The hyoid complex of Rattus rattus rufescens

The hyoid apparatus of the rat consists of an anteroposterior compressed and somewhat arched basihyal, the small anterior cornua and the more prominent posterior cornua. The ceratohyal is the only movably articulated element of the anterior cornu and is generally lost during the normal methods of preparing skeleton. The absence of stylohyal has resulted in modifications in the origins and insertions of Mm. stylohyoideus, styloglossus, and stylopharyngeus. The study of the hyoid region of rats, gerbils and squirrels supports the view that the muroid rodents have originated from the more generalized squirrel-like forms.     

Histochemical study on the nerve endings in the lung of Rattus rattus rufescens and Francolinus pondicerianus

Presence and the relation of the nerve endings with associated structures in the lund of Rattus rattus rufescens (Indian black rat) and Francolinus pondicerianus (grey partridge or safed teeter) has been studied by cholinesterase technique. Dot, plate, and Vater pacini Corpuscles like nerve endings in the lung of Rattus and dot, and bulb like nerve endings with axis cylinder covered with myelinated sheath in the lung of Francolinus were recorded. The nerve endings were AChE-positive.     

Male contraception properties of a new synthetic steroid derivative (danazol) in Rattus rattus rufescens

Chronic administration of Danazol (25 mg/kg body wt) caused lesions in the testes of Rattus rattus Rufescens. Depletion of spermatocytes, spermatids and spermatozoa was conspicuous. Impairment of Leydig cell function was correlated with reduced cell size and depressed accessory sex organ weights. Epididymal cell height was greatly reduced. The lumen was devoid of spermatozoa. Danazol administration inhibited the synthesis of RNA, protein, sialic acid in the testes and accessory sex organs. Total cholesterol of the testes was increased, whereas the acid phosphatase enzyme activity was reduced. Testosterone propionate did not enhance the growth of accessory sex organs in castrated rats receiving Danazol. In conclusion, Danazol inhibits the system of steroidogenesis and spermatogenesis in Rattus rattus, when treated chronically for a period of 40 days. These effects are reversible after 60 days of cessation of drug administration.     

Neurohistological and histochemical observations on the lung of Rattus rattus rufescens (Indian black rat).

The intrinsic innervation of the lungs (right and left) has been studied by the cholinesterase technique, considering the effect of various pH, incubation periods and temperatures. Cholinergic innervation dominated. The peribronchial ganglia, large, medium-sized and irregular-shaped, rounded and small, showed a positive cholinesterase reaction. Maximum ChE activity was noticed in the bronchi and their branches and on the periphery of the alveoli.     

Reproduction in common house rat, Rattus rattus rufescens (Gray), in semi arid region of Indian desert

R. r. rufescens litter throughout the year with two peaks. The prevalence of pregnancy was maximum during early summer and postmonsoon seasons. Day length and day temperature influenced the breeding pattern which was supplemented by the availability of stored foodgrains in the habitat.     

Neurohistological observations on the kidney of Rattus rattus rufescens (Indian black rat) as revealed by cholinesterase technique.

The intrinsic innervation of the kidney in Rattus rattus rufescens (Indian black rat) has been studied by cholinesterase technique, under various temperatures, incubation periods and different pH values. The percentage of myelinated nerves was rather high in the medulla region, whereas the non-myelinated nerves dominated in association with the uriniferous tubules and their branches, glomerulus and renal vein in the cortex region. Periarterial AChE-positive ganglia were recorded in the medulla region. The perivenous and periglomerulus plexuses were formed by the non-myelinated nerves and their branches.     

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.     

Frequency of chromosome polymorphism in Rattus rattus collected in Japan

This paper deals with a population survey of chromosome polymorphism of Rattus rattus collected in Japan and the results of their test crosses. All the animals had diploid 42 chromosomes, but three chromosome pairs, Nos. 1, 9 and 13, were polymorphic in respect to acro- and subtelocentric chromosomes. Frequency of No. 1 chromosome polymorphism in 453 rats collected in 19 localities showed 343 rats (75.5%) with acrocentric homomorphic pair (A/A), 90 (19.9%) with aerocentric and subtelocentric heteromorphic pair (A/S) and the remaining 20 (4.4%) with subtelocentric homomorphic pair (S/S). All animals collected in northern and northwestern Japan showed only the A/A pair, while those collected in southern and southeastern Japan showed A/A, A/S and S/S polymorphism. The latter group was also classified into 3 populations (east, southeast and south) by the different frequency of the subtelocentric chromosome. Progeny tests revealed that segregation of A/A, A/S and S/S types from F₁ hybrids between various chromosome combinations was not significantly different from the theoretical one. However, the number of animals with A/S pair was always slightly higher than the other two types, while those with S/S pair slightly fewer. Local differences of the chromosome polymorphism in Japan were considered due to the result of migration and selection of the rats with S/S chromosome type.Contribution No. 817 from the National Institute of Genetics, Japan. Supported in part by a grant-in-aid from the Ministry of Education of Japan (Scientific Expedition in 1968, and No. 8801 in 1969).     

