Seasonal Changes in the Genetic Diversity of Two Rodent Populations, Midday Gerbil (Meriones meridianus) and Northern Three-Toed Jerboa (Dipus sagitta), Detected by ISSR

Seasonal changes in genetic diversity of Meriones meridianus and Dipus sagitta populations in the Ningxia Hui Autonomous Region were monitored using inter-simple sequence repeats. There were 45 discernible DNA fragments isolated from 33 samples of M. meridianus, and 25 from 40 samples of D. sagitta. The differences in gene frequencies are statistically significant for some alleles. Nei's index revealed that the greatest genetic differentiation was distributed within the seasonal groups. Nei's and Shannon's indexes exhibited similar seasonal trends, indicating that the spring group has the highest level of genetic diversity and that genetic diversity changes with the seasons. Correlation analysis found no statistically significant correlation between genetic diversity and population density. The results suggest that the seasonal changes in genetic diversity of the two species depend mainly on reproduction and dispersal.     

Geographic pattern of cranial differentiation in the Asian Midday Jird Meriones meridianus (Rodentia: Muridae: Gerbillinae) and its taxonomic implications

The existence of cryptic species in the midday jird (Meriones meridianus) has been suggested in literature, although based on little empirical data to support this hypothesis. In this study, a two‐dimensional landmark‐based geometric morphometric approach was used to investigate whether patterns in intraspecific variation in skull shape and size exist, using 110 skull specimens from more than 20 different localities along the distribution range of M. meridianus. This is the first study of morphological differences on such a big sample size and geographical range, and it tries to find whether skull shape variation in this species is best described as being clinal or rather reflecting cryptic diversity. The latter seems to be the case, as a dimorphic skull phenotype was found, reflecting a geographic disparity between the Middle East and the Far East specimens both in shape and in size. Distinct cranial differences were found in the overall cranial size and, also at the level of the inflation of the bulla, the elongation of the nasal, the length of the teeth row and the incisive foramen, as well as the distance in between the latter two. It thus seems that M. meridianus from Middle East is morphologically distinct from that of the Far East. Furthermore, our results also demonstrate that clinal variation could explain variation within Middle East populations, whereas a more heterogenous pattern is found for those of the Far East. The hypothesis that the observed phenotypic variation may reflect cryptic species is discussed, with the recommendation for a thorough taxonomical revision of the genus in the region.     

Phylogeography,phylogeny, and taxonomical revision of the Midday jird (Meriones meridianus) species complex from Dzungaria

The Midday jird Meriones meridianussensu lato is a widely distributed and highly variable species complex, whose taxonomy is still controversial despite several genetic and morphological studies. Dzungaria is a crucial region for understanding the phylogeny and phylogeography of this species complex. In this work, the genetic variation of M. meridianus in Dzungaria and adjacent areas was studied based on mitochondrial (Cytb) and nuclear (BRCA1 and IRBP) genes. To compare morphological and genetic differentiation among lineages, craniological variation of the genotyped specimens was examined. Moreover, environmental data were used to estimate the most probable dispersal routes of M. meridianus clades in the studied area. Three clades of M. meridianus with interspecific level of differentiation were found and treated as distinct species: M. psammophilus (Milne-Edwards, 1871); M. meridianus (Pallas, 1773); and M. penicilliger (Heptner, 1933). The distribution ranges of all three species overlap in Dzungaria. According to the molecular data, M. psammophilus and M. meridianus are sister taxa that diverged ca. 500 kya, while M. penicilliger separated from the common ancestor of the other two lineages ca. 800 kya. These three species have significantly different cranial measurements. Moreover, traces of hybridization between M. psammophilus and M. meridianus were detected, but not between M. penicilliger and the other two species. Finally, the dispersal scenarios for M. psammophilus, M. meridianus, and M. penicilliger are herein discussed. It is suggested that M. meridianusand M. penicilligerindependently colonized Dzungaria from the west via Dzungarian gates.     

Geographical variation in the cranial measurements of the midday jird Meriones meridianus (Rodentia: Muridae) and its taxonomic implications

Cranial variation was studied across the geographical range of the Meriones meridianus species complex using 665 specimens from 112 localities. Morphometric results were compared with previously published data on genetic variation. Unsupervised model‐based clustering analysis implemented in Mclust software was employed to identify the number and content of morphological clusters. Three clearly defined morphological groups corresponding to mtDNA clades were found. The results of the morphometric analysis are consistent with the hypothesis that these 3 groups should be treated as distinct species; specifically, M. psammophilus Milne‐Edwards, 1871, M. penicilliger Heptner, 1933 and M. meridianus Pallas, 1773. M. psammophilus inhabits the Mongolian–Chinese part of the superspecies range, except for the Mongolian Dzungaria region, which is inhabited by M. meridianus. The range of the latter species extends westwards to north‐west Kazakhstan and Kalmykia. M. penicilliger inhabits the southern part of the superspecies range from Tian Shan to Turkmenistan. M. dahli is craniometrically similar to M. meridianus; hence, its species status remains questionable.     

