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The success as well as the increasing complexity of organisms in the course of evolution is thought of have depended on few of major transitions in how the information is moved from one to the next generation. One of such transition was the shift of solitary organisms to societies with a marked reproductive division of labor. This transition has led to the enormous ecological success of the social insects, which are now dominating most of the terrestrial ecosystems. This success is due to the benefits conferred by sociality, which allows the individuals in a group to modify their environment more efficiently and carry out tasks that could not be performed by single individuals. Insect societies exemplify the full sweep of ascending levels of organization, from molecule to society. Here, we will look into the various levels of development of insect societies & the advantages and disadvantages of these societies. We will also take a brick look at the various theories put forward to explain these components.
A society is a group of individuals that belong to the same species and are organized in a cooperative manner. The expression "social insect" has been give different definitions by different authors. Wheeler (1928) defined social insects as those in which progeny are not only protected and fed by the mother, but eventually cooperate with her in rearing additional broods of young so that parent 8s offspring live together in an annual or perennial society. According to O.W and Maud J. Richards (1951) "Real social life appears when the mother 86 her offspring cooperate in making a nest 86 feeding their young. O.W Richards later said "the term 'social' is reserved for communities in which there is more than one female, one or more usually being sterile, unfertilized and nursing the young derived from one of a few of them. The mother that actually lays the eggs usually does no other work in the mature colony". The present status of insect sociology can be made clearer by recognizing three stages in its historical development.
(A) The Natural History Phase:
The discovery description of the social insects and the cataloging and evolutionary interpretation of their behavior 86 ecology were the first unavoidable steps. This phase, a necessary precursor to succeeding developments, is far from completed.
(B) Physiological Phase:
The experimental analysis of the social systems & their physiological bases constituted the logical next step. This approach is being applied vigorously to such diverse topics as caste determination, food exchange etc.
(C) The Population Biology Phase:
3 It attempts to account for social phenomena in terms of first principles of population genetics & population ecology. Here, we attempt to provide a modern synthesis of insect sociology & molding the rudiments of true evolutionary theories of sociality through which explanations can be supplied for the presence of the underlying physiological phenomena in terms of maximal efficiency and fitness at colony level.
Table 1 Ecological and life history preconditions/correlates of Eusocial
Claustral Familial Associations
Safe, initially small, long-lasting (multigeneratiortal), expandable, food rich habitats; nesting in protected cavities keeps 'relatives together, thus providing opportunities for kin-selected reproductive altruism; Nesting aggregations make it easy for parents to parasitize the food- gathering behavior of their offspring.
PARENTAL CARE (SUBSOCIALITY)
Family (kin groups)
Slow Development, Long Generation Time, Overlap of Generations
Long life span, especially of reproductive (parents evolve to live longer than their helper offspring)
Gradual metamorphosis (individuals begin helping as Miniatures, and can improve in helping ability as they age)
Genetic asymmetries increase
the reproductive advantage
of a female tending full Siblings rather than producing offspring High Chromosome Numbers
Relatively high chromosome
numbers would reduce the
ability of sibs to differentiate among
each other based on relatedness, and would also reduce inclusive
fitness variance among sibs,
Thus facilitating social evolution
MATING SYSTEM: SINGLE FATHER
In haploid-diploid groups monogamy assures that sisters shares all the genes from their father and thus, on average, 3/4 of their gene are identical by immediate descent
Eusocial Hymenoptera, termites, naked mole rats, shrimp, ambrosia beetles, gall-dwelling aphids, thrips.
Eusocial Hymenoptera, termites, aphids, ambrosia beetle, thrips, naked mole rat shrimp
Eusocial Hymenoptera, termites, naked mole rat
Termites, naked mole rat, shrimp
Most social Hymenoptera, termites
Primitive condition in social Hymenoptera
Table 1 (Continuedâ€¦)
In diploid groups monogamy renders siblings genetically indifferent as to whether they rear fertile siblings or their own offspring
Older offspring care for younger siblings
HIGH RISK AND/ OR TIME INVESTMENT IN DISPERSAL AND
FOUNIDING OF NEW NESTS
Remaining as a helper in the parental nest may be substantially safer and more efficient than attempting dispersal and successful development of a new nest
OPPORTUNITIES FOR SUBSTANTIAL
Replacement Reproductive Opportunities
Possibility of maturing and reproducing within the group, either as a replacement or supplementary reproductive, and thus inheriting group resources
Need for group defence against predators
Need for group defence against intra- and inter specific competitors
Specialized defence: sting, (facilitated the evolution of eusociality among Hymenoptera in exposed locations); major or soldier caste (ants, termites, aphids, thrips); major claw (shrimp)
Termites, naked mole-rat, possibly shrimp
All eusociaI animals
Hymenoptera., termites, naked mole rat
Termites, wasps, ants and bees produce male eggs, naked mole rat
Hymenoptera, aphids, thrips, shrimp
THE DEGREES OF SOCIAL BEHAVIOUR
The "truly' social insects, or eusocial insects as they are sometimes more technically labeled, include ants, all termites and the more highly organized bees wasps.
Majority of entomologists intuitively define eusociality on the base of following three qualities
Individuals of the same species cooperate in caring for the young
There is a reproductive division of labor, with more or less sterile individuals working on behalf of fecund individuals; and
There is an overlap of at least two generations in life stages capable of contributing to colony labor, so that the offspring assist parents during some period of their life.
Within this broad category there can be recognized a series of lower social stages, for which Michener (1969) has provided the most recent and sound clarification
Solitary: showing none of the three traits listed immediately above.
Sub social: the adults care for their own nymphs or larvae for some period of time.
Communal: Members of the same generation use the same composite nest without cooperating in broad care.
