Behaviour And Sociobiology Of Insects Sociology Essay

Any of numerous species of insects that live in colonies and manifest three characteristics: group integration, division of labour, and overlap of generations. Social insects are best exemplified by all termites (Isoptera) and ants (Formicidae) and by various bees and wasps (Hymenoptera).

Ant colonies, bird flocks, rain forests, businesses, organizations, communities, the stock market and the global economy all have something in common. They are complex adaptive systems. Complex means composed of many parts which are joined (literally “twisted”) together. Adaptive refers to the fact that all living systems dynamically adapt to their constantly changing environments as they strive to survive and thrive. And systems means everything is interconnected and interdependent.

Unlike nonadaptive complex systems, such as the weather, complex adaptive systems have the ability to internalize information, to learn, and to modify their behavior (evolve) as they adapt to changes in their environments. In other words, they have brains. Examples of complex adaptive systems include:

Social insects are differentiated in structure, function, and behaviour into castes, the major ones being the reproductives (e.g., the queen) and the steriles (workers and soldiers). Besides carrying out the basic function of reproduction, the members of the reproductive caste generally select the site for a new colony and excavate the first galleries.

Social insects (ants, bees, wasps and termites) are among the most diverse and ecologically important organisms on earth. As superorganisms, they live in intricately governed societies that rival our own in complexity and internal cohesion. They are particularly well suited to post-genome era biology because they can be studied at multiple different levels of biological organization, from gene to ecosystem, and much is known about their natural history. The sequencing of the honey bee genome provides additional tools and information that can be used to examine all insect societies.

Animal Behaviour and Sociobiology

The evolution of cooperation and altruism in animal societies is being studied using social insects such as ants, bees and wasps as experimental model systems. Social insects are used because they exhibit the most spectacular examples of cooperation and altruism and because they are easy to manipulate and study. Questions being addressed include how the members of a social insect colony divide labour among themselves, regulate each other’s reproduction, communicate with each other, distinguish their nestmates from non nestmates and how natural selection can lead either to the origin and elaboration or to the loss of sociality. The techniques used include behavioural observations, pheromone extractions and bioassays and the use of microsatellite based molecular markers to estimate genetic relatedness and genetic structure of populations.

Termites

Termite colonies are found in regions of Africa, South America, Australia and the United States. They are social insects but less advanced than ant colonies. Termites are related more to cockroaches.

The termite colony has three classes of individuals and each class includes both sexes. The reproductive class is represented by the king and the queen. These two individuals are locked away in a chamber in the centre of the termite nest.

The queen becomes huge soon after fertilization as her abdomen swells with eggs. She lays these eggs at a rate of several thousand each day throughout her lifetime. The soldiers have enormous heads with powerful jaws. The queen, king and soldiers are fed by the workers.

Termites digest wood and paper. They do great damage to woodwork in houses, as well as to furniture and books. Some species of termites build nests up to 6 metres in height

Social Insects.

The fascination of social insects

The social insects represent one of evolution’s most magnificent, successful, and instructive developments. Ever since the behavior of ants, bees, wasps, and termites was first recorded in antiquity, these insects have exerted a powerful hold on our imaginations.

Three characteristics of social insects account for this interest. The first is the very habit of living in social groups. To biologists, this way of life represents a fascinating evolutionary innovation, yet it also poses a basic dilemma. Contrary to what we may have commonly learned, the essential history of life on Earth has not been the story of the rise and fall of dominant groups of animals like the dinosaurs. Instead, life’s history has been the succession of what evolutionary biologists J. Maynard Smith and E. Szathmary termed “major transitions” in evolution. Without any one of these transitions, living things today would be fundamentally different.

Two of these major transitions are the evolution of sexually reproducing organisms from those that reproduce asexually, and the evolution of multicellular from single-celled organisms. These transitions share a radical reorganization of living matter. In particular, at each transition, existing units coalesced to form larger units. In the process, the original units lost some or all of their power of independent reproduction, and the way genetic information is transmitted was changed. The social insects are the prime examples of the next major transition, from solitary organisms to social organisms. As a result of this change, workers of social insects have largely lost the power of reproducing independently, and genetic information has come to be primarily transmitted from generation to generation via the reproduction of the queens (and kings in termites). Why these workers have foregone their power of reproduction is a basic dilemma that insect sociality poses for biologists.

