Isolation and characterization of microsatellites in Rattus rattus

We isolated and characterized 10 microsatellite loci in the black rat Rattus rattus (Muridae, Rodentia), a widespread invasive species largely known to cause serious problems in agriculture and human health. Polymorphism was studied in two populations, one from Madagascar and one from Senegal. It ranged from three to 12 alleles in Madagascar, and from two to five alleles in Senegal. Together with the loci previously adapted from Rattus norvegicus, this set of markers should allow the conduct of thorough studies on the genetic structure of natural populations of R. rattus.     

Use of habitat by the black rat (Rattus rattus) at North Head,New South Wales: an observational and experimental study

This study investigated the habitats used by an introduced species of rodent, the black rat Rattus rattus (Linnaeus), at North Head in New South Wales, Australia. At a coarse scale, combined live‐trapping and radio‐tracking indicated that animals used forest proportionately more than open, heath or scrub macrohabitats that were available. To identify the components contributing to this pattern, microhabitat use was assessed by scoring vegetative and structural features around trap stations, and by using spool‐and‐line tracking. The results indicated that rats preferred microhabitats providing a deep cover of leaf litter and dense understorey with numerous vertical stems. As statistical analysis did not distinguish which of these components was more important in determining habitat use, we designed an experiment to test the importance of a single component: leaf litter. Cover of litter was enhanced experimentally at 75 trap stations and reduced at 75 others, and the response of rats monitored by live‐trapping on two occasions. Although no clear response was found in the first run of the experiment, due to low numbers, rats strongly selected trap stations with enhanced leaf litter in the second run. These results indicate that litter cover affects use of habitat by the black rat. Access to food resources and avoidance of predators may contribute to the observed local patterns of abundance.     

Island colonization and founder effects: the invasion of the Guadeloupe islands by ship rats (Rattus rattus)

The stepwise colonization of islands within an archipelago is typically punctuated by successive founder effects, with each newly founded population being a subsample of the gene pool of the source island. Thus, the genetic signature of successive bottlenecks should be detected when analysing the genetic structure between islands of an archipelago. To test this prediction, we investigated introduced ship rat populations, Rattus rattus (Linnaeus, 1758), in the Guadeloupe Archipelago. Three different methods, commonly named the heterozygosity excess, the mode-shift indicator and the M ratio method, were used to detect bottlenecks from genetic data obtained with eight microsatellite markers on Guadeloupe and two neighbouring islands, Petite-Terre and Fajou. Moreover, a recent eradication failure on Fajou allowed us to test the accuracy of the methods in an 'experimental-like' situation. The results indicate that rats were introduced on Guadeloupe first, which then became the source population for independent secondary colonization of Fajou and Petite-Terre. Moreover, the heterozygosity excess and the mode-shift indicator only detected bottlenecks for the recent colonization of Petite-Terre and the eradication failure on Fajou. However, bottlenecks were detected for all the populations using the M ratio method. This could be interpreted as the remaining signature of the early introduction of the ship rat in the archipelago.     

Assessment of Rhodamine B for labelling the plague reservoir Rattus rattus in Madagascar

The black rat is the main plague reservoir in rural foci in Madagascar, inside the villages as well as in the cultivated areas around. We have evaluated the potentialities of mass‐marking of rats, using baits containing Rhodamine B (RB) in order to get a tool to study the movements of rats and to understand the spread of plague. Laboratory experiments demonstrated that: (i) rats were more attracted by the rodent granules and peanut butter; (ii) incorporation of RB in baits did not reduce their appetence; (iii) RB lasted for 60 days in rat vibrissae and 180 days in rat hairs; and (iv) consumption of baits during a week was under the lethal dose. Field tests have been realized comparatively among 24 highland villages where plague is endemic, in different contexts: baits inside houses or around the village, baits with and without RB, rats captured 1, 2 and 3 months after the marking. No negative effect of the RB on population dynamics of rats or fleas on them was observed. The effectiveness of the marking was comparable between males and females. This technique of collective marking appears very valuable for monitoring rat movements in plague foci.     