Quasisocial: Members of the same generation use the same composite nest & also cooperate in brood care.
Semisocial: As in quasi social, but there is also reproductive division of labour, that is, worker caste cares for the young of the reproductive caste.
Eusocial: As in semi social, but there is also an overlap in generations so that offspring assist parents. It is of two types:
Primitively eusocial: Individuals are not morphologically different.
Highly eusocial: Morphological distinction between worker reproducing individuals.
Presocial refers to the expression of any degree of social behaviour beyond sexual behaviour, yet short of eusociality. It applies to all the intermediate stages between solitary and eusocial. Another term "parasocial" was introduced by Michener to embrace those presocial states in which members of the same generations interact namely, communal, quasisocial , and semisocial. This system provides a means of making a graphic contest between the two alternate routes to eusociality, the parasocial and the subsocial. The logical possibilities framed by the terminology are present in Tables 1.1 and 1.2. Sociality confers many advantages, but there are a few disadvantages of sociality as well. Before proceeding further, we should first take a look of these advantages and disadvantages:
DISADVANTAGES OF BEING SOCIAL:
Social parasitism by members of the same species (females and males on a given nest are taking care of individuals who are least related to them.)
Increased vulnerability towards parasites and predators
ADVANTAGES OF BEING SOCIAL
Better defense against parasites/ Predators.
Ability to exploit good food source in a short time.
Protection of progeny from infanticidal effects.
Table 1.1 Degrees of sociality, showing intermediate parasocial states
DEGREE OF SOCIALITY
QUALITIES OF SOCIALITIES
Cooperative Brood Care
Overlap between generations.
Solitary, Subsociai, communal
Table: 1.2 Degrees of sociality, showing intermediate sub social states.
DEGREE OF SOCIALITY
QUALITIES OF SOCIALITIES
Cooperative Brood Care
Overlap between Generations
Primitively sub social
Intermediate sub social 1
Intermediate sub social 2
Early hypotheses for evolution of sociality
Imagining the conditions in which eusociality could have evolved proved to be a problem for Charles Darwin. Darwin was not sure how to explain the presence of sterile individual generations after generation. In his book, the Origin of the species, he described the existence of sterile worker caste in the social insects as" the one special difficulty, which at first appeared to me insuperable 8v actually fatal to my whole theory"
In the next paragraph of his book, he described a solution. It the trait of sterility can be carried by some individuals without expression and those individuals that do express sterility help reproductive relatives, the sterile trait can persist and evolve. He said in such cases, "selection is at the level of family and not at the level of individual." Darwin illustrated that "A breed of cattle always yielding oxen (castrates) with extraordinary long horns could be slowly formed by carefully watching which individual bulls and cows, when matched produced oxen with the largest horns; and yet no one oxen could ever have propagated its kind."
THEORIES FOR EVOLUTION OF SOCIALITY
The First theory proposed was:
Inclusive fitness and kin selection theory:
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to their own survival and / or reproduction.
The basic concept was given by R.A. fisher (1930), J.B.S Haldane (1955), but it was Hamilton who formalized the concept in (1963) and (1964). Kin selection refers to changes in gene frequency across generation that are driven at least in part by interactions between related individuals and this forms much of the conceptual basis of the theory of social evolution. Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within population and a gene that decreases the fitness of its carrier individuals should be eliminated. However, a hypothetical gene that prompts behaviors which enhances the fitness of relatives but lowers that of the irdividual displaying the behaviour may nonetheless increase in frequency, because relatives often carry the same gene (fundamental principle behind kin selection theory). According to the theory, the enhanced fitness of relatives can at times more than compensate for fitness loss incurred by the individuals displaying the behaviour. So, Kin selection is considered to be a special case of Inclusive Fitness. Inclusive fitness describes how an individual's behaviour affects the combination of an individual's direct fitness & the fitness of others individuals with similar genes. This theory has two components:
DIRECT FITNESS: Standard evolution/ fitness component derived reproduction (own progeny)
INDIRECT FITNESS: Derived through helping genetic relatives to reproduce. (Progeny of genetic relatives)
Inclusive Fitness is epitomized by Hamilton's Rule, which states that:
Where, C= reproductive cost to the altruist (helper)
B= reproductive benefits to the recipient of the altruistic behaviour.
R= coefficient of relatedness or degree of genetic relatedness.
Hamilton Proposed that eusociality arose in social hymenoptera (ant, bees Ar. wasps) by kin selection due to their interesting genetic sex determination trait of haplodiploidy. As males are produced parthenogenetically females are produced from fertilized eggs, sisters are 75% related to each other whereas mothers are only 50% related to their daughters. Thus, sisters will benefits more by helping their mothers to raise more sisters than to leave the nest and raise their own daughters. Hamilton's proposal of the importance of haplodiploidy in the evolution of eusociality reigned supreme amongst scientists who studied social hymenoptera for the rest of the century.
FAILURES OF THE KIN SELECTION THEORY:
Although Hamilton's argument appears to work nicely for ants, bees and wasps, it excludes eusocial organisms that are not haplodiploid. These organisms include aphids, thrips, some beetles.
In Hymenoptera, haplodiploid system of sex determination:
Fertilized egg (Female)
Unfertilized egg (Mal)
The systems in which sociality is present are all Female Societies
The relationship between females in these societies is 0.75
The relationship between male 86 female in their societies is 0.25 female male
The most striking example is that of the social ISOPTERA the termites which have highly sophisticated colonies but do not display haplodiploidy.
This theory also does not explain about the species that are haplodiploid but are not eusocial, such as solitary wasps and bees.
