Charles D. Michener

Evolution of Sociality in Insects

Kin selection has been used to explain evolution of man altruistic traits found in those social insect castes which have reduced reproductivity. Kin selection is most probable among organisms living in family groups. It is commonly assumed, therefore, that (1) the most primitive social insects, like the more specialized ones, live in mother-daughter (eusocial) colonies, (2) colonies of individuals of the same generation and showing castes (semisocial colonies) are abnormal or originate only in inbreeding populations, and (3) transfer of individuals among colonies must be selected against, except in inbreeding populations. Numerous Hymenoptera are cited, however, in which semisociality or transfer occurs in populations lacking evidence for inbreeding; and we believe that, in explaining the origin of social behavior in insects, Hamilton and others have placed too much emphasis on the evolution of altrustic behavior through kin selection. There is considerable evidence that social behavior in insects is in part mutualistic. Social colonies without altruism are therefore considered a probability. Factors in addition to kin selection that could promote social behavior are examined, and it is our view that a whole series of factors acting jointly or alternately is responsible for the numerous origins of sociality in Hymenoptera, compared to only one in all the other insects. An important factor favoring mutual tolerance and initial colony formation is the need for defense. Hymenopteran workers are commonly reproductive and produce most of the male offspring in some primitively as well as highly eusocial forms (90% of the males in a species of Bombus; 95% in a Trigona). Individual selection for sources of males should favor production of workers. Presence of ovaries and of reproductive behavior in many workers suggests that reproductivity is retained by selection. In the most primitive social Hymenoptera, queens and workers together vary little more than do females of related solitary species. If both the more and the less reproductive individuals profit from the association, selection will favor colonies. The more reproductive individuals tend to start nests first and to be joined by delayed reproducers that are often workerlike. Thus semisocial colonies of very similar castes can arise without kin selection or altruism; they are preadaptations to eusocial evolution and provide immediate improved protection for the nest. Joiners will be more certain to arrive, although much delayed, if they are progeny of the colony or lone founder. This leads to eusocial colonies among which kin selection can operate. Eusocial colonies need not, but probably often do, arise from semisocial ones, as is suggested (1) by the frequency of nest aggregations providing numerous acceptors and joiners of the same generation, and (2) by the ontogeny of many bee and wasp colonies. There is no certainty that kin selection and altruism will arise with eusociality, but they probably usually do; they may also arise in semisocial groups if the individuals are closely enough related as a result of inbreeding. Eusocial colonies without altruism are possible if male production by workers is important enough. Long life, and ability to produce female offspring under suboptimum conditions so that they will become joiners, or ability to dominate other females with the same result, and other queenlike features should be favored by individual selection operating on queens, regardless of the origin of the society. Male haploidy is related to many aspects of hymenopteran evolution. Among these is the origin and evolution of social behavior because of (1) partial immunity to inbreeding resulting from the loss of lethals, allowing long-term aggregations and colonies and effective kin selection to arise, (2) sperm storage by females, absence of a king in social groups, and the control of the sex of offspring, permitting the extraordinary sex ratios found in highly social Hymenoptera, (3) the importance of male-production by workers in primitively social groups and some highly social ones, and (4) the closer relation of sisters to one another than to their daughters, an arrangement that ecourages effective kin selection. Male-producing workers increase genetic recombinations and permit retention of the advantages of a haplodiploid genetic system while permitting also some advantages of the ordinary fully diploid system. The loss of variation due to male haploidy may be partly responsible for the evolution of outbreeding devices, including acceptance of joiners. The joiners are ordinarily workers which, as male-producers, will increase variation, but may in error be members of related species, a situation resulting in the potential for evolution of social parasites. Immunity to inbreeding permits aggregations, in which pressure from natural enemies is likely to promote development of colonies. None of the special features described above applies to termites, in which the need to transfer intestinal symbionts must be the prime factor that encouraged social evolution. In the initial stages (as in the roach, Cryptocercus) there is no altruism, a feature that, however, characterizes subsequent stages in termite evolution.

A QUANTITATIVE APPROACH TO A PROBLEM IN CLASSIFICATION

The purpose of the study reported in this paper was to determine whether certain statistical procedures might aid persons interested in the relationships among organisms. The objectives of our study were to investigate numerous characters simultaneously in a considerable group of species; to quantify the relations shown among the species, using objective methods; and to indicate these relationships. The organisms selected as an example for use in this study are solitary bees in the family Megachilidae. This choice was made because one of us (C. D. M.) has made recent systematic studies of these insects, so that conclusions as to the relationships obtained by usual systematic procedures could be compared

Kin recognition in animals.

