Racial mixing in South African honeybees: the effects of genotype mixing on reproductive traits of workers

To test the hypothesis that the honeybee hybrid zone in South Africa is a tension zone due to increased reproductive conflict in colonies that contain both Apis mellifera capensis and Apis mellifera scutellata worker genotypes, we constructed mixed subspecies and hybrid colonies via a combination of artificial and natural matings. We measured emergence weight, ovary activation, and the presence/absence of a spermatheca on workers of different genotypes. We show that the measured characteristics were all affected by genotype with some traits also affected by the social environment in which the worker was reared. Workers with both an A. m. capensis mother and father had the highest emergence weight. When workers had an A. m. capensis mother, paternity affected emergence weight with A. m. capensis fathers producing heavier workers. When the queen was A. m. scutellata, paternity had less effect on weight. Presence of spermatheca was highest in mixed colonies irrespective of maternity and colonies containing pure A. m. capensis workers only. Paternity had a significant effect on the presence of a spermatheca within mixed colonies, with workers that had an A. m. capensis father being more likely to possess a spermatheca. Rates of ovary activation were highest in colonies with an A. m. scutellata queen mated to drones of both genotypes, suggesting that mixed subspecies colonies likely suffer increased reproductive strife among workers. Our results provide support for the hypothesis that the South African honeybee hybrid zone is a tension zone arising from reduced fitness of genetically mixed colonies.     

Estimating the Density of Honeybee Colonies across Their Natural Range to Fill the Gap in Pollinator Decline Censuses

Abstract: Although pollinator declines are a global biodiversity threat, the demography of the western honeybee (Apis mellifera) has not been considered by conservationists because it is biased by the activity of beekeepers. To fill this gap in pollinator decline censuses and to provide a broad picture of the current status of honeybees across their natural range, we used microsatellite genetic markers to estimate colony densities and genetic diversity at different locations in Europe, Africa, and central Asia that had different patterns of land use. Genetic diversity and colony densities were highest in South Africa and lowest in Northern Europe and were correlated with mean annual temperature. Confounding factors not related to climate, however, are also likely to influence genetic diversity and colony densities in honeybee populations. Land use showed a significantly negative influence over genetic diversity and the density of honeybee colonies over all sampling locations. In Europe honeybees sampled in nature reserves had genetic diversity and colony densities similar to those sampled in agricultural landscapes, which suggests that the former are not wild but may have come from managed hives. Other results also support this idea: putative wild bees were rare in our European samples, and the mean estimated density of honeybee colonies on the continent closely resembled the reported mean number of managed hives. Current densities of European honeybee populations are in the same range as those found in the adverse climatic conditions of the Kalahari and Saharan deserts, which suggests that beekeeping activities do not compensate for the loss of wild colonies. Our findings highlight the importance of reconsidering the conservation status of honeybees in Europe and of regarding beekeeping not only as a profitable business for producing honey, but also as an essential component of biodiversity conservation.     

Brood pheromone modulates honeybee (Apis mellifera L.) sucrose response thresholds

Foraging behavior and the mechanisms that regulate foraging activity are important components of social organization. Here we test the hypothesis that brood pheromone modulates the sucrose response threshold of bees. Recently the honeybee proboscis extension response to sucrose has been identified as a ”window” into a bee’s perception of sugar. The sucrose response threshold measured in the first week of adult life, prior to foraging age, predicts forage choice. Bees with low response thresholds are more likely to be pollen foragers and bees with high response thresholds are more likely to forage for nectar. There is an associated genetic component to sucrose response thresholds and forage choice such that bees selected to hoard high quantities of pollen have low response thresholds and bees selected to hoard low quantities of pollen have higher response thresholds. The number of larvae in colonies affects the number of bees foraging for pollen. Hexane-extractable compounds from the surface of larvae (brood pheromone) significantly increase the number of pollen foragers. We tested the hypothesis that brood pheromone decreases the sucrose response threshold of bees, to suggest a pheromone- modulated sensory-physiological mechanism for regulating foraging division of labor. Brood pheromone significantly decreased response thresholds as measured in the proboscis extension response assay, a response associated with pollen foraging. A synthetic blend of honeybee brood pheromone stimulated and released pollen foraging in foraging bioassays. Synthetic brood pheromone had dose-dependent effects on the modulation of sucrose response thresholds. We discuss how brood pheromone may act as a releaser of pollen foraging in older bees and a primer pheromone on the development of response thresholds and foraging ontogeny of young bees. Received: 24 May 2000 / Revised: 26 September 2000 / Accepted: 15 October 2000     

Higher soybean production using honeybee and wild pollinators, a sustainable alternative to pesticides and autopollination

This is the first report showing that using honeybee (Apis mellifera) and wild pollinators complementary pollination can enhance soybean productivity (Glycine max). Current industrial production of soybean involves autopollination and high loads of pesticides. Therefore, growers have neglected possible biotic pollination despite suggestions that soybean benefit from insect pollinators. Reports advocating possible biotic pollination are based on experiments where bees are caged with flowering plants and the absence of pesticides, thus not in field conditions. Therefore, here we compared in field conditions soybean yield produced (1) independently of biotic pollinators, (2) with wild pollinators and (3) with honeybee colonies. Results showed an increase of +6.34 % of soybean yield in areas where wild pollinators had free access to flowers. The introduction of honeybee colonies further raised the yield of +18.09 %. Our findings therefore show that, though soybean is autogamous, allowing pollination by wild pollinators leads to higher yields. Moreover, adding honeybee mitigates pollination deficits and improves yield compared to current practices.     

Does a polyandrous honeybee queen improve through patriline diversity the activity of her colony’s scouting foragers?

Recent studies indicate that the foraging success of a honeybee colony is enhanced when it has numerous genetically diverse patrilines because of queen polyandry. We determined whether foraging is improved in part because patriline diversity generates more responsive populations of scouting foragers. Scouts search for new food sources and advertise them with waggle dances to inform other foragers about unexploited discoveries. We moved multiple-patriline and single-patriline colonies to unfamiliar locations so that colonies relied heavily on successful scouts to initiate recruitment and then compared the development of foraging effort between the two types of colonies. More waggle dance signals were produced during the incipient stages of foraging in multiple-patriline colonies compared to single-patriline colonies because scouts reported food discoveries with longer dances. Scouts also returned to multiple-patriline colonies at rates that were two thirds higher than those of single-patriline colonies, although return rates for general forager populations were not significantly different between colony types. The distance of reported food sources from hives increased with time for all colonies, but by the end of their first day in an unfamiliar environment, maximal foraging reach was greater if colonies had multiple patrilines. Most scouts in multiple-patriline colonies came from a minority of scout-rich patrilines that were generally not those from which general forager populations were derived; the presence of such scout-rich patrilines was correlated with the extent of recruitment signaling in colonies. We show how a honeybee colony’s scouting effort is (and is not) enhanced when extremely polyandrous queens produce genetically diverse colonies.     

Comparative biometry of Eunicella singularis (Gorgonian) sclerites at East Mediterranean Sea (North Aegean Sea, Greece)

The two forms of Eunicella singularis sclerites, spindles and clubs, were examined in two sites in East Mediterranean Sea, Greece. The comparison of the sclerites size was based on the hydrodynamic profile of the sites (the site of Arethoussa was exposed and the Phidonissi site was sheltered), on the sites bathymetry (AR 5–8 m, AR 9–13 m, PH 5–10 m, PH 11–13 m) and on the position occupied by the sclerites on the gorgonian colonies (top, middle and base). With the usage of image system analysis the following microfeatures were measured or calculated: projection, length, width, elongation factor, compactness factor, length × width and length/width. The present study confirms the hypothesis that spindles are involved in the recovering of the gorgonian colonies and clubs contribute to the flexion capacity of the colonies. The spindles of the shallow E. singularis colonies (AR 5–8 m) were significantly bigger (length, width) compared with the others, in order to assure the best recovery of the colonies after their flexion, induced by higher water current velocity in shallow water. The clubs occupy the intern part of the mesoglea and their size (length, width) increased in colonies from the shallow exposed site in order to facilitate the gorgonian flexion. The present study demonstrates the gorgonian adaptation (in a microscopic scale) to the environmental pressure of hydrodynamic conditions.     

