Similarity of giemsa banding patterns of chromosomes in several species of the Genus Rattus

Giemsa banding patterns of chromosomes in seven Rattus species were compared. Four species (R. rattus tanezumi, R. norvegicus, R. exulans and R. muelleri) had all 2n=42 and their karyotypes and banding patterns were similar, although slight differences were observed. Another subspecies (R. rattus rattus) and two other species (R. fuscipes and R. conatus) had fewer chromosomes than the above species by having large biarmed chromosomes developed probably by Robertsonian fusion. The origin of the arms of biarmed chromosomes was recognized by their characteristic banding patterns. The remaining species, R. sabanus, had a karyotype markedly different from the other species by having two small metacentrics although in the others their number was 7. Banding patterns of the chromosomes in this species, however, were also very similar to those of the other, and therefore the 7 small metacentrics seemed to have originated by pericentric inversion of small acrocentrics.Contribution No. 912 from the National Institute of Genetics, Japan. Supported by a grant-in-aid from the Ministry of Education of Japan, Nos. 90183, 90375 and 744002.     

Commensal Rats and Humans: Integrating Rodent Phylogeography and Zooarchaeology to Highlight Connections between Human Societies

Phylogeography and zooarchaeology are largely separate disciplines, yet each interrogates relationships between humans and commensal species. Knowledge gained about human history from studies of four commensal rats (Rattus rattus, R. tanezumi, R. exulans, and R. norvegicus) is outlined, and open questions about their spread alongside humans are identified. Limitations of phylogeographic and zooarchaeological studies are highlighted, then how integration would increase understanding of species’ demographic histories and resultant inferences about human societies is discussed. How rat expansions have informed the understanding of human migration, urban settlements, trade networks, and intra- and interspecific competition is reviewed. Since each rat species is associated with different human societies, they identify unique ecological and historical/cultural conditions that influenced their expansion. Finally, priority research areas including nuclear genome based phylogeographies are identified using archaeological evidence to understand R. norvegicus expansion across China, multi-wave colonization of R. rattus across Europe, and competition between R. rattus and R. norvegicus.     

Sexual-size dimorphism in two synanthropic rat species: Comparison and eco-evolutionary perspectives

Sexual dimorphism is a common trait in many mammal species and sexual-size dimorphism (SSD) represents its commonest form. Rattus rattus and Rattus norvegicus are two cosmopolitan, polygynous species, for which a male-biased SSD has been anecdotally reported, but never quantified. In this work, we assessed the occurrence of SSD in both species and we tested the hypothesis that R. norvegicus has a more evident SSD than R. rattus, in agreement with their body mass-testes size ratio, intra-male aggressive behaviour and mating system. We collected weight data of 40 (20 males and 20 females) adult R. rattus and 27 (13 males and 14 females) adult R. norvegicus from 4 localities in Italy characterized by different habitat typologies. We used a t-test based on Bayesian inference to compare the SSD in both species. The results were in line with our expectation supporting a higher SSD in R. norvegicus than in R. rattus. This study aimed to identify the eco-evolutionary drivers of SSD, and provides further support to well established life history theories on two widely distributed rodent species.     

Intra- and Interspecific Variation of the Mitochondrial Genome in RATTUS NORVEGICUS and RATTUS RATTUS: Restriction Enzyme Analysis of Variant Mitochondrial DNA Molecules and Their Evolutionary Relationships

Restriction endonuclease analysis has revealed extensive mtDNA polymorphism in two species of rats, Rattus rattus and Rattus norvegicus. Sequence divergence values for the eight detected R. norvegicus variants range from 0.2% to 1.8% and for the eight R. rattus variants, from 0.2% to 9.6%. Three of the most closely related R. norvegicus mtDNA's appear to differ by deletions/insertions of about 4 base pairs apiece. Restriction sites for seven enzymes have been mapped for 11 of these variants. The 31 intraspecific and 41 interspecific variant sites appear to be evenly distributed on the mtDNA molecule outside of the rRNA cistrons. The location of sites present in all the DNAs suggests that the rRNA genes and possibly the light strand origin of replication may be more highly evolutionarily conserved than other parts of the molecule. The sequence divergences among the mtDNAs of animals whose geographic origins are separated by major barriers, such as oceans, were significantly greater than those among animals found within large land masses, such as the continental United States. Dendrograms (phenograms), which have been constructed to depict the relationships among the various DNAs, indicate that East Asian members of the R. rattus species are more closely related to American rats of this species than to other Asian R. rattus animals from Sri Lanka. Moreover, it appears that R. norvegicus comprises a group taxonomically distinct from any of the R. rattus subspecies.     