Disease and competition,not just predation,as drivers of impacts of the black rat (Rattus rattus) on island mammals

Hanna & Cardillo (2014) report an association between the presence of black rats (Rattus rattus) and extinctions of endemic mammals on Australian islands. Although we agree that introductions of the black rat are likely to have had a significant impact on island ecosystems, we suggest that there is little empirical support for their main conclusion, that predation (and thus mesopredator processes) is the causal mechanism driving the association between the presence of black rats and extinctions of native mammals on Australian islands. We present a brief literature review of evidence for two alternative mechanisms – introduction of novel diseases and competition – which suggest there are multiple explanations for how native mammal extinctions on Australian islands may have occurred. The potential impact of these processes interacting across different trophic levels is rarely considered, but is applicable across many different ecosystems world‐wide.     

The home range of ship rats (Rattus rattus) in beech forest in the Eglinton Valley,Fiordland, New Zealand: A pilot study

Abstract

Three male and two female ship rats (Rattus rattus) were radio‐tagged and tracked in beech (Nothofagus) forest in the Eglinton Valley, Fiordland, New Zealand over two field periods in 1996 and 2000. The home range of each animal was calculated using the minimum convex polygon method. Ranges of three male rats were 7.5, 9.1, and 11.4 ha whereas those of the female rats were 0.89 and 0.27 ha. The home ranges recorded for male rats were considerably larger than those reported from other studies in non‐beech forest. Ship rats are important predators of forest birds, and home range information could be used to provide a guide for trap or bait station spacing in beech forests. To carry out rat control in beech forests effectively, further studies are needed to determine if the results of this pilot study are typical, and if home ranges of ship rats change with season, or at various stages of the beech mast cycle.     

Denning behaviour of ship rats (Rattus rattus) on Taukihepa,a seabird breeding island

Abstract

Den sites of 14 ship rats (Rattus rattus) were located daily during the rat breeding season on Taukihepa (Big South Cape), a seabird island southwest of Rakiura (Stewart Island). In contrast to other New Zealand studies, no arboreal dens were found. Den sites on Taukihepa were in ferns, under logs, in woodpiles, or underground in sooty shearwater (Puffinusgriseus) breeding burrows. The number of times known den sites used was positively related to the amount of leaf litter and woodpiles near the den sites. Overall, 24% of radio‐tagged rats were sharing den sites on any given day. While there was considerable individual variation in the number of times den sites were used, female rats tended to reuse den sites more than males. Many rats were found in dens alone, but frequently males and females shared. Occasionally two females and one male denned together, as did two females, whereas males never denned with another male.     

The Black Rat Rattus rattus in the United Kingdom in 1989

The loss of ground by the Black Rat in the late 1950s continued through the next decade. Since then the number of site records has fluctuated and there has been less constancy in the places recording the presence of the rat. This impermanence of populations together with their small size suggests that introductions are short lived and that the species has only a tenuous foothold in the United Kingdom today. Port records show that rats are still arriving regularly by ship and it is suggested that future developments in climate and trade might further assist entry and make the environment more favourable for the Black Rat.     

小良热带人工阔叶混交林中屋顶鼠施氏亚种的食性及其生态学意义

Rattus rattus slandeni的食性资料是在小良人工阔叶混交林中通过200个鼠箱观察残留食物的方法收集到的。屋顶鼠摄食植物39种,主要为果实、种子部分,并大量捕食金龟子、蝉和蝗虫等昆虫,偶尔捕食小脊椎动物。植物性和动物性两大类残食的总出现率相近,5-10月以动物性食物为主,11-4月以植物性食物为主。该鼠搬运和遗弃果实、种子的行为,有助于植物种类的传布,大量捕食害虫,有利于该系统的生态平衡,故对其益害问题应作客观评价。     

Phylogeography of the introduced species Rattus rattus in the western Indian Ocean,with special emphasis on the colonization history of Madagascar

