i.e., social behavior not in the context of mating or parenting). The spiny mouse, Acomys cahirinus, is a cooperatively breeding rodent that lives in large groups and is a species that holds great potential for studying a wide range of social behaviors in reproductive and non-reproductive contexts. Here, we characterize the basic social behaviors in male and female A. cahirinus to obtain a foundation for future study. We tested adult A. cahirinus in social approach, social preference, social interaction, social recognition, and group size preference paradigms. Regardless of sex, novelty, or familiarity, we found that both males and females rapidly approach conspecifics demonstrating high social boldness. Additionally, both sexes are significantly more prosocial than aggressive when freely interacting with conspecifics. However, we observed effects of sex on social preferences, such that males exhibit a preference to affiliate with same-sex conspecifics, whereas females exhibit a preference for affiliating with opposite-sex conspecifics. We discuss how this preference may relate to the cooperative breeding system of spiny mice. Lastly, both sexes show a robust preference for affiliating with large over small groups, indicating they may be an ideal species for the study of mammalian gregariousness. These data lay a basic foundation for future studies that seek to assess complex group dynamics and the mechanisms underlying reproductive and non-reproductive social behaviors in a highly social mammal.     

Interspecific variation in the phenology of advertisement calling in a temperate Australian frog community

Spatial and temporal partitioning of resources underlies the coexistence of species with similar niches. In communities of frogs and toads, the phenology of advertisement calling provides insights into temporal partitioning of reproductive effort and its implications for community dynamics. This study assessed the phenology of advertisement calling in an anuran community from Melbourne, in southern Australia. We collated data from 1432 surveys of 253 sites and used logistic regression to quantify seasonality in the nightly probability of calling and the influence of meteorological variables on this probability for six species of frogs. We found limited overlap in the predicted seasonal peaks of calling among these species. Those shown to have overlapping calling peaks are unlikely to be in direct competition, due to differences in larval ecology (Crinia signifera and Litoria ewingii) or differences in calling behavior and acoustics (Limnodynastes dumerilii and Litoria raniformis). In contrast, closely related and ecologically similar species (Crinia signfera and Crinia parinsignifera; Litoria ewingii and Litoria verreauxii) appear to have staggered seasonal peaks of calling. In combination with interspecific variation in the meteorological correlates of calling, these results may be indicative of temporal partitioning of reproductive activity to facilitate coexistence, as has been reported for tropical and temperate anurans from other parts of the globe.     

Amensalism via webs causes unidirectional shifts of dominance in spider mite communities

Competitive displacement is considered the most severe consequence of interspecific competition; if a superior competitor invades the habitat of an inferior species, the inferior species will be displaced. Most displacements previously reported among arthropods were caused by exotic species. The lack of investigation of displacement among native species may be due to their apparently harmonious coexistence, even if it is equivalent to an outcome of interspecific association. A seasonal change in the species composition of spider mites, from Panonychus ulmi to Tetranychus urticae, is observed in apple trees worldwide. Previous laboratory experiments have revealed amensal effects of T. urticae on P. ulmi via their webs. Using manipulation experiments in an orchard, we tested whether this seasonal change in species composition occurred as the result of interspecific competition between these spider mites. Invasion by T. urticae prevented an increase in P. ulmi densities throughout the experimental periods. Degree of overlap relative to the independent distribution on a leaf-surface basis (ω _S) changed from positive to negative with increasing density of T. urticae. T. urticae invasion drove P. ulmi toward upper leaf surfaces (competitor-free space). The niche adjustment by P. ulmi occurred between leaf surfaces but not among leaves. Our findings show that asymmetrical competition between T. urticae and P. ulmi plays an important role in this unidirectional displacement and that the existence of refuges within a leaf produces the apparently harmonious coexistence of the mites and obscures their negative association.     

Three carnivorous plant species (Drosera spp.) in European Russia: peaceful coexistence?

In spite of the recent improvements in the understanding of carnivorous plants’ biology, some questions have remained unanswered. In this study, the segregation of food niches (i.e. specialization on different categories of prey) for three sympatric carnivorous temperate Drosera species with different shapes of trapping leaves is tested. Potentially available prey was also taken into account, by using artificial traps. Almost all the prey trapped by the three Drosera species and by passive traps belonged to four insect orders: Diptera, Hymenoptera, Coleoptera, Homoptera, as well as Araneae. Diptera specimens were the main prey for all the species. This study demonstrates that arthropods caught by the three temperate sympatric sundew species (D. rotundifolia, D. obovata and D. anglica), belong to the same orders. The proportions of prey from different orders, caught by different sundew species did not differ significantly. The result does not necessarily imply the absence of interspecific competition for prey: arthropods were identified only to order, and competition may have resulted in specialization on prey taxa of lower rank.     

