Periodontopathic micro-organisms in the rice rat (Oryzomys palustris)

The rice rat spontaneously develops periodontal disease, and this process can be accelerated if the animal is placed on a high sucrose diet. As the aetiological agent(s) is unknown, this study was undertaken to determine the micro-organisms associated with bone loss. Animals at weaning were placed on either a high sucrose diet or on regular rat chow and were sampled periodically for a variety of micro-organisms. Bacteroides spp., spirochetes, and Actinobacillus actinomycetemcomitans were not isolated from any animals, but fusiform-like organisms and Capnocytophaga spp. were isolated occasionally. An unidentified organism which had characteristics of both A. actinomycetemcomitans and Haemophilus aphrophilus was isolated from all animals at every sampling. Whether this organism is the primary aetiological agent of periodontal disease in the rice rat remains to be determined. Over the 12 week experimental period the animals on the high sucrose diet had significantly more exposed root surface than animals on regular rat chow.     

Effects of age and photoperiod on reproduction and the spleen in the marsh rice rat (Oryzomys palustris)

To examine the interactions between age and photoperiod on reproduction and spleen weights, we exposed adult male and female rice rats of various ages to photoperiods of 16:8-h light-dark photoperiods (16L:8D) or 12L:12D. After 10 wk, animals were killed and the following data were recorded: weights of testes, seminal vesicles, uterus, ovaries, body, and spleen and, in addition, vaginal patency. Young adult males displayed a greater degree of testicular and seminal vesicle regression in short photoperiods than did older males; the testes of most older males did not regress in response to short photoperiods. Spleen weight was unresponsive to short photoperiods in all males, but was affected by age. Females, however, exhibited reproductive organ regression and decreased vaginal patency in response to short photoperiods at all ages examined. Body weights were affected by photoperiod in young females, and, as in males, photoperiod had no effect on spleen weights. These data suggest that the reproductive response to photoperiod in adult male rice rats declines with age, whereas in adult females it does not.     

Biology of the rice rat (Oryzomys palustris natator) in a laboratory environment. IX. Preweaning growth of the skull.

The pattern of skull growth of the rice rat (Oryzomys palustris natator) over the pre-weaning period of development reveals a characteristic triphasic outline which stems, in part, from the interplay of the external environment and the genetic endowment. Within the triphasic spectrum the neural skull growth exhibits an accelerated rate of growth during the early phases which eventually reverses to a rapid deceleration in the final phase. In contrast, the facial skull growth shows increased growth rate following the decline of the neural group, eventually reaching a slow linear deceleration. Thus the neural components appear to be synchronised to the brain growth while the facial elements gain a new and greater impetus following the neural decline. The general growth of the skull throughout these changes, i.e. triphasic and neural/facial, continues to show a basic slow linear increase.     

Biology of the rice rat (Oryzomys palustris natator) in a laborabory environment. X. Postweaning growth of the skull.

A survey of skull development of the rice rat (Oryzomys palustris natator) covering a period of 21 days to 16 months involving equal numbers of males and females (108) was undertaken using various skull parameters. Sexual dimorphism in relation to body weight and length emerged before that of the skull which was only clearly marked by 2 months. A number of the skull parameters by virtue of their individual growth potential did not show sexual differences in size for a long time, whereas others were clearly marked. Once the differences between the sexes had been established they were maintained. One parameter - lenght of cranium - represents those parameters which show changes and it was found that the male rat continued to show a steady linear increase in length up to 16 months, whereas the female cranial length shows a deceleration with termination around 12 months. The skull differences are mirrored in the weight and length findings and it suggested that the earlier sexual maturity of the females is compensated by an earlier cessation of growth compared to the males which mature later and have a correspondingly later cessation.     

Biology of the rice rat (Oryzomys palustris natator) in a laboratory environment. VII. Pre-weaning growth of the body.

Body growth using weight and length parameters have been examined following the introduction of the rice rat to laboratory conditions and a history of breeding covering some 15 generations. The pattern of growth shows a characteristic enphasic form which appears to be determined by the interplay of the external environment and the genetic endowment. The external environmental factors include the waxing and waning of the lactational performance of the mother and the intake of solid food, resulting in the first phase being mainly controlled by the maternal environment, the second phase being mainly controlled by a lessening maternal environment + external (solid food) environment + some genetics, the third phase being influenced by external environment + genetic endowment.     

Skrjabinoclava kinsellai n. sp. (Nematoda: Acuarioidea) from the rice rat Oryzomys palustris in Florida

Skrjabinoclava kinsellai n. sp. from the stomach of Oryzomys palustris in Florida is most similar to S. thapari Teixeira de Freitas, 1953, but can be distinguished mainly by the structure of the terminal end of the left spicule which curves ventrally to form a shoe-like structure. Also the tail in both sexes ends in a nipple-like elevation not noted in the types of S. thapari.     