Differential feeding of worker larvae affects caste characters in the Cape honeybee,<Emphasis Type="Italic"> Apis mellifera capensis</Emphasis>

Sections of brood from colonies of the Cape honeybee ( Apis mellifera capensis), the African honeybee ( A. m. scutellata), and hybrid bees of the two races were exchanged between colonies to study the effect of different brood-origin/nurse-bee combinations on development of caste characters. When Cape larvae were raised by African workers the amount of food provided almost doubled in comparison with Cape larvae reared by their own workers. In contrast, African larvae raised by Cape workers were provided with only half the amount they received from their own workers. After the bees emerged, we found a large degree of plasticity in characters related to caste differentiation, which corresponded closely to the amount of food provided. Super-fed Cape bees had enlarged spermathecae, were heavier than normal workers and developed more rapidly, and had reduced pollen combs, all typical for a more queen-like condition. Ovariole numbers did not appear to be enhanced by additional feeding. Cape bees that behave as social parasites in African bee colonies were most queen-like in the characters studied, albeit within the range that was found for Cape bees from normal colonies, suggesting within-colony selection for characters that enhance reproduction.Communicated by R. Page     

A comparison of visual and olfactory learning performance in the bumblebee Bombus terrestris

Animals use cues from a range of sensory modalities to discriminate stimuli and as predictors of reward. Whilst there is appreciable variation in the cognitive performance of animals, we know surprisingly little about the extent to which learning varies among individuals across different sensory modalities. Do individuals that are good at learning in one sensory modality also perform well in another (performance is correlated between modalities), or do individuals demonstrate specialisation in learning performance in one modality (trading-off performance between modalities)? We tested these hypotheses by examining the performance of 76 Bombus terrestris workers, from four colonies, in both an odour-and visual learning task. Olfactory learning was assessed using proboscis extension reflex (PER) conditioning and visual (colour) learning was examined using a well-established free-flying paradigm. Our results showed neither a correlation, nor a trade-off, in individual performance for learning tasks using different sensory modalities. However, there was considerable variation among workers within each colony in their performance in both learning tasks. This extent of interindividual variation in learning ability across sensory modalities could be adaptive for colonies dealing with changeable foraging conditions. There was also significant intercolony variation in final task performance level in the olfactory learning task, and both the strength and persistence of blue preference in the colour learning task. This is the first study to demonstrate variation in olfactory learning performance across multiple bumblebee colonies using PER conditioning, suggesting this is an effective paradigm for assessing associative olfactory learning performance both within and among colonies.     

Social parasitism of queens and workers in the Cape honeybee (<Emphasis Type="Italic">Apis mellifera capensis</Emphasis>)

Workers of a queenless honeybee colony can requeen the colony by raising a new queen from a young worker brood laid by the old queen. If this process fails, the colony becomes hopelessly queenless and workers activate their ovaries to lay eggs themselves. Laying Cape honeybee workers (Apis mellifera capensis) produce female offspring as an additional pathway for requeening. We tested the frequency of successful requeening in ten hopelessly queenless colonies. DNA genotyping revealed that only 8% of all queens reared in hopelessly queenless colonies were the offspring of native laying worker offspring. The vast majority of queens resulted from parasitic takeovers by foreign queens (27%) and invading parasitic workers (19%). This shows that hopelessly queenless colonies typically die due to parasitic takeovers and that the parasitic laying workers are an important life history strategy more frequently used than in providing a native queen to rescue the colony. Parasitism by foreign queens, which might enter colonies alone or accompanied by only a small worker force is much more frequent than previously considered and constitutes an additional life history strategy in Cape honeybees.     