Systematics and evolution of the subfamily Gerbillinae (Mammalia, Rodentia, Muridae)

Although they represent a quarter of the mammalian species, the evolutionary relationships among as well as within, the main murid lineages are still controversial. The subfamily Gerbillinae is no exception as previous studies based on morphological, karyotypical, and allozyme characters are highly incongruent. Here, we present the first molecular phylogeny for gerbils based on cytochrome b and 12S rRNA mitochondrial genes. Results are largely congruent between the two genes as well as with the concatenated data set with most of the nodes being well-supported. Based on the topologies retrieved here, we (1) propose the identification of three main clades, (2) support the split of Tatera genus into an Asian and an African group, the latter including Gerbillurus species, and (3) provide some evidence towards the inaccuracy of subgeneric divisions within both Gerbillus and Meriones. In addition, the sharp contrast between the genetic characters and morphological data sets suggest high levels of convergence, probably as a result of strong environmental constraints imposed on these rodents adapted to arid and semi-arid regions. Finally, molecular datings for the various cladogenetic events are in good agreement with the known gerbilline fossil record and support an African origin with subsequent migrations to Asia.     

Chromatin Organization and Remodeling of Interstitial Telomeric Sites During Meiosis in the Mongolian Gerbil (Meriones unguiculatus)

Telomeric DNA repeats are key features of chromosomes that allow the maintenance of integrity and stability in the telomeres. However, interstitial telomere sites (ITSs) can also be found along the chromosomes, especially near the centromere, where they may appear following chromosomal rearrangements like Robertsonian translocations. There is no defined role for ITSs, but they are linked to DNA damage-prone sites. We were interested in studying the structural organization of ITSs during meiosis, a kind of cell division in which programmed DNA damage events and noticeable chromatin reorganizations occur. Here we describe the presence of highly amplified ITSs in the pericentromeric region of Mongolian gerbil (Meriones unguiculatus) chromosomes. During meiosis, ITSs show a different chromatin conformation than DNA repeats at telomeres, appearing more extended and accumulating heterochromatin markers. Interestingly, ITSs also recruit the telomeric proteins RAP1 and TRF1, but in a stage-dependent manner, appearing mainly at late prophase I stages. We did not find a specific accumulation of DNA repair factors to the ITSs, such as γH2AX or RAD51 at these stages, but we could detect the presence of MLH1, a marker for reciprocal recombination. However, contrary to previous reports, we did not find a specific accumulation of crossovers at ITSs. Intriguingly, some centromeric regions of metacentric chromosomes may bind the nuclear envelope through the association to SUN1 protein, a feature usually performed by telomeres. Therefore, ITSs present a particular and dynamic chromatin configuration in meiosis, which could be involved in maintaining their genetic stability, but they additionally retain some features of distal telomeres, provided by their capability to associate to telomere-binding proteins.     

Soil biological activity in the Chernye Zemli, Kalmykia, inhabited by gerbils Meriones tamariscinus and M. meridianus

The influence of tamarisk (Meriones tamariscinus) and midday (M. meridianus) gerbils on soil biological activity in the Chernye Zemli, Kalmykia, was studied. Nitrogen fixation, denitrification, and CO₂ emission were measured in soil samples from different parts of gerbil burrows. Functional biodiversity of the microbial community was evaluated using multisubstrate testing and comparison of bacterial group composition in samples from gerbil burrows. The impact of gerbils on soil biological activity was mediated by the changes in the group composition of microorganisms.     

The pathology of the Mongolian Gerbil (Meriones unguiculatus): a review.