The second characteristic of social insects, which explains why they command attention, is their overwhelming numerical and ecological dominance. Ants, for example, occur from the Arctic tundra to the lower tip of South America. They swarm in diverse habitats, ranging from desert to rainforest, and from the depths of the soil to the heights of the rainforest canopy. The abundance and ubiquity of social insects give them an ecological importance that is unmatched among land-dwelling invertebrates.

The third and final fascinating characteristic of social insects is the way in which they perform work. Clearly, social insects carry out cooperative tasks, such as building nests, with results that are stunningly complex and precise. Termites build nests that are towering hills of red clay, with intricate internal architecture designed to maintain a cool, stable interior. The nests of honey bees house waxen combs composed of thousands of exquisitely arrayed hexagonal cells. Social wasps construct nests in which parallel tiers of cells are enclosed within a delicate paper globe.

These nest forms point to the ability of social insects to achieve, as a collective, impressive feats of architectural complexity. However, biologists have long puzzled over how social insects complete these complex tasks as a group when individual workers frequently strike us as inept. “It seems to me that in the matter of intellect the ant must be a strangely overrated thing,” wrote Mark Twain after watching the fumbling meanderings of a worker carrying a grasshopper’s leg back to its nest. The ant’s seemingly unnecessary scaling of an obstacle was, Twain went on to say, “as bright a thing to do as it would be for me to carry a sack of flour from Heidelberg to Paris by way of Strasburg steeple.” In this chapter, we first review some basic biology of social insects, then consider the three principal characteristics of social insects in turn.

COLLECTIVE INTELLIGENCE IN SOCIAL INSECTS
Introduction

It wasn’t so long ago that the waggledance of the honey bee, the nest-building of the social wasp, and the construction of the termite mound were considered a somewhat magical aspect of nature. How could these seemingly uncommunicative, certainly very simple creatures be responsible for such epic feats of organisation and creativity? Over the last fifty years biologists have unravelled many of the mysteries surrounding social insects, and the last decade has seen an explosion of research in fields variously referred to as Collective Intelligence, Swarm Intelligence and emergent behaviour. Even more recently the swarm paradigm has been applied to a broader range of studies, opening up new ways of thinking about theoretical biology, economics and philosophy. It turns out that not only might we, as multi-cellular organisms, be composed of swarms, but so could our societies, economies and perhaps even our minds. In this essay I will outline three of the most promising areas of social insect-inspired AI: ant-based search algorithms, Particle Swarm Optimisation and swarm robotics, and hopefully provide an insight into how these studies have grown out of a small niche of A-life research into an all-encompassing new way of thinking.

In the Beginning

Konrad Lorenz (1903-1989) is widely credited as being the father of ethology, the study of animal behaviour, with his early work on imprinting and instinctive behaviour, however it might be argued that an even earlier pioneer of the field was a South African, Eugene Marais (1872-1936). Marais was a brilliant man – poet, writer, lawyer, psychologist and naturalist. He made ground-breaking studies into societies of wild apes a full sixty years before any other. He also studied termites, known in his day as white ants, publishing articles as early as 1925. In 1937 a book, The Soul of the White Ant[1] was published posthumously in which he described in painstaking detail the resemblance between the processes at work within termite society to the workings of the human body. He regarded red and white soldiers as analogous to blood cells, the queen as the brain and the termites’ mating flight in which individuals from separate termitaries leave to produce new colonies as exactly equivalent to the movement of sperm and ova.

Like many geniuses, Marais’ life ended in tragedy. A spiralling drug addiction and depression was worsened when in 1927, a Belgian author, Maurice Maeterlinck (1862-1949) published The Life of the White Ant[2] which was largely plagiarised from Marais’ articles. In 1936, Marais committed suicide. The full text of The Soul of the White Ant is available on the web, and is well worth looking at since the implications of his insights have yet to be fully understood.

Stigmergy: Invisible Writing

Although Marais had created a detailed document on termites, he was unaware of the mechanics of termite communication. How is it that a group of tiny, short-sighted, simple individuals are able to create the grand termite mounds, sometimes as high as six metres, familiar to inhabitants of dry countries? The answer to this question was first documented by the French biologist, Pierre-Paul Grasse in his 1959 study of termites[3]. Grasse noted that termites tended to follow very simple rules when constructing their nest:

First, they simply move around at random, dropping pellets of chewed earth and saliva on any slightly elevated patches of ground they encounter. Soon small heaps of moist earth form.