Genetic Differentiation among Karyotypic Forms of the Black Rat, RATTUS RATTUS

The black rat, Rattus rattus, consists of five karyotypic forms—2n = 42 (high C-banding); 2n = 42 (low C-banding); 2n = 40; 2n = 38; 2n = 42 Mauritius. Here, we use isozyme electrophoresis and microcomplement fixation to elucidate the genetic distance and phylogenetic relationship among each of the various karyotypic forms of R. rattus and R. norvegicus . The results show that (1) the 2n = 42 Mauritius black rat (2n = 42Mau) is genetically very similar to the 2n = 38 form, suggesting that this island population has undergone very rapid chromosomal evolution; (2) the 2n = 40 form from the highlands of Sri Lanka is genetically distinct from the 2n = 38 form from the lowlands; the genetic difference is probably insufficient, however, to prevent future introgression; (3) the level of genetic differentiation occurring between the 2n = 42 forms on the one hand and the 2n = 38, 2n = 40 and 2n = 42 Mau forms on the other support the hybrid incompatability data in suggesting that the two groups are either full species or incipient species; (4) in contrast to data from amino acid composition of transferrin and from restriction endonuclease digests of mtDNA, the present data suggest that the various karyotypic forms of R. rattus are phylogenetically more closely related to each other than any is to R. norvegicus, and that they are related by a series 2n = 42 → 2n = 40 → 2n = 38; (5) the R. rattus/R. norvegicus divergence occurred 2–8 million years ago, whereas the various chromosomal forms of R. rattus diverged over the last 4 million years.     

Evolutionary history of rat‐borne Bartonella: the importance of commensal rats in the dissemination of bacterial infections globally

Emerging pathogens that originate from invasive species have caused numerous significant epidemics. Some bacteria of genus Bartonella are rodent‐borne pathogens that can cause disease in humans and animals alike. We analyzed gltA sequences of 191 strains of rat‐associated bartonellae from 29 rodent species from 17 countries to test the hypotheses that this bacterial complex evolved and diversified in Southeast Asia before being disseminated by commensal rats Rattus rattus (black rat) and Rattus norvegicus (Norway rat) to other parts of the globe. The analysis suggests that there have been numerous dispersal events within Asia and introductions from Asia to other regions, with six major clades containing Southeast Asian isolates that appear to have been dispersed globally. Phylogeographic analyses support the hypotheses that these bacteria originated in Southeast Asia and commensal rodents (R. rattus and R. norvegicus) play key roles in the evolution and dissemination of this Bartonella complex throughout the world.     

Competition, coexistence, and adaptation amongst rodent invaders to Pacific and New Zealand islands

Variation in skull size was investigated for three species of rats (kiore –Rattus exulans Peale; ship rat –R. rattus L.; Norway rat –R. norvegicus Berkenhout) which were introduced by humans to various islands in New Zealand and other Pacific islands. Data from seventy-one islands and 882 specimens are examined for evidence of the effects of latitude, island size and interspecific competition among rats and the house mouse (Mus musculus L.) on skull size, using multiple regressions. For R. exulans, skull size increases with latitude as predicted by Bergmann's rule, but no such effect occurs for the other two rats. There was a positive relationship between island size and the number of species inhabiting it, and some species combinations were more likely to occur than others. For example, R. exulans and R. norvegicus were more likely to occur together, while R. rattus and R. exulans were rarely sympatric. R. exulans and R. rattus skull size was negatively correlated with the number of other rodents on the same island. R. exulans skull size increased on smaller islands in some island groups, perhaps because increased density and consequent increased intraspecific competition on smaller islands favours increased body size. This effect is more pronounced in tropical islands (Solomon islands), than in subtropical ones (Hawaiian islands) and less so in temperate New Zealand. Collectively the data demonstrate that rapid evolution of body size in predictable directions can follow within 150 years of the introduction of species to new receiving communities.     