Kin recognition - the differential treatment of kin and non-kin by an individual within a species - is one of the most interesting and quickly developing topics in modern biology. Researchers have been astonished and fascinated to discover the sophistication and subtlety of the ways individuals in even simple species, distinguish not only kin from non-kin, but also siblings, half-siblings and cousins. In many cases these forms of social behaviour appear to enhance the survival of the group rather than the individual and it is a matter of considerable sociological interest to establish how far such altruistic behaviour is the result of genetically determined traits, and how far it is learnt. Research on this subject is necessarily widely spread across many taxa and many disciplines. This edited collection of papers from academics gives an overview of the whole field, presenting (in some cases, original) research on all the major animal groups which have been studied. It pays particular attention to general methodology and to the specific methods employed in experimental work, but its main strength concerns its treatment of concepts. These are clearly presented and are evaluated from the different points of view of various contributors. Some concepts, especially that of nepotism (the favouring of kin) emerge with greatly enhanced significance.

Reproduction and Castes in Social Halictine Bees

Parasocial and primitively eusocial bees are found in various families of the Apoidea, but the majority of such forms are in the Halictinae (Family Halictidae, the sweat bees). The Halictinae are an enormous and abundant group, worldwide in distribution, arctic to tropical, and every continent has forms whose social biologies remain unknown. Although a few species nest in rotting wood, most make burrows in the soil. New and interesting types of social organization probably remain to be discovered in this subfamily, for only a tiny fraction of the species have been studied behaviorally.

Interactions in colonies of primitively social bees

SummaryThirty-seven laboratory colonies (two to six females in each) of a primitively social halictid bee were observed for a total of 13160 min to obtain data on intranidal differentiation in behavior. Nine behavioral patterns or categories were repeated often enough for numerical analysis of the behavior, i.e., ethometrics.Although the castes are externally indistinguishable and intergrade with one another in ovarian development, the bee with the largest ovaries in each colony shows certain behavioral specializations that justify her designation as queen. She is the most active bee. Pre-eminent among characteristic queen behavioral categories is backing—the queen in every colony backed away from other bees more frequently than any other bee in the colony. Queens are usually maximal nudgers of other bees in the colony, while they are in the low ranks for pollen collecting and guarding. Both backing and nudging are directly related to ovarian size. Other behavioral categories have more complex relationships; e.g., following and guarding are usually minimal for queens and progressively more common for workers with smallest to largest ovaries. Thus the ovarially most queenlike workers are behaviorally the least queenlike for these attributes. The two workers in a colony of three bees are behaviorally different and their counterparts are easily recognizable in larger colonies. The maximal guard, which has ovaries larger than the average for workers, is usually the least active bee, showing minimal backing and minimal working on cells. The maximal pollen collector commonly shows minimal nudging and high passing. She usually has the smallest or nearly the smallest ovaries in the colony. “Other” workers (in colonies of more than three bees) are not specialized as either guards or pollen collectors although they do some of both; they tend to be rather inactive.A principal components analysis of individuals in colonies of three bees, based on all behavioral characteristics except pollen collecting, clustered the bees into two groups, queens and workers, with guards and foragers at opposite extremes of the worker cluster. A discriminant function (canonical) analysis verified the distinctness of these groups, placing the workers into two clusters; when the “other” workers in colonies of four or more bees were also considered, they mostly fell between, but partially mixed with, foragers and guards.In 11 out of 12 colonies, removal of queens resulted in another bee (commonly one of the “other” workers) showing queenlike behavior, sometimes noted in less than four hours. Such replacement queens had enlarged ovaries when later dissected; thus caste determination in the adult stage is verified.It appears as if the bees discriminate among individuals on the basis of ovarian size—for example, the queen concentrates her nudging on the bee with next largest ovaries, commonly the guard. The mechanism by which the queen inhibits ovarian development of her nest mates remains unknown but may be purely mechanical—disturbance by her great activity and frequent nudging of other bees, and drawing bees down, away from the entrance, by her frequent backing.Oophagy was observed three times when the identity of the layer and egg eater were known. In each case the egg had been laid by a worker and was eaten by a queen.

Some Future Developments in Taxonomy

It is no longer fantastic to imagine that man might reach a new planet and find there a rich biota. For practical as well as for study purposes, he would need to devise a taxonomy for the organisms if he were to stay there long. Under such circumstances, taxonomists would have an opportunity to design a biotaxonomy better than the one we now use. In the more than 200 years since Linnaeus began our present system, we ought to have learned some useful things that would enable us to improve on the taxonomy currently being practiced. Moreover, after considering such a problem

Castes in xylocopine bees.