These heaps of salivated earth encourage the termites to concentrate their pellet-dropping activity and soon the biggest heaps develop into columns which will continue to be built until a certain height, dependent on the species, is reached.

Finally, if a column has been built close enough to other columns, one other behaviour kicks in: the termites will climb each column and start building diagonally towards the neighbouring columns.

Obviously, this does not tell the whole story but a key concept in the collective intelligence of social insects is revealed: the termites’ actions are not coordinated from start to finish by any kind of purposive plan, but rather rely on how the termite’s world appears at any given moment. The termite does not need global knowledge or any more memory than is necessary to complete the sub-task in hand, it just needs to invoke a simple behaviour dependent on the state of its immediate environment. Grasse termed this stigmergy, meaning ‘incite to work’, and the process has been observed not just in termites, but also in ants, bees, and wasps in a wide range of activities.

The application of stigmergy to computation is surprisingly straightforward. Instead of applying complex algorithms to static datasets, through studying social insects we can see that simple algorithms can often do just as well when allowed to make systematic changes to the data in question.

Self Organisation

Moving earth around is only one of many ways in which social insects communicate through their environment. Another famous example of stigmergy is pheromonal communication, whereby ants engaging in certain activities leave a chemical trail which is then followed by their colleagues.

This ability of ants to collectively find the shortest path to the best food source was studied by Jean-Louis Deneubourg[4], when he demonstrated how the Argentine ant was able to successfully choose the shortest of two paths to a food source. Deneubourg was initially interested in self organisation, a concept which until then had been the fare of chemists and physicists seeking to explain the natural order occurring in physical structures such as sand dunes and animal patterns.

A self organising (SO) system is any dynamic system from which order emerges entirely as a result of the properties of individual elements in the system, and not from external pressures. The classic example of SO is Benard cellular convection, named after the French scientist who discovered it. A Benard cell consists, very simply, of a layer of fluid which is heated from below. Under the right circumstances, a perfect vertical temperature gradient is set up within the fluid, causing the system to become ‘top heavy’, with warmer molecules at the bottom compelled to rise to the top. You might expect the liquid to simply bubbling away with no pattern or organisation, but instead an ordered system is formed. Millions of molecules self organise into a hexagonal pattern, something like a honeycomb, which enables the most efficient convection for energy-dissipation.

Deneubourg saw the potential for this concept, which by 1989 had turned into a sizeable research project amongst physicists, to be applied to biology. In his experiment, a group of ants are offered two branches leading to the same food source, one longer than the other. Initially, there is a 50% chance of an ant choosing either branch, but gradually more and more journeys are completed on the shorter branch than the longer one, causing a denser pheromone trail to be laid. This consequently tips the balance and the ants begin to concentrate on the shorter route, discarding the longer one. This is precisely the mechanism underpinning an ant colony’s ability to efficiently exploit food sources in sequential order: strong trails will be established to the nearest source first, then when it is depleted and the ants lose interest, the trails leading to the next nearest source will build up

Bees and Social Insects

1. Definition of Eusociality

Many animals live together as a group, but they are not necessarily social (e.g. a school of fish) because there is a very precise definition when it comes ot sociality. True sociality (eusociality) is defined by three features: 1). There is cooperative brood-care so it is not each one caring for their own offspring, 2). There is an overlapping of generations so that the group (the colony) will sustain for a while, allowing offspring assist parents during their life, and 3). That there is a reproductive division of labor, i.e. not every individual reproduces equally in the group, in most cases of insects, this means there is one or a few reproductive(s) (“queen”, or “king”), and workers are more or less sterile.

2. Degrees of sociality

Obviously not all insects are eusocial. Michener (1969) provided some other classifications of various stages of social insects:

Solitary: showing none of the three featured we mentioned above (most insects)

Subsocial: the adults care for their own young for some period of time (cockroaches)

Communal: insects use the same composite nest without cooperation in brood care (digger bees)

Quasisocial: use the same nest and also show cooperative brood care (Euglossine bees)

Semisocial: in addition to the features in quasisocial, also has a worker caste (Halictid bees)

Eusocial: in addition to the features of semisocial, there is overlap in generations (Honey bees).

