The effect of starvation and alloxan-diabetes on the contents of citrate and other metabolic intermediates in rat liver

1. The content of citrate in ;freeze-clamped' livers from starved and alloxan-diabetic rats was measured by using the specific citrate assay method of Gruber & Moellering (1966). 2. The content of citrate fell progressively during a period of 48hr. starvation to reach a plateau value that is 50% of the value for livers from fed rats. Some possible explanations for the conflicting reports of changes in hepatic citrate content during starvation are discussed. 3. The hepatic contents of ATP, pyruvate, lactate, glycogen and the hexose phosphates were decreased during starvation, whereas those of acetyl-CoA and AMP were increased. 4. Acute alloxan-diabetes produced similar changes in the contents of these metabolic intermediates. 5. The effects of starvation and diabetes on the citrate and acetyl-CoA contents are discussed in relation to control of gluconeogenesis, fatty acid synthesis and the activity of citrate synthase.     

Bialaphos selection of stable transformants from maize cell culture

Summary Stable transformed Black Mexican Sweet (BMS) maize callus was recovered from suspension culture cells bombarded with plasmid DNA that conferred resistance to the herbicide bialaphos. Suspension culture cells were bombarded with a mixture of two plasmids. One plasmid contained a selectable marker gene, bar, which encoded phosphinothricin acetyl transferase (PAT), and the other plasmid encoded a screenable marker for -glucuronidase (GUS). Bombarded cells were selected on medium containing the herbicide bialaphos, which is cleaved in plant cells to yield phosphinothricin (PPT), an inhibitor of glutamine synthetase. The bialaphos-resistant callus contained the bar gene and expressed PAT as assayed by PPT inactivation. Transformants that expressed high levels of PAT grew more rapidly on increasing concentrations of bialaphos than transformants expressing low levels of PAT. Fifty percent of the bialaphos-resistant transformants tested (8 of 16) expressed the nonselected gene encoding GUS.     

The effects of ambient temperature,nature and temperature of the floor and radiant heat on the metabolic rate of the new—born pig

Using a closed circuit technique, the oxygen consumption of 108 piglets below one week of age have been measured while modifying the physical attributes of the thermal environment. Moving the piglets onto a wooden floor from concrete reduced the oxygen consumption rate from 37.8 ml to 34.5 ml/kg. min) at 10°C, and from 33.7 to 31.4 ml/(kg. min) on a rubber floor at the same temperature. Oxygen consumption was also significantly reduced when the piglets were placed on a straw floor, were supplied with radiant heat and when the floor temperature was raised independently of chamber temperature. It is concluded that the provision of supplementary heating either in the floor or by overhead radiation can greatly reduce the effects of a cold environment on the new-born pig and so enhance the animal's viability.

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Zusammenfassung Der Sauerstoff-Umsatz von 108 Ferkeln, die jünger als eine Woche waren, wurde unter wechselnden Bedingungen der thermischen Umwelt gemessen. Das Verlegen der Ferkel von einem Zement- auf einen Holzboden führte zur Senkung des 0₂-Umsatzes von 37,8 auf 34,5 ml O₂/kg. min) und von 33,7 auf 31,4 ml O₂/(kg. min) bei 10°C auf einem Gummiboden. Auf einem strohbedecktem Boden war der O₂-Umsatz ebenfalls vermindert. Den gleichen Effekt hatte die Anwendung von Strahlungswärme oder die Erhöhung der Bodentemperatur. Danach kann zusätzliche Erwärmung vom Boden oder von der Decke die Kälteeinwirkung auf das Ferkel aus der Umgebung stark reduzieren und die Lebensfähigkeit der Tiere erhöhen.

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Resume Au moyen d'un appareil à circuit fermé, on a mesuré la consommation en oxygène le 108 porcelets âgés de moins d'une semaine soumis à divers régimes thermiques et cela dans une température ambiante constante. En transférant les porcelets d'un sol de béton à un plancher de bois, leur consommation d'oxygène a passé de 37,8 à 34,5 ml/(kg. min), et de 33,7 à 31,4 ml/(kg. min) en passant du béton à un sol recouvert de caoutchouc. La consommation d'oxygène a également été réduite de façon significative pour un sol recouvert de paille. Il en est allé de même pour des lampes à infra-rouge et si le sol était chauffé indépendamment du local. On en conclut qu'un chauffage supplémentaire soit dans le sol soit par rayonnement peut réduire sensiblement les effets néfastes d'une ambiance froide sur lesporcelets nouveau-nés et rehausser leurs chances de survie.