New microsatellite markers for the bush rat,Rattus fuscipes greyii: characterization and cross‐species amplification

We describe here 16 new microsatellite markers for the bush rat, Rattus fuscipes greyii, and characterize their cross‐species amplification within the Australian Rattus and at a greater level of divergence in Rattus rattus and Rattus norvegicus. Within R. f. greyii, all of the loci are highly polymorphic, with six to 24 alleles per locus across the species range and expected heterozygosity ranging from 0.48 to 0.90 per locus within a sample of 24 rats from a large population on Kangaroo Island. Cross‐species amplification rates were approximately 87% within the Australian Rattus and approximately 50% within R. rattus and R. norvegicus. These loci are highly polymorphic with a high success rate of cross‐species amplification, making them potentially useful for a wide range of genetic studies.     

A mathematical epidemiological model of gram-negative Bartonella bacteria: does differential ectoparasite load fully explain the differences in infection prevalence of Rattus rattus and Rattus norvegicus?

We postulate that the large difference in infection prevalence, 24% versus 5%, in R. norvegicus and R. rattus, respectively, between these two co-occurring host species may be due to differences in ectoparasite and potential vector infestation rates. A compartmental model, representative of an infectious system containing these two Rattus species and two ectoparasite vectors, was constructed and the coefficients of the forces of infection determined mathematically. The maximum difference obtained by the model in the prevalence of Bartonella in the two Rattus species amounts to 4.6%, compared to the observed mean difference of 19%. Results suggest the observed higher Bartonella infection prevalence in Rattus norvegicus compared to Rattus rattus, cannot be explained solely by higher ectoparasite load. The model also highlights the need for more detailed biological research on Bartonella infections in Rattus and the importance of the flea vector in the spread of this disease.     

Assignment of 22 loci in the rat by somatic hybrid and linkage analysis

Twenty structural genes and two unique anonymous DNA fragments have been mapped in the rat (Rattus norvegicus) with a panel of mouse x rat hybrids and linkage analysis. Ten of the 20 autosomes are represented by at least one of these markers. A new syntenic relationship among rat Chromosome (Chr) 16, mouse Chr 14, and human Chr 10q was established. Results of this study further support the extensive conservation of syntheny between the rat and mouse and, to a lesser degree, between rat and human.     

Rat kappa-chain allotypes

The distribution of rat kappa-chain allotype specificities (RI-1a and 1b) was studied amongRattus rattus and a variety of other Asian rodents. No sera other than those ofRattus norvegicus showed the presence of RI-1a (DA type), whereas many cross-reacted with RI-1b (LEW-type). While manyR. rattus showedtotal cross-reactivity with RI-1b, various sera from the generaRattus, Bandicota, andTokudaia showed different levels ofpartial cross-reactivity. These results indicate that (1) anti-RI-1b reagents can detectmultiple specificities on LEW-type kappa chains, and (2) these RI-1b specificities, butnot RI-1a, are widely distributed among murid rodents, in seeming contradiction to amino acid sequence data suggesting that RI-1b is more closely related to ancestral rat kappa chains.     