Seasonally fluctuating resources and temporal variability of interspecific competition

Summary The influence of seasonal availability of two critical resources (food and substrates from which food was harvested) on interspecific competition between striped surfperch (Embiotoca lateralis) and black surfperch (Embiotoca jacksoni) was examined. There was a strong depth-related gradient in density of prey and in cover of foliose algae; both declined with increasing bottom depth. Density of prey was reduced 5–10 fold during the winter season, but cover of substrates remained constant throughout the year. Although both fishes co-occurred throughout the same depth range, striped surfperch were more common in shallow habitats and black surfperch were more abundant deeper. Local abundance and distribution patterns of both surfperch species did not change seasonally. Stepwise regression analyses suggested that availability of favored substrates was a proximate influence on local patterns of surfperch distribution and abundance, and that interspecific competition depressed abundance of the two species to the same degree. Removal experiments conducted during the cold-water season revealed that interspecific competition influenced depth distribution of black surfperch but not striped surfperch. Seasonal change in density of prey was accompanied by marked changes in overlap in use of foraging substrates by the surfperches. The pattern of change in interspecific overlap suggested that surfperch competed for food only when prey were seasonally scarce. There was no difference in the agonistic tendencies of the two fishes, and the absolute and relative frequency of interspecific chases was independent of food level. These results have important implications regarding the impact of temporal variability of interspecific competition in natural communities. In the surfperch system, competition was characterized by constant and time-varying elements that had symmetrical and asymmetrical effects and involved both interference and exploitation mechanisms.     

Seasonal Changes in Feeding Ecology and Activity Patterns of Two Sympatric Mouse Lemur Species,the Gray Mouse Lemur (<Emphasis Type="Italic">Microcebus murinus</Emphasis>) and the Golden-brown Mouse Lemur (<Emphasis Type="Italic">M. ravelobensis</Emphasis>), in Northwestern Madagascar

Because closely related species are likely to be ecologically similar owing to common ancestry, they should show some degree of differentiation in order to coexist. We studied 2 morphologically similar congeneric species, the golden-brown mouse lemur (Microcebus ravelobensis) and the gray mouse lemur (M. murinus). These species are found in partial sympatry in the dry deciduous forest in northwestern Madagascar. We investigated whether 1) feeding niche differentiation and/or 2) a reduction in locomotor activity during periods of food shortage, which might reflect an energy saving strategy, can explain the coexistence of these 2 lemur species. To obtain feeding and behavioral data, we conducted focal observations of 11 female Microcebus murinus and 9 female M. ravelobensis during 11 months from 2007 to 2008 and collected fecal samples for 6 mo. We monitored the phenology of 272 plant specimens and trapped arthropods to determine food availability. Results revealed interspecific differences in 1) relative proportion of consumed food resources, resulting in a merely partial dietary overlap, and in 2) relative importance of seasonally varying food resources throughout the year. In addition, females of Microcebus murinus showed a reduction in locomotor activity during the early dry season, which might reflect an energy-saving strategy and might further reduce potential competition with M. ravelobensis over limited food resources. To conclude, a combination of interspecific feeding niche differentiation and differences in locomotor activity appears to facilitate the coexistence of Microcebus murinus and M. ravelobensis.     

The Natural Feeding and Resource Partitioning of Erpobdella octoculata L. and Erpobdella testacea SAV. in Lake Esrom,Denmark

The natural feeding and competitive interactions between populations of Erpobdella ostoculata and Erpobdella testacea were investigated in Lake Esrom, Denmark, during 1979/80. Statistical analysis revealed that the size of the leeches was the main factor involved in resource utilization. Size-specific feeding included differences in the numerical composition of diets and the size of individual prey. Five weight classes of Erpobdella spp. were distinguished. The number of prey per leech increased from 1.63-2.84 for the first to the fifth weight class, whereas diversity in feeding averaged 1.71 prey per leech. Quantification of competitive interactions indicated that the temporal differences in weight class composition of the two species were sufficient to explain coexistence, although both species have an annual life cycle, and neither species showed taxonomic food refuges.     

