Effects of photoperiod, temperature, and host plant age on induction of reproductive diapause and development time in Danaus plexippus

Abstract 1. Diapause induction in monarch butterflies Danaus plexippus was studied using adults captured from the wild in Minnesota and Wisconsin, and individuals reared under outdoor and controlled conditions.
2. Oocyte presence in females and ejaculatory duct mass in males were used to indicate reproductive status.
3. Some wild individuals were in diapause in mid-August, and all males and females were in diapause by late August and early September respectively.
4. Individuals reared under decreasing day lengths and fluctuating temperatures were more likely to be in diapause than were individuals reared under long or short day lengths or constant temperatures.
5. Individuals fed potted old Asclepias curassavica plants were more likely to be in diapause than were those fed potted young host plants; when cuttings of Asclepias syriaca plants from the field or greenhouse pots were used, there was no effect of host plant age.
6. Extremely high temperatures increased the number of day-degrees required for development from egg to adult, while decreasing day lengths and older host plants tended to decrease the number of day-degrees required for development.
7. There appears to be a continuum of reproductive development in monarchs, with gradual declines in mean ejaculatory duct mass and oocyte production during the late summer.
8. None of the experimental treatments led to 100% diapause, and diapause was more likely to occur in monarchs subjected to more than one diapause-inducing cue.     

Multiple conformations of deoxyribonuclease A. Their separation at alkaline pH and low ionic strength in the presence of Ca2+.

Gel filtration on Sephadex G-100 at pH 9.0 in 1 mM Tris buffer produces denaturation and inactivation of pancreatic DNAase A. Limiting concentrations of Ca2+ in the suspension and elution buffer, reactivates some of the enzyme molecules in an amount proportional to the calcium added. Stable active and inactive forms were separated on Sephadex columns. A model for the conformational role of Ca2+ on DNAase A demonstrates that at least one Ca2+ is involved (Kapp = 8.3 . 10(-5) M) in the correct folding of the polypeptide chain. Na+ was unable to reactivate the enzyme.     

Cotranslation of activated mutant p53 with wild type drives the wild-type p53 protein into the mutant conformation

Activating mutations of p53 promote tumor progression. The mutant protein adopts a characteristic conformation, which lacks the growth suppressor function of wild-type p53. We show that mutant p53 can drive cotranslated wild-type p53 into the mutant conformation: a similar effect in vivo would block wild-type suppressor function with dominant negative effect. The cotranslational effect of mutant p53 on wild-type conformation depends upon interaction between nascent polypeptides and oligomerization of the full-length proteins. We also show that oligomers of p53 proteins can be induced to change conformation in a cooperative manner. Cell growth stimulation induces a similar conformational change in p53, and our present results indicate that this may involve allosteric regulation.     

Influences on koala habitat selection across four local government areas on the far north coast of NSW

Conserving habitats crucial for threatened koala (Phascolarctos cinereus) populations requires rating habitat quality from a fine spatial scale to patches, landscapes and then regions. The koala has a specialized diet focused on the leaves of a suite of Eucalyptus species. We asked: what are the key regional influences on habitat selection by koalas in the far north coast of New South Wales? We addressed this question by investigating the multi-scale factors, and within-scale and cross-scale interactions, that influence koala habitat selection and distribution across four local government areas on the far north coast of New South Wales. We assembled and analysed a large data set of tree selection, identified by the presence of scats, in a wide range of randomly selected 5 × 5 km grids across the region. This resulted in more than 9000 trees surveyed for evidence of koala use from 302 field sites, together with associated biophysical site features. The dominant factor influencing habitat use and koala occurrence was the distribution of five Eucalyptus species. Koalas were more likely to use medium-sized trees of these species where they occurred on soils with high levels of Colwell phosphorous. We also identified new interactions among the distribution of preferred tree species and soil phosphorous, and their distribution with the amount of suitable habitat in the surrounding landscape. Our study confirmed that non-preferred species of eucalypts and non-eucalypts are extensively used by koalas and form important components of koala habitat. This finding lends support to restoring a mosaic of koala-preferred tree species and other species recognized for their value as shelter. Our study has provided the ecological foundation for developing a novel regional-scale approach to the conservation of koalas, with adaptability to other wildlife species.     

Haemodynamic responses to nonhypotensive central hypovolaemia induced by lower body negative pressure in men and women.

Haemodynamic responses to low levels of lower body negative pressure (LBNP) were investigated in two groups of healthy, normotensive volunteers (8 men and 8 women) during two repeated experimental runs on two occasions, the latter determined by the different phases of the menstrual cycle in the women. The data consisted of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean blood pressure (MBP), pulse rate (fc), forearm blood flow (FBF) and forearm vascular conductance (FC). The resting cardiovascular status was similar in men and women, except that women had a significantly higher fc than men. LBNP (1.3, 2.7 and 4 kPa) had no significant effect on any BP variable or on fc. However, FBF and FC were reduced at all levels of LBNP. Significant overshoots in FBF and FC were seen in all subjects following the release of LBNP of 2.7 and 4 kPa and, in most cases, after release of LBNP of 1.3 kPa. There were no significant gender differences in any of the responses to LBNP. Furthermore, none of the cardiovascular variables measured showed significant differences between the follicular and luteal phases of the menstrual cycle in women, either at rest or during exposure to LBNP, and the responses in the men on the two occasions were not different. These findings indicate that gender differences in responses to LBNP hypothesized previously are not apparent during and after exposure to low levels of LBNP.     

Knowledge-based models for predicting species occurrence in arable conditions

This paper explores the potential of rule-based habitat models to predict the occurrence of some common species in arable conditions. Models were developed for 10 arable plant species, 7 Hemiptera species, 8 carabid species and for 5 bird species whose ecology was sufficiently known. Rule sets linking species occurrence to environmental variables were produced using available literature and expert knowledge about ecological requirements of the selected species. Environmental variables described the nature and condition of habitats at various scales, ranging from vegetation quadrat to the landscape in a 1 km radius of species sampling sites. The performance of the 34 models developed was assessed in two areas of England. Results show the rule-based habitat models developed for arable plants and birds were not very successful with Cohen's k values often <0.4 for plants and very close to 0 for all bird species. Conversely, rule-based models performed surprisingly well for carabids and Hemiptera with k values on average >0.4. This suggests that ecological knowledge on these invertebrate species is more complete than we expected. The effect of species prevalence on model performance and the potential application of knowledge-based habitat models in the context of biodiversity assessment are discussed.     

Evaluation of comparative protein modeling by MODELLER

We evaluate 3D models of human nucleoside diphosphate kinase, mouse cellular retinoic acid binding protein I, and human eosinophil neurotoxin that were calculated by MODELLER , a program for comparative protein modeling by satisfaction of spatial restraints. The models have good stereochemistry and are at least as similar to the crystallographic structures as the closest template structures. The largest errors occur in the regions that were not aligned correctly or where the template structures are not similar to the correct structure. These regions correspond predominantly to exposed loops, insertions of any length, and non-conserved side chains. When a template structure with more than 40% sequence identity to the target protein is available, the model is likely to have about 90% of the mainchain atoms modeled with an rms deviation from the X-ray structure of ≈ 1 Å, in large part because the templates are likely to be that similar to the X-ray structure of the target. This rms deviation is comparable to the overall differences between refined NMR and X-ray crystallography structures of the same protein. © 1995 Wiley-Liss, Inc.