Physiology, thermoregulation and bipedalism

It has long been recognized that the bipedal posture reduces the surface area of the body exposed to the sun. In recent years, a theory has been developed by Wheeler that bipedalism evolved in the ancestor of the Hominidae in order to help relieve thermal stress on the animals in open equatorial environments. Bipedalism was said to afford a distinct adaptive advantage over quadrupedalism by permitting hominids to remain active in the open throughout the day. The heat load of the hypothetical hominid comprises the external environment as modelled by Wheeler and the animal's internal environment (i.e., the internal heat generated by its metabolic and locomotor activities, and its evaporative and respirative cooling capacities). When these factors are integrated in the calculation of the animal's thermal budget, the putative advantage of the bipedal over the quadrupedal posture is considerably reduced. The simulations conducted in this study suggest that the increased time afforded to early hominids in the open by bipedalism was relatively short and, therefore, of little or no adaptive significance. These results suggest that thermoregulatory considerations cannot be implicated as a first cause in the evolution of bipedalism in the hominid ancestor.     

Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

Effect of nitrogen supply on frost resistance, nitrogen metabolism and carbohydrate content in white clover (Trifolium repens)

Effects of mineral nitrogen (2, 4, 6 and 8 m M NH₄NO₃) and nodulation with Rhizobium on frost hardiness in seedlings of white clover ( Trifolium repens ) have been studied. Seedlings of a population from Bodø (67°N lat.) were grown in Leonard jars under controlled conditions in a phytotron. For induction of frost hardening, plants were first exposed to 12 h photoperiod conditions for 2 weeks at 18°C, then for 2 weeks at 6°C and finally for 2 weeks at 0.5°C. Frost hardiness after treatments at 6 and 0.5°C was significantly enhanced by increasing nitrogen supply and was positively correlated with total nitrogen content of the stolons. Frost hardiness of nodulated plants correlated to the tissue nitrogen concentration. Content of soluble proteins in stolons decreased during hardening at 6°C but did not change during treatment at 0.5°C. There were minor changes in total amount of free amino acids during hardening. Both absolute and relative amounts of proline and arginine increased, and those of asparagine decreased during hardening. Absolute amounts of all free amino acids increased with increasing nitrogen supply, but the changes during hardening were similar in all treatments. There was a significant increase in the content of soluble carbohydrates during hardening. However, this increase was inversely related to nitrogen supply.     

The influence of encapsulation upon the ability of Klebsiella pneumoniae to survive whilst airborne and to cause lung disease in mice

Cultures of a strain of Klebsiella pneumoniae were prepared, both with intact capsules and with only a residual layer of exopolysaccharide remaining. No significant difference in the survival of the two sets of bacteria was observed in aerosols at 60% relative humidity. The decapsulated bacteria multiplied less rapidly in mouse lungs than did the intact bacteria for the first 24 h after animal exposure. However, no subsequent difference in multiplication rate was observed.     

Partial migration: niche shift versus sexual maturation in fishes

Summary Many fish populations have both resident and migratory individuals. Migrants usually grow larger and have higher reproductive potential but lower survival than resident conspecifics. The decision about migration versus residence probably depends on the individual growth rate, or a physiological process like metabolic rate which is correlated with growth rate. Fish usually mature as their somatic growth levels off, where energetic costs of maintenance approach energetic intake. After maturation, growth also stagnates because of resource allocation to reproduction. Instead of maturation, however, fish may move to an alternative feeding habitat and their fitness may thereby be increased. When doing so, maturity is usually delayed, either to the new asymptotic length, or sooner, if that gives higher expected fitness. Females often dominate among migrants and males among residents. The reason is probably that females maximize their fitness by growing larger, because their reproductive success generally increases exponentially with body size. Males, on the other hand, may maximize fitness by alternative life histories, e.g. fighting versus sneaking, as in many salmonid species where small residents are the sneakers and large migrants the fighters. Partial migration appears to be partly developmental, depending on environmental conditions, and partly genetic, inherited as a quantitative trait influenced by a number of genes.     

