Unnatural Contexts Cause Honey Bee Guards to Adopt Non‐Guarding Behaviours Towards Allospecifics and Conspecifics

Context plays an important role in a discriminator's ability to make appropriate recognition decisions, such as accepting what is acceptable and rejecting what is not acceptable. Previously it was shown that in both honey bees and stingless bees, discriminating workers (guards) make more errors towards conspecific non‐nestmates when the guards are removed from the natural hive entrance. However, it may be that guards, in addition to making incorrect recognition decisions, also may adopt non‐guarding behaviours. Here, we tested honey bee guards in two contexts (natural versus unnatural) against five types of introduced arthropods (conspecific nestmates and non‐nestmates; allospecific wasps, beetles and woodlice), which should be rejected without error. We scored a guard's response as accept, reject, avoid and ignore. Total errors significantly increased from natural to unnatural contexts. Specifically, guards were significantly more likely to make an acceptance error, guarding and accepting both conspecific and allospecific non‐nestmates, in the unnatural context. Importantly, guards were significantly more likely to adopt a non‐guarding behaviour in the unnatural context, which usually involved ignoring or avoiding, where a guard makes contact but then immediately retreats, the introduced arthropod. Overall, these data demonstrate the context is important. Removing a guard from the home that it protects elicits either incorrect discrimination or, additionally, a complete lack of discriminator behaviour altogether.     

Nest‐Site Defense by Competing Honey Bee Swarms During House‐Hunting

Cavity‐nesting animals must often defend their homes against intruders, especially when the availability of suitable cavities is limited. Competition for nest sites is particularly strong when multiple groups of the same species migrate synchronously to found a new home. This may be the case for honey bees during the reproductive season, because neighboring colonies often cast swarms simultaneously, leading to potential competition for high‐quality nesting cavities. To test the idea that honey bee swarms may compete for and defend potential nest sites as they search for a new home, we observed pairs of artificial swarms that were house‐hunting concurrently. Workers from one swarm in each pair carried a gene influencing body color, so that the bees from the two swarms were easily distinguished. We set up a high‐quality nest box and waited for nest‐site scouts from each swarm to explore and recruit swarm mates to it. We recorded all the interactions between competing scouts at the nest box and found that when scouts from both swarms explored the box simultaneously they behaved agonistically toward bees from the other swarm. The level of aggression depended on the number of scouts from each swarm present at the nest box. When only one to three scouts from each swarm were at the box, they rarely fought. But when the scouts from one swarm outnumbered those from the other swarm (4–20 vs. one to three bees), those in the majority advertised their presence with a buzzing behavior at the entrance opening, and started mobbing and killing those in the minority. When one swarm gained clear control of the nest box (20+ vs. zero to one bees), some of its scouts guarded the box’s entrance, preventing entry by foreign scouts. Our study exemplifies how cavity‐nesting animals may compete for and defend suitable nesting sites.     

The Role of the Vibration Signal during Nest‐Site Selection by Honey Bee Swarms

The vibration signal may influence nest‐site selection by honey bee swarms by enhancing scouting and recruitment. We investigated this hypothesis by comparing (1) the number of nest sites and the distances communicated by nest‐site dancers on swarms from which vibrators were and were not removed and (2) the behavior of scouts visiting higher‐quality (HQ) and lower‐quality (LQ) nest boxes. The removal of vibrators from swarms did not alter the number of nest sites investigated, the distances traveled to nest sites, or the time required to select a new nest cavity. In contrast, vibrator removal tripled the time required for swarms to achieve liftoff after a cavity had been selected, although all swarm eventually became airborne and moved to a new site. About 14% of the scouts that visited the HQ and LQ nest boxes performed vibration signals; however, nest‐box quality did not influence the tendency to produce the signal or intermix vibration signals and recruitment dances. However, we did find a significant, positive correlation between overall levels of vibration signal activity and nest‐site recruitment during the house‐hunting process. When viewed in concert, our results suggest that the vibration signal contributes to the house‐hunting process by operating in a non‐specific manner that may enhance scouting and recruitment in general during nest‐site selection and facilitate rapid swarm liftoff after a new nest site has been chosen. The vibration signal is therefore a component in the cascade of communication signals that orchestrate house‐hunting and colony relocation decisions.     

