Genetic diversity within honeybee colonies increases signal production by waggle-dancing foragers

Recent work has demonstrated considerable benefits of intracolonial genetic diversity for the productivity of honeybee colonies: single-patriline colonies have depressed foraging rates, smaller food stores and slower weight gain relative to multiple-patriline colonies. We explored whether differences in the use of foraging-related communication behaviour (waggle dances and shaking signals) underlie differences in foraging effort of genetically diverse and genetically uniform colonies. We created three pairs of colonies; each pair had one colony headed by a multiply mated queen (inseminated by 15 drones) and one colony headed by a singly mated queen. For each pair, we monitored the production of foraging-related signals over the course of 3 days. Foragers in genetically diverse colonies had substantially more information available to them about food resources than foragers in uniform colonies. On average, in genetically diverse colonies compared with genetically uniform colonies, 36% more waggle dances were identified daily, dancers performed 62% more waggle runs per dance, foragers reported food discoveries that were farther from the nest and 91% more shaking signals were exchanged among workers each morning prior to foraging. Extreme polyandry by honeybee queens enhances the production of worker-worker communication signals that facilitate the swift discovery and exploitation of food resources.     

The within-nest behaviour of honeybee pollen foragers in colonies with a high or low need for pollen

Numerous studies have documented that honeybee colonies can rapidly adjust the number of foragers collecting pollen in response to changes in quantities of brood, pollen and nectar in the nest. However, few studies have examined the behaviour of individual pollen foragers while in the nest between trips. Thus, little is known about how a pollen forager actually assesses its colony's needs. To understand this process better, we observed the behaviour of 319 pollen foragers while in their nests between foraging trips. We observed foragers in two types of nest environments: one with a relatively high need for pollen and one with a relatively low need for pollen. Foragers performed as many as 14 activities during two phases demarcated by the unloading of pollen loads. They inspected empty cells and cells with pollen, and performed the waggle dance at higher relative frequencies before unloading (P≤ 0.0004 each act). They antennated nestmates, autogroomed and received trophallaxis at higher relative frequencies after unloading (P≤ 0.0004 each act). All acts were performed both before and after unloading, but not always by each bee. Pollen foragers discriminated among cells based on cell contents in two contexts. First, they inspected cells already containing pollen more often than expected by chance. Second, their pattern of inspecting cells with different contents differed from their pattern of unloading pollen loads in those cells. Pollen foragers performed 42.3±4.6% (least square mean±SE) of preunloading inspection events on empty cells, but unloaded in them only 19.9±4.6% of the time. They performed 42.2±4.6% of preunloading inspection events on cells already containing pollen, but unloaded in them 79.4±4.6% of the time (P< 0.0001). Our data show that pollen foragers can determine the contents of cells in the nest and suggest that the regulation of pollen collection involves direct assessment of colony need by pollen foragers. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Females produce larger eggs for large males in a paternal mouthbrooding fish.

When individuals receive different returns from their reproductive investment dependent on mate quality, they are expected to invest more when breeding with higher quality mates. A number of studies over the past decade have shown that females may alter their reproductive effort depending on the quality/attractiveness of their mate. However, to date, despite extensive work on parental investment, such a differential allocation has not been demonstrated in fish. Indeed, so far only two studies from any taxon have suggested that females alter the quality of individual offspring according to the quality/attractiveness of their mate. The banggai cardinal fish is an obligate paternal mouth brooder where females lay few large eggs. It has previously been shown that male size determines clutch weight irrespective of female size in this species. In this study, I investigated whether females perform more courtship displays towards larger males and whether females allocate their reproductive effort depending on the size of their mate by experimentally assigning females to either large or small males. I found that females displayed more towards larger males, thereby suggesting a female preference for larger males. Further, females produced heavier eggs and heavier clutches but not more eggs when paired with large males. My experiments show that females in this species adjust their offspring weight and, thus, presumably offspring quality according to the size of their mate.     