Aim To describe the phylogeographic patterns of the black rat, Rattus rattus, from islands in the western Indian Ocean where the species has been introduced (Madagascar and the neighbouring islands of Réunion, Mayotte and Grande Comore), in comparison with the postulated source area (India). Location Western Indian Ocean: India, Arabian Peninsula, East Africa and the islands of Madagascar, Réunion, Grande Comore and Mayotte. Methods Mitochondrial DNA (cytochrome b, tRNA and D‐loop, 1762 bp) was sequenced for 71 individuals from 11 countries in the western Indian Ocean. A partial D‐loop (419 bp) was also sequenced for eight populations from Madagascar (97 individuals), which were analysed in addition to six previously published populations from southern Madagascar. Results Haplotypes from India and the Arabian Peninsula occupied a basal position in the phylogenetic tree, whereas those from islands were distributed in different monophyletic clusters: Madagascar grouped with Mayotte, while Réunion and Grand Comore were present in two other separate groups. The only exception was one individual from Madagascar (out of 190) carrying a haplotype that clustered with those from Réunion and South Africa. ‘Isolation with migration’ simulations favoured a model with no recurrent migration between Oman and Madagascar. Mismatch distribution analyses dated the expansion of Malagasy populations on a time‐scale compatible with human colonization history. Higher haplotype diversity and older expansion times were found on the east coast of Madagascar compared with the central highlands. Main conclusions Phylogeographic patterns supported the hypothesis of human‐mediated colonization of R. rattus from source populations in either the native area (India) or anciently colonized regions (the Arabian Peninsula) to islands of the western Indian Ocean. Despite their proximity, each island has a distinct colonization history. Independent colonization events may have occurred simultaneously in Madagascar and Grande Comore, whereas Mayotte would have been colonized from Madagascar. Réunion was colonized independently, presumably from Europe. Malagasy populations may have originated from a single successful colonization event, followed by rapid expansion, first in coastal zones and then in the central highlands. The congruence of the observed phylogeographic pattern with human colonization events and pathways supports the potential relevance of the black rat in tracing human history.     

褐家鼠精母细胞中联会复合体的研究Ⅳ.常染色体联会复合体的发育和偶线期节的研究

采用表面铺展-SDS处理、硝酸银和磷钨酸（Phosphotungsticacid,PTA）染色电镜技术,研究了褐家鼠精母细胞中常染色体联会复合体（Synaptonemacomplex,SC）的发育及偶线期节（Zygotenenodule,ZN）。在褐家鼠精母细胞的细线期,常染色体轴心（Axialcores,ACs）已形成,同源轴心在空间上靠近,偶线期SCs开始形成,到粗线期SCs完全形成,于双线期SCs开始解体。在双线期除了个别SCs侧生组分分开外,大多数SCs发生碎片化（fragmentation）．在偶线期未配对的ACs和SCs侧生组分及中央组分上均发现电子密度高的球形或椭圆形的节状结构──偶线期节,ZNss在同源染色体配对过程中起很重要的作用。     

Heavy rimu (Dacrydium cupressinum) mast seeding and rat (Rattus spp.) population eruptions on Stewart Island/Rakiura

Abstract

This study aimed to quantify changes in rat abundance and population structure before, during, and after a rimu (Dacrydium cupressinum) mast seed event in lowland forest on Stewart Island, New Zealand. Rats, primarily ship rats (Rattus rattus), were trapped in low numbers throughout the study period (March 2000‐March 2003), except when they erupted to very high abundance in spring 2002, shortly after heavy rimu seed fall. In the immediate post‐peak phase, scavenging of trapped rats increased substantially; rats were seen and trapped in daylight; and weights of adult female rats were low in relation to their size, which suggests that food shortage was the cause of the subsequent steep decline in abundance. Rat eruptions have been observed on Stewart Island after heavy rimu seed fall several times over the past 40 years. Eruptions of rats caused by heavy rimu seed‐fall may have triggered the invasion of nearby islands by rats, and caused the extinction of several native species on Stewart Island.     

基于线粒体细胞色素b基因分析海南岛褐家鼠种群遗传多样性

褐家鼠(Rattus norvegicus)是海南岛的主要害鼠之一,海南岛是我国南方海上的重要交通口岸,但关于海南岛褐家鼠的种群遗传多样性以及和邻近地区褐家鼠种群间的基因交流情况还缺乏了解。本研究测序分析了来自海南岛、广东、越南等地91只褐家鼠的细胞色素b基因,分析了不同种群中的Cyt b单倍型,种群间的遗传分化程度(F_(st)),构建了全世界60个褐家鼠的Cyt b单倍型之间的系统进化关系。结果发现,海南岛琼中/澄迈和崖城的褐家鼠种群没有共享的Cyt b单倍型,种群间出现了明显的遗传分化(F_(st)=0.453),但这两个群体分别与广东和菲律宾/越南的褐家鼠分享共同的单倍型,表明海南岛褐家鼠与广东和菲律宾/越南褐家鼠近代存在着基因交流。系统进化分析结果表明,多数海南岛和广东褐家鼠的Cyt b单倍型来自共同的单倍型组CⅢ和CⅦ,说明海南岛和广东省的褐家鼠可能由一个或多个共同的祖先种群扩散而来。由于褐家鼠喜欢与人伴生,褐家鼠很可能随着黎族人在新石器时代中期(大约3 000年前)或更早以前,从广西、广东沿海地区迁移至海南。     