Both naturally occurring disease processes and experimental models of human disease in the Mongolian gerbil were reviewed. The gerbil was highly susceptible to cerebral infarction following unilateral ligation of one common carotid artery and was useful in studies of the pathogenesis of stroke. Spontaneous epileptiform seizures mimicked those of human idiopathic epilepsy, and both seizure-sensitive and resistant strains have been bred. Perhaps because of its more efficient nephron, the gerbil accumulated four to six times as much renal lead as the rat, and the gerbil has been proposed as an experimental model of lead nephropathy. On standard diets, about 10% of the animals became obese, and some showed decreased glucose tolerance, elevated serum immunoreactive insulin and diabetic changes in the pancreas and other organs. Some breeders exhibited hyperactivity of the adrenal cortex associated with hyperglycemia, hyperlipidemia and degenerative vascular disease. Although dietary supplements of cholesterol were toxic and did not induce atherosclerosis, the gerbil was useful in other studies of cholesterol absorption and metabolism. Spontaneous, insidious periodontal disease became evident after about 6 months on standard diets, and dental caries were induced by cariogenic diets or by pathodontic streptococci. Spontaneous neoplasia occurred in 8.4--24% of gerbils, usually after 2 years of life. Adrenal cortical, ovarian and cutaneous tumors were the most consistently reported neoplasms.     

Long Term Effects of Social Deprivation during Early Adulthood in the Mongolian Gerbil (Meriones unguiculatus)

The influence of isolation on ♂-♀♀ relationships was investigated. Animals isolated between 90 and 200 days of age showed more agonistic behaviour in paired encounters than controls. This difference disappeared when the animals had been housed with a cagemate. A secondary isolation late in life resulted in a more rapid onset of agonistic behaviour in the early isolates than in the controls. Thus it is concluded that the early isolation had a lasting influence, which only became evident after renewed isolation treatment.     

Anatomy of the cecum of the gerbil Meriones unguiculatus (Mammalia,Rodentia, Cricetidae)

Summary The macroscopic and microscopic anatomy of the cecum of the gerbil was investigated using dissections, dried specimens and vascular injections as well as light-, scanning- and transmission electron microscopy.The cecum of the gerbil is a voluminous organ, possessing slight sacculations and only poorly developed taeniae. The base or ampulla ceci is slightly dilated and more voluminous than the corpus ceci, which decreases gradually in diameter to the blind-end, the apex ceci. A half ring-fold limits the entrance to the proximal colon from the ampulla. A wide-opened communication exists between ampulla and corpus ceci. The scanning microscopical appearance of the cecal wall takes the form of raised elevations circumventing a central depression. The cecum is lined internally by a tall columnar epithelium displaying a well-developed microvillar border and possessing numerous cellular organelles.     

Molecular phylogeny and biogeography of Oriental voles: genus Eothenomys (Muridae, Mammalia)

Oriental voles of the genus Eothenomys are predominantly distributed along the Southeastern shoulder of the Qinghai-Tibetan Plateau. Based on phylogenetic analyses of the mitochondrial cytochrome b gene (1143 bp) obtained from 23 specimens (eight species) of Oriental voles collected from this area, together with nucleotide sequences from six specimens (two species) of Japanese red-backed voles (Eothenomys andersoni and Eothenomys smithii) and five species of the closely related genus Clethrionomys, we revised the systematic status of Eothenomys. We also tested if vicariance could explain the observed high species diversity in this area by correlating estimated divergence times to species distribution patterns and corresponding paleo-geographic events. Our results suggest that: (1) the eight species of Oriental voles form a monophyletic group with two distinct clades, and that these two clades should be considered as valid subgenera--Eothenomys and Anteliomys; (2) Eothenomys eleusis and Eothenomys miletus are not independent species; (3) Japanese red-backed voles are more closely related to the genus Clethrionomys than to continental Asian Eothenomys taxa; and (4) the genus Clethrionomys, as presently defined, is paraphyletic. In addition, the process of speciation of Oriental voles appears to be related to the Trans-Himalayan formation via three recent uplift events of the Qinghai-Tibetan Plateau within the last 3.6 million years, as well as to the effects of the mid-Quaternary ice age.     

Melanocytes in the Stria Vascularis and Vestibular Labyrinth of the Mongolian Gerbil (Meriones unguiculatus)

Inner ear melanocytes are mainly present in the cochlea, vestibular organ, and endolymphatic sac, but their exact biological function has not been determined. In this investigation, we study the pigment cells in the membranous labyrinth of the gerbil. The inner ear melanocytes of M. unguiculatus show an irregular dendritic shape with cytoplasmic processes. These cells are disposed following the distribution of striai marginal and vestibular dark cells that have an important metabolic activity. Gerbil inner ear melanocytes are characterized by the presence of melanosomes, which are homogeneously dense organelles, of variable size and shape, that are surrounded by a membrane. In these cells, the Golgi apparatus plays a important role in melanin synthesis. When melanocytes were incubated in L-DOPA solution, the vesicles and cisterns of the Golgi apparatus exhibited a positive tyrosinase reaction. An interesting observation is the relation between melanocytes and inner ear capillaries. Sometimes, near to sensory vestibular areas, the melanocytes were in contact with Schwann cells and with myelinated fibres of vestibular nerve. The ultrastructural findings of this investigation are consistent with the hypothesis that melanocytes may have functional significance in the inner ear.     