There are also cases of eusocial haplodiploid species that have low levels of relatedness such that sisters no longer share an average 75% of their genes. This may be due to having multiple queens or by multiple matings by a queen prior to starting a colony, which reduces the genetic relatedness among females in a colony to 0.5 86 thus the average related ness of the entire colony becomes 0.37
This shows that theory of Kin Selection alone is not sufficient to explain the evolution of eusociality.
The other theories i.e. Mutualism and Parental Manipulation (Sub- fertility Hypothesis) are traditionally presented as alternatives to the Kin Selection for the evolutionary origin of eusociality.
THEORY OF MUTUALISM: (Lynn and Mischner)
This theory says that unrelated individuals form groups and these groups are more successful than solitary individuals and thus take over the solitary pattern. This theory says that larger the group, better is the ability to detect threat .but these groups later on become related and this enhances the success rate .This theory has been tested in Belding ground squirrel.
The individuals who are outside burrow start giving alarm calls when they see predator. It was calculated that this increases the chances of the individual to be spotted 86 captured by the predator by 47%. But by giving alarm calls it decreases the prospects of its nest mates being captured by 91%.
It was discovered that the frequency of giving alarm calls is more only when the individual is living with close relatives.
THEORY OF RECIPROCAL ALTRUISM: (Trivers, 1971)
This theory states that the individual benefits another individual at a little cost 86 the situation is later reciprocated. This type of altruism exists between unrelated individuals.
To test these two theories, we can take, individuals from solitary species, place them in different arenas. Then keep different types of individuals together and test the final outcome. It the number of progeny produced in cooperative state is more, and then they will replace the solitary ones. But, if this is not the case, then solitary strategy will remain.
THEORY OF SUB FERTILITY (Eberhard)
PARENTAL MANIPULATION (Alexander)
Parental manipulation theory says that certain parents manipulate their Progeny so that these progeny help the parents to produce more progeny.
The probable factors which may cause an individual to stay back 86 help Parents may be:-
Limited nesting sites.
Limited food resources.
This has seen in many birds (e.g. Kingfisher) that the young ones stay back and help the parents to raise more progeny.
It has been shown that most of the birds that stayed back and helped parents in raising brood gave rise to better & more progeny.
In some of the wasps, it is seen that they return to the same site for nesting where they were raised.
This was given as evidence to show that there are limited nesting sites but this can also mean that the way to that nesting site is imprinted in wasp's neural circuit.
THE SUB FERTILITY HYPOTHESIS:
Certain proportion of individuals has less reproductive potential than others; these individuals will help others who are reproductively more capable. This was tested in Ropalidea marginata (wasp)
In the experiment, the Queen and workers were forced to nest on their own, both in field as well as in lab.
It was found that in the lab, the queen and the worker who were separated raised similar number of individuals but in the field, the queen raised more progeny than the workers.
This suggests that all individuals have the same potential to produce progeny, and that the difference is not in their fertility but in their foraging ability.
So, the parent is not actually manipulating with the fertility of the individuals but with foraging or other abilities such as difference in the time interval at which the larvae are fed. This also makes difference in the ability of larva to become an egg layer or not. (As shown in experiment conducted on Ropalidea marginata)
In 2009, Sub fertility theory was disapproved by Adam Smith
It was found that smaller individuals always played the role of helper. But when they were separated in lab, they also gave rise to about the similar number of progeny as the bigger individuals.
Experiment conducted by
R. Gadagkar et. al
To show the role of larval nutrition in
Pre-imaginal biasing of caste in the
Primitively Eusocial wasp
No. of eggs
No. of larvae
No.of parasitized cells
No. of empty cells
Total no. of cells
No. of males
No. of females
No. of eclosing females tested
No. of egg layers among female tested
No. of times an average larva was fed pe hour
Table 2 Logistic regression analysis. Larval nutrition as a determinant of the probability of egg laying by eclosing females of R.marginata..
Table 1 Characteristic of the six R.marginata nests used in this study.
Variables Estimated coefficient (Î²) Standard error Test statistic p
Intercept -0.5612. 0.3963 -1.4160 0.1556
No. of times an average 3.5462 1.6525 2.1459 0.0316
larva is fed per hour
Table 3 Goodness of fit of the model tested in Table 2. Probability classes with zero in all four columns are not shown. Them is no significant difference between the observed number of egg-layers and the number expected under the model (y=O.251, df =1, P>U.05) to compute Ï‡2 adjacent rows were pooled when the expected value was less than 5
Probability (of becoming an egg layer) Class
In, 2010 Nowak Et al. outlined a path by which sociality could have evolved by means of multi level selection in 5 steps:
FORMATION OF GROUPS:
Groups could consist of parent: offspring groups or unrelated groups (in situations where cooperation is beneficial) living in a structured nest.
Pre-adaptations for social living will push the group further towards sociality.
Mutations will arise 86 be selected. Some genes are known to have been silenced in social insect history, leading to the reduction of dispersal behaviour 86 the origin of the wingless caste.
NATURAL SELECTION ACTS ON EMERGENT TRAITS:
The interactions of the individuals can be considered as part of the extended phenotypes of the queen. These interactions produce emergent properties upon which natural selection can act.
MULTI LEVEL SELECTION
More cooperative groups out-complete less cooperative groups.
But none of these theories were able to pinpoint exactly how eusociality evolved. Most of the researchers still think that Kin Selection remains the best explanation.
THE PRE-SOCIAL INSECTS
The evolutionary roads of pre-sociality have been travelled by many kinds of arthropods besides the hymenopterans & termites.
According to Wheeler, an insect society is a family of at least 2 parental individuals along with offspring.
There are more than 30 families distributed in 5 orders that show some indication of social behavior. Much more interesting is the fact that behaviour & communication in the most advanced sub-social species is as complex as that found in the eusocial insects. In both instances, we find such behaviour patterns as the building of elaborate nests, nest guarding and cleaning, solicting for food, transport of young & alarm signaling.
