A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation

Development of Social Relationships in Insects Andrej Gogala

Social communities of ants, honey- the division of sexual individuals from bees, bumble-bees, wasps and termites infertile workers as well as at least two have always been the source of wonder generations living together, developed and amazement to people. Division of twelve times in insects and eleven labour and cooperation of individuals times in the Hymenoptera. So he in their tendering for the growth and concluded some characteristics of development of the community hymenopterans must stimulate the reminded us of the relationships within evolution of sociality. A peculiarity of the human society. There is, however, hymenopterans is the way how sex is an important difference between the determined in individuals. Males highly developed social insects and our develop from infertilized eggs and are society. Whereas the majority of haploid, have only one set of people is fertile and can reproduce the chromosomes inherited from the majority of individuals in the insect mother, not two like females, which family is barren and without offspring. inherit one set from the mother and the Only males and fertile females other from the father. Because of this reproduce, and the latter are few. As a all sisters inherit the same father's rule, there is only one fertile female in genes, only by the mother's genes are an insect family. She is the mother to they distinct from each other. On all workers in the nest and to the young average, their genes are equal in 75 %. sexual individuals who only occur in If females of bees, ants or wasps have the family in a specific season. daughters, they share only 50 % of Workers are usually females, as a rule their genes. So it should be better for without developed ovaries. They spend them to help sisters, which are more their lives providing for the related to them than daughters. community, taking care of their The theory prevailed probably also younger brothers and sisters and the because it uses mathematics, which is a mother, who spends most of her time characteristic tool for sciences which laying new eggs. can calculate all even before the Even Charles Darwin admitted that the phenomenon is observed (physics). existence of infertile workers was the People often reproach biology not to most difficult question to be explained be true science if it is founded on by his theory of evolution or, as he observations only. But the kin called it, natural selection. How could selection theory has many deficiencies. traits distinguishing infertile indivi- The queen can mate with several males duals from sexual ones develop, if they and her daughters (workers) are then do not leave descendants and cannot less related. But this fact is not crucial pass their genes to the next generation? to the theory. We can imagine that Why workers selflessly care for their mating with several males evolved family and give up their own only after the sociality was already reproduction? developed. It enables the colony to be In past decades the kin selection more adaptable as different workers theory, put forward by British biologist react differently to changes in the W.D. Hamilton, came into pro- environment. minence. Eusociality, characterized by

1 A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation

It is more important that only sisters majority of time and energy from are more related to the hymenopteran animals building nests. Nests protect females than daughters. When young progeny and enable safe first steps in queen has descendants, they are less life for them. Such nests have to be related to sisters helping the old queen protected from parasites, thieves of than their own daughters would be. collected food and intruders. That is Descendants of the community, cared possible only in communities where for selflessly by the workers, are only part of their members leave the therefore not related to them more than nest to collect food. Initiation of new they would be in case the workers nests is a demanding and risky reproduced on their own. And only the business because of shortage of next generation is importat to suitable places, predators outside and evolution. great amount of energy, spent during In spite of attractiveness of the theory construction by the female. More than at first sight, it is not possible to half of solitary bee females die before imagine a selective mechanism their nest is finished. So it is better for favouring those descendants of the them if they can use an already colony that would cooperate better existing nest. Many bee and wasp only because they are related. If sisters species developed cleptoparasitic life. are closely related, it is insignificant They do not build their own nests but who among them will reproduce, in lay their eggs in nests of other species, best instance. Those that care for the like cuckoos. In some species, others and do not lay eggs by however, females return to their natal themselves cannot have influence on nests and care for progeny of their traits of the next generation. Only mother or sister. A social community is those females that reproduce in spite of formed. relatedness, what means they are least Several forms of sociality can be found adapted to social life, will have in bees. Most simple is a communal descendants. This does not lead to the life. Females share a common entrance development of sociality. Besides that, to the nest, but in it, each one of them eusociality with infertile workers prepares own brood cells and lays eggs evolved also in termites, shrimps living on provisions. Quasisocial commu- in sponges and even in mammals nities are similar, only the females mole-rats which all have diploid males. cooperate in provisioning cells with A common feature to all animals living food. In semisocial communities, however, one of them earns a dominant in eusocial communities is not the way sex is determined, but construction of position. Usually it is the largest one nests or, respectively, dwellings in who earns dominance by physical which they live and care for their superiority. She stays in the nest, progeny. Ants, bees, wasps, termites guards it and examines brood cells. If and mole-rats all build complicated she finds an egg of her nestmate in burrows, combs, even several meters them, she will eat it and lay her own high residencies, and build their nests egg in its place. In this way she in hollows or cavities, which are succeeds to mother almost all usually rare in the environment. descendants of her community in Sponges in which eusocial shrips live which other females, usually her are also fewer than individuals. sisters, fly to pastures for pollen and Construction of nests takes the honeydew.