High resource overlap and small dietary differences are widespread in food-limited warbler (Parulidae) communities

Although both interspecific competition and coexistence mechanisms are central to ecological and evolutionary theory, past empirical studies have generally focused on simple (two-species) communities over short time periods. Experimental tests of these species interactions are challenging in complex study systems. Moreover, several studies of ‘imperfect generalists’, consistent with Liem's Paradox, raise questions about the ability of evolved species differences to partition niche space effectively when resources vary considerably across the annual cycle. Here we used a recently developed theoretical framework to combine past research on population-level processes with observational data on resource use to test for ongoing interspecific competition and understand the nature of resource overlap. We compared species diet overlaps and differences in several distinctive communities centred on a focal species, the American Redstart Setophaga ruticilla replicated both spatially and seasonally, in combination with documentation of population regulation to assess the ability of similar species to partition dietary niche space and limit interspecific competition. Our results document high dietary overlap in most of the communities studied, with only subtle differentiation consistent with known species differences in foraging behaviour and morphology. These findings are largely consistent with species foraging as imperfect generalists. However, in contrast to past studies, the high diet overlaps observed here during times of inferred resource scarcity were driven by low-value prey taxa (e.g. small ants) and did not involve truly ‘private’ resources. All of these factors increase the potential negative impacts of interspecific competition, and limit the ability of these birds to avoid competition if food availability deteriorates further than observed in our study, either seasonally or at longer intervals.     

Seasonal variation in prey preference,diet partitioning and niche breadth in a rich large carnivore guild

Large carnivore community structure is affected by direct and indirect interactions between intra-guild members. Co-existence between different species within a carnivore guild may occur through diet, habitat or temporal partitioning. Since carnivore species are highly dependent on availability and accessibility of prey, diet partitioning is potentially one of the most important mechanisms in allowing carnivores to co-exist. Intra-guild interactions may vary over time as carnivore prey preference and diet overlap can change due to seasonal changes in resource availability. We conducted scat analysis to compare the seasonal changes in prey preference, diet partitioning and niche breadth of four large carnivore species, namely leopard Panthera pardus, spotted hyena Crocuta crocuta, brown hyena Parahyaena brunnea and wild dog Lycaon pictus in central Tuli, Botswana. Large carnivores in central Tuli display a high dietary overlap, with spotted hyena and brown hyena displaying almost complete dietary overlap and the other carnivore species displaying slightly lower but still significant dietary overlap. Dietary niche breadth for both hyena species was high possibly due to their flexible foraging strategies, including scavenging, while leopard and wild dog showed a relatively low niche breadth, suggesting a more specialised diet. High dietary overlap in central Tuli is possibly explained by the high abundance of prey species in the area thereby reducing competition pressure between carnivore species. Our research highlights the need to assess the influence of diet partitioning in structuring large carnivore communities across multiple study sites, by demonstrating that in prey rich environments, the need for diet partitioning by carnivores to avoid competition may be limited.     

Space use and temporal partitioning of sympatric Tasmanian devils and spotted‐tailed quolls

Sympatric species can minimise interspecific competition by spatial avoidance or by altering their temporal activity to reduce encounter rates. The Tasmanian devil (Sarcophilus harrisii), the largest carnivorous marsupial, coexists with the smaller spotted‐tailed quoll (Dasyurus maculatus) in Tasmania, Australia. Quolls may be susceptible to interspecific competition from devils, because they utilise similar habitats, consume similar prey species and are displaced by devils at food sources. Such competition might cause quolls to spatially or temporally avoid devils. To investigate whether spatial or temporal avoidance occurred, we deployed GPS collars on sympatric devils and quolls and conducted a camera survey at a site in northwest Tasmania where the devil population was not affected by devil facial tumour disease. GPS tracking coincided with the lactation period when devils and quolls had young in dens and continued until weaning occurred. We found little spatial segregation of home range and core area placement between devils and quolls and among devils. Quolls showed more spatial segregation within the sexes than between them. Devils had larger home ranges than quolls. Male devils had larger home ranges than females, but there was no difference in home range size between the sexes of quolls. Females of both species travelled significantly further per night than did males. There was moderate temporal partitioning between the two species: devil activity peaked after dusk and devils remained active until the early morning, while quoll activity showed distinct peaks around dusk and dawn. In conclusion, quolls did not spatially avoid devils but moderate temporal partitioning occurred. It is plausible that quolls are active at different times of the diel cycle to reduce encountering devils, but further studies are needed to resolve the cause of this temporal partitioning.     