In line with the system used to designate the evolutionary stages leading to eusociality, the pre-social behaviour in arthropods to be considered now can be classified into one or the other of three principal categories:-
Subsociality in strict sense.
Communal behaviour or aggregation of individuals who cooperate to some extent in foraging for food or in the building of nests.
Quasi social behaviour, in which individuals cooperate in the rearing of the young, whether or not joins in foraging & nest construction.
Parental care indicates sub-social behaviour. It has been observed in many insects such as:-
PARENTAL CARE IN HEMIPTERA:
Care is limited to providing protection to the young one. There are three groups:
Protection given by female:-
eg. Pachycoris fabric, Gargaphia solani
Protection given by male:
eg. Rhinocoris alboputatus, Phyllornolpha lacinata
Protection given by male & Female
eg. Lethocerus americanus
ADVANCED PARENTAL CARE IN CRICKETS:
The big brown cricket of India, Brachytrupes achatinus (female) seals itself in underground burrow with its eggs & young nymphs. In Anurogryllus muticus (South East American cricket), after mating, the female excavates an underground burrow which is deep. At this point, they become very aggressive 86 viciously attack other members of the species who intrude into the nest, including males. The eggs are laid in batches on the floor of the brood chamber 86 partly covered with soil. When the nymphs hatch, then the female occasionally palpates a nymph and gently manipulates it in her mouthparts. From time to time the mother lays miniature eggs, which immediately carry away and eat. Female carries it into the burrow and shares it with nymphsâ€¦â€¦â€¦â€¦â€¦â€¦..21
3. Minotaurus typhaeus
The male is more involved. He makes the fecal pellets and lowers them to the female who tears the dung into pieces and packs it into the bottom of the borrow.
They have carried division of labor between the sexes still further. After the pair has begun to excavate the nestâ€ž the male creates a "Courtyard" around the entrance. This is a circular area from which humus, stones and branches are removed. The male gathers fresh leaves and buds, which he shears off with his heavy, nipper-like mandibles. Then female presses them into elliptical balls fitted to the interior of the brood cells.
4. Copris hispnust
Male and female participate in excavation and preparation of dung pellets which become the larval food. After this, the male leaves and female stays behind until the larval growth (4 months). Female keeps on remaking the dung pellet, so that the food doesn't become less. Female escorts the young adults out of the burrow. Here, the role of female ends.
5. Nacrophorus beetles.
They feed on the carcass of small mammals. If a male encounters a corpse first, he takes the (strerzelndes) posture, lifting the hind part of the body into the air and releasing a pheromone to attract the females. If more than a single pair assembles on the corpse, fighting ensues, male against male and female against female, until only a single pair is left. The winner now partly bury their prize and at the same time chew and work the putrefying mass until it is roughly spherical in shape. Then they seal the burrow off from below. The female eats out a crater shaped depression on top of ball and spreads her faeces over its surface. When the larvae hatch, the beetle stand directly over the larvae, female opens her mandibles and larvae take food by inserting its head between the mandibles & tightly into mouth opening. When the larvae are 4-5 hours old, they begin to feed on the ball directly. It mother is removed when the larvae are immature, they start to pupate, but are unable to complete adult transformation.
AGGREGATION BEHAVIOR IN DIFFERENT LARVAE:
(i) Neodiprion pratti (Jack pine sawfly)
Feed on the pine tissue. Because the tissue is hard, larvae are successful in penetrating it only when they are in aggregates. It has been observed that if larvae are present in large numbers, the survival percentage increases. It is possible that one among them with slightly harder mandibles bites the tissue and then others join in to enter the hole. So, it cannot be said that which comes first:
Hole made by a larvae and then congregation
(ii) Perga affinis: (Australian Sawfly)
The eggs of this species are laid in "pods" within the tissue of the leaf blade. When the larvae hatch, they must rupture the overlying leaf tissue in order to escape 85 thus to survive. If none of the progeny from a small pod succeeds in making hole, all of them die.
SUB SOCIALITY AND QUASISOCIALITY IN SPIDERS:
There are no known cases of eusociality in the spiders. Communal nesting behavior is relatively common, however, and a few examples have been reported in which adult spiders cooperate in the construction of both webs and brood refugia. Also, some truly remarkable cases of communication have been reported between the parents and the young. Among the primitive spiders, parental care is apparently exhibited by some of the tarantulids. Otherwise, Pre sociality is limited chiefly to the Agelenidae, Erecidae, Decobiidae, Theridiidae and Uloboridae.
The West African spider Agelena consociata is notable for having both quasisocial and subsocial habits and is, in fact, as close to the brink of sociality as any arthropod species known outside the hymenoptera & isoptem.
The webs are upto 3m in greatest diameter and are woven through shrubby vegetation along the borders of the rain forest. They consist of numerous sheets spun in an irregular manner by the hundreds of spiders that inhabit each nest. Small preys are captured 86 eaten singly by the individuals that happen to be closest at hand, but larger preys are pursued and killed by groups. The Agelena are completely friendly towards all their nestmates, frequently touching them with their legs and palps without any show of hostility. They also tolerate the introduction of members of other colonies.
An even more remarkable feature of the behaviour of A. consociatct is the treatment accorded to the young. The spiderlings seldom join in hunting. They cluster in groups of 50 or more individuals in the dense silken retreats and wait for food to be brought to them. These groups are apparently to crèches. For the adults shows no sign of even being able to distinguish their own offspring much less of singling them out for favoured treatment. Discrimination is made even less likely by the fact that the egg mass laid by each female contains no more than 30 eggs, so that individual spiderling groups must contain the offspring of more than a single female. Spiderling mortality rate is also decreased when they live in large groups. Lower mortality rate is indicated indirectly by the existence of lower natality rate.