Focus: Zoonotic Disease: Prevalence and Diversity of the Streptobacillus Rat-bite Fever Agent,in Three Invasive,Commensal Rattus Species from South Africa

Rat-bite fever is an over-looked, global zoonotic disease that has a mortality rate of up to 13%, if untreated. Historically, this rat-borne disease has been attributed to one of two causative agents, Streptobacillus moniliformis or Spirillum minus. Given the confirmed presence of multiple invasive Rattus host species, high rat densities in urban, informal human settlements and increasing reports of rat bites in South Africa, we undertook a retrospective assessment of Streptobacillus in rats sampled from 16 urban sites, in Gauteng, the smallest but most populous Province in South Africa. Using a multi-gene PCR-sequencing approach, we confirmed Streptobacillus presence in 50.9% of oral swabs from three rat species and the presence of two Streptobacillus species, viz. S. moniliformis and S. notomytis. The two members of the cryptic Rattus rattus species complex (R. rattus and R. tanezumi), which are morphologically indistinguishable from each other, had markedly different colonization rates. Whereas 48.6% of rats from this species complex were Streptobacillus-positive, only 32.3% of Rattus tanezumi were positive compared to 61.5% R. rattus. Rattus norvegicus had an intermediate prevalence of 55.6%. Phylogenetic analysis of four gene regions (16S rRNA, gyrB, groEL, recA) identified two discrete lineages; S. moniliformis occurred exclusively in R. norvegicus, and S. notomytis was restricted to the two members of the R. rattus species complex; this represents the first report of Streptobacillus in R. tanezumi. These results highlight a largely overlooked zoonotic threat posed by invasive rats and confirm the presence of two discrete and potentially host-specific Streptobacillus lineages in South Africa.     

Ecology of cutaneous leishmaniasis in Sinai: linking parasites,vectors and hosts

Cutaneous leishmaniasis (CL) is a neglected clinical form of public health importance that is quite prevalent in the northern and eastern parts of Egypt. A comprehensive study over seven years (January 2005-December 2011) was conducted to track CL transmission with respect to both sandfly vectors and animal reservoirs. The study identified six sandfly species collected from different districts in North Sinai: Phlebotomus papatasi, Phlebotomus kazeruni, Phlebotomus sergenti, Phlebotomus alexandri, Sergentomyia antennata and Sergentomyia clydei. Leishmania (-)-like flagellates were identified in 15 P. papatasi individuals (0.5% of 3,008 dissected females). Rodent populations were sampled in the same districts where sandflies were collected and eight species were identified: Rattus norvegicus (n = 39), Rattus rattus frugivorous (n = 13), Rattus rattus alexandrinus (n = 4), Gerbillus pyramidum floweri (n = 38), Gerbillus andersoni (n = 28), Mus musculus (n = 5), Meriones sacramenti (n = 22) and Meriones crassus (n = 10). Thirty-two rodents were found to be positive for Leishmania infection (20.12% of 159 examined rodents). Only Leishmania major was isolated and identified in 100% of the parasite samples. The diversity of both the vector and rodent populations was examined using diversity indices and clustering approaches.     

Genetics of the ceramide/sphingosine-1-phosphate rheostat in blood pressure regulation and hypertension

Background

South Africa's long and extensive trade activity has ensured ample opportunities for exotic species introduction. Whereas the rich biodiversity of endemic southern African fauna has been the focus of many studies, invasive vertebrates are generally overlooked despite potential impacts on biodiversity, health and agriculture. Genetic monitoring of commensal rodents in South Africa which uncovered the presence of Rattus tanezumi, a South-East Asian endemic not previously known to occur in Africa, provided the impetus for expanded studies on all invasive Rattus species present.

Results

To this end, intensified sampling at 28 South African localities and at one site in Swaziland, identified 149 Rattus specimens. Cytochrome b gene sequencing revealed the presence of two R. tanezumi, seven Rattus rattus and five Rattus norvegicus haplotypes in south Africa. Phylogenetic results were consistent with a single, recent R. tanezumi introduction and indicated that R. norvegicus and R. rattus probably became established following at least two and three independent introductions, respectively. Intra- and inter-specific diversity was highest in informal human settlements, with all three species occurring at a single metropolitan township site. Rattus norvegicus and R. rattus each occurred sympatrically with Rattus tanezumi at one and five sites, respectively. Karyotyping of selected R. rattus and R. tanezumi individuals identified diploid numbers consistent with those reported previously for these cryptic species. Ordination of bioclimatic variables and MaxEnt ecological niche modelling confirmed that the bioclimatic niche occupied by R. tanezumi in south Africa was distinct from that occupied in its naturalised range in south-east Asia suggesting that factors other than climate may influence the distribution of this species.

