Spermicide by females: what should males do?

The female reproductive tract can be particularly aggressive towards ejaculates, often leading to the death of large numbers of sperm. It has been suggested that males can respond to these actions by investing more in sperm and donating larger ejaculates. Such counteractions may lead to arms races, which can have significant implications for the mating system. In a series of simple models we first show that arms races are not necessarily supported: in fact, sperm killing may even favour no change or reductions in sperm allocation. Second, we identify a simple mechanistic rule for sperm killing that determines whether an arms race or sperm reduction will be favoured. Which of these responses is favoured by selection depends on whether a certain number, or proportion, of sperm are killed. When a specific number is killed, larger investment in sperm is favoured and when a specific proportion is killed, no change or lower investment in sperm is favoured. Both of these mechanisms are biologically plausible.     

Dimensions of global population projections: what do we know about future population trends and structures?

The total size of the world population is likely to increase from its current 7 billion to 8–10 billion by 2050. This uncertainty is because of unknown future fertility and mortality trends in different parts of the world. But the young age structure of the population and the fact that in much of Africa and Western Asia, fertility is still very high makes an increase by at least one more billion almost certain. Virtually, all the increase will happen in the developing world. For the second half of the century, population stabilization and the onset of a decline are likely. In addition to the future size of the population, its distribution by age, sex, level of educational attainment and place of residence are of specific importance for studying future food security. The paper provides a detailed discussion of different relevant dimensions in population projections and an evaluation of the methods and assumptions used in current global population projections and in particular those produced by the United Nations and by IIASA.     

Primary aldosteronism: who should be screened?

Primary aldosteronism (PA) has a prevalence in the general hypertensive population from 5 to 10%, and is widely recognized as the most frequent form of secondary hypertension. The 2 main PA subtypes are aldosterone producing adenoma (APA) and bilateral adrenal hyperplasia (BAH) that account for 95% of all PA cases. The diagnosis of PA is a 3-step process that comprises screening, confirmatory testing, and subtype differentiation. The different categories of patients at an increased risk of PA who should thus undergo a screening test were described in the first Endocrine Society (ES) Practice Guidelines for diagnosis and treatment of PA published in 2008. These categories include patients with Joint National Committee Stage 2, Stage 3, or drug-resistant hypertension; hypertension, and spontaneous or diuretic-induced hypokalemia; hypertension with adrenal incidentaloma; hypertension and a family history of early-onset hypertension or cerebrovascular accident at a young age and all hypertensive first degree relatives of patients with PA. Recently, a growing number of studies have linked PA with the metabolic syndrome, diabetes, and obstructive sleep apnea that may be partly responsible for the higher rate of cardio and cerobrovascular accidents in PA patients. The aim of this review is to discuss, which patients should be screened for PA, focusing not only on the well-established categories of the ES Guidelines, but also on additional other group of patients with a potentially high prevalence of PA that has emerged from recent research.     

Prevention of avian influenza epidemic: what policy should we choose?

Human-to-human transmission of the avian influenza has been extremely rarely reported, and is considered as limited, inefficient and unsustained. However, experts warn an occurrence of “mutant avian influenza”, which can easily spread among humans, because the avian influenza is already endemic, in particular in Asian poultry, and it is evolving in domestic and wild birds, pigs and humans. Outbreak of such mutant avian influenza in the human world may have devastating consequences, which are comparable with these for the 1918 “Spanish influenza”. In this paper we develop a mathematical model for the spread of the mutant avian influenza, and explore the effectivity of the prevention policies, namely the elimination policy which increases the effective additional death rate of the infected birds and the quarantine policy which reduces the number of infective contacts.     

POPP the question: what do LEA proteins do?

Late embryogenesis abundant (LEA) proteins are produced in maturing seeds and anhydrobiotic plants, animals and microorganisms, in which their expression correlates with desiccation tolerance. However, their function has remained obscure for 20 years. We argue that novel computational tools devised for non-globular proteins might now overcome this problem. Predictions arising from bioinformatics fit well with recent data on Group 3 proteins, which potentially form cytoskeletal filaments, and suggest experimentally testable functions for these and other LEA protein groups.     

Cancer of the lung: what should be the present approach?

The best opportunities at present for improving the results in the treatment of patients with cancer of the lung are by way of (a) utilizing the information obtained on routine x-ray examination of the chest, (b) decreasing the delay between the time of the first symptoms and the time the patient consults a physician, and (c) decreasing the delay between the time the patient first consults a physician and the time the cancer is surgically removed. The medical profession must increase its index of suspicion of cancer of the lung and persist in efforts to make a diagnosis when lung cancer is suspected. Exploratory thoracotomy should be used in suspicious cases when the diagnosis cannot be established by other methods.     

Models of social evolution: can we do better to predict ‘who helps whom to achieve what’?