Estimating tree-based dynamic treatment regimes using observational data with restricted treatment sequences

A dynamic treatment regime (DTR) is a sequence of decision rules that provide guidance on how to treat individuals based on their static and time-varying status. Existing observational data are often used to generate hypotheses about effective DTRs. A common challenge with observational data, however, is the need for analysts to consider “restrictions” on the treatment sequences. Such restrictions may be necessary for settings where (1) one or more treatment sequences that were offered to individuals when the data were collected are no longer considered viable in practice, (2) specific treatment sequences are no longer available, or (3) the scientific focus of the analysis concerns a specific type of treatment sequences (eg, “stepped-up” treatments). To address this challenge, we propose a restricted tree–based reinforcement learning (RT-RL) method that searches for an interpretable DTR with the maximum expected outcome, given a (set of) user-specified restriction(s), which specifies treatment options (at each stage) that ought not to be considered as part of the estimated tree-based DTR. In simulations, we evaluate the performance of RT-RL versus the standard approach of ignoring the partial data for individuals not following the (set of) restriction(s). The method is illustrated using an observational data set to estimate a two-stage stepped-up DTR for guiding the level of care placement for adolescents with substance use disorder.     

Evaluation of Probiotic Properties of Novel Brazilian Lactiplantibacillus plantarum Strains

Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,...     

PATTERNS OF PLANT ONTOGENY THAT MAY INFLUENCE GENOMIC STASIS

It is an axiom in biology that genes control the ontogeny and ultimately the final form of an organism. In plants a given morphological form can often arise through more than one ontogenetic pattern of cell divisions. Different ontogenetic patterns have different properties with regard to the final age in cell divisions of the initials in the meristems for a given morphological form. If mutation per genome per cell division is an important biological metric, then since the age of a cell in cell divisions is a function of ontogeny, the cellular ontogeny will influence the degree of mutation-loading in meristematic initials. Thus, ontogeny and form may affect the genes (by promoting or lessening genomic stasis) as well as, of course, being determined by the genes. This paper explores mathematically the relationship between different patterns of cell division and mutation-loading.     

Effect of Carbon Source and the Role of Cyclic Adenosine 3′,5′-Monophosphate on the Caulobacter Cell Cycle

The expression of cell cycle events in Caulobacter crescentus CB13 has been shown to be associated with regulation of carbohydrate utilization. Growth on lactose and galactose depends on induction of specific enzymes. Prior growth on glucose results in a delay in enzyme expression and cell cycle arrest at the nonmotile, predivisional stage. Dibutyryl cyclic adenosine 3',5'-monophosphate (AMP) was shown to stimulate expression of the inducible enzymes and, thus, the initiation of the cell cycle. beta-Galactosidase-constitutive mutants did not exhibit a cell cycle arrest upon transfer of cultures from glucose to lactose. Furthermore, carbon source starvation results in accumulation of the cells at the predivisional stage. The cell cycle arrest therefore results from nutritional deprivation and is analogous to the general control system exhibited by yeast (Hartwell, Bacteriol. Rev. 38:164-198, 1974; Wolfner et al., J. Mol. Biol. 96:273-290, 1975), which coordinates cell cycle initiation with metabolic state. Transfer of C. crescentus CB13 from glucose to mannose did not result in a cell cycle arrest, and it was demonstrated that this carbon source is metabolized by constitutive enzymes. Growth on mannose, however, is stimulated by exogenous dibutyryl cyclic AMP without a concomitant increase in the specific activity of the mannose catabolic enzymes. The effect of cyclic AMP on growth on sugars metabolized by inducible enzymes, as well as on sugars metabolized by constitutive enzymes, may represent a regulatory system common to both types of sugar utilization, since they share features that differ from glucose utilization, namely, temperature-sensitive growth and low intracellular concentrations of cyclic guanosine 3',5'-monophosphate.