Conclusions

This study has highlighted the value of genetic typing for detecting cryptic invasive species, providing historical insights into introductions and for directing future sampling. The apparent ease with which a cryptic species can become established signals the need for broader implementation of genetic monitoring programmes. In addition to providing baseline data and potentially identifying high-risk introduction routes, the predictive power of ecological niche modelling is enhanced when species records are genetically verified.     

Sequence-ready physical map of the mouse Chromosome 16 region with conserved synteny to the human Velocardiofacial syndrome region on 22q11.2

Proximal mouse Chromosome (Chr) 16 shows conserved synteny with human Chrs 16, 8, 22, and 3. The mouse Chr 16/human Chr 22 conserved synteny region includes the DiGeorge/Velocardiofacial syndrome region of human Chr 22q11.2. A physical map of the entire mouse Chr 16/human Chr 22 region of conserved synteny has been constructed to provide a substrate for gene discovery, genomic sequencing, and animal model development. A YAC contig was constructed that extends ca. 5.4 Mb from a region of conserved synteny with human Chr 8 at Prkdc through the region conserved with human Chr 3 at DVL3. Sixty-one markers including 37 genes are mapped with average marker spacing of 90 kb. Physical distance was determined across the 2.6-Mb region from D16Mit74 to Hira with YAC fragmentation. The central region from D16Jhu28 to Igl-C1 was converted into BAC and PAC clones, further refining the physical map and providing sequence-ready template. The gene content and borders of three blocks of conserved linkage between human Chr 22q11.2 mouse Chr 16 are refined. Received: 4 November 1998 / Accepted: 21 December 1998     

Herbivory in invasive rats: criteria for food selection

Three species of rats (Rattus exulans, R. rattus, R. norvegicus) are widely invasive, having established populations in terrestrial habitats worldwide. These species exploit a wide variety of foods and can devastate native flora and fauna. Rats can consume a variety of plant parts, but may have the most dramatic effects on plant populations through consumption and destruction of seeds. The vulnerability of vegetation to rat consumption is influenced by many factors including size of plant part, and mechanical and chemical defenses. We reviewed the literature to find out what plant species and plant parts invasive rats are consuming and what characteristics these sources share that may influence selection by rats. Many of the studies we found were preformed in New Zealand and our analyses are, therefore, focused on this location. We also performed feeding trials in the laboratory with R. norvegicus to determine if seed hardness and palatability would influence rat consumptive choices. We found more reports of rat consumption of fruits and seeds versus vegetative plant parts, and smaller fruits and seeds versus larger. R. norvegicus are reported to consume proportionally more vegetative plant parts than either R. exulans or R. rattus, possibly due to their more ground dwelling habits. Large size and hard seed coats may deter rat feeding, but unpalatable chemicals may be even more effective deterrents to rats. Scientists and managers can better manage vegetation in rat invaded areas by understanding the criteria rats use to select food.     

Laboratory evaluation of a toxicant-sterilant, alpha-chlorohydrin, for the control of Indian mole rat Bandicota bengalensis

A toxicant-sterilant, alpha-chlorohydrin, was evaluated against the Indian mole rat Bandicota bengalensis and the ship or house rat Rattus rattus. It caused 100% mortality of B. bengalensis at 100 mg/kg but no mortality was observed in R. rattus even at 300 mg/kg. The acute oral LD₅₀ for B. bengalensis was found to be 82 mg/kg. The survivors of B. bengalensis, which received 60 - 90 mg/kg of alpha-chlorohydrin by oral intubation, showed dose-dependent decreases in testicular weight, and cauda epididymal sperm concentration, live sperm count and sperm motility. The values of these parameters indicated that mole rats receiving the above doses would be sterile. In contrast, these changes were observed in R. rattus only at doses of 200 and 300 mg/kg. The toxic and antifertility effects of alpha-chlorohydrin observed on B. bengalensis suggest that it should be evaluated for the management of this species under held conditions.     