Trophic interactions and the diet composition of sympatric finfish predators in the tropical demersal ecosystem in the Bay of Bengal

The dietary composition, foraging strategies, and interspecific trophic interactions were identified for four major demersal carnivorous finfishes, namely, croaker Otolithes ruber, hairtail Trichiurus lepturus, threadfin bream Nemipterus japonicus, and lizardfish Saurida undosquamis, along the north-western part of Bay of Bengal from 2014 to 2016. Two species, Trichiurus lepturus and Saurida undosquamis, were identified as finfish feeders due to the high number of teleost (clupeids and engraulids) prey. One species, Nemipterus japonicus, had a significantly different diet of metapenaeids and charybdids, and was identified as a shellfish feeder. The final species, Otolithes ruber, preyed equally on crustaceans and teleosts, and was identified as a shellfish-finfish feeder. The feeding activity of all four species was lower during peak spawning periods and tended to increase with maturity. Feeding preferences varied with seasons. The trophic level ranged from 3.49 to 4.01, classifying the four species as medium-carnivores or meso-predators. Niche breadth ranged from 0.170 to 0.421, with seasonal and ontogenetic variations. Individual or subgroup specialization was observed on dominant prey, but intraspecific diet variations indicated all four species to be opportunistic predators. There was substantial prey overlap for Saurida undosquamis with Otolithes ruber and Trichiurus lepturus, which increased ontogenetically and coincided with their peak spawning. Sharing of abundant prey resources together with temporal and ontogenetic resource partitioning at intra- and interspecific levels possibly lowered dietary competition, thereby facilitating the coexistence of these demersal predators. This study provides new information on feeding interactions from a tropical demersal ecosystem that can be applied for the ecosystem-based management of trawl fisheries.     

Comparative Feeding Ecology of Sympatric <Emphasis Type="Italic">Microcebus berthae and M. murinus</Emphasis>

Most Malagasy primate communities harbor a diverse assemblage of omnivorous species. The mechanisms allowing the coexistence of closely related species are poorly understood, partly because only preliminary data on the feeding ecology of most species are available. We provide an exemplary feeding ecology data set to illuminate coexistence mechanisms between sympatric gray and Madame Berthe’s mouse lemurs (Microcebus murinus, M. berthae). We studied their feeding ecology in Kirindy Forest/CFPF, a highly seasonal dry deciduous forest in western Madagascar. Between August 2002 and December 2007, we regularly (re-)captured, marked, and radiotracked females of both species. A combination of direct behavioral observations and fecal analyses revealed that both Microcebus species used fruit, arthropods, gum, insect secretions, and small vertebrates as food sources. However, Microcebus berthae and M. murinus differed in both composition and seasonal variation of their diets. Whereas the diet of Microcebus murinus varied seasonally and was generally more diverse, M. berthae relied mainly on insect secretions supplemented by animal matter. The differences were also reflected in a very narrow feeding niche of Microcebus berthae and a comparatively broad feeding niche of M. murinus. Resource use patterns of Madame Berthe’s and more so of opportunistic gray mouse lemurs broadly followed resource availability within the strongly seasonal dry forest. Feeding niche overlap between the 2 sympatric species was high, indicating that food resource usage patterns did not reflect niche partitioning, but can instead be explained by constraints due to food availability.     

The comparative gastrointestinal morphology of five species of muroid rodents found in Saudi Arabia

Meriones rex (King jird), Meriones libycus (Libyan jird), Acomys dimidiatus (Eastern spiny mouse), Acomys cahirinus (Egyptian spiny mouse), and Dipodillus dasyurus (Wagner's dipodil) are five species of small rodents of the superfamily Muroidea with distributions in Eastern Africa, Egypt, and the desert regions of the Arabian Peninsula. Water is scarce in these regions and may result in relatively low‐digestible food. The aim of the present study is to describe and compare the gastrointestinal tract morphology and morphometry of these five species in order to elucidate whether morphology is influenced by phylogeny or dietary preference. Each segment of the gastrointestinal tract of each species was macroscopically examined and the length and basal surface area of each segment was measured. Standard histologic procedures were performed to determine a surface enlargement factor to determine the mucosal luminal surface area. A unilocular‐hemiglandular stomach was observed in all the species examined. The caeca of all the species were long and arranged into a loose spiral toward the caecal tip with the ileocaecal and caeco‐colic openings positioned close together. Two rows of oblique folds could be observed in the proximal colon of all species except in D. dasyurus which had longitudinal folds. Morphometric analysis showed the largest stomach in A. cahirinus and the largest caecum and colon in M. libycus. All the species can be grouped in the family Muridae in two subfamilies and similarities were observed including the hemiglandular stomach and relatively large caecum. It could be concluded that phylogeny plays an important role in determining gastrointestinal morphology while diet plays a subordinate role in the desert rodents in the present study. J. Morphol. 275:980–990, 2014. © 2014 Wiley Periodicals, Inc.