Endopolyploidy Changes with Age-Related Polyethism in the Honey Bee,Apis mellifera

Honey bees (Apis mellifera) exhibit age polyethism, whereby female workers assume increasingly complex colony tasks as they age. While changes in DNA methylation accompany age polyethism, other DNA modifications accompanying age polyethism are less known. Changes in endopolyploidy (DNA amplification in the absence of cell division) with increased larval age are typical in many insect cells and are essential in adults for creating larger cells, more copies of essential loci, or greater storage capacity in secretory cells. However, changes in endopolyploidy with increased adult worker age and polyethism are unstudied. In this study, we examined endopolyploidy in honey bee workers ranging in age from newly emerged up to 55 days old. We found a nonsignificant increase in ploidy levels with age (P < 0.1) in the most highly endopolyploid secretory cells, the Malpighian tubules. All other cell types decreased ploidy levels with age. Endopolyploidy decreased the least amount (nonsignificant) in neural (brain) cells and the stinger (P < 0.1). There was a significant reduction of endopolyploidy with age in leg (P < 0.05) and thoracic (P < 0.001) muscles. Ploidy in thoracic muscle dropped from an average of 0.5 rounds of replication in newly emerged workers to essentially no rounds of replication (0.125) in the oldest workers. Ploidy reduction in flight muscle cells is likely due to the production of G1 (2C) nuclei by amitotic division in the multinucleate striated flight muscles that are essential to foragers, the oldest workers. We suggest that ploidy is constrained by the shape, size and makeup of the multinucleate striated muscle cells. Furthermore, the presence of multiple 2C nuclei might be optimal for cell function, while higher ploidy levels might be a dead-end strategy of some aging adult tissues, likely used to increase cell size and storage capacity in secretory cells.     

Non‐Visual Mate Choice Ability in a Cavefish (Poecilia mexicana) is not Mechanosensory

One of the most important decisions any female has to make is selecting a mate. In many animals, this involves a strong visual component, but in cave‐dwelling fishes, mate preferences have to be exercised in darkness. In a cave‐dwelling Poeciliid fish, the cave molly (Poecilia mexicana), visual mate choice is still possible because they have functional, albeit reduced eyes. In a previous laboratory study, it was documented that females prefer larger males in light and in darkness. In the present study, we investigated the role of the mechanosensory lateral line in this mate preference. We temporarily knocked out the lateral line using antibiotics. We found that even in the functional absence of the lateral line, females showed a clear preference for larger males, indicating that the lateral line is not crucial for mate choice. This points toward a strong role of chemical communication in cave molly mate choice.     

Mitosis is not the only distributor of mutated cells: Non‐mitotic endopolyploid cells produce reproductive genome‐reduced cells

Giant endopolyploid nuclei (>16n) can spontaneously fragment by endomitosis (nuclear internal division) into near‐diploid cells with reproductive capacity (depolyploidization), and endotetra/octopolyploidy can undergo chromosome‐visible meiotic‐like genome reductional divisions also to replicative subcells. These unconventional divisions are associated with production of aneuploidy, which led to the question in this study of whether endopolyploidy, in general, can contribute genetic variability to tumorigenic potential. For this purpose, non‐proliferative endopolyploid cells (range: 4n–32n) in near‐senescence of normal diploid cell strains were analysed for nuclear–morphogenic changes associated with the presence of diploid‐sized nuclei in the cytoplasm. A one‐by‐one nuclear‐cutoff process gave rise to reproducing genome‐reduced cells. It was concluded that these unconventional cell divisions are, indeed, suspects of originating genetic variability. Details of these irregular mitoses were compared to ‘mitotic–meiosis’ in primitive organisms, which suggested activation of an ancestral trait in the mammalian cells.     

Production of the Catechol Type Siderophore Bacillibactin by the Honey Bee Pathogen Paenibacillus larvae

The Gram-positive bacterium Paenibacillus larvae is the etiological agent of American Foulbrood. This bacterial infection of honey bee brood is a notifiable epizootic posing a serious threat to global honey bee health because not only individual larvae but also entire colonies succumb to the disease. In the recent past considerable progress has been made in elucidating molecular aspects of host pathogen interactions during pathogenesis of P. larvae infections. Especially the sequencing and annotation of the complete genome of P. larvae was a major step forward and revealed the existence of several giant gene clusters coding for non-ribosomal peptide synthetases which might act as putative virulence factors. We here present the detailed analysis of one of these clusters which we demonstrated to be responsible for the biosynthesis of bacillibactin, a P. larvae siderophore. We first established culture conditions allowing the growth of P. larvae under iron-limited conditions and triggering siderophore production by P. larvae. Using a gene disruption strategy we linked siderophore production to the expression of an uninterrupted bacillibactin gene cluster. In silico analysis predicted the structure of a trimeric trithreonyl lactone (DHB-Gly-Thr)₃ similar to the structure of bacillibactin produced by several Bacillus species. Mass spectrometric analysis unambiguously confirmed that the siderophore produced by P. larvae is identical to bacillibactin. Exposure bioassays demonstrated that P. larvae bacillibactin is not required for full virulence of P. larvae in laboratory exposure bioassays. This observation is consistent with results obtained for bacillibactin in other pathogenic bacteria.     

