Workers' sons rescue genetic diversity at the sex locus in an invasive honey bee population.

The hallmark of eusociality is the division of labour between reproductive (queen) and nonreproductive (worker) females. Yet in many eusocial insects, workers retain the ability to produce haploid male offspring from unfertilized eggs. The reproductive potential of workers has well-documented consequences for the structure and function of insect colonies, but its implications at the population level are less often considered. We show that worker reproduction in honey bees can have an important role in maintaining genetic diversity at the sex locus in invasive populations. The honey bee sex locus is homozygous-lethal, and, all else being equal, a higher allele number in the population lead to higher mean brood survival. In an invasive population of the honey bee Apis cerana in Australia, workers contribute significantly to male production: 38% of male-producing colonies are queenless, and these contribute one-third of all males at mating congregations. Using a model, we show that such male production by queenless workers will increase the number of sex alleles retained in nascent invasive populations following founder events, relative to a scenario in which only queens reproduce. We conclude that by rescuing sex locus diversity that would otherwise be lost, workers' sons help honey bee populations to minimize the negative effects of inbreeding after founder events and so contribute to their success as invaders.

Thelytokous parthenogenesis in unmated queen honeybees (Apis mellifera capensis): central fusion and high recombination rates.

The subspecies of honeybee indigenous to the Cape region of South Africa, Apis mellifera capensis, is unique because a high proportion of unmated workers can lay eggs that develop into females via thelytokous parthenogenesis involving central fusion of meiotic products. This ability allows pseudoclonal lineages of workers to establish, which are presently widespread as reproductive parasites within the honeybee populations of South Africa. Successful long-term propagation of a parthenogen requires the maintenance of heterozygosity at the sex locus, which in honeybees must be heterozygous for the expression of female traits. Thus, in successful lineages of parasitic workers, recombination events are reduced by an order of magnitude relative to meiosis in queens of other honeybee subspecies. Here we show that in unmated A. m. capensis queens treated to induce oviposition, no such reduction in recombination occurs, indicating that thelytoky and reduced recombination are not controlled by the same gene. Our virgin queens were able to lay both arrhenotokous male-producing haploid eggs and thelytokous female-producing diploid eggs at the same time, with evidence that they have some voluntary control over which kind of egg was laid. If so, they are able to influence the kind of second-division meiosis that occurs in their eggs post partum.

Chromatic photoacclimation, photosynthetic electron transport and oxygen evolution in the chlorophyll d-containing oxyphotobacterium Acaryochloris marina.

Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O(2) electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206+/-51 micromol m(-2) s(-1) (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109+/-27 micromol m(-2) s(-1) (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73+/-7 micromol mg Chl d(-1) h(-1). The gross photosynthesis/respiration ratio (P(g)/R) of Acaryochloris under optimum conditions was about 4.02+/-1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris.