View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Magazine R861 Primer essentially a new kind of nest, and the oldest ones foraging organism built up of organisms of outside the nest. Just as cells are the old kind. more fixed in function, so are they Consider the famous honeybee more fixed in space. Social insects, Eusociality waggle dance. This dance, in contrast, are not physically performed by returning foragers, connected, and their colonies give David C. Queller1 and Joan E. tells other workers the direction us examples of organismal entities Strassmann and distance of rich food sources. that are dispersed in space. A final The colony benefits by exploiting important difference is the lack of Most biologists devote their the hard-won knowledge of those centralized control in social insect research careers to working out the foragers that find food bonanzas. colonies. Despite the controlling intricacies of how their favorite The dance is celebrated as a rare image conveyed by use of the term organism functions, how it example of symbolic “queen”, there is nothing like a processes energy, transmits communication between individual colonial brain. No individual information from one place to organisms, but it can also be perceives the state of the entire another, regulates metabolites, viewed as a part of a signaling colony and sends out instructions. gets rid of waste, builds itself, cascade of the larger Instead, actions are usually self defends itself and reproduces superorganism that regulates work organized by simple rules. Different itself. If one wants to step back according to the supply and individuals each have small pieces and consider what it means to be demand. If the supply of food is of information, which are an organism, it is obviously great, there will be more waggle integrated by the colony as a necessary to broaden one’s scope dancers stimulating more foraging whole. A returning forager doesn’t and to consider the full range of to harvest it. But that is not the know how many foragers and organisms. But an even broader only adjustment necessary. processors are at work. Instead, strategy is to consider entities that Foragers, with their knowledge of she just experiences an indirect have organismal properties but are valuable food sources, do not effect of those numbers — the time outside the realm of standard waste time processing the food, required to offload her nectar or organisms. Man-made artifacts but hand it off to another set of pollen — and acts accordingly. have long been mined for fruitful bees inside the hive. If a forager Despite these differences, the analogies about particular has trouble finding a processor key defining similarity remains; organisms and functions. bee, she begins a different dance, colonies are like organisms, but Computer viruses and artificial life the tremble dance, which both unlike anything in the non- programs also capture some activates bees to become biological world, with respect to important similarities. But perhaps processors and inhibits waggle their degree of integration and the best we can do in this area is to dancing. The result is a negative cooperation for the good of the study eusocial colonies. feedback system that allocates whole. The key question then is an Eusociality is a term coined to workers to foraging and processing evolutionary one. How did this cover ants, bees, wasps, and tasks according to need (Figure 1). organismal degree of cooperation termites that have three Additional links in the system evolve, given that the Darwinian properties: overlap of include the needs of the brood and norm is closer to a struggle of all generations, cooperative rearing the degree to which storage against all? This is a question that of young and non-reproducing capacity is filled. Such regulatory doesn’t trouble us much for most worker castes. Other organisms feedback systems operate in multicellular organisms. Genes in a that have these traits have since nearly every aspect of social insect macrophage can easily be selected been added: some aphids and colony functioning, just as they do to cause their cells to specialize on thrips, a beetle, some snapping in other organisms. non-reproductive tasks, because shrimp and the naked mole rat. In Besides the clear similarities they are the same genes that will eusocial species, non- between organisms and be transmitted through the germ reproductive workers care for the superorganismal colonies, there line. This is ensured by clonal young of the reproductive queens are some differences that show us descent from a single-celled (and sometimes kings). As such, that entities with organism-like zygote. William D. Hamilton workers are analogous to the functionality and integration can showed that the same kind of somatic cells of an organism, operate in unfamiliar ways. For explanation applies to eusocial which work for the transmission example, the cells of organisms insects, but in a less absolute way. of their genes by proxy, via the terminally differentiate into Members of social insect colonies germ line cells. Like the cells of numerous specialized types, while are relatives, sometimes just a an organism, the members of a social insect colonies have at most single queen and her progeny. eusocial colony have evolved only a few terminally differentiated Therefore, though they are not elaborate mechanisms to castes. Instead, much of the clonal, the do share a large fraction enhance the survival and division of labor is carried out by of their genes. A gene causing self reproduction of the larger unit. means of a temporal specialization, sacrifice can thus be favored by The colony consisting of one or often with the youngest adults selection if it aids relatives who more queens and workers has tending the brood, older ones might bear copies of the gene, but been called a superorganism, carrying out other activities in the the aid has to be large enough to Current Biology Vol 13 No 22 R862 expansion in this area, it may be Nectar Nectar better to stay at home and help Search collecting processing than to take the risks of dispersing time rate rate to find a new home. Fortress defenders would include aphids and thrips that live in plant galls, termites that inhabit wood, the social shrimp that live in sponges, Number Number and the naked mole rats in their Waggle Tremble of of food dancing dancing extensive subterranean tunnel foragers storers systems. In contrast, life insurers, which may include most ants, bees, and wasps, forage outside Current Biology their nest to bring food back to their helpless young. This is a Figure 1. difficult lifestyle to follow as a Regulatory network controlling allocation of honeybee workers to nectar gathering solitary individual, because outside the hive and nectar processing within the hive. After Figure 6.14 of Seeley (1995). foraging entails risks of predation, and the death of the adult means compensate for the chance that had evolved over a dozen times in the death of all her dependent the aided relative does not carry a the Hymenoptera as against once young. It works much better when copy of the gene. So honeybee or twice in the diploid termites, and groups of adults share the risk; if workers can gain by stinging large also why workers are only female one dies, her investments in young vertebrate intruders, because they in the Hymenoptera, but both are not wasted because the may save their whole colony full of sexes in the termites. surviving adults can carry on. relatives who pass on the genes This elegant hypothesis Despite the organismal quality of for stinging. They have even dominated discussions of the eusocial colonies, there are limits evolved barbs on their stingers that evolution of eusociality for many to cooperation. If the worker increase the effectiveness of years, but has been weakened by honeybee’s use of her sting wins stinging by anchoring tightly in the further analysis. Once models prizes for altruism, the young victim, even though it also incorporated all the details of honeybee queen puts her sting to disembowels and kills the worker. reproductive value, sex ratios, and a strikingly different use. Honeybee This selection via effects on especially the fact that a female’s colonies reproduce by splitting. relatives, known as kin selection, is high relatedness to sisters is The old queen departs with the quantified in Hamilton’s rule, the countered by an unusually low majority of the worker force (Figure simplest version of which is c < b*r. relatedness to brothers, it became 2), leaving the remaining workers The fitness cost for the altruist (c) evident that any haplodiploid to await the emergence of several must be less than the fitness relatedness effect was not only new queens, who have been benefit to its relative (b), multiplied smaller than had been thought, but developing in specially prepared by the relatedness (r). In diploid transitory. Even though Hamilton’s cells. If the worker force is still species, the relatedness is 1/2 to specific haplodiploid hypothesis quite large, the first new queen to mothers, fathers, children, and full has been weakened, his general emerge may also leave with some siblings; it is 1/4 to half siblings, theory of kin selection remains of them to start another colony. If, uncles, aunts, nephews and central to the understanding of the however, the worker force is nieces, and so on. Hamilton also origin of eusociality. However, the smaller, the new queen stays and noticed that these relatedness focus has shifted from kin selection battles to the death with her sister values do not all apply to the ants, driven by unusually high queens for the right to set up bees, and wasps.