Intracolonial genetic diversity in honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis>) colonies increases pollen foraging efficiency

Multiple mating by honeybee queens results in colonies of genotypically diverse workers. Recent studies have demonstrated that increased genetic diversity within a honeybee colony increases the variation in the frequency of tasks performed by workers. We show that genotypically diverse colonies, each composed of 20 subfamilies, collect more pollen than do genotypically similar colonies, each composed of a single subfamily. However, genotypically similar colonies collect greater varieties of pollen than do genotypically diverse colonies. Further, the composition of collected pollen types is less similar among genotypically similar colonies than among genotypically diverse colonies. The response threshold model predicts that genotypic subsets of workers vary in their response to task stimuli. Consistent with this model, our findings suggest that genotypically diverse colonies likely send out fewer numbers of foragers that independently search for pollen sources (scouts) in response to protein demand by the colony, resulting in a lower variety of collected pollen types. The cooperative foraging strategy of honeybees involves a limited number of scouts monitoring the environment that then guide the majority of foragers to high quality food sources. The genetic composition of the colony appears to play an important role in the efficiency of this behavior.     

Is the bee louse Braula coeca (Diptera) using chemical camouflage to survive within honeybee colonies?

The bee louse Braula coeca is a highly specialised flattened, wingless fly that spends its entire adult life on adult honeybees. It feeds by stealing food directly from bees during social feeding (trophallaxis). The Braula fly has a preference to infest the honeybee queen. The queen is the most attended individual in the colony but despite this the adult flies remain undetected by the workers. This is due to Braula possessing a cuticular hydrocarbon profile that mirrors that of their host honeybee colony, despite Diptera and Hymenoptera orders having separated over 290 million years ago. This chemical camouflage is most likely through odour acquisition from the honeybee host since even small colony-specific differences in the alkene isomer patterns present in the honeybees were also detected in the Braula’s profile. This finding further supports the idea that the honeybee recognition cues are contained within the alkene part of their hydrocarbon profile and Braula exploit this to remain undetected within an otherwise hostile colony.     

High degree of polyandry in Apis dorsata queens detected by DNA microsatellite variability

Workers of six colonies of the giant honeybee Apis dorsata from Sabah, Malaysia (five colonies) and Java (one colony) were genotyped using single locus DNA fingerprinting. The colonies from Sabah nested in colony aggregations of 5 and 28 nests respectively on two trees. Three DNA microsatellite loci (A14, A76, A88) with a total of 27 alleles provided sufficient genetic variability to classify the workers into distinct sub-families revealing the degree of polyandry of the queens. Queens mated on average with 30.17 ± 5.98 drones with a range from 19 to 53. The average effective number of matings per queen was 25.56 ± 11.63. In the total sample of 192 workers, 22 individuals were found that were not offspring of the colony's queen. Three of these were potentially drifted offspring workers from genotyped queens of colonies nesting on the same tree.     

Lack of kin recognition in swarming honeybees ( Apis mellifera )

Honeybee colonies reproduce by colony fission and swarming. The primary swarm leaves the nest with the mated mother queen. Further “after-swarms” can leave the nest. These are composed of virgin queens and sister workers. Since all workers in the primary swarm have the same relationship to the mother queen, kin recognition cannot have any effect on the worker distribution in the swarm. Because of polyandry of the mother queen, the after-swarm is composed of super- and halfsister workers of the virgin queen. In this case kin recognition might affect swarm composition if workers increase their inclusive fitness by preferentially investing in a supersister queen. The distribution of workers in the mother colony, the primary and the after-swarm was analyzed using single-locus DNA fingerprinting in two colonies of the honeybee (Apis mellifera). The colonies were composed of 21 and 24 worker subfamilies because of multiple mating of the queen. The subfamily distribution in the mother colonies before swarming was significantly different from the subfamily frequencies in the primary swarm. This indicates different propensities for swarming in the various subfamilies. The subfamily distribution was also significantly different between the mother colony and the after-swarm. There was however no significant difference between the subfamily composition of the primary and the after-swarm. The average effects of kin recognition on the distribution of the subfamilies in the two after-swarms were less than 2%. We conclude that colony-level selection sets the evolutionary framework for swarming behaviour. Received: 22 May 1996 / Accepted after revision: 2 November 1996     

Colony take-over and brood survival in temporary social parasites of the ant genus Formica