CONDITIONS FAVOURING PRESOCIALITY IN INSECTS:
The evidence shows that presociality is an eclectic and convergent evolutionary phenomenon; generated almost haphazardly in response to any one of large set of independent environmental forces. Elaborate forms of parental care are seemingly limited to situations where the physical environment is usually favourable or unusually harsh. "Ordinary", "intermediate" environments do not seem especially to promote the evolution of this kind of behavior.
At the favorable pole we find a class of highly subsocial species that utilize food sources that are very rich but at the same time scattered & ephemeral like dung (scarabidae), carrion (necrophorus) etc. At the opposite extreme are the species that are frequently threatened by difficult conditions in the physical environment rather than by the onslaught of competitors in a physically desirable environment.
Adults of the intertidal staphylinid Bledius spertabilis are forced to remain with their young constantly in order to prevent their suffocation. So, the main conditions favoring presociality in in.q.Pot can be listed as follows:
Competition for perishable resources.
Protection from unfavourable environment.
Protection from predators and parasites.
Collective exploitation of inhospitable environmental conditions
Hymenoptera is the insect order containing maximum of the eusocial insects Le, Wasps, Bees and Ants. The only other highly social insects are the termites in the order Isoptera.
THE SOCIAL WASPS
In spite of the relatively small number of wasp species that are truly social, the study of their behaviour has repeatedly yielded results of major interest. Four of the basic discoveries of insect sociology either originated in wasp studies or were based primarily on them. These discoveries are as follows:
Nutritional control of cast (Marchal)
The use of behavioural characters in studies of taxonomy and Phylogeny (Ducke)
Dominance behaviour (Heldmann , Pardi)
Even more importantly, the living species of wasps exhibit in clearest detail the finely divided steps that lead from solitary life to advanced eusocial states.
Wasps are classified into 3 families.
Provides link between
Solitary and social Species Has solitary and sub social species
all social species
Sternogastrinae: Sub- social & communal
Polystinae: Sub Social and Primitively eusocial
Wasps are like living fossils for understanding the evolution of sociality because there is entire spectrum from solitary to social. Ants and termites are completely eusocial. Different wasp species tell us different steps in evolutionary behaviour:
1. Nest construction
Primary step towards development of social behavior.
Euntenes architectus is the link between solitary and social wasp, builds nest with mud and makes a paper envelope over this cell
2. Mass Provisioning for young
This is a sort of parental care.
3. Progressive Provisioning
Adult may be giving incomplete food to the young. No communication between adult 86 young one.
Truncated progressive provisioning
Mother starts provisioning after egg hatches into larva. Parent offspring communication occurs.
(c) Fully progressive provisioning
Parent provides prey item at a constant rate to the larva. Continuous communication between larva and parent.
In Synagris spiniventris there is mass provisioning in abundance of prey Os progressive provisioning when the prey is scarce.
4. Overlap of generations.
Eumenins and masarins are mainly solitary, but there are certain exceptions.
In Stendoynerus clasemantensis (eumenin) young ones stay back on parental nest for some time as then disperse but one of the female progeny comes back to that nest for starting her own brood. In Zathus miniatus, about 15 individuals build nest together. The large female selects an empty cell or takes over a cell made by another female and deposits her own eggs.
In sternogastrinae, when female is ready to lay eggs then it produces a gelatinous substance from its abdomen. This substance serves as a substrate for oviposition, serves as a storage space for storing prey and liquid foods. Once larva is ready to pupate, the mother seals the cells. After a few days mother punches a hole as removes meconium.
This is the transitory behaviour from solitary to social as solitary insects never remove meconuim as there is no interaction between the adult and larva.
Some of the species show Haplometrosis (nest initiation by single female) and others show Pleometroris (nest initiation by more than one female).
Although the traditional reconstruction of social behaviour in the vespid and sphicid wasps seems generally persuasive, our information is still relatively week and uncertain in many social aspects. The degree of reproductive dominance and the relation of division of labor to age & size are mostly unknown. It seems that the details of evolutionary scheme will have to be altered frequently as new studies are conducted.
Bees consist of 9 families which can be categorized into 5 different groups
Eusociality has arisen at least 8 times within the bee superfamily apoidea by both the parasocial and subsocial routes and presociality of nearly every concievable degree has emerged on an uncounted number of other occasions. This prevelance & great capability of social behaviour in bees provides an opportunity to study the evolution of social behaviour, paralleled only in wasps. Even more than in wasps, the steps in the evolutionary progression of bee sociality can be delimited within small groups of related species & faunal units. All the bees together comprise the superfamily apoidea. On morphological grounds, they fall close to the Sphecoid wasps, although the lack of an adequate fossil record has made it impossible to pinpoint the exact ancestral pyretic line.
SWEAT BEES IN THE SUBFAMILY HALICTINAE:
They contain both solitary species and species in the earliest evolutionary stages of eusocialty. Majority are solitary. Those that have attained sociality are still only at a relatively primitive level in this behavioural category, Kneerer & Cecile (1966) have documented the following multiple changes by which advances in eusociality can be measured within Halictinae:
There is an increased tendency in workers to keep the brood cells open, to inspect them and even to add nectar and pollen. The intensity of such direct contact can be taken as a convenient measure of eusociality.
During early colony development, the females are organized in a semi-social state. As the first generation of workers appears, the colony becomes eusocial.
There is an increase in size difference between the queen and the workers.
There is an increased tendency towards, the production of 2 or 3 annual broods instead of only one and a concomitant reduction in the proportion of males produced.
These four criteria are convenient, satisfying & correlated. There is another interesting criterion that some of the species as Dialictus versatus lack colony odors.
