Reproductive division of labour and thelytoky result in sympatric barriers to gene flow in honeybees (Apis mellifera L.).

Determining the extent and causes of barriers to gene flow is essential for understanding sympatric speciation, but the practical difficulties of quantifying reproductive isolation remain an obstacle to analysing this process. Social parasites are common in eusocial insects and tend to be close phylogenetic relatives of their hosts (= Emery's rule). Sympatric speciation caused by reproductive isolation between host and parasite is a possible evolutionary pathway. Socially parasitic workers of the Cape honeybee, Apis mellifera capensis, produce female clonal offspring parthenogenetically and invade colonies of the neighbouring subspecies A. m. scutellata. In the host colony, socially parasitic workers can become pseudoqueens, an intermediate caste with queenlike pheromone secretion. Here, we show that over an area of approximately 275.000 km², all parasitic workers bear the genetic signature of a clone founded by a single ancestral worker genotype. Any gene flow from the host to the parasite is impossible because honeybee workers cannot mate. Gene flow from the parasite to the host is possible, as parasitic larvae can develop into queens. However, we show that despite sympatric coexistence for more than a decade, gene flow between host and social parasite (F(st) = 0.32) and hybridizations (0.71%) are rare, resulting in reproductive isolation. Our data suggest a new barrier to gene flow in sympatry, which is not based on assortative matings but on thelytoky and reproductive division of labour in eusocial insects, thereby suggesting a new potential pathway to Emery's rule.

Temporal variation in the genetic structure of a drone congregation area: an insight into the population dynamics of wild African honeybees (Apis mellifera scutellata).

The mating system of the honeybee (Apis mellifera) has been regarded as one of the most panmictic in the animal kingdom, with thousands of males aggregating in drone congregation areas (DCAs) that virgin queens visit to mate with tens of partners. Although males from many colonies gather at such congregations, the temporal changes in the colonies contributing drones remain unknown. Yet, changes in the DCAs' genetic structure will ultimately determine population gene flow and effective population size. By repeatedly sampling drones from an African DCA over a period of 3 years, we studied the temporal changes in the genetic structure of a wild honeybee population. Using three sets of tightly linked microsatellite markers, we were able to reconstruct individual queen genotypes with a high accuracy, follow them through time and estimate their rate of replacement. The number of queens contributing drones to the DCA varied from 12 to 72 and was correlated with temperature and rainfall. We found that more than 80% of these queens were replaced by mostly unrelated ones in successive eight months sampling intervals, which resulted in a clear temporal genetic differentiation of the DCA. Our results suggest that the frequent long-range migration of colonies without nest-site fidelity is the main driver of this high queen turnover. DCAs of African honeybees should thus be regarded as extremely dynamic systems which together with migration boost the effective population size and maintain a high genetic diversity in the population.

Chemical mate recognition and release of male sexual behavior in polybiine wasp,Belonogaster petiolata (Degeer) (Hymenoptera: Vespidae).

The results of bioassays using freshly killed gynes ofBelonogaster petiolata (Degeer) and hexane extracts of their tagmata and abdominal glands provide evidence for the existence of chemical signals in the venom, thorax, and head of gynes that serve as mate recognition cues and releasers of copulatory behavior in conspecific males. Attraction of males to the source of the chemicals occurs over short distances (a few centimeters).

Persistence of hepatitis B antigen in Culex quinquefasciatus (Diptera: Culicidae).

Groups of wild-caught Culex quinquefaciatus Say, previously tested for the presence of hepatitis B surface antigen (HBsAg), were tested for the presence of hepatitis B e antigen (HBeAg). This antigen was detected at low levels in blood-fed, half-gravid, and gravid groups. A colony of Cx. quinquefasciatus was established in the laboratory and tested for the persistence of HBsAg and HBeAg. Five days after feeding on blood infected with HBsAg and HBeAg, 9 of 20 (45%) pools of Cx. quinquefasciatus were HBeAg-positive and 5 of 20 (25%) pools were HBeAg-positive; low levels of HBsAg and HBeAg were still detectable 28 d after the infective meal in 2 of 20 (10%) and 1 of 20 (5%) pools, respectively. A crude protease extract was prepared from colony mosquitoes, and the effect of this extract on HBsAg and HBeAg present in human serum was tested in vitro. After 20 h, tests for both antigens were still strongly positive. Low levels of HBsAg were detected in ovaries 7 d after infection. Salivary glands were HBsAg- and HBeAg-negative.

Respiratory gas exchange in the tick Amblyomma hebraeum (Acari: Ixodidae).

Respiratory gas exchange was studied in unfed adult Amblyomma hebraeum Koch. Carbon dioxide emission was measured at 25 degrees C using flow-through respirometry to determine standard metabolic rate and the temporal pattern of gaseous emission. The standard CO2 production rate (sVCO2) of inactive ticks was 0.0135 +/- 0.0085 ml g-1 h-1, and the standard O2 consumption rate (sVO2) was 0.0158 +/- 0.0097 ml g-1 h-1. Ventilation was discontinuous and was characterized by periodic bursts of CO2 emissions at frequencies of 0.33 h-1-1.11 h-1. Low metabolic rate coupled with discontinuous ventilation may contribute to the ability of adult A. hebraeum to withstand prolonged periods of starvation and desiccation in the absence of a host.