Xylocopinae are not usually thought of as having castes and two of the three major included tribes are not or scarcely mentioned in accounts of social behavior in bees (e.g., Michener 1974a). The methods and objectives of this review are the same as for the Halictinae treated in the preceding chapter. The only xylocopine tribe treated in detail in 1974 is now called the Allodapini (Michener 1974a, Chapter 27), then called simply the allodapine group of Ceratinini. We now know that some species in the other tribes are also, in varying degrees, social. Such species have, in some nests, two or more adult females with division of activities among them and sometimes behaviorally recognizable castes. This chapter is devoted largely to a descriptive account of the evidence for castes in xylocopine bees, with enough general natural history to show the relations of the castes to the life cycles of the species. So far as known no xylocopines are obligately eusocial.

Social, Stimulatory and Motivational Factors Involved in Intraspecific Nest Defense of a Primitively Eusocial Halictine Bee

SummaryThe major releasing stimulus in intraspecific nest defense ofLasioglossum zephyrum is the odor emitted by a non-resident bee. Non-resident bees older than two days emit the releasing odor and elicit aggressiveness by guard bees, whereas younger non-resident bees are accepted more often. Defense motivation is a function of nest age and/or ontogeny. As nests become older and cells are constructed and provisioned, there is a gradual increase in guard aggressiveness, although no one attribute of nest ontogeny (such as cell construction) seems to be a definitive point at which nest defense is initiated, nor is there any specific day after the emergence of the first bee when nest defense begins. The guard plays the major role in rejecting intruders, although other members of the colony may do so if a non-resident bee passes the guard and enters the nest.

Division of labor among workers ofPolistes metricus (Hymenoptera: Vespidae): Laboratory foraging activities

SummaryDivision of labor in foraging activities of workers was studied in laboratory colonies ofPolistes metricus. Individual foraging activity was strongly affected by the foraging activities of nestmates. Usually the oldest worker of a colony became the principal forager. Other workers, in the presence of an active forager, did relatively little foraging regardless of age. Relatively inactive workers showed increased foraging rates when the older, active foragers were either removed or became less active with age, or when colony needs were greater (as evidenced by a marked rise in larval numbers). There was no temporal change in distribution of foraging tasks. The only indication of permanent task specialization was for paper collecting. All workers foraged for prey, water and honey but collection of paper was confined almost exclusively to the oldest workers of the colony.ZusammenfassungAn Laborkolonien vonPolistes metricus wurde die Arbeitsteilung der Arbeiterinnen bei der Nahrungssuche studiert. Die Sammelaktivität der einzelnen Individuen hing stark von der Sammelaktivität Nesgenossen ab. In der Regel sammelte hauptsächlich die älteste Arbeiterin. Andere Arbeiterinnen, gleich welchen Alters, unternahmen vergleichsweise wenige Sammelflüge, solange eine aktive Sammlerin vorhanden war. Wenn ältere, aktive Sammlerinnen aus der Kolonie entfernt wurden oder mit zunehmendem Alter in ihrer Aktivität nachließen, so flogen die vorher vergleichsweise wenig aktiven Arbeiterinnen öfter. Ein Anstieg ihrer Sammeltätigkeit war auch dann zu verzeichnen, wenn sich der Nahrungsbedarf der Kolonie erhöhte (was man an einer deutlichen Zunahme der Larvenzahl ablesen konnte). Eine zeitliche Anderung der Aufgabenteilung beim Sammeln wurde nicht beobachtet. Der einzige Hinweis auf eine dauerhafte Spezialisierung betraf das Sammeln von Papier. Während alle Arbeiterinnen Wasser, Honig und tierische Beute eintrugen, war das Sammeln von Papier fast ausschliesslich den ältesten Arbeiterinnen vorbehalten.

Observations on the behavior of brasilian halictid Bees. V,Chloralictus

The purpose of this paper is to make known observations on the nest ing behavior (ff certain species of Chloralictus. This group, consisting of small greenish black bees, is usually regarded as a subgenus of Lasioglossum. The name Chloralictus is here used as though it were a genus, since this is the practice of Moure who described the species which we s tudied, but a generic revision of the Halictinae will be necessary to settle this and similar problems. In any event it is a group of monotonously similar bees when only morphology and appearance are considered. In social evolution, however, various levels can be recognized from solitary to nearly as social as Bombus. Chloralictus is only one of the groups among the Halictinae in which societies have arisen. Our observat ions were made over more thau a year (July, i955 to August, 1956), and da ta were gathered at various localities on the southern Brasiliaa plateau in thc state of Paran~.