The most advanced social structure among halictid bees is that of Evylaeus marginatus.
They are of special interest because of two reasons:
In contrast to the larvae of other bees, those of most allodapines are kept together in open chamber and fed progressively with small meals.
As a concomitant of this peculiar habit, allodapine species display among themselves the evolutionary transition from solitary to social behaviour by way of subsocial stage.
Alladape angulata is a good example of a social allodapine.
Bumble Bees: All the species of bumble bees studied till date are eusocial
Stingless bess: - (Tribe Meliponini): - Their stings are vestigial and cannot be used in defence. They are all eusocial. There are strong morphological 86 behavioral differences between workers and queens. Intermediates are lacking.
HONEY BEES :- (APIS SPECIES)
By the general intuitive criteria of social complexity, the honeybee is at about the level of the other highest eusocial insects. i.e stingless bees, termites, polistine i.e. vespine wasps. But one feature which makes it stand truly apart from other insects is "WAGGLE DANCE",
The really remarkable aspect of the waggle dance is that it is a ritualized reenactment of the out ward flight to food or new nest sites, it is performed within the nest and somehow understood by the others workers in the colony which are then able to translate it back into an actual, unrehearsed flight of their own.
THE ORIGIN OF SOCIALITY IN BEES
In 1958, Michener cited new lines of evidence to indicate that a different evolutionary route has been followed by bees except for the allodapines, he suggested that eusociality has been reached by parasocial steps. Michener's sequences of events are as follows:-
THE PARASICAL ROUTES IN EVOLUTION (Some Bees)
Female of same generation aggregate and cooperate in building the nest- communal behavior.
Next, they cooperate in brood care- Quasi Social behavior
Then they divide into queen and workers- Semi Social behavior
Finally, some live long enough to coexist irj the same colony with their daughters or nieces Eusocial behaviour
THE SUBSOCIAL ROUTES IN EVOLUTON (Other Social Insects)
A single female builds the nest and stays around to care for her brood- Subsocial behavior.
The female lives long enough to be around when her daughters reach adult stage 86 they help her raise more of her daughters- Eusocial behavior.
Both routes lead from solitary to eusocial. The crux of this whole scheme depends on whether truly semisocial species exists or not Hamilton (1964) has doubted the existence of such a step in evolution, which means doubting that eusociality can be attained by parasocial route as postulated by Michener. The evidence for a true and persistent semisocial state is still limited to the tribes Augachlorini and is circumstantial in nature.
Research says that evolution of sociality in bees is accompanied by evolution f stronger antimicrobial compounds. The data suggest that selection pressure from microbial pathogens was so intense that even minimal sociality required substantially stronger antimicrobials. (Stow, et, al.)
Phylogenetic analyses of DNA sequence information from the rnitochondrial genome of representative apid bees suggest that advanced eusociality evolved twice independently within the assemblage. (Sydney A. Comeron).
On several counts, ants can be regarded as the premier social insects. They are the most widely distributed of the major eusocial groups. At any given moment, there are least 1015 living ants on the earth. The ants contain a greater number of known genera and species than all other eusocial groups combined. The diversity of their ecological and social adaptations is truly remarkable. Food specialization is extreme. Nesting habits are diverse.
The success of ants might be explained in part by the ability of all primitive species 86 most of their descendants to nest in soil and leaf mould and perhaps this behavioral adaptation was made possible in turn by the origin of the METAPLEURAL GLAND, the acid secretion of which inhibits growth of micro organisms in the nest chambers.
The ants constitute all of the single super family Formicoidea and within that, the single family Formicidae, Brown divided the formicidae into two major braches:
1. The myrmecioid
2. The poneroid group of subfamilies.
THE ORIGIN OF SOCIAL BEHAVIOUR IN ANTS
Except for some specialized modes of colony reproduction, such as the budding exemplified in Monornorium pharaonis and the army ants, the details of the colony life cycle do not very greatly within the formicidae. The partially elaustral method of colony foundation that characterizes Myrinecia is shared with many ponerinae. Within the ponerinae we can further observe the finely graded steps leading from the partial to the fully cluster mode of colony foundation in which the queen never leaves the nest.
At the highest level of explanation, that of ecosystem, the large numbers of kinds of ants give a panoramic view of the evolution of colonial patterns. The very exuberance of diversity makes the correlative analysis of adaptation easier and more rigorous. The small size of ants as well as the ease with which they can be cultured in the laboratory facilitates this research.
Ants are extraordinary among social insects in the swiftness with which they adapt to radically altered environments. Ants are premier organisms for research in behavioral ecology and sociobiology. They exemplify principles in these relatively new disciplines Eis offer exceptional opportunities for testing and extension of the theory. They provide, for example, some of the best documentation of the following phenomenon:
Kin Selection and selection at the level of colony.
Competition at each of the three levels of organization:
Among individuals of the same colony,
Among colonies of the same species and
The effects of competition on community structure.
The shaping of an organization and the development of societies by natural selection.
The nature of physiological and behavioral regulatory processes in social organization
Hierarchy in control processes.
But ants are highly eusocial. As for back as the late cretaceous period, the ants as we know them have reached a point of no return in sociality. The earliest stages of eusociality have not been found in any living species of ant and no solitary aculeate are known that might have originated from ants through a secondary loss of eusociality. But the extraordinary phylogenetic spread of ants and the immense diversity of their social system make them the most favourable group for reconstruction of middle and advanced stages of eusocial evolution.
In almost literal sense, termites can be called as "social cockroaches." Comparisons made between the most primitive termite family, the Mastotermitidae and the Primitive Blattoid cockroaches have revealed tailed resemblances in a multitude of unrelated characters:
Wing venation, internal anatomy of female genitalia, bacteriocytes etc.