Pheromonal dominance and the selection of a socially parasitic honeybee worker lineage (Apis mellifera capensis Esch.).

The recent invasion by self-replicating socially parasitic Cape honeybee workers, Apis mellifera capensis, of colonies of the neighbouring African subspecies Apis mellifera scutellata represents an opportunity to study evolution of intraspecific parasitism in real time. As honeybee workers compete pheromonally for reproductive dominance, and as A. m. capensis workers readily produce queen-like pheromones, we hypothesized that these semiochemicals promoted the evolution of intraspecific social parasitism. Remarkably, the offspring of a single worker became established as a parasite in A. m. scutellata's range. This could have resulted from extreme selection among different clonal parasitic worker lineages. Using pheromonal contest experiments, we show that the selected parasitic lineage dominates in the production of mandibular gland pheromones over all other competitors to which it is exposed. Our results suggest that mandibular gland pheromones played a key role in the evolution of intraspecific social parasitism in the honeybee and in the selection of a single genotype of parasitic workers.

Individual versus social pathway to honeybee worker reproduction (Apis mellifera): pollen or jelly as protein source for oogenesis?

Honeybee workers, Apis mellifera, can reproduce in queenless colonies. The production of queen-like pheromones may be associated with their reproductive activity and induce nestmates to respond by feeding them. Such frequent trophallaxis could supply their protein needs for oogenesis, constituting a social pathway to worker reproduction. However, some individuals can develop ovaries without producing queen pheromones. The consumption of protein-rich pollen could be an alternative solitary pathway for them to satisfy this dietary requirement. In order to investigate the way in which workers obtain proteins for oogenesis, we created orphaned worker groups and determined ovarian and pheromonal development in relation to pollen consumption of selected workers. Individuals that did not consume pollen had significantly more developed ovaries and produced significantly more queen mandibular pheromone than workers that fed directly on pollen. Our results suggest that workers producing queen-like secretions are fed trophallactically. However, reproductive workers that lacked queen pheromones had consumed little or no pollen, suggesting that they also obtained trophallaxis. Although pollen consumption might contribute to sustaining oogenesis, it does not appear to be sufficient. Trophallaxis as a means of obtaining proteins seems to be necessary to attain reproductive status in queenless honeybee colonies.

Vertical transmission of hepatitis B virus in Culex quinquefasciatus.

An investigation of the vertical transmission of hepatitis B virus (HBV) in Culex quinquefasciatus Say revealed the presence of low levels of the virus in adult F1 progeny from the first ovarian cycle of mosquitoes infected by feeding on HBV positive human blood. HBV was not transmitted vertically during the second, third and fourth ovarian cycles nor to the F2 generation. The salivary glands, ovaries and faeces of the F1 generation did not contain detectable levels of HBV. Progeny of female Cx quinquefasciatus mated with F1 males were negative for HBV.

Pheromonal contest between honeybee workers (Apis mellifera capensis).

Queenless workers of the Cape honeybee (Apis mellifera capensis) can develop into reproductives termed pseudoqueens. Although they morphologically remain workers they become physiologically queenlike, produce offspring, and secrete mandibular gland pheromones similar to those of true queens. However, after queen loss only very few workers gain pseudoqueen status. A strong intracolonial selection governs which workers start oviposition and which remain sterile. The "queen substance", 9-keto-2(E)-decenoic acid (9-ODA), the dominant compound of the queen's mandibular gland pheromones, suppresses the secretion of queenlike mandibular gland pheromones in workers. It may act as an important signal in pseudoqueen selection. By analysing the mandibular gland pheromones of workers kept in pairs, we found that A. m. capensis workers compete to produce the strongest queen-like signal.

The ontogenetic pattern of mandibular gland components in queenless worker bees (Apis mellifera capensis Esch.).

The quantity and composition of the six major mandibular gland components of young queenless workers of the Cape honeybee (Apis mellifera capensis) were determined. The total amount of the six components increased with age. The relative quantities in the mandibular gland secretion of queenless caged workers were found to change rapidly during the first 4 days after emergence and to become dominated by the queen substance, 9-keto-2(E)-decenoic acid. Also the relative amounts of 9-hydroxy-decenoic acid, a precursor of the queen substance, showed an increase of an order of magnitude within the first 4 days of imaginal life. The relative amounts of the aromatic compounds typical to the queen pheromone remained similar in this developmental time window. The increase of queenlike compounds is particularly strong between days two and three after emergence. These queen-like pheromones play a major role in the development of reproductive hierarchies among workers under queenless conditions. This may be an important factor in the socio-parasitic pathway of A. m. capensis.