Review of negative effects of introduced rodents on small mammals on islands

In this first comprehensive review of negative effects of introduced rodents on insular small mammals, the focal species Rattus rattus, R. norvegicus, R. exulans and Mus musculus are implicated in at least 11 extinctions. Furthermore, removal experiments, eradication campaigns and control programmes provide evidence for negative effects on extant populations. While data are currently insufficient for meaningful generalisation with regard to the most threatening rodents, the most threatened small mammals, and the true extent of the problem, it is interesting that R. rattus is implicated in the majority of impacts. This may be explained by its extensive distribution and ecological plasticity. I conclude with methodological recommendations to guide data collection for impact quantification and the study of impact mechanism. This information should facilitate the prioritisation and justification of eradication campaigns, control programmes and biosecurity measures while ensuring that much-needed attention is paid to the conservation of insular small mammals.     

Ecological Segregation and Population Structuring of the Cormorant Phalacrocorax carbo in Europe, in Relation to the Recent Introgression of Continental and Marine Subspecies

Populations of the “continental” Great Cormorant P. c. sinensis have expanded from north-eastern Europe towards the western part of the range of the “marine” P. c. carbo breeding in the United Kingdom and France. The aim of the study was to test the hypothesis of ecological segregation between subspecies by analysing the structuring of the European populations. Sequencing the mtDNA of 231 birds belonging to 20 colonies revealed 38 haplotypes based on 25 polymorphic sites (5.76% sequence divergence). P. c. sinensis (“S”) was well confirmed, but usual P. c. carbo formed two coastal populations, the real P. c. carbo “C” mainly in the western part of the range (United Kingdom, coastal France), and also in Norway and Sardinia, and “N”, branched to the Japanese Cormorant P. capillatus and probably isolated by glaciations, mainly present in the Nordic range (Norway, but also on the coasts from Sweden to Brittany), we named P. c. norvegicus. In a variable position in the trees but close to C is a group of undetermined origin haplotypes, named U, also present in both traditional ranges. The new tree-nesting colonies in Brittany are clearly a mixture of S and the two clades C and N previously described as P. c. carbo, with a decreasing proportion of C + N between 1993 (67%), 1996 (60%) and 2002 (33%) for the pioneering Grand-Lieu colony. These results confirmed the current introgression of continental populations in the western range, with probable hybridization. Although the subspecies can switch habitats locally due to social behaviour and migrations, the ecological segregation between the two usual subspecies appears to be largely confirmed in Europe.     

Comparative phylogeography of invasive Rattus rattus and Rattus norvegicus in the U.S. reveals distinct colonization histories and dispersal

Invasive Rattus are arguably the most costly and destructive invasive species on the planet, but little is known concerning their invasion history and population structure in the U.S. We utilized both nuclear microsatellites and mitochondrial DNA sequences (mtDNA) to compare the colonization history, patterns of gene flow, and levels of genetic diversity of Rattus rattus and R. norvegicus in the U.S. Analyses of mtDNA suggest R. rattus is characterized by a single rapid expansion into the U.S. from one or two very closely related mtDNA lineages or geographic sources. For R. norvegicus, mtDNA analyses suggest at least four invasions distinct in space and/or time have occurred to establish its distribution in the U.S. Microsatellite analyses suggest for R. rattus that dispersal is characterized by an isolation-by-distance pattern, suggesting a relatively low frequency of long distance dispersal, and low levels of establishment for novel propagules. In contrast, microsatellite analyses of R. norvegicus suggest high frequencies of long distance dispersal and essentially panmixia among nearly all sampled populations, as well as a high frequency of novel propagules entering at the east and west coasts and assimilating into established populations. We discuss these results in the context of invasive Rattus management in the U.S. and their implications for invasive species in general, as well as the implications for managing the spread of rat-borne pathogens.