The spiny rat louse, Polyplax spinulosa, as a parasite of the rice rat, Oryzomys palustris, in North America

The spiny rat louse, Polyplax spinulosa, was collected, as adults and embryonated ova from the rice rat, Oryzomys palustris, a cricetid rodent, in Davidson Co., Tennessee. This sucking louse is typically parasitic on domestic rats, which are murid rodents. Because most sucking lice are normally host specific, such cross-familial host infestation is noteworthy.     

Physiological ecology of acetylene reduction (nitrogen fixation) in a Delaware salt marsh

The effects of several fixed nitrogen compounds on acetylene reduction activity (nitrogen fixation) of surface sediments from a Delaware salt marsh were studied. Ammonia addition caused little decrease in activity early in the summer but resulted in a considerable decrease (85–95%) in activity late in the summer and early in the fall. Nitrate caused a near complete suppression of activity at all times. Other compounds such as glutamate, urea, and yeast extract caused a slight increase in activity in tallSpartina sediments and caused more than a 2.5-fold increase in shortSpartina sediments. There was a lag period (1–2 days) before the commencement of in vitro acetylene reduction activity during the spring and early summer, but this lag period was not present in the late summer. The addition of chloramphenicol to samples from a shortSpartina zone caused decreases in activity similar to those obtained with ammonia, whereas chlorate amendments yielded results which, when compared on an electron basis, were comparable to those obtained with nitrate. These results indicated that the observed lag period may be the result of a physiological response to the in situ levels of ammonia and/or nitrate. It is suggested here that in situ nitrogenase activity may be controlled by two processes: (a) repression and derepression of nitrogenase synthesis mediated by the levels of ammonia, and (b) competition for reducing power (electrons) and energy (ATP) between the processes of nitrate reduction and nitrogen fixation.     

Ecology of eutrophic waterbodies in a coastal grazing marsh

The ecology of a mainly interconnected, complex system of smallwater-bodies on a coastal grazing marsh in the Greater Thames estuary,north-east of London, England, is described. Sixteen sites were sampled on aregular basis over a two-year period while 37 sites were sampled once in Mayto develop a site classification. Most sites were brackish and alkaline but,following re-wetting after drying out, the pH in some water-bodies decreasedsharply (minimum pH 2.7). All sites had high concentrations of phosphorusbut there were large differences; some, with good growths of submergedaquatic macrophytes, having lower phosphorus than other sites, which weredevoid of macrophytes. Internal loading with phosphorus was important.Nitrate levels were low. Waters were mostly turbid, Secchi depths sometimes falling as low as 2cm, while chlorophyll a was very high, indicating extreme hypertrophy.Diatoms and euglenoids were characteristic members of the phytoplankton;cyanobacterial blooms did not occur. The zooplankton was dominated bycopepods, while Cladocera were much less numerous, largely due to predationby shrimps in waterbodies without macrophytes. The classification of siteswas influenced primarily by water depth, some waterbodies drying out, whilephosphorus and turbidity were also important in differentiating sites. Animal guano is the likely cause of the hypertrophic state but livestockgrazing is an essential management tool for grazing marshes. The dredging ofwaterbodies (with removal of sediments from the site) and the instigation ofa flushing regime, requiring a new system of sluices, should reduce nutrientloading and assist the establishment of submerged macrophytes, providingrefuges for cladocerans from predation.     

Shrimps and eutrophication in the waterbodies of a coastal grazing marsh

The influence of shrimps on turbidity was examined in laboratory and field experiments. Palaemonetes varians in the laboratory stimulated populations of both rotifers and Anabaena, which was the main cause of increased turbidity. In field experiments, P. varians increased and Neomysis integer decreased turbidity. In feeding trials P. varians took cladocerans and culicids in preference to copepods. It is considered that shrimps are likely to be important predators of cladocerans in shallow, coastal waterbodies and result in phytoplankton blooms, with reduced water transparency. This revised version was published online in July 2006 with corrections to the Cover Date.     

The feeding ecology of mink (Mustela vison) in coastal habitat

The diet of a coast-living population of mink was investigated from the scats collected over a three-year period, and compared with information on the availability of principal prey species. Lagomorphs were the single most important prey, and predation upon them matched the abundance of rabbits as determined by monthly counts. Aquatic foraging was particularly important, with rockpool-inhabiting fish accounting for 29–1% occurrence of food items. Fish predation was more pronounced during winter months when lagomorph prey was less available. Crustacean prey, particularly the shore crab, Carcinus maenas , occurred frequently in the diet. Seabirds figured regularly in the diet; these were either taken as carrion from the strand-line or through predation on breeding colonies during the summer months.