The adaptive value of inactive foragers and the scout-recruit system in honey bee (Apis mellifera) colonies

In honey bee (Apis mellifera) colonies, scouts search for productiveforage sites and then recruit other workers to those locationsusing a waggle dance. A simple and tractable mathematical modelof the honey bee scout-recruit system was developed to studythe relationship between nectar availability, the efficiencyof the honey bee's recruitment system, and the optimal proportionof scouts that maximizes net gain (benefit - cost), or, energeticefficiency (benefit/cost - 1). The models consider both theenergetic costs and benefits of active scouts and recruits aswell as the cost of an inactive forager reserve. They predictconditions when individual foraging is favored over the honeybee's recruitment system, when the colony should abandon foragingaltogether, and the optimal proportion of scouts (when thescout-recruit system is favored). The models' predictions qualitativelymatch empirical data. Surprisingly, previous empirical datafrom the honey bee suggest that recruits' costs are greaterthan scouts'—recruits spend significantly longer searchingfor a forage patch than do scouts—thereby causing researchersto rethink how the scout-recruit system might be adaptive.Using average returns, the models demonstrate how the scout-recruitsystem is adaptive despite these apparent higher recruit costsrelative to the scouts'. A sensitivity analysis demonstratesthat the results are robust to a broad range of relative costsof active workers, inactive workers, and the energetic benefitsof the forage. Consequently, the model is demonstrated to berelevant to many insect societies that employ a scout-recruitsystem.     

Crystallographic refinement by knowledge-based exploration of complex energy landscapes

Although X-ray crystallography remains the most versatile method to determine the three-dimensional atomic structure of proteins and much progress has been made in model building and refinement techniques, it remains a challenge to elucidate accurately the structure of proteins in medium-resolution crystals. This is largely due to the difficulty of exploring an immense conformational space to identify the set of conformers that collectively best fits the experimental diffraction pattern. We show here that combining knowledge-based conformational sampling in RAPPER with molecular dynamics/simulated annealing (MD/SA) vastly improves the quality and power of refinement compared to MD/SA alone. The utility of this approach is highlighted by the automated determination of a lysozyme mutant from a molecular replacement solution that is in congruence with a model prepared independently by crystallographers. Finally, we discuss the implications of this work on structure determination in particular and conformational sampling and energy minimization in general.     

Rugged adaptive landscapes shape a complex,sympatric radiation

Strong disruptive ecological selection can initiate speciation, even in the absence of physical isolation of diverging populations. Species evolving under disruptive ecological selection are expected to be ecologically distinct but, at least initially, genetically weakly differentiated. Strong selection and the associated fitness advantages of narrowly adapted individuals, coupled with assortative mating, are predicted to overcome the homogenizing effects of gene flow. Theoretical plausibility is, however, contrasted by limited evidence for the existence of rugged adaptive landscapes in nature. We found evidence for multiple, disruptive ecological selection regimes that have promoted divergence in the sympatric, incipient radiation of ‘sharpfin’ sailfin silverside fishes in ancient Lake Matano (Sulawesi, Indonesia). Various modes of ecological specialization have led to adaptive morphological differences between the species, and differently adapted morphs display significant but incomplete reproductive isolation. Individual fitness and variation in morphological key characters show that disruptive selection shapes a rugged adaptive landscape in this small but complex incipient lake fish radiation.     

Prey processing in central place foragers

The importance of prey processing as an integral part of foraging behaviour has long been acknowledged, but little theoretical consideration has been given to the optimization of the processing behaviour itself. Processing renders food down to ingestible, palatable portions, and also removes non-essential mass thus reducing transport costs. Here, several models of processing are developed for a central place forager. When the forager has to make a simple choice between processing the prey and not, a critical distance from the central place can be calculated, beyond which it is optimal to process prey. If the forager also decides on how much of the prey to remove, the optimal amount to be removed can also be calculated. Imposing a ceiling on overall metabolic expenditure is shown to reduce the distances at which processing becomes the optimal strategy. The models are tested using parameters derived for a provisioning merlin, Falco columbarius, and alternative explanations as to why observed behaviours should differ from the optimal behaviour predicted are discussed.     

Helper (OKT4) T cells from human T cell colonies produce potent colony-stimulating activity

Confluent T cell colonies were grown by culturing blood mononuclear cells in double agar layers containing autologous plasma and phytohemagglutinin (PHA) for one week (37 degrees C, 5% CO2). The plates were then overlaid with serum-free alpha medium which was harvested after 24 h. This medium was demonstrated to have colony-stimulating activity (CSA) of greater potency than conventionally prepared PHA-leukocyte conditioned medium, which was prepared by incubating cells from the same donors. Removal of OKT4-positive cells using a monoclonal antibody and complement abolished CSA production by cells from T cell colonies while the removal of OKT8-positive cells had no effect.     

