Effects of photoperiod, melatonin, and the pineal gland on compensatory gonadal hypertrophy during postnatal development in the marsh rice rat (Oryzomys palustris)

The roles of photoperiod, melatonin, and the pineal gland in regulating the magnitude of compensatory gonadal hypertrophy (CGH) and other reproductive and non-reproductive organ growth during post-weaning development were examined in the marsh rice rat Oryzomys palustris. Juvenile rice rats of both sexes were left gonadally intact (control group) or unilaterally castrated (ULC) and housed on 12L:12D, 14L:10D, or 16L:8D. Within a photoperiod (14L:10D and 16L:8D, but not 12L:12D), growth of the remaining testis, but not the remaining ovary, as well as several additional organs in both sexes were significantly affected, suggesting that the compensatory hypertrophy of the testis is photoperiod-dependent. There was no effect of testis asymmetry on CGH as ULC of either testis in rice rats housed on 14L:10D resulted in a comparable increase of CGH. Melatonin implants in rice rats maintained on 16L:8D had little to no effect (CGH included) on most parameters examined. Both melatonin implants and pinealectomy (separate experiments) in rice rats transferred to 12L:12D prevented short photoperiod-induced effects on CGH, the growth of the reproductive organs and the Harderian glands. Evening melatonin injections had a significant inhibitory effect on the growth of the remaining testis (no CGH was observed) and all other parameters measured. Lastly, ULC did not alter the percentage of males which successfully mated compared to intact animals. Taken together, these data suggest that photoperiod, melatonin, and the pineal gland can affect and regulate reproductive (e.g., CGH in some cases) and non-reproductive growth during postnatal development in the marsh rice rat.     

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.     

Population ecology of the Rice rat (Oryzomys palustris) in a coastal marsh

Rice rats were studied for four years by grid trapping in a tidal marsh on the northern Gulf of Mexico. Preliminary trapping indicated that marshes are preferred over other coastal habitats. Population densities fluctuated from spring lows of about 2/ha to highs of about 25/ha in the autumn and early winter. Reproduction occurred throughout the year, the major season being late spring to late autumn. Recruitment of juveniles was at a maximum from May to September. Males were more abundant than females in population samples, and had a higher mean body weight. This was because weight classes of 40 g and below were slightly skewed in favour of females and weight classes above 40 g heavily favoured males. The survival rate was low, with less than 20% of animals marked remaining on the grids for more than three months. Maximum longevity was 24 months. Results are compared to those of previous studies done on an offshore island and in the Florida everglades.     

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.     

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. 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 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.     

Limited perceptual range and anemotaxis in marsh rice ratsOryzomys palustris

Dispersal among suitable habitat patches could be crucial to the regional persistence of wetland species. Dispersal success of animals will depend, in part, on the distance from which they can detect suitable habitat (ie, perceptual range). We investigated the perceptual range of marsh rice rats Oryzomys palustris Harlan, 1837 during the wet season in a region of central Florida characterized by small, isolated depression marshes. O. palustris had a limited perceptual range (<10 m) indicating that individuals moving through unfamiliar habitat have restricted information from which to make movement decisions. O. palustris displayed anemotaxis during our experiment; individuals generally moved either upwind or downwind but rarely crosswind. This anemotaxis might reflect use of wind by rice rats to maintain a straight course while searching for new habitat located beyond their perceptual range.     

Parental age and reproduction in the Marsh Tit Paras palustris

In the Marsh Tit Parus palustris , breeding performance improved with the age of both the male and the female parent—older birds produced larger clutches earlier in the season. The effect of male age, however, was mainly due to a positive association with the age of the female. When the effect of laying date was accounted for, there was no additional effect of female age on clutch-size. However, pairs with previous breeding experience laid larger clutches than newly formed pairs of the same age. There was some evidence that young females that laid late in the season were less likely to survive to breed again, leading to an age effect on reproductive performance. There was no evidence that individual birds laid earlier or produced larger clutches when they became older.     

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.     

Effects of photoperiod and social variables on reproduction and growth in the male musk shrew (Suncus murinus)

In Exp. 1, the time course for the photoperiodic response in juvenile male musk shrews was examined by exposing animals to short (10L:14D) or long (14L:10D or 18L:6D) daylengths for 10, 20, 40 or 56 days. When compared with the response of animals maintained in long days, those exposed to short days showed an inhibition of reproductive maturation by 40 days of treatment. In Exp. 2, the combined effects of photoperiod and social cues were investigated in juvenile males that were either housed in short days (with or without a female) or in long days (with or without a female) for 40 days. The short photoperiod was generally inhibitory to sexual maturation, while the presence of an adult female was generally stimulatory, i.e. animals living with a female in long days had the greatest level of sexual maturity, while those living alone in short days had the lowest level of maturity. Animals that received opposing signals, i.e. short days in the presence of a female, had an intermediate response which was equivalent to the response seen in males living alone in long days. These results suggest that the presence of a female can partly reverse inhibitory effects of short days. In Exp. 3, the effects of photoperiod and social cues on the reproductive physiology of the adult male (same design as in Exp. 2) were investigated. The results show that the adult male musk shrew is responsive to both photoperiodic and social cues, in a manner similar to that of juvenile animals.(ABSTRACT TRUNCATED AT 250 WORDS)