Parasites reduce host fitness, and so instigate counter adaptations by their hosts. In temporary social parasitism, usurpers must not only enter the colony unharmed, but also have their eggs reared by the host workers. We introduced parasitic Formica lugubris and Formica aquilonia queens into queen right and orphaned fragments of three host species, Formica cinerea, Formica picea and Formica fusca, and show that workers of all three host species kill over 40 % of the introduced queens within 10 days, regardless of the presence/absence of a resident queen, and parasite species. More parasite queens died in F. cinerea than in F. picea and F. fusca. There were no major differences in survival between the parasite species (except that F. lugubris survived longer than F. aquilonia in F. fusca colonies compared to F. picea colonies), but parasite queens survived longer in orphaned than in queen right fragments of F. fusca. Experimental introduction of parasite (F. aquilonia) eggs into orphaned colonies of F. fusca showed that none of the parasite eggs were reared until pupation; whereas on average, 12 % of the con-specific hetero-colonial eggs introduced in the same manner were reared until pupation. In all colonies that received parasite brood, all offspring consisted of worker-laid males, whereas the corresponding value was 50 % for colonies that received con-specific hetero-colonial brood. Thus, when the risks of entering host colonies and brood failure are combined, the rate of successful colony take-over is very low. Moreover, the host workers can to some extent alleviate the costs of parasitism by producing a final batch of own offspring.     

Pairing patterns in relation to body size,genetic similarity and multilocus heterozygosity in a tropical monogamous bird species

The relative influence of genetic and phenotypic quality on pairing status and mating patterns in socially monogamous species remains poorly documented. We studied social status and pairing patterns in relation to genetic similarity and multilocus heterozygosity (MLH) estimates from 11 microsatellite markers, and both tarsus length and wing chord (as a measure of competitive ability in territorial defence) in a socially monogamous tropical bird species where individuals defend territories year-round, alone or in pairs, the Zenaida dove, Zenaida aurita. Tarsus length and wing chord did not differ between unpaired territorial birds and paired ones in either sex, whereas paired females, but not paired males, tended to be more heterozygous than unpaired ones. Among 84 pairs, we found no evidence for assortative mating for tarsus length, wing chord, MLH or genetic similarity. However, within pairs, male wing chord was positively related to female MLH and female tarsus length was positively related to male MLH, with no evidence for local effects, suggesting assortative mating by individual quality. Although the observed pattern of mating in Zenaida doves may be the product of mutual mate choice, further assessment of this hypothesis requires direct investigation of both mating preference in each sex and lifetime reproductive success in relation to body size and MLH.     

Coral architecture affects the habitat choice and form of associated gobiid fishes

Gobiid fishes of the genus Gobiodon live in strong association with certain reef-building corals that vary considerably in size and architecture. These fishes hence are excellent model systems for studying evolutionary adaption to specific microhabitats. Using a sample of Gobiodon histrio and G. rivulatus and their most important host corals (Acropora digitifera and A. gemmifera) from the northern Red Sea, we assess (1) how corals that are occupied by gobies differ in their architecture from colonies that are not occupied and (2) how fish body shape is associated with the architecture of their host coral. Fish body shape was assessed by geometric morphometric techniques. Coral measurements included colony size, branch length (BL), and interbranch as well as branch tip distance of adjacent branches, for which we applied a new and non-destructive measurement technique based on casts of two-component epoxy resin. The most important factor influencing the occupation of corals was a BL of more than 5 cm. The distance between coral branches was clearly related to the width of the fishes and hence constrained overall fish size. G. histrio and G. rivulatus differ in adult body shape as well in their allometric development of lateral body compression, resulting in different maximum body sizes attainable in the restricted interbranch space of corals. The strong dependence of coral-associated fishes on large coral colonies with specific architectures increases the extinction risk of fishes within deteriorating coral reefs.     