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Presented during the Fifth International Biometeorological Congress, 1–6 September 1969, Montreux, Switzerland.     

Fragment size affects plant herbivory via predator loss

Fragmentation and resultant changes in patch size are predicted to alter species diversity and community composition, yet the consequences of these differences for species interactions are poorly understood. Theory predicts that predators are more sensitive to fragmentation than their prey, resulting in greater predator loss in small patches. Predator loss, in turn, is predicted to 1) increase herbivory rates overall, and 2) cause herbivores to shift feeding from plants that act as refugia to those that are preferred forage. We tested these predictions in an old‐field community using two experiments. The first was a large‐scale experiment that included hundreds of arthropod species in fragments of various sizes, and used goldenrod and switchgrass to assess herbivory. Our second experiment manipulated densities of a focal predator species and a focal prey species to determine if changes in densities, rather than other characteristics of fragments, were sufficient to cause the trends observed in the first experiment. We found that predator densities declined in small fragments whereas herbivore densities showed the opposite trend. Total herbivory mirrored herbivore densities by increasing in small patches, and this mean increase was driven by large increases in goldenrod herbivory but declines in switchgrass herbivory. Experimental manipulation of densities confirmed that herbivores preferentially feed on goldenrod, and that predators depress herbivory on goldenrod but have a negligible effect on switchgrass. Our results suggest that fragmentation alters trophic interactions by causing declines in predator densities and increases in herbivore densities, but that feeding preferences of herbivores may generate unequal impacts among plant species.     

Predator personality structures prey communities and trophic cascades

Intraspecific variation is central to our understanding of evolution and population ecology, yet its consequences for community ecology are poorly understood. Animal personality – consistent individual differences in suites of behaviours – may be particularly important for trophic dynamics, where predator personality can determine activity rates and patterns of attack. We used mesocosms with aquatic food webs in which the top predator (dragonfly nymphs) varied in activity and subsequent attack rates on zooplankton, and tested the effects of predator personality. We found support for four hypotheses: (1) active predators disproportionately reduce the abundance of prey, (2) active predators select for predator‐resistant prey species, (3) active predators strengthen trophic cascades (increase phytoplankton abundance) and (4) active predators are more likely to cannibalise one another, weakening all other trends when at high densities. These results suggest that intraspecific variation in predator personality is an important determinant of prey abundance, community composition and trophic cascades.     

Plant sex alters Allee effects in aggregating plant parasites

Species interactions are central to our understanding of population dynamics. While density typically strengthens competition, reducing absolute fitness, Allee effects can reverse this pattern, increasing fitness with density. Allee effects emerge in host–parasite systems when higher parasite densities dilute immune responses or increase resource‐mobilization. The optimal density of individuals in these systems should be influenced by how host quality alters the rates at which facilitative and competitive effects change across densities. We tested these ideas using sumac Rhus typhina and a gall‐forming parasite Melaphis rhois that attacks sumac leaves. Fitness peaked at intermediate densities, indicating an Allee effect, but the fitness peak depended on host sex. Patterns of abundance mirrored fitness patterns, with galls clustered on leaves and female hosts supporting greater numbers of galls. Within leaves, galls near the stem were more fit, and gall‐makers preferentially oviposited near to the stem. The patterns of fitness and abundance are consistent with Allee effects caused by increased resource mobilization at higher gall‐maker densities rather than diluted immune responses. Our results suggest that Allee effects in parasites can be described as the summative effects of competitive and facilitative processes and, because both are common, Allee effects are likely common in host–parasite systems.     

Sensory reinforcement and illumination preference in sheep and calves

The preferences of sheep or calves for light or darkness have been examined by placing animals in light-proof chambers in which they could turn the lights on or off by interrupting an infrared beam switch with their muzzles. Sheep spent an average of 77% of each 24 h period in light while the calves spent an average of 67% of each 24 h in light. The experiments show that sheep and calves prefer light to darkness. The strength of their motivation for light was examined by means of an operant task in which they were rewarded with only 40 s of light for each interruption of the i.r. beam. Sheep then obtained an average of 1.5 h of light per 24 h and calves 1.0 per 24 h. Finally, the animals were subjected to a situation in which the light only remained on for as long as the i.r. beam was interrupted. In this experiment sheep obtained 4.8 min of light per 24 h and calves 3.2 min per 24 h. Quantitative operant methods can provide an objective means for measuring environmental preferences in farm animals.