The Rat Populations of NIMH: Density, Reproduction, and the Neocortex

Investigations of the effects of crowding on social behaviorhas long been a major focus of the research on rodent populationsconducted in the laboratory of John B. Calhoun, at the NationalInstitute of Mental Health. In these studies, rats living undercrowded conditions exhibited many behavioral abnormalities,including poor parental behavior, and excessive aggression.These behavior patterns are similar to those displayed by ratswith neocortex damage except that the latter were tested undercontrolled, uncrowded conditions. An experiment was designedto examine the concomitant effects of forebrain lesions andpopulation density upon a rat's capacity to cope with socialcomplexity. The behaviors of rats with less than 50 percentof the normal neocortex, resulting from prenatal chemical treatment,were compared at two population densities to similar groupsof normal rats. The micrencephalic rats were initially and generallyless capable parents and were more aggressive than normals.In both types of rats, females in populations of eight bisexualpairs reared proportionally fewer of their offspring to weaningage than females in populations of four pairs. The overall reproductivesuccess of normal rats at the higher population density wasas poor as that of the micrencephalic rats at the lower populationdensity. These results have been interpreted as showing thatrats are sensitive to differences in population density evenat relatively low absolute population sizes, and that increasedpopulation density interferes with the capacity of the neocortexto cope with environment complexity.     

The structure of the female reproductiiye system in the Agaonidae (Chalcidoidea,Hymenoptera)

An account is given of the gaster, ovipositor mechanism and reproductive system in female Agaonidae. The structure and possible functions are compared with that of other chalcid families and the phylogenetic relationships of the group are discussed.     

Arid Recovery – A comparison of reptile and small mammal populations inside and outside a large rabbit,cat and fox‐proof exclosure in arid South Australia

Australian arid zone mammal species within the Critical Weight Range (CWR) of 35 g–5.5 kg have suffered disproportionately in the global epidemic of contemporary faunal extinctions. CWR extinctions have been attributed largely to the effects of introduced or invasive mammals; however, the impact of these threatening processes on smaller mammals and reptiles is less clear. The change in small mammal and reptile assemblages after the removal of rabbits, cats and foxes was studied over a 6‐year period in a landscape‐scale exclosure in the Australian arid zone. Rodents, particularly Notomys alexis and Pseudomys bolami, increased to 15 times higher inside the feral‐proof Arid Recovery Reserve compared with outside sites, where rabbits, cats and foxes were still present. Predation by cats was thought to exert the greatest influence on rodent numbers owing to the maintenance of the disparity in rodent responses through dry years and the differences in dietary preferences between rabbits and P. bolami. The presence of introduced Mus domesticus or medium‐sized re‐introduced mammal species did not significantly affect resident small mammal or reptile abundance. Abundance of most dasyurids and small lizards did not change significantly after the removal of feral animals although reductions in gecko populations inside the reserve may be attributable to second order trophic interactions or subtle changes in vegetation structure and cover. This study suggests that populations of rodent species in northern South Australia below the CWR may also be significantly affected by introduced cats, foxes and/or rabbits and that a taxa specific model of Australian mammal decline may be more accurate than one based on body weight.     

Applying the light : nutrient hypothesis to stream periphyton

1. The light : nutrient hypothesis (LNH) states that algal nutrient content is determined by the balance of light and dissolved nutrients available to algae during growth. Light and phosphorus gradients in both laboratory and natural streams were used to examine the relevance of the LNH to stream periphyton. Controlled gradients of light (12–426 μmol photons m^?2 s^?1) and dissolved reactive phosphorus (DRP, 3–344 μg L^?1) were applied experimentally to large flow‐through laboratory streams, and natural variability in canopy cover and discharge from a wastewater treatment facility created gradients of light (0.4–35 mol photons m^?2 day^?1) and DRP (10–1766 μg L^?1) in a natural stream. 2. Periphyton phosphorus content was strongly influenced by the light and DRP gradients, ranging from 1.8 to 10.7 μg mg AFDM^?1 in the laboratory streams and from 2.3 to 36.9 μg mg AFDM^?1 in the natural stream. Phosphorus content decreased with increasing light and increased with increasing water column phosphorus. The simultaneous effects of light and phosphorus were consistent with the LNH that the balance between light and nutrients determines algal nutrient content. 3. In experiments in the laboratory streams, periphyton phosphorus increased hyperbolically with increasing DRP. Uptake then began levelling off around 50 μg L^?1. 4. The relationship between periphyton phosphorus and the light : phosphorus ratio was highly nonlinear in both the laboratory and natural streams, with phosphorus content declining sharply with initial increases in the light : phosphorus ratio, then leveling off at higher values of the ratio. 5. Although light and DRP both affected periphyton phosphorus content, the effects of DRP were much stronger than those of light in both the laboratory and natural streams. DRP explained substantially more of the overall variability in periphyton phosphorus than did light, and light effects were evident only at lower phosphorus concentrations (≤25 μg L^?1) in the laboratory streams. These results suggest that light has a significant negative effect on the food quality of grazers in streams only under a limited set of conditions.     

Immunochemical Identification Of α-Amylass In Developing, Mature And Germinated Triticale Seeds

Extracts from triticale (Triticale hexaploide Lart.) cultivar 6A190 kernels harvested at 10 days post anthesis (developing), 41 days post anthesis (mature) and after 7 days' germination, were analyzed for their α-amylase isoenzymic composition by electro-phoretic and immunochemical techniques. One antigenic α-amylase (I) was common to both developing and germinated seeds but was present in greater quantity during germination. A second antigenic cr-amylase (II) was found in germinated seeds only and was barely detectable, even in an inactive state, in developing seeds. A third antigenic α-amylase (III) was found only in developing seeds. In mature seeds the α-amylase (II) predominated. α-Amylase (I) was also present but to a lesser extent than that found in developing seeds. It was concluded that the abnormally high levels of a amylase found in triticale 6A190 in the mature, non-sprouted kernel arose due to a lack of dormancy in the grain, resulting in the de novo synthesis of α-amylase (II).