Food preferences of an insular population of Rattus rattus

The food preferences of an insular population of Rattus rattus inhabiting colonies of the Short-tailed shearwater Puffinus tenuirostris are described from results obtained during analyses of stomach contents and droppings collected from Big Green Island, Furneaux Group, Tasmania. It was found that rats on the island maintained themselves by eating a predominantly vegetarian diet and results suggest that there was some selective feeding on monocotyledons rather than the dicotyledons present in the area. Green parts of plants were taken throughout the year and rats may select these as a water source during the summer months. Plants made up 77.2% of the 254 stomach contents analysed and of this 57.7% was green material. Insect remains were found in 24.8% of the 1400 droppings examined and made up 14.3% of the stomach contents. Few feathers of the shearwater Puffinus tenuirostris were found in the stomachs or droppings and preliminary behavioural experiments suggested that the rat does not actively predate the bird though it may remove unattended eggs and eat dead chicks.     

Litter stimulus factors in maternal retrieval (Rattus rattus)

Maternal retrieval by rats was compared for sedated and control pups at 2, 5, 10, and 15 days of age. The control animals were retrieved more quickly than the experimentals only on day 5. The results were interpreted as demonstrating that stimuli of the pups determining maternal care have varying effects with age.     

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.     

Invasion facilitates hybridization with introgression in the Rattus rattus species complex

Biological invasions result in novel species interactions, which can have significant evolutionary impacts on both native and invading taxa. One evolutionary concern with invasions is hybridization among lineages that were previously isolated, but make secondary contact in their invaded range(s). Black rats, consisting of several morphologically very similar but genetically distinct taxa that collectively have invaded six continents, are arguably the most successful mammalian invaders on the planet. We used mitochondrial cytochrome b sequences, two nuclear gene sequences (Atp5a1 and DHFR) and nine microsatellite loci to examine the distribution of three invasive black rat lineages (Rattus tanezumi, Rattus rattus I and R. rattus IV) in the United States and Asia and to determine the extent of hybridization among these taxa. Our analyses revealed two mitochondrial lineages that have spread to multiple continents, including a previously undiscovered population of R. tanezumi in the south‐eastern United States, whereas the third lineage (R. rattus IV) appears to be confined to Southeast Asia. Analyses of nuclear DNA (both sequences and microsatellites) suggested significant hybridization is occurring among R. tanezumi and R. rattus I in the United States and also suggest hybridization between R. tanezumi and R. rattus IV in Asia, although further sampling of the latter species pair in Asia is required. Furthermore, microsatellite analyses suggest unidirectional introgression from both R. rattus I and R. rattus IV into R. tanezumi. Within the United States, introgression appears to be occurring to such a pronounced extent that we were unable to detect any nuclear genetic signal for R. tanezumi, and a similar pattern was detected in Asia.     

Sugar preferences of "black rats", Rattus rattus L.

The choice of "black rats", Rattus rattus L ., for common sugars - sucrose, jaggery, glucose, fructose and lactose are described. In laboratory colonies, the sugars were preferred in the order glucose > sucrose > jaggery > fructose > lactose; but in another sequence - sucrose > jaggery > glucose > fructose > lactose, in the free living colonies. The discrepancy is accounted for by the characteristics of sugars which influence consummatory behaviour in the two situations.     

Chromosomal polymorphism in Rattus rattus (L.) collected in Kusudomari and Misima

Summary Chromosomes of Rattus rattus (L.), collected in Kusudomari (Nagasaki) and Misima (Sizuoka) were examined. The karyotype revealed a remarkable heteromorphism in chromosome no. 1. The homozygotic, i.e. standard type, was characterized by 13 pairs of telocentric and 7 pairs of metacentric chromosomes. Chromosome pair no. 1 was telocentric. X and Y chromosomes were also telocentrics. 18.4 per cent of rats from Kusudomari and 40 per cent from Misima showed heteromorphic pair in chromosome no. 1. One chromosome of the heteromorphic pair is conspicuous by the subtelocentric centromere. Total length of the telocentric chromosome of no. 1 is almost the same as of its subtelocentric partner. These facts indicate that the subtelocentric no. 1 chromosome might have arisen by a centromeric inversion of the telocentric chromosome. Individuals homozygous for the subtelocentric no. 1 chromosome could not be found in either population. The difference in the frequency of the dimorphics collected in Kusudomari and Misima was statistically significant. Possible causes of the difference are discussed.Dedicated to Professor H. Bauer on the occasion of his sixtieth birthday. — Contributions from the National Institute of Genetics, Misima, Japan, No. 533