Social wasps (Vespidae: Polistinae) on carcasses of Rattus norvegicus (Mammalia: Muridae) in the Central Amazonia,Brazil: possible forensic implications

We evaluated the occurrence of social wasps in the decomposition process in tropical rainforest in central Amazonia (Ducke Reserve, Manaus, Brazil), using cadavers of rats as attractants, exposed in suspended cages. Ten species, in three genera, of social wasps were collected only in the initial stages of decay (fresh and bloated). Five species were collected, mainly in the fresh stage, feeding on flesh: Agelaia angulata, Agelaia constructor, Agelaia fulvofasciata, Agelaia pallipes and Angiopolybia pallens. Five species were collected, mainly in the bloated stage, feeding on flesh and eggs and first instar larvae of dipteran: Agelaia testacea, Angiopolybia obidensis, Apoica arborea, Apoica pallens and Apoica thoracica. Due to the aspect of the injuries caused by the wasps to the carcass, they may be mistaken as skin ulcers, burns or abrasions, which may mislead a forensic investigation.     

不同干扰荒漠生境中子午沙鼠的繁殖及种群动态特征

子午沙鼠(Merionesmeridianus)广泛分布于我国西北部地区,是荒漠啮齿动物群落的优势鼠种。种群繁殖特征是动物生活史参数中的一个重要组成部分,是种群数量补充的重要来源,而干扰是影响繁殖特征的重要因素。本研究于2012~2014年,在位于蒙古阿拉善左旗南部典型荒漠的野外实验区,设置禁牧、开垦、过牧、轮牧4种不同干扰样地,使用铗日法对实验样地子午沙鼠相对数量及繁殖特征进行调查。4种不同干扰生境中的子午沙鼠种群数量具有显著差异,禁牧过牧轮牧开垦;雌雄性比在轮牧生境中最高,开垦生境次之,禁牧生境最低;4种干扰生境中,轮牧样地子午沙鼠雌鼠怀孕率显著高于禁牧、过牧和开垦样地;雄鼠的睾丸下降率在过牧干扰样地显著高于其他3种干扰方式样地,轮牧样地雄鼠睾丸下降率最低;雌鼠平均胎仔数在4种干扰生境间无显著性差异;轮牧干扰样地繁殖指数显著高于其他3种干扰方式样地;繁殖指数、怀孕率及睾丸下降率对密度的反馈作用最为明显,但在不同的干扰生境中其反馈特征有差异。综上,子午沙鼠在轮牧生境中各繁殖特征指数最高,繁殖能力最强,种群密度相对较高,更适合其生存,其密度制约效应表现最为明显。     

中国柽柳沙鼠线粒体DNA 的地理变异及其亚种分化

柽柳沙鼠广泛分布于中亚荒漠地区,在我国分布于蒙新干旱区西部。本研究采用线粒体Cyt b 基因和D-loop控制区两个片段共1 569 bp作为分子标记,对我国蒙新区西部45 个柽柳沙鼠的核苷酸多样性、单倍型多样性及系统发生进行分析,并探讨其亚种分化。45 个柽柳沙鼠线粒体DNA 共定义33 个单倍型,包含142 个核苷酸变异位点(占全序列的9.05% ),其中单态位点34 个,简约信息位点108 个,未发现碱基插入或缺失的现象。基于单倍型的系统发生树和网络关系图显示,柽柳沙鼠的谱系分为两大支:伊犁盆地的种群聚为独立的一支,准噶尔盆地和额济纳地区的种群聚为一支,两大支的分歧时间为0.24 Ma年前,大约在庐山冰期。通过Beast 模拟,柽柳沙鼠在近15 000年有一次快速的种群衰退,表明柽柳沙鼠种群受到了末次盛冰期的影响。基于Cyt b 基和D-loop 序列的证据,我们认为分布于新疆伊犁盆地的柽柳沙鼠为哈萨克亚种(M. t. jaxartensis),分布于我国新疆准噶尔盆地以及甘肃、内蒙地区的为敦煌亚种(M. t. satchouensis)。     

Mitochondrial DNA and karyotypic data confirm the presence of Mus indutus and Mus minutoides (Mammalia,Rodentia, Muridae,Nannomys) in Botswana

We use a combination of cytochrome b sequence data and karyological evidence to confirm the presence of Mus indutus and Mus minutoides in Botswana. Our data include sampling from five localities from across the country, including one site in northwestern Botswana where both species were captured in syntopy. Additionally, we find evidence for two mitochondrial lineages of M. minutoides in northwestern Botswana that differ by 5% in sequence variation. Also, we report that M. minutoides in Botswana have the 2n=34 karyotype with the presence of a (X.1) sex-autosome translocation.     