3. A survey of eusocial animals

Eusociality was considered extremely rare in the whole animal kingdom, and even in insects it was only found in Hymenoptera (ants, bees, and wasps) and Isoptera (termites). However, recently this has expanded to a few more groups: in gall aphids (Homoptera) there are sterile soldiers who would sacrifice their lives to their clone sisters who can reproduce, so they are considered eusocial because these soldiers do not reproduce while others do. This is also the case for social thrips that are gall-forming (Thysanoptera). In 1992 a social weevil ( Austroplatypus incompertus, Curculionidae Coleoptera).was discovered. In non-insects, eusociality only appeared twice: in a mammal and a marine animal. Naked mole rats live in complex underground tunnel systems in Africa and animals in the same nest are closely related, only one female (the queen) reproduces, although workers, normally sterile, can ovulate when removed from the nest, presumably due a lack of inhibition from the queen. Snapping shrimp (Synalpheus regalis) lives inside sponges and each ‘colony’ has 200-300 individuals, but only one queen reproduces, again the caster is probably not fixed – the workers remain totipotent and can potentially become a queen when the queen shrimp is removed.

The table below summarizes the above information. Notice that “the number of times eosociality has evolved” does not mean the number of cases of eusociality (there would be tens of thousands if so, because there are about 9 thousand species, of ants alone). Instead it means how many times it has independently evolved (for example, there are 9 species of honey bees, if all of them shared a common eusocial ancestor, it would be considered to be evolved once here, actually you trace back to the lower branch of the taxonomic tree, and count only once at the lowest level).

4. Evolution of sociality

How could eusociality evolve? Darwin, in his “Origin of Species” (1859) thought that sterile workers in a bee colony, being unable to transmit their genes, represent a special challenge to his theory of natural selection. This is because natural selection depends on the transmission of ‘traits’ that convey selective advantages to the individuals, and these traits have to be determined genetically (so they are heritable). If workers are sterile, how can they transmit the “helping traits” to the next generation?

4.1. Genetic explanations

This problem continued to trouble biologists until William Hamilton (1964) found an ingenious way to explain how a trait can be inherited without direct reproduction. Hamilton introduced a brave new concept, ‘inclusive fitness’, which basically says someone could still have a reproductive fitness, even if he/she has no direct offspring. This is while the ‘traditional fitness’ only count how many children one has, but inclusive fitness takes account of all others who share genes with the person (or animal). For example, I should share approximately 50% of gene with my full brother, therefore if I decide not to marry and have kids, but I help my brother to raise 4 children, it is equivalent to myself having two children. This inclusion of anyone elses’ fitness, who shares common genes by descent, factored by a coefficient of relatedness, is called inclusive fitness. Therefore although workers do not reproduce, if they share genes with their mother (the queen) to raise more sisters (future queens), their genes would be transmitted too, to the next generation.

In fact in honey bees and other hymenoptera, the relatedness among sisters are higher than among other animals. This is because of the haplo-diploidy sex determination: drone develop from unfertilized eggs and carry one copy of chromosomes (haploid) from their mother only (no father), while females are fertilized and carry two copies of chromosomes (diploid). Haploid drones do not have the complimentary copy of genes to do exchange (across the two copies of genes, alleles), so all the sperms produced by a single drone are identical (clones), if not considering newly produced mutations. Assume the queen is mated only to one drone (which is not true, we will come back to this point later), then all her daughters will share 50% genes from the father (since they are all the same), but 25% of their genes from the mother. The coefficient of relatedness among the offspring is therefore 0.75 (1?0.5 + 0.5*0.5). This is much higher than the 0.5 for sister-sister in a diploid organism (such as humans). The workers who share the same father and mother, are therefore also called ‘super-sisters’ because of this higher relatedness. This theory of one can pass genes through relatives and gain fitness is called ‘kin selection’.

Hamilton postulated that because supersisters share 75% of their genes, it is actually a better deal to be a worker, to whom, a new queen would have 75% of genes by common descent with her, whereas from the queen’s point of view, she only transmitted 50% of her genes to the new queen. In this sense, the inclusive fitness is actually higher for the sterile worker sisters, than for the fertile mother. Further, Hamilton argued that haplodiploidy must have played an important role in the evolution of sociality because it occurred 11 times in Hymenoptera, but much fewer times in other organisms combined. Note at that time the only other eusocial organisms are termites. Among the recently discovered social animals, thrips also have haplodiploidy as in hymenopteran insects.