Models of social evolution and the evolution of helping have been classified in numerous ways. Two categorical differences have, however, escaped attention in the field. Models tend not to justify why they use a particular assumption structure about who helps whom: a large number of authors model peer-to-peer cooperation of essentially identical individuals, probably for reasons of mathematical convenience; others are inspired by particular cooperatively breeding species, and tend to assume unidirectional help where subordinates help a dominant breed more efficiently. Choices regarding what the help achieves (i.e. which life-history trait of the helped individual is improved) are similarly made without much comment: fecundity benefits are much more commonly modelled than survival enhancements, despite evidence that these may interact when the helped individual can perform life-history reallocations (load-lightening and related phenomena). We review our current theoretical understanding of effects revealed when explicitly asking ‘who helps whom to achieve what’, from models of mutual aid in partnerships to the very few models that explicitly contrast the strength of selection to help enhance another individual''s fecundity or survival. As a result of idiosyncratic modelling choices in contemporary literature, including the varying degree to which demographic consequences are made explicit, there is surprisingly little agreement on what types of help are predicted to evolve most easily. We outline promising future directions to fill this gap.     

So what do your sugars do?

Up to about fifteen years ago the above question was quite often asked of glycoconjugates enthusiasts. It was always a silly question, the answer being ‘How many doings do you want to hear about?’ Since then our understanding of the structures, biosynthesis and varied functions of the glycoconjugates has developed incredibly and come to have a major impact on much of present-day biological and medical research.     

Cardiovascular pressure-flow relationships: what should be taught?

Cardiovascular physiology reflects the interrelations of flow, pressure, and resistance. Undergraduate students are often confused by the complexity of the system. This symposium presents a sequential presentation of the underlying concepts, building on analogies, past experience, and conceptual models to allow students to develop a physiologically appropriate understanding of cardiovascular physiology.     

Genome data: what do we learn?

Genome sequence information has continued to accumulate at a spectacular pace during the past year. Details of the sequence and gene content of human chromosome 22 were published. The sequencing and annotation of the first two Arabidopsis thaliana chromosomes was completed. The sequence of chromosome 3 from Plasmodium falciparum, the second sequenced malaria chromosome, was reported, as was that of chromosome 1 from Leishmania major. The complete genomic sequences of five microbes were reported. Approaches to using data from completely sequenced microbial genomes in phylogenetic studies are being explored, as is the application of microarrays to whole genome expression analysis.     

Antioxidant activity: what do we measure?

Inhibition of oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) by free radicals generated by decomposition of 2,2'-azobis(2-amidopropane) (ABAP) by antioxidants and biological material was studied. A correlation was found between the ability of various substances to delay the onset of ABTS oxidation and their rapid reduction of the ABTS+* cation radical, and between the ability to reduce the maximal rate of ABTS oxidation and slow reduction of ABTS+*. The length of the lag period of ABTS oxidation was found to be independent of ABTS concentration. Similar decrease of peroxynitrite-induced ABTS+* formation by antioxidants was observed when the antioxidants were added before and after peroxynitrite. All these findings indicate that the main effect of antioxidants in this system is reduction of ABTS+* and not prevention of its formation. Reduction of oxidation products rather than inhibition of their formation may be the predominant mode of action of antioxidants in various assays of antioxidant activity.     

Aposematism: what should our starting point be?

The evolution of aposematism is considered to be a major evolutionary problem because if new aposematic forms emerged in defended cryptic populations, they would face the dual problems of rarity and conspicuousness. We argue that this commonly assumed starting point might not have wide validity. We describe a novel evolutionary computer model in which prey evolve secondary defences and become conspicuous by moving widely over a visually heterogeneous habitat. Unless crypsis imposes high opportunity costs (for instance, preventing prey from efficient foraging, thermoregulation and communication), costly secondary defences are not predicted to evolve at all. However, when crypsis imposes opportunity costs, prey evolve secondary defences that facilitate raised behavioural conspicuousness as prey exploit opportunities within their environment. Optimal levels of secondary defence and of behavioural conspicuousness increase with population sizes and the costs imposed by crypsis. When prey are already conspicuous by virtue of their behaviours, the evolution of aposematic appearances (bright coloration, etc.) is much easier to explain because aposematic traits add little further costs of conspicuousness, but can bring large benefits.     

Mechanisms of tolerance to herbivore damage:what do we know?

Identifying mechanisms of tolerance to herbivore damage will facilitate attempts to understand the role of tolerance in the evolutionary and ecological dynamics of plants and herbivores. Investigations of the physiological and morphological changes that occur in plants in response to herbivore damage have identified several potential mechanisms of tolerance. However, it is unlikely that all physiological changes that occur following damage are tolerance mechanisms. Few studies have made direct comparisons between the expression of tolerance and the relative expression of putative mechanisms. I briefly review empirical evidence for some of the better-studied potential mechanisms, including increased photosynthetic activity, compensatory growth, utilization of stored reserves, and phenological delays. For each of these mechanisms I discuss reasons why the relationship between tolerance and these characters may be more complicated than it first appears. I conclude by discussing several empirical approaches, including herbivore manipulations, quantitative trait loci (QTL) analysis, and selection experiments, that will further our understanding of tolerance mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.