2 A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation

Communal life, quasisociality and neighbouring cells. Also because of semisociality can be understood also as that we can look at an eusocial steps in evolution leading to highly community as a superorganism. This developed eusocial communities. But conception was introduced by W.M. such development is not inevitable, it Wheeler already in 1911. can stop at certain step or even return We observe semisocial communities to solitary life of females, depending most frequently as a step in the on conditions in the environment development of a halictid bee colony, affecting each species specifically. Halictus scabiosae for example. In this Among halictid bees there are many species, sisters overwinter in their natal solitary species and species with nest and renew it in spring. One of different kinds of sociality. Social life them becomes a functional queen. evolved several times in the group and When her daughters grow up in the several times returned to solitary life. nest taking over the role of workers, That is the only explanation of the fact she does not allow her sisters to enter that in almost all large halictid genera the nest any more. Some of them some social and some solitary species excavate new nests in the vicinity and exist. soon nestmates who do not like to dig A key condition for the evolution of a burrow join them. A new semisocial communities with infertile workers is community is soon established, while exactly the achievement of dominant in the old nest eusociality with infertile females in semisocial communities that workers of the new generation formed. enabled them to mother all descendents The other path leading to eusocial in their nests. Queens in eusocial communities also exists. Some solitary colonies must, as they are the only bees, members of the genus Ceratina individuals which transmit genes to the for example, do not close brood cells progeny, determine also features of and leave like other solitary species. future infertile workers with their They guard the nest and care for the genes, not only of future sex progeny cleaning cells or bringing in individuals. Queens, as well as additional food. Such community is workers, have all genes needed to called subsocial. In some species, a become a queen or a worker. Which daughter can stay in the nest of her genes are expressed in certain mother as a worker. As these bees are, individual depends on conditions in the like bumble-bees and honey-bees, environment in which it develops: members of the family Apidae, this available food, pheromones of the could be the way leading to queen, or simply physical violence of communities that we know in the the dominant female, causing stress in domestic bee. workers. The latter possibility is the most primitive, succeeded in evolution If only one female in a community has usually soon by chemical substances monopoly over reproduction, modified emitted by the queen – pheromones. genes can accumulate in genomes of The development of multicellular her descendants, determining beha- organism from a fertilized egg cell is viour and body shape of workers, as similar. All cells formed by the well as those genes determining division have the same genes, but some features of fertile individuals. Workers of them become skin cells, some liver distinguish often from queens not only cells, nerve cells and so on, all under by the behaviour, but also by size, influence of substances excreted by colour, body shape and other traits. In

3 A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation many ants even several castes of but because that is beneficial to the workers exist that differ in size, shape community or in other words, it and behaviour. assures their parents a more successful During competition among colonies reproduction. (communities) of a species for food Let as return to Darwin at the end. sources and during more or less Although he knew nothing about successful nest construction and mechanisms of inheritance, he protection natural selection occurs. We correctly explained the origin of can say that selection operates on infertile workers and differences better and less well adapted colonies or among them in his book On the origin on better and worse genes of their of species (1859). He wrote: …I queens and males that mated them. If believe the natural selection could, we concentrate on the former acting on fertile parents, form a viewpoint we talk about group species regularly rearing infertiles, selection, while the latter viewpoint only large ones or only little ones, and instructs us that only the genomes of finally, a group of workers of the same sex individuals are selected upon. If so, size and constitution and at the same workers are only autonomous organs time another group of workers with a of the queen, detached from the body. different size and constitution… Altruists are not by their own choice,

A halictid bee Lasioglossum xanthopus is a solitary species.

4 A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation

Halictus scabiosae females live in semisocial and eusocial colonies. Sociable are even their males who gather in the evening to a collective rest.

Lasioglossum marginatum workers are leaving their underground nest. This species lives in perennial eusocial colonies with many workers.

5 A. Gogala: Razvoj družbenosti pri žuželkah. Proteus, dec. 2010, 73 (4): 150-155. Translation

Literature: Darwin, Ch., 2009 (1859): O nastanku vrst z delovanjem naravnega odbiranja ali ohranjanje prednostnih ras v boju za preživetje. Založba ZRC, Ljubljana, 421 str. Gogala, A., 1990: Grintovčanke: življenje divjih čebel. Proteus, 53 (3): 83-89. Gogala, A., 1991: Initiation of new nests in a social bee, Halictus scabiosae Rossi (Hymenoptera: Halictidae). Opuscula zoologica fluminensia, 67: 1-7. O'Toole, Ch., A. Raw, 1991: Bees of the World. Blandford, London, 192 str. Wilson, D. S., E. O. Wilson, 2007: Rethinking the theoretical foundation of sociobiology. The Quarterly review of Biology, 82 (4): 327-348.

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