Because the termites have climbed the heights of eusociality from a base extremely remote in evolution from Hymenoptera, it is of surpassing interest to know whether their social organization differs in any fundamental way.
The termites have adopted mechanisms that are mostly but not entirely similar to those in the social hymenoptera. Also, the level of complexity of termite societies is approximately the same as that in the more advanced Hymenopteran societies. The similarities are remarkable in themselves. They seem to tell us that there are constraints in the machinery of the insect brain that limit not only the options in the evolution of social organization but also the upper limit that the degree of organization can attain.
All of the termites together comprise the Order Isoptera. Emerson has recognized six families:-
1. Mastotermitidae 4. Rhinoterrnitidae,
2. Kalotermitidae 5. Serritermitidae,
3. Termitidae 6. Hodotermitidae
The first four are referred to as "Lower termites" the Termitidae are called as "Higher termites" and are exceptionally diverse being comprised of more genera and species than all the other families put together.
ORIGIN OF SOCIALITY IN TERMITES:
Eusociality in Isoptera converges along many lines with colony organization and, highly social behaviour in the phylogenetically distinct insect order Hymenoptera. Unlike the haplodiploid hymenoptera, however, both sexes of Isoptera are diploid. Termite families thus lack asymmetric degrees of genetic relatedness, generated by meiosis and fertilization, so explanations for eusocial evolution based on such asymmetric are not applicable to Isoptera.
It is unlikely that eusociality in termites arose as a result of evolutionary forces acting on any one dynamic or on any single life- history component. Circumstances such as cyclic inbreeding, confined, subsocial groups with a poor diet, or intra group competition may have all provided impetus towards eusociality in termites, but at this point no single condition can be identified as the dominant driving force. The additional ecological and life history, attributes that termites share with other eusocial animals as apparent correlates of eusociality are a particularly compelling ensemble because termites have all of these except haplodiploidy. Against this frame work of favourable preconditions one must still define evolutionary dynamics that would have promoted the most extreme eusocial characteristic, highly skewed reproductive division of labor within a colony.
In termites, the "colonies" in which eusociality evolved were small families. Individual prototermites in a young family would have faced three options. First, they could spend no time or energy helping, instead develop directly into a winged alate. Dispersal and colony initiation would have been risky with no direct fitness payoff until a successful colony produce fertile offspring. Second choice would be for offspring within a family to kill their parents and take over there reproduction in the excavated next galleries. Such behaviour would not be favoured by natural selection because it is in the interest of the offspring to have their parent (the king and the Queen) keep producing their siblings, especially given the neutrality of genetic relatedness between offspring and sibling (one half in a diploid system). Further, parents would likely evolve mechanism to supplant mutinies among progeny.
TABLE 6-1 .Basic similarities and differences in social biology between termites and higher social Hymenoptera (wasps, ants, bees). Similarities are due to 'evolutionary convergence.
1.The castes are similar in number and kind, especially between termites and ants
2.Trophallaxis (exchange of liquid food) occurs and is an important mechanism in social regulation
3.Chemical trails are used in recruitment as in the ants, and the behavior of trail laying and following is closely similar
4.Inhibitory caste pheromones exist, similar in action to those found in honeybees and ants
5.Grooming between individuals occurs frequently and functions at least partially in the transmission of pheromones
6.Nest odor and territoriality are of general occurrence
7.Nest structure is of comparable complexity and, in a few members of the Termitidae (e.g.Apicotermes, Macroiermes) of considerably greater complexity. Regulation of temperature and humidity within the nest operates at about the same level of precision
8.Cannibalism is widespread in both groups (but not universal, at least not in the Hymenoptera)
1. Caste determination in the lower termites is based primarily on pheromones; in some of the higher termites it involves sex, but the other factors remain. unidentified
2. The worker caste's consist of both females and males
3. Larvae and nymphs contribute to colony labor, at least in later instars.
4.There are no dominance hierarchies among individuals In the same colonies
5.Social parasitism between species almost wholly absent
6.Exchange of liquid anal food occurs universally in the lower termites, and trophic eggs arc Unknown
7. The primary reproductive male (the "king') stays with the queen after the.' nuptial flight, helps her construct the first nest, and fertilizes her intermittently as the colony develops; fertilization does not occur during the nuptial flight
1. Caste determination is based primarily on nutrition although pheromones play a role in some cases.
2.The worker castes consist of females only
3.The immature stages (larvae and pupae) are helpless and almost never contribute to colony labor
4. A Dominance hierarchies are commonplace, but not universal
5.Social parasitism between Species is common and widespread
6. Anal trophallaxis is rare, but trophic eggs are exchanged in many species of bees and ants.
7.The male fertilizes the queen during the nuptial, flight and dies soon afterward without helping the queen in nest construct on
Final choice for offspring developing slowly with in a monogamous, iteroparous, family living in a confined cavity within an expandable resource would be to remain in the nest, for at least a while to help rear siblings. In animals like termites, this might have been an especially productive strategy because fertile siblings provide an identical fitness pay off (genetic relatedness = one-half) as offspring.
Further the ability of termites to develop into neotenic reproductive's offers the possibility that helper individuals may become replacement reproductives which confers a fitness advantage augmented by inheritance of the nest, labor food resource. In primitive, developmentally flexible termites the helping alternative might have been relatively low risk because, except for soldiers and reproductive, all individuals retained the option of differentiating into an alate.
Thus, the trade off faced by individuals within small prototermite families was no helping, no boost in inclusive fitness and early, high risk dispersal as an alate versus temporary helping and the cost of delayed high risk dispersal as an alate. Ultimately, or perhaps immediately some temporary helpers served their entire lifetime within the colony, thus becoming permanently helpers in a eusocial system.