One difficulty with the above argument is that the honey bee queen actually mates with more than one male (drone), in some cases as many as more than 30 drones, because half-sisters (workers who share the same mother, but fathered by different males) are only related to one another by 0.25 (0*0.5+0.5*0.5) the average relatedness among the workers in such a colony is close to the average between 0.75 and 0.25, which is 0.5, not different from other diploid organisms. Of course, one could argue that multiple mating is adaptive for other reasons, and arose AFTER sociality has been evolved.

While the genetic system might predispose some organisms to have eusociality, it is easy to see that haplodiploidy is neither necessary (since there are other non-haplodiploid organisms being eusocial), nor sufficient (since not every species in Hymenopetera is eusocial). It is easy to see though, that eusociality can evolve easier in groups within which individuals are highly related, either due to haplodiploidy, or due to mating systems. In both termites and the naked mole rats, animals within a group are all highly related, perhaps due to inbreeding, although it is known in named mole rats, some males would migrate to other nests to accomplish periodic outcrossing, which might be necessary to reduce the cost of inbreeding. In aphids, all colony members are ‘clones’ because the mother can reproduce asexually (parthenogenesis). However, the marine shrimps do not show high degrees of inbreeding.

4.2. Ecological considerations

There appear to be common ecological features for other eusocial animals other than hymenoptera. For example, for newly discovered aphids, thrips, beetles and shrimps, they all have a commonly held, valuable resource (nest mounds, galls, or sponges). Queller and Strassmann (1998) distinguish these eusociality (fortress defenders) from the ‘life insurers”, in which cooperation creates benefits mainly through reducing the risk of reproductive failure (most Hymenoptera). Crespi (1994) argued that three conditions are sufficient to explain occurrences of eusociality for the fortress defenders. The first is the food and shelter are in enclosed habits, representing higly valuable and long lasting resources. Because of the high value of the resources, there should be strong competition for these resources. Lastly, because of the competition, selection should promote effective defense among the organisms. This has been shown to be true for aphids, thrips and shrimps. Interestingly, in shrimps the non-reproducing soldiers are mostly male, perhaps because they have larger claws and would better suit the job. Contrast this with males in Hymenoptera societies, their other name ‘drone’ suggest laziness and they do not perform work in the colony, perhaps because of their lack of weapon (no sting).

4.3. Life history considerations

Because one criteria for eusociality is overlap in generations, parental care has been recognized as an important prerequisite for eusociality. Other traits, such as high adult mortality (e.g. foraging honey bees only survives 7-10 days), long periods of offspring dependence (21 days development for honey bee workers), and delayed age of reproduction, can favor the development of helpers. More recent studies in marine shrimps suggest that mutualistic interactions and restricted dispersal can also foster evolution of sociality.

References for further reading:

Crespi, B. J. 1992 Eusociality in Australian gall thrips. Nature 359:724-726.

Crespi, B.J. 1994. Three conditions for the evolutions of eusociality: are they sufficient? Insectes Soc. 41: 395-400.

Duffy, J. E. 1996. Eusociality in a coral-reef shrimp. Nature 381:512-514. See also

Ito, Y. 1989. The evolutionary biology of sterile soldiers in aphids. Trends in Ecology and Evolution 4:69-73.

Ito, Y. 1994. A new epoch in joint studies of social evolution: molecular and behavioural ecology of aphid soldiers. Trends in Ecology and Evolution 9:363-365.

Kent, D. S., and J. A. Simpson 1992. Eusociality in the beetle Austroplatypus incompertus (Coleoptera: Curculionidae). Naturwissenschaften 79:86-87.

Jarvis,JUM 1981 Eusociality in a mammal: Cooperative breeding in naked mole-rat colonies. Science 212, 571-573.

Queller D.C; Strassmann, J.E. 1998. Kin selection and social insects: social insects provide the most surprising predictions and satisfying tests of kin selection. Bioscience. 48,165-175

Rypstra, A. L. 1993. Prey size, social competition, and the development of reproductive division of labor in social spider groups. American Naturalist 142:868-880.

Strassman, J. E., Z. Zhu, and D. C. Queller 2000. Altruism and social cheating in the social amoeba Dictyostlium discoideum. Nature 408:965-967.