Non‐parametric habitat models with automatic interactions

Questions: Can a statistical model be designed to represent more directly the nature of organismal response to multiple interacting factors? Can multiplicative kernel smoothers be used for this purpose? What advantages does this approach have over more traditional habitat modelling methods? Methods: Non‐parametric multiplicative regression (NPMR) was developed from the premises that: the response variable has a minimum of zero and a physiologically‐determined maximum, species respond simultaneously to multiple ecological factors, the response to any one factor is conditioned by the values of other factors, and that if any of the factors is intolerable then the response is zero. Key features of NPMR are interactive effects of predictors, no need to specify an overall model form in advance, and built‐in controls on overfitting. The effectiveness of the method is demonstrated with simulated and real data sets. Results: Empirical and theoretical relationships of species response to multiple interacting predictors can be represented effectively by multiplicative kernel smoothers. NPMR allows us to abandon simplistic assumptions about overall model form, while embracing the ecological truism that habitat factors interact.     

Non‐acidic activation of pain‐related Acid‐Sensing Ion Channel 3 by lipids

Extracellular pH variations are seen as the principal endogenous signal that triggers activation of Acid‐Sensing Ion Channels (ASICs), which are basically considered as proton sensors, and are involved in various processes associated with tissue acidification. Here, we show that human painful inflammatory exudates, displaying non‐acidic pH, induce a slow constitutive activation of human ASIC3 channels. This effect is largely driven by lipids, and we identify lysophosphatidylcholine (LPC) and arachidonic acid (AA) as endogenous activators of ASIC3 in the absence of any extracellular acidification. The combination of LPC and AA evokes robust depolarizing current in DRG neurons at physiological pH 7.4, increases nociceptive C‐fiber firing, and induces pain behavior in rats, effects that are all prevented by ASIC3 blockers. Lipid‐induced pain is also significantly reduced in ASIC3 knockout mice. These findings open new perspectives on the roles of ASIC3 in the absence of tissue pH variation, as well as on the contribution of those channels to lipid‐mediated signaling.     

The Evolution of Multiple Mating Behavior by Honey Bee Queens (APIS MELLIFERA L.)

A model is presented showing that natural selection operating at the individual level can adequately explain the evolution of multiple mating behavior by honey bee queens. Group selection need not be invoked. The fitness of a given female genotype is a function of the number of sex alleles in the population, the number of matings by an individual female and the specific parameters that determine the relationship of brood viability to individual fitness. Even though the exact relationship is not known, it is almost certainly not linear. A nonlinear relationship between worker brood viability and fitness and a significant genetic load associated with the sex-determination system in honey bees are the essential components of this model.     

Nitrogen‐fixing tree abundance in higher‐latitude North America is not constrained by diversity

The rarity of nitrogen (N)‐fixing trees in frequently N‐limited higher‐latitude (here, > 35°) forests is a central biogeochemical paradox. One hypothesis for their rarity is that evolutionary constraints limit N‐fixing tree diversity, preventing N‐fixing species from filling available niches in higher‐latitude forests. Here, we test this hypothesis using data from the USA and Mexico. N‐fixing trees comprise only a slightly smaller fraction of taxa at higher vs. lower latitudes (8% vs. 11% of genera), despite 11‐fold lower abundance (1.2% vs. 12.7% of basal area). Furthermore, N‐fixing trees are abundant but belong to few species on tropical islands, suggesting that low absolute diversity does not limit their abundance. Rhizobial taxa dominate N‐fixing tree richness at lower latitudes, whereas actinorhizal species do at higher latitudes. Our results suggest that low diversity does not explain N‐fixing trees' rarity in higher‐latitude forests. Therefore, N limitation in higher‐latitude forests likely results from ecological constraints on N fixation.