Although we may never definitely identify and prove the driving forces behind the evolution of eusociality in termites, the probable life history characteristics of their immediate ancestors suggest some compelling possible scenarios for eusosical evolution based on individual selection. Eusociality in Isoptera was possibly fostered by a suite of contributing factors and the concurrent and cumulative selective pressures that they generated.
After looking at these examples and routes to development of eusociality, the ways to origin of eusociality and its consequences, were proposed by E.O.Wilson and Bert Holldobler (2005).
EUSOCIALITY: ORIGIN AND CONSEQUENCES
The Forces of Natural Selection
Research during the past half century has incrementally clarified the nature of the collective forces that create and shape eusociality. At the most basic level an allele or ensemble of alleles prescribing phenotypic plasticity that includes self sacrifice of some members of groups will spread if the positive intergroup component of the altruist fitness exceeds the negative within group component of the altruist's fitness. The forces that determine altruism are:
Group selection, individual direct selection and Kin (indirect) selection
The inclusive fitness of the prescribing genotype of individual colony member & hence statistically the colonies they compose, is the non- additive product of the three forces.
The degree of relatedness the similarity across the whole genome of individual as a result of recent common ancestry is a factor that biases the direction and strength of the forces. When elevated, say by lower individual dispersal rates, relatedness can bring alleles for presociality and eusociality together more quickly. Relatedness can also increase variance in presocial and eusocial alleles among group, thus quickening the pace of colony selection. But relatedness is relevant only insofar as it affects the frequency of alleles that prescribe social behaviour. Eusociality arises by the superiority of organized groups over solitaries and cooperative pre-eusocial groups. Conversely, eusociality cannot arise without the driving force of group selection, regardless of the degree of relatedness within local populations or cooperative aggregations.
The Point of NO Return
An abundance of evidence suggests that the strength of the biasing role of relatedness within a species depends on the stage of its social evolution. The key transition occurs at a point in colony evolution that can be conveniently called the point of no return. Beyond this level it is impossible, or least difficult & uncommon, for a species to regress from the eusocial to a more primitively eusocial, presocial or solitary condition.
When in evolution does eusociality become irreversible? When an anatomically distinct caste first appears then a colony can most meaningfully be called as super organism. Not a single reversal is known among the >11,000 described species of ants or 2,000 described termites. The same evidence concerning lack of reversal is offered by the scores of lines of polistine and vespine wasp species that possess an anatomical worker caste.
The only exception to this rule are several lines of Thrips (16) and Aphids (17) that have lost the non reproductive solider caste and hence reverted from eusociality to cooperative breeding.
BEYOND THE POINT OF NO RETURN
In the later stages of eusocial evolution, past the point of no return, the favoring of close collateral kin has been depicted as dissolutive in some respects but also and much more importantly as a strong binding force crucial to the maintenance of altruism and eusociality. A growing body of evidence of several kinds now suggests otherwise. It includes the rarity of male production by workers in social hymenoptera, with one single mated queen, the lack of favouring bias by workers of their respective mother in colonies with multiple queens, also at variance with the traditional expectations.
The effect favoring group selection as opposed to Kin selection as the binding force may be due to improved genetic resistance to disease or to the enhancement of division of labor by genetic proneness to specialization by the workers. At the same time a great many studies have implicated Kin selection as a weak dissolutive force arising from nepotism and conflict among colony members.
A second phenomenon possibly biased by relatedeness and established in the later, irreversible stage of eusocial evolution is policing, the use of harassment or selective egg removal to restrict reproduction to the reproductive individual.
Fig.1 The two competing hypotheses of the origin of eusociality in insect and hence before the point of no return. (A) Holds that in the earliest stage, kin selection is binding, making dose relatedness a key feature; if combined with group selection, kin selection favors primitively eusocial colonies in a population of solitary or pre eusocial insects (far left)
THE RARENESS OF EUSOCIALITY:-
Of the 2600 living taxonomic families of insects and other arthropods currently recognized only 15 are known to contain social species. It follows that, some property of nature has set a very high bar for the attainment of eusocialty. Even the large number of phyletic lines where the individuals nest in aggregates and disperse to a limited degree including those that reproduce by cloning, have not in vast majority of case vaulted the bar. It seems to follow that only some additional extraordinary circumstance or set of circumstances in their prior history an in the environmental challenge they faced lifted them over the bar.
EUSOCIALITY AND PREEMPTIVE ECOLOGICAL SUCCESS:
The breakthrough by two of the lines to eusociality has conferred on them spectacular ecological success. Although ants and termites together compose only 2% of the 900000 insect species known globally, they make up more than half the insect biomass. Their dominance is ecological in origin. Colonies control nest sites and foraging grounds in competition with solitary insects. They use chemical communication to assemble nest mates and organized maneuvers to defeat adversaries. The disposition of workers to risk or surrender their lives enhances the genetic fitness of the colony. In general, ants in particular dominate the central, more stable areas of habitats, whereas solitary insects are best able to flourish in the peripheral, more ephemeral areas.
In the ants and other social insects, we are thus privileged to see not only how complex societies have evolved independently of those of humans and in a different sensory modality but also, with increasing clarity, the relations between levels of biological organizations and the forces of natural selection that formed and shaped them. We have begun to glimpse the connections between major features of sociobiology, ecology and biogeography of these insects.
These conclusions could have implications for advanced social behaviors outside the arthropods. Rarity and the prominences of group selection in unusual environments that favor cooperation are shared by the Bathyergid rodents, the only highly eusocial phylad known in the vertebrates. Rarity of occurrence and unusual pre adaptations characterized the early species of Homo and were followed in similar manner during the advancement of ants and termites by the spectacular ecological success and preemptive exclusion of competing forms by Homo sapience.
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