Carriage of Clostridium difficile by Wild Urban Norway Rats (Rattus norvegicus) and Black Rats (Rattus rattus)

Clostridium difficile is an important cause of enteric infections in humans. Recently, concerns have been raised regarding whether animals could be a source of C. difficile spores. Although colonization has been identified in a number of domestic species, the ability of commensal pests to serve as a reservoir for C. difficile has not been well investigated. The objective of this study was to determine whether urban rats (Rattus spp.) from Vancouver, Canada, carry C. difficile. Clostridium difficile was isolated from the colon contents of trapped rats and was characterized using ribotyping, toxinotyping, and toxin gene identification. Generalized linear mixed models and spatial analysis were used to characterize the ecology of C. difficile in rats. Clostridium difficile was isolated from 95 of 724 (13.1%) rats, although prevalence differed from 0% to 46.7% among city blocks. The odds of being C. difficile positive decreased with increasing weight (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.53 to 0.87), suggesting that carriage is more common in younger animals. The strains isolated included 9 ribotypes that matched recognized international designations, 5 identified by our laboratory in previous studies, and 21 “novel” ribotypes. Some strains were clustered geographically; however, the majority were dispersed throughout the study area, supporting environmental sources of exposure and widespread environmental contamination with a variety of C. difficile strains. Given that urban rats are the source of a number of other pathogens responsible for human morbidity and mortality, the potential for rats to be a source of C. difficile for humans deserves further consideration.     

Genotyping of Toxoplasma gondii from Rats (Rattus rattus) in Riyadh,Saudi Arabia

Toxoplasma 3 main clonal lineages are designated as type I, II, and III; however, atypical and mixed genotypes were also reported. This study was conducted for detection of Toxoplasma gondii genotypes in rats (Rattus rattus) in Riyadh region, Saudi Arabia. PCR test on T. gondii B1 gene was conducted on ELISA IgM positive samples for confirmation of the infection. However, genetic analysis of the SAG2 locus was performed to determine T. gondii genotypes using PCR-RFLP technique. PCR test on T. gondii B1gene showed that 22 (81.5%) out of the 27 ELISA IgM positive samples have T. gondii DNA. Genotypic analysis shows that, of the total 22 PCR positive samples, only 13 (59.1%) were of type II, 7 (31.8%) were of type III, and 2 (9.1%) were of an unknown genotype. It is obvious that the prevalence of both type II and III is high in rats. No reports have been available on T. gondii genotypes among rats in Riyadh region, and only little is known about its seroprevalence in rats. Future studies on T. gondii genotypes in rats using multi-locus markers is needed in Riyadh region, Saudi Arabia for better understanding of T. gondii pathogenesis and treatment in humans and animals.     

Crystalloid formation in Leydig cells of rats (Rattus fuscipes)

Summary The ultrastructure of Leydig cells in a seasonally breeding rodent, Rattus fuscipes, was studied in the breeding and non-breeding season and compared with Leydig cell morphology after suppression of gonadotrophin secretion induced by hypophysectomy or chronic administration of testosterone. Serum luteinizing hormone (LH) and testosterone (T) were measured and in-vitro T production by testes was assessed by stimulation with human chorionic gonadotrophin (hCG). In non-breeding wild-trapped rats and rats with experimental suppression of gonadotrophins, the Leydig cells were atrophied and exhibited variable amounts of cytoplasmic lipid and crystalloid inclusions, the latter commonly dominating the cytoplasmic area. Compared with fertile rats, serum LH and hCG-stimulated T production of experimentally regressed rats was significantly reduced, confirming structural features indicative of Leydig cell inactivity. Atrophy of Leydig cell nuclei was accompanied by the formation of unusual intranuclear vesicles sometimes containing small crystalloids. Ultrastructural analysis suggested transfer of the vesicles to the cytoplasm where their unification gave rise to much larger crystalloid bodies. Crystalloids occurred when serum LH was depressed and with either full (T treatment) or arrested spermatogenesis (hypophysectomy) suggesting that their formation is governed by pituitary function and is not dependent upon the degree of spermatogenic activity.