Laying workers in queenless honeybee (Apis mellifera L.) colonies have physiological states similar to that of nurse bees but opposite that of foragers

Honeybee workers shift their labors from nursing their brood to foraging according to their age after eclosion. When the queen is lost from the colony, however, some workers become 'laying workers' whose ovaries develop to lay eggs. Here we investigated whether the physiological state of laying workers is more similar to that of nurse bees or foragers by examining the hypopharyngeal gland (HPG) and hemolymph vitellogenin titers. In a normal colony, nurse bees have well-developed HPGs that synthesize 'major royal jelly proteins' and high hemolymph vitellogenin titers, whereas foragers have shrunken HPGs that synthesize 70-kDa alpha-glucosidase and low hemolymph vitellogenin titers. In queenless colonies, however, workers with developed ovaries (laying workers) tended to have more developed HPGs and to synthesize major royal jelly proteins, whereas workers with shrunken HPGs tended to synthesize alpha-glucosidase and to have undeveloped ovaries. Furthermore, the workers with developed ovaries had higher vitellogenin titers than nurse bees, whereas those with undeveloped ovaries had lower vitellogenin titers. These findings indicate that the physiological state of laying workers is similar to that of nurse bees, but opposite that of foragers.     

Competition in a group of equal foragers

Abstract Using techniques from renewal process theory, we build a stochastic model for gain accumulation in a group of equal competitors foraging in a patchy environment. The model for gain of the individuals is based on the waiting times between subsequent prey encounters by the group. These waiting times depend on the number of foragers in the group. A single parameter of this dependency encompasses a variety of foraging scenarios, from co-operation to scramble. With constant patch size, correlations between gains of any pair of foragers are negative. This dependency is most intense in small groups. Increased variation in patch size makes correlations in gains between group members positive irrespective of the group size. For a solitary forager, variance in gain approaches zero with increasing time in the patch. For an individual member in a group, variance grows monotonically. Thus, depending on the patch departure rule controlling the time to be spent in the patch, solitary foragers may have a smaller variance in gain than members in a group. As solitary foragers also potentially harvest all prey in the patch, it is hard to believe that grouping behavior would evolve solely on the basis of foraging.     

Nest mate recognition in ants with complex colonies: within- and between-population variation

The ability to recognize kin is widespread, and especially importantin highly social organisms. We studied kin recognition by assessingpatterns of aggression within and between nests of the antLeptothorax longispinosus. Colonies of this species can befractionated into subunits, a condition called polydomy. Theproblem of recognizing relatives is therefore more complexwhen those relatives can live in two or more different places.We hypothesized that spatial subdivision may have resulted ina stronger genetic component to kin recognition than in caseswhere colonies live in a single location. To test our hypothesiswe assessed recognition capabilities for two populations ofthis ant that differ in the complexity of their colonies. Ina New York, USA, population, polydomy is very common, and coloniesalso can have multiple queens. By contrast, a population inWest Virginia, USA, has colonies that typically are monogynousand rarely are polydomous. We conducted introductions of antsbetween different nests collected in the same neighborhood,with self-introductions and alien introductions as controls.Nests from the two populations showed corresponding differencesin their aggression towards intruders. For New York nests, the extent of genetic similarity was the single best predictor ofaggression, whereas for West Virginia nests aggression wasjointly influenced by genetic similarity and spatial distance.In both populations, we found nest pairs for which aggressionwas nonreciprocal; these probably reflect recognition errors by one of the nests. After the ants were maintained in the laboratoryfor 3 months, their aggression scores rose and fewer recognitionerrors were made. Thus nest-mate and colony-mate recognitionin this species are mediated primarily by endogenous cues (geneticsimilarity); the importance of exogenous cues for nest materecognition depends on the population's social system.     

Sex differences in spatial cognition among Hadza foragers

This paper describes sex differences in spatial competencies among the Hadza, a mobile hunter–gatherer population in Tanzania. It addresses the following questions: (a) Is the usual male advantage in Euclidean spatial abilities found in this population, where both women and men are highly mobile? (b) Do Hadza women have better object location memory than men, as the gathering hypothesis predicts? (c) Do women who are nominated by others as being good at finding bushfoods excel at the object location memory task? We tested object location memory with a version of the memory game using cards of local plants and animals. This allowed us to also ask whether women and men would have better spatial memory for the plant and animal cards, respectively. We found that Hadza men were significantly better than women in three tests of spatial ability: the water-level test, targeting, and the ability to point accurately to distant locations (the latter only in the less mobile groups). There was a trend toward a male advantage at the object location memory task, in contrast to results found previously in nonforaging populations, and women's performance at the task deteriorated with age, while that of men did not. The women who were nominated by peers as being good at finding bushfoods were consistently older women. We discuss the probable hormonal causes and functional consequences of age changes in the spatial competencies of female foragers.     

The allocation of foragers in red wood ants

Abstract. 1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers.
2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest.
3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source.
4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails.
5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.