Somatic Maintenance Resources in the Honeybee Worker Fat Body Are Distributed to Withstand the Most Life-Threatening Challenges at Each Life Stage

Aamodt RM (2013) Somatic Maintenance Resources in the Honeybee Worker Fat Body Are Distributed to Withstand the Most Life-Threatening Challenges at Each Life Stage. PLoS ONE 8(8): e69870. doi:10.1371/journal.pone.0069870 Somatic Maintenance Resources in the Honeybee Worker Fat Body Are Distributed to Withstand the Most Life- Threatening Challenges at Each Life Stage Siri-Christine Seehuus 0 Simon Taylor 0 Kjell Petersen 0 Randi M. Aamodt 0 Christoph Englert, Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI), Germany 0 1 Department of Aquaculture and Animal Sciences, Norwegian University of Life Sciences , Aas , Norway , 2 Queen Maud University College, Early Childhood Education , Trondheim , Norway , 3 Centre for Integrative Genetics (CIGENE), Norwegian University of Life Sciences , Aas , Norway , 4 Computational Biology Unit, Uni Computing, Uni Research AS , Bergen , Norway In a global transcriptome analysis of three natural and three manipulated honeybee worker phenotypes at different ages, we have investigated the distribution of investment in somatic maintenance of the fat body. Gene expression is modulated so that the bees are able to resist the most life-threatening challenges at the actual life stage. Different modes of maintenance and repair are regulated, apparently to meet the environmental challenges most detrimental to survival and reproductive potential for the hive. We observed a broad down-regulation of genomic and cellular maintenance in the short-lived foragers and nurse bees compared to the long-lived winter bees. Our results show that survival and reproduction of the entire hive is given priority over the individual bees, hence supporting the idea of the honeybee society as a superorganism. Our results also fit the disposable soma theory of aging. - In the insect world a broad array of different forms and degrees of social organisation can be found. In the more highly developed forms, social insect colonies are so tightly integrated that they have been suggested to function as a single organism, a superorganism [1,2,3]. Honeybees are eusocial insects where the fundamental components that underlie superorganismal order are the female forms [4]. Like sterile somatic cells, the workers differentiate and communicate to produce coordinated patterns of growth, homeostasis, provisioning and defence before death [4]. In the Apis mellifera subspecies in Old World temperate climates, workers spend the first weeks performing in-hive activities like brood care (nurse bees), and switch at age 34 weeks to foraging tasks (foragers) [5,6]. Workers emerging in autumn develop into so called diutinus [7] or winter bees that survive for 810 months [8,9,10]. The following spring, winter bees will begin either nursing or foraging, and simultaneously start to age [7]. We have performed a global transcriptome analysis of the fat body of three naturally occurring honeybee worker phenotypes, in addition to three manipulated worker types. The fat body is the insect equivalent to white adipose tissue or liver [11]. We observed a broad down-regulation of the somatic maintenance machinery in the foragers. In nursing bees, body maintenance is extensively upregulated at the external level, i.e. the cuticula. In the long lived winter bees however, but not in the other phenotypes, a broad array of maintenance and repair functions of cells, proteins and nucleic acids took place. Different modes of maintenance and repair thus seem to be expressed to meet the environmental challenges most detrimental to survival and reproductive potential at the actual life stage. If a clear pattern of resource allocation between reproduction and repair and between different modes of maintenance and repair could be observed on a colony level, in would support the theory of the honeybee society being a superorganism, since such a pattern would indicate that the whole society must be under selection and not only its individual parts. We therefore consider that these results support the concept of the honeybee society as a superorganism, and also give substantial support to the disposable soma theory of aging [12] at this level of biological organisation. If the disposable soma theory is correct, an ageing programme would be expected to spare crucial functions but to down-tune others to a level just necessary to sustain functionality for the remains of an estimated life span under the actual environmental risks and circumstances [13]. This theory states that aging results from the bodys need to budget the amount of energy available, resulting in imperfect maintenance of the soma. Materials and Methods Nurse bees and foragers Honeybees were paint marked on emergence and introduced to production hives in the apiary of the Norwegian University of Life Sciences (Aas, Norway). After eight days painted bees with head and thorax in cells containing larvae were gathered as nurse bees. Foragers were marked at the hive entrance in a second colour. When most of the marked bees were verified foraging, the double marked returning foragers were gathered at the hive entrance. After removing the intestines the bees were rapidly frozen on dry ice and transferred to 280uC for storage until further processing. Reversion Approximately 6000 bees were marked on emergence and introduced into a six frame host colony containing a mated queen, unmarked bees of various ages, brood and food. The host colony had an empty hive unit on top. Entrance counts of marked bees returning from foraging were performed four times daily. When the number was declining, the hive was manipulated to separate marked foraging bees from marked foragers still engaged in hive activities. At the high of foraging activity, the host colony was removed from its original site. The queen was replaced in a new host colony with three frames of open brood and two frames of honey and pollen, but devoid of worker bees. The new hive box was placed at the original site of the colony with the original flight entryway. The old host colony was placed on top with a divider between the two hive boxes. The top box got a new entranceway 180 degrees from the original one. Experienced foragers returned to the new hive box. Four and eight days after reversal nursing foragers were collected and frozen as described. RNA interference and methoprene treatment Maurizio hives were established by caging the queen, removing all open brood from the host colonies and giving an excess of food. After most of the sealed brood had emerged RNA interference knockdowns were established as described [14]. Newly emerged workers were injected with 1.5 ml of dsRNA (5 mg/ml). The dsRNA was synthesised by RiboMax Express Large Scale RNA production system (#P1320, Promega) with DNA template from vitellogenin (GenBank accession no. AJ517411) clone Ap4a5 (kind gift of Dr. Zila Luz Paulino Simoes). The injected bees were marked with a spot of paint and introduced in equal (...truncated)