Searching for a new home--scouting behavior of honeybee swarms

Honeybee scouting, where individual bees search the environmentwithout prior information about the possible location of foodsources or nest sites, is notoriously difficult to study. Yet,understanding scouting behavior is important as it providesinsights into how social insects trade-off exploitation withexploration. The use of simulation models is an ideal way toinvestigate the possible mechanisms behind the regulation ofscouting at the group level as well as the ways in which theswarm searches its environment. We used an individual-basedsimulation model to study the scouting behavior of honeybeeswarms. In our model, we implemented a simple decision rulethat regulates the number of scouts: individual bees first attemptto find a dance to follow but become scouts if they fail todo so. We show that this rule neatly allows the swarm to adjustthe number of scouts depending on the quality of the nest sitesknown to the swarm. We further explored different search strategiesthat allow the swarm to select good-quality nest sites independentof their distance from the swarm. Assuming that it is costlyto move to a site that is far away, the best search strategywould be to give precedence to nearby sites while still allowingthe discovery of better sites at distances farther away.     

Respiration in bumblebee queens: effect of life phase on the discontinuous ventilation cycle

Evidence for discontinuous ventilation cycles (DVC) has been obtained for many insects under various experimental conditions. Here, we show that DVC's exist for queens of the bumblebee Bombus terrestris in different phases of their life cycle: before entering diapause (pre-diapause queens) and when a colony has been established (post-diapause queens). Pre- and post-diapause queens experience distinct environmental conditions (ambient O₂ and CO₂ concentrations) which is reflected in their DVC: both ventilation frequency and amount of carbon dioxide emitted change with differences in ambient CO₂ concentration.     

A concise preparation of the fluorescent amino acid l-(7-hydroxycoumarin-4-yl) ethylglycine and extension of its utility in solid phase peptide synthesis

Incorporation of the unnatural amino acid l-(7-hydroxycoumarin-4-yl)ethylglycine (7-HC) is a powerful and reliable approach for the preparation of fluorescently labeled proteins. The growing popularity of this valuable amino acid prompted us to pursue an improved protocol for its synthetic preparation. The optimized procedure here described provides ready access to multi-gram quantities of 7-HC. Also reported is an extension of the utility of 7-HC in the generation of a protected building block suitable for use in solid phase peptide synthesis. The building block was successfully incorporated at various positions in a series of model peptides, including analogues of the cell penetrating HIV-Tat peptide, further illustrating the utility of this unique amino acid.     

Levels of 25-hydroxyvitamin D in familial longevity: the Leiden Longevity Study

Background:

Low levels of 25(OH) vitamin D are associated with various age-related diseases and mortality, but causality has not been determined. We investigated vitamin D levels in the offspring of nonagenarians who had at least one nonagenarian sibling; these offspring have a lower prevalence of age-related diseases and a higher propensity to reach old age compared with their partners.

Methods:

We assessed anthropometric characteristics, 25(OH) vitamin D levels, parathyroid hormone levels, dietary vitamin D intake and single nucleotide polymorphisms (SNPs) associated with vitamin D levels. We included offspring (n = 1038) of nonagenarians who had at least one nonagenarian sibling, and the offsprings’ partners (n = 461; controls) from the Leiden Longevity Study. We included age, sex, body mass index, month during which blood sampling was performed, dietary and supplemental vitamin D intake, and creatinine levels as possible confounding factors.

Results:

The offspring had significantly lower levels of vitamin D (64.3 nmol/L) compared with controls (68.4 nmol/L; p = 0.002), independent of possible confounding factors. There was no difference in the levels of parathyroid hormone between groups. Compared with controls, the offspring had a lower frequency of a genetic variant in the CYP2R1 gene (rs2060793) (p = 0.04). The difference in vitamin D levels between offspring and controls persisted over the 2 most prevalent genotypes of this SNP.

Interpretation:

Compared with controls, the offspring of nonagenarians who had at least one nonagenarian sibling had a reduced frequency of a common variant in the CYP2R1 gene, which predisposes people to high vitamin D levels; they also had lower levels of vitamin D that persisted over the 2 most prevalent genotypes. These results cast doubt on the causal nature of previously reported associations between low levels of vitamin D and age-related diseases and mortality.Vitamin D plays a critical role in bone formation,¹ immune cell differentiation, and in the inhibition of proliferation and angiogenesis in cancer.² Low serum levels of 25-hydroxyvitamin D3 (25[OH] vitamin D) are associated with increased mortality, cardiovascular disease, diabetes mellitus, cancer, multiple sclerosis, allergy, asthma, infection, depression, mental illness and musculoskeletal pain.^3–6 However, because of design limitations, previous studies have not been able to infer causality.⁷ A meta-analysis that included 51 studies and more than 30 000 individuals in each treatment group showed no reduction in all-cause or cardiovascular mortality with vitamin D supplementation,⁸ suggesting that low serum levels of vitamin D are a consequence rather than a cause of disease.Vitamin D status is routinely assessed by measurement of serum concentration of the prohormone 25(OH) vitamin D, which is the most stable and abundant metabolite of vitamin D in circulation. In the current study, we investigated the association between serum levels of 25(OH) vitamin D and familial longevity. We assessed vitamin D levels in the offspring of nonagenarian siblings whom we have previously shown to have a lower prevalence of cardiovascular diseases and lower mortality compared to age- and environmental-matched controls.^9,10 We also assessed whether genetic variation in 3 genes¹¹ was associated with 25(OH) vitamin D levels among the offspring of nonagenarians who had at least 1 nonagenarian sibling, and their partners.     

Genomics of human longevity

In animal models, single-gene mutations in genes involved in insulin/IGF and target of rapamycin signalling pathways extend lifespan to a considerable extent. The genetic, genomic and epigenetic influences on human longevity are expected to be much more complex. Strikingly however, beneficial metabolic and cellular features of long-lived families resemble those in animals for whom the lifespan is extended by applying genetic manipulation and, especially, dietary restriction. Candidate gene studies in humans support the notion that human orthologues from longevity genes identified in lower species do contribute to longevity but that the influence of the genetic variants involved is small. Here we discuss how an integration of novel study designs, labour-intensive biobanking, deep phenotyping and genomic research may provide insights into the mechanisms that drive human longevity and healthy ageing, beyond the associations usually provided by molecular and genetic epidemiology. Although prospective studies of humans from the cradle to the grave have never been performed, it is feasible to extract life histories from different cohorts jointly covering the molecular changes that occur with age from early development all the way up to the age at death. By the integration of research in different study cohorts, and with research in animal models, biological research into human longevity is thus making considerable progress.     

Irrational decision-making in an amoeboid organism: transitivity and context-dependent preferences

Most models of animal foraging and consumer choice assume that individuals make choices based on the absolute value of items and are therefore ‘economically rational’. However, frequent violations of rationality by animals, including humans, suggest that animals use comparative valuation rules. Are comparative valuation strategies a consequence of the way brains process information, or are they an intrinsic feature of biological decision-making? Here, we examine the principles of rationality in an organism with radically different information-processing mechanisms: the brainless, unicellular, slime mould Physarum polycephalum. We offered P. polycephalum amoebas a choice between food options that varied in food quality and light exposure (P. polycephalum is photophobic). The use of an absolute valuation rule will lead to two properties: transitivity and independence of irrelevant alternatives (IIA). Transitivity is satisfied if preferences have a consistent, linear ordering, while IIA states that a decision maker''s preference for an item should not change if the choice set is expanded. A violation of either of these principles suggests the use of comparative rather than absolute valuation rules. Physarum polycephalum satisfied transitivity by having linear preference rankings. However, P. polycephalum''s preference for a focal alternative increased when a third, inferior quality option was added to the choice set, thus violating IIA and suggesting the use of a comparative valuation process. The discovery of comparative valuation rules in a unicellular organism suggests that comparative valuation rules are ubiquitous, if not universal, among biological decision makers.     

The role of female dominance hierarchies in the mating behaviour of mosquitofish

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.