The distribution of Asellus aquaticus and A. meridianus (Crustacea, Isopoda) in Britain

SUMMARY. Asellus aquaticus and A. meridianus are freshwater isopods common more or less throughout Britain. It has been suggested that the former species is replacing the latter. To investigate this, the distributions of the species were determined in the English Lake District, near Merseyside, and elsewhere. Additionally, some field transference experiments were conducted in Anglesey and near Merseyside. Particular attention was given to changes in distribution with time; many of the observations reported relate to a time span of almost 20 years. Taken together, the results provide qualified support for the suggestion that A. aquaticus is replacing A. meridianus .     

Structure, histochemistry, and ultrastructure of the epithelium and stroma in the gerbil (Meriones unguiculatus) female prostate

The female prostate has aroused scientific interest because it is subjected to the same diseases compromising the male prostate during aging. The objective of this work was to characterize structurally, cytochemically, and ultrastructurally the tissue compartments of the normal adult female prostate of Meriones unguiculatus gerbils. The morphological analyses showed that the gerbil's female prostate is constituted of a cluster of glands and ducts inserted in a musculofibrous stroma. The alveolar epithelium is differentiated and consisted of basal proliferating cells, intermediary cells, and secretory cells. The secretory cells are the most numerous cell type and continuously secrete glycoproteins. The basal cells are the source of the secretory cells and they are then responsible for the alveolus renovation. The prostatic stroma is abundant and rich in elastic and collagen fibers, which are closely associated with smooth muscle cells and fibroblasts. The results showed that the gerbil's female prostate shows morphological and ultrastructural homology to the human female prostate (Skene's gland), and despite being a small organ, it is a mature and physiologically active gland.     

Karyotypes of three rat species (Mammalia: Rodentia: Muridae) from Hainan Island, China, and the valid specific status of Niviventer lotipes

The karyotypes of three rat species from Hainan Island, China, were examined. Niviventer fulvescens (Gray, 1847) had 2n=46 and FN=64, similar to the karyotypes reported for N. fulvescens from Southeast Asia, while Niviventer lotipes () had 2n=52 and FN=66, which is distinct from the known karyotypes of other Niviventer species. Niviventer lotipes was recently considered conspecific with N. tenaster (), but the two were found to have extremely different karyotypes (2n=52 and FN=66 in N. lotipes; 2n=46 and FN=54 in N. tenaster). Therefore, in this paper N. lotipes is considered a valid species for the first time; it is distinct from N. tenaster and endemic to Hainan Island, where N. lotipes is differentiated from N. fulvescens by larger body and skull sizes, a shorter tail, and darker coloration. Rattus nitidus (Hodgson, 1845) from Hainan Island had 2n=42 and FN=62, which is similar to the reported karyotypes of conspecific populations in Southeast Asia.     

Temporal Pattern of Agonistic Interaction in Two Gerbil Species (Rhombomys opimus and Gerbillus perpallidus) Differing in Resistance to Social Pressure

This study compares temporal patterns of intraspecific agonistic interactions in two gerbil species in order to indicate interspecific differences in levels of social resistance. Both cross-sex and same-sex pairs of great gerbils (Rhombomys opimus Licht., 1823), and only same-sex male pairs of pallid gerbils (Gerbillus perpallidus Setzer 1958) were observed during staged encounters on a neutral arena. Analysis of three latency measures—latency to first agonistic interaction; latency to overt aggression (attack and/or ‘arrested’ fight); and latency to establishment of a stable winner-loser asymmetry among opponents—revealed both similarities and differences among the species. Latencies to first agonistic interaction were similar (did not differ significantly) among species and sexes. However, great gerbil males showed significantly more long latencies to establishment of a stable asymmetry among opponents, than great gerbil females or pallid gerbil males. So, the periods of symmetrical struggle in agonistic conflict last longer in great gerbil males, than in great gerbil females or pallid gerbil males. These differences in temporal pattern of agonistic interaction may reflect sex and species differences in resistance to social stress.