Genetic influence on caste in the ant Camponotus consobrinus

Genetic influences on polyethism within social insect colonies are well known, suggesting that the determination of caste (soldiers and minor workers) may also be genetically mediated. The Australian sugar ant Camponotus consobrinus is suitable for such a study, having soldiers and minor workers that follow a complex allometry. Further, although most C. consobrinus colonies are monogynous, 13 of 42 surveyed using microsatellites were found to be polygynous. Thus, although a minority of colonies were polygynous, the great majority of queens live in polygynous colonies. From the 29 monogynous colonies studied, we inferred that the queens are monandrous. Ants from four polygynous colonies were assigned to families on the basis of microsatellite genotypes, after measurements had been taken of head width and scape length. These measurements reflect a complex allometry interpretable as soldier and minor worker growth curves with a large changeover zone. Genetic influence on caste determination was examined by testing for differences between families within colonies in the distribution of scape lengths, residuals from the overall colony allometric curve, and proportions of soldiers and minor workers (as determined by head width falling above or below the inflection point of the overall colony allometric curve). Families in all four colonies differed significantly in caste proportions and in head-width distributions, and three of the four colonies showed significant differences between families in residuals from the overall colony growth curve. Nested ANOVAs using head widths and scape-length residuals showed that when the effect of family is removed, intercolony differences in allometry are negligible. This evidence indicates genetic rather than environmental causes for the observed differences between families. We speculate that this variation may reflect some selective advantage to within-colony heterogeneity between families or that selective differences are few between a wide array of family growth patterns. Received: 16 June 1999 / Received after revision: 13 September 1999 / Accepted: 25 September 1999     

Limited flexibility in the temporal caste system of the honey bee

Caste theory predicts that social insect colonies are organized into stable groups of workers specialized on particular task sets. Alternative concepts of organization of work suggest that colonies are composed of extremely flexible workers able to perform any task as demand necessitates. I explored the flexibility of workers in temporal castes of the honey bee Apis mellifera by determining the ability of colonies to reorganize labor after a major demographic disturbance. I evaluated the flexibility of temporal castes by comparing the foraging rates of colonies having just lost their foragers with colonies having also lost their foragers but having been given a week to reorganize. The population sizes and contents of the colonies in each group were equalized and foraging rates were recorded for one week. Colonies given a weeks initial recovery time after the loss of their foragers were found to forage at significantly higher rates than those colonies given no initial recovery time. This result was consistent for nectar and pollen foraging. These results suggest that honeybee workers lack sufficient flexibility to reorganize labor without compromising foraging. This finding is consistent with the caste concept model of organization of work in insect societies.     

Seasonality in reproduction of the deep-water pennatulacean coral Anthoptilum grandiflorum

The deep-sea pennatulacean coral Anthoptilum grandiflorum exhibits a cosmopolitan distribution and was recently determined to serve as habitat for other invertebrates and fish larvae in the northwest Atlantic. Colonies collected at bathyal depths between 2006 and 2010 in eastern Canada were analysed to determine their fecundity and characterize spatial and temporal trends in their reproductive cycle. Anthoptilum grandiflorum is a gonochoric broadcast spawner with a sex ratio that does not differ significantly from equality (although one hermaphrodite colony was observed). In male colonies, all the spermatocysts synthesized become mature over the annual cycle, while only ~21 % of the initial production of oocytes reaches maturity in female colonies. Female potential fecundity based on mature oocytes just before spawning was on average 13 oocytes polyp^?1; male potential fecundity was 48 spermatocysts polyp^?1. The spawning period of A. grandiflorum differs between geographic regions, from April (in southern Newfoundland) to July (in Labrador), closely following regional spring phytoplankton blooms after accounting for the deposition of planktic detritus. Release of oocytes by a live colony held in the laboratory was recorded in April 2011, coincident with field data for similar latitudes. Seawater temperatures at the time of spawning were around 3.6–4.8 °C in all regions and in the laboratory. Early stages of gametogenesis were detected in colonies collected shortly after the spawning season, and early and late growth stages occurred successively until December. Mature colonies were observed between April and July (depending on latitude). The diameter of mature oocytes (~1,100 μm maximum diameter) is consistent with lecithotrophic larval development.     

Larval settlement in the echiuran worm Bonellia viridis: Settlement on both the adult proboscis and body trunk

It is widely documented that in Bonellia viridis Rolando (Echiura), the larvae settle on the proboscis of the adult female and differentiate into males. This study shows that although settlement on the proboscis is preferred, the larvae can also settle on the body trunk of the adult and differentiate into males. Aqueous extracts of homogenized trunk tissues are as effective as those of proboscis tissues in masculinizing the larvae. The natural secretion of the female body trunk, which is produced when the worm is disturbed, has potent masculinizing properties. The preferential settlement on the probiscis may not result from a different chemical nature of the substratum.