Sociobiology: Elementary Concepts PDF

Sociobiology SOCIAL EVOLUTION: ELEMENTARY CONCEPTS OF SOCIOBIOLOGY  Socialization  Multiplier effects can speed social evolution still more when an individual's behavior is strongly influenced by the particularities of its social experience.  This process i...

Sociobiology SOCIAL EVOLUTION: ELEMENTARY CONCEPTS OF SOCIOBIOLOGY  Socialization  Multiplier effects can speed social evolution still more when an individual's behavior is strongly influenced by the particularities of its social experience.  This process is called Socialization.  Socialization appears to amplify phenotypic differences among primate species.  As an example, the diverging pathways of development of social behavior observed in young olive baboons (Papio anubis ) as opposed to Nilgiri langurs (Presby tis johnii) (Eimerl and DeVore, 1965 ; Poirier, 1972b).  Socialization  The olive baboon infant stays close to its mother during the first month of its life, and the mother discourages the approach of other females. But afterwards the growing infant associates freely with adults.  From the age of nine months, male baboons progressively lose the protection of their mothers, who reject them with increasing severity.  As a result, they come to mingle with other members of the troop even more quickly and freely.  The social structure of the olive baboon is consistent with this program of socialization.  Adult males and females mingle freely, and peripheral groups of males and solitary individuals are rare or absent.  Socialization  Langur social development is far more sex oriented than that of baboons.  The infant is given up readily to other adult females, who pass it around with little contact with adult males.  Juvenile males begin to associate with adult males only after eight months, while young females do not permit contact until the onset of sexual activity at the age of 3 years.  The young males spend most of their free time playing, as the play fighting becomes rougher, they tend to drift to the periphery of the group.  The langur society reflects this form of segregated rearing in which adult males and females tend to remain apart.  The Evolutionary Pacemaker  Evolutionary changes in behavior generally occur before changes in body structures involved in the behavior.  Evolution involves both structure and behavior.  Behavior should change first and then structure.  Wolfgang Wicker has found good evidence of this in fishes & birds  Example: the puffer fishes: What starts as adaptive anti-predator behavior has evolved into structural properties of some species within the same group of fishes.  The Evolutionary Pacemaker  Among the tetraodontiform fishes, a number of species are able to inflate themselves tremendously with water or air as a protective device against predators.  In young porcupine fishes of the genus Diodon, the median fins disappear into pouches of the skin that fold inward during inflation.  The inflated stage has become irreversible in the diodontid genus Hyosphaera , while the tetraodontid globe fish, Kanduka michiei, not only is permanently inflated but also has lost the dorsal fin and reduced the anal fin to vestigial form. porcupine fish tetraodontid globe fish  The Concept of Adaptive Demography Adaptive demography:  Relative proportions of individuals of different ages and sizes can be influenced by selection in favor of groups vs the individual.  For example, a colony of social insects is vital to the fitness of the colony as a whole and particularly to that of the progenitrix queen.  If too few soldiers are present at the right moment, the colony may be demolished by a predator.  If too few nurse workers of the appropriate age are not always available, the larvae may starve to death.  Thus, the demographic distribution is adaptive, in the sense that it is tested directly by natural selection.  Qualities of Sociality 1. Group size:  Joel Cohen (1969 ,a,b, 1971) has shown the existence of orderly patterns in the frequency of distribution of group size among primate troops.  In the case of closed, relatively stable groups, much of the information can be accounted for with:  Constant gain rates through birth and immigration.  Constant loss rates through death and emigration.  Qualities of Sociality 2. Demographic distribution:  Discussed in the previous section on adaptive demography. 3. Cohesiveness:  The closeness of group members to one another is an index of the sociality of the species.  Qualities of Sociality 4. Amount and pattern of connectedness:  The network of communication within a group can be patterned or not.  That is, different kinds of signals can be directed preferentially at particular individuals or classes of individuals.  In the unpatterned case, all signals can be directed randomly for periods of time at any individuals close enough to receive them, such as fish schools.  In the case of patterned networks, the situation is radically different.  Hierarchies with multiple levels can be constructed, provided the members are also performing separate functions, the degree of coordination and efficiency of the group as a whole can be vastly increased over an unpatterned network.  Qualities of Sociality 5. Permeability:  To say that a society is closed means that it communicates relatively little with nearby societies of the same species and seldom if ever accepts immigrants.  A troop of langurs (Presbytis entellus ) is an example of a society with low permeability.  Exchanges between troops consist mostly of aggressive encounters over territory, and, at least in the dense populations of southern India, immigration is mostly limited to the intrusion of males who take the position of the dominant male.  Qualities of Sociality  Permeability  At the opposite extreme are the very permeable troops of chimpanzees, in which groups temporarily fuse and exchange members freely.  An increase in permeability should result in an increase in gene flow through entire populations.  Qualities of Sociality 6. Compartmentalization:  The extent to which the subgroups of a society operate as discrete units is another measure of the complexity of the society.  When confronted with danger, a herd of wildebeest flees as a disorganized mob, with the mothers turning individually to defend themselves and their calves only if overtaken.  Zebra herds, in contrast, sort out into family groups, with each dominant stallion maneuvering to place himself between the predator and his females.  When the danger passes, the families merge again into a single formation.  Qualities of Sociality 7. Differentiation of roles:  Specialization of members of a group is a hallmark of advance in social evolution.  Packs of African wild dogs, break into two "castes“ during hunts :  The adult pack that pursues, and the adults that remain behind at the den with the young.  Qualities of Sociality 8. Integration of behavior:  The inverse of differentiation is integration : a set of specialists cannot be expected to function as well as a group of generalists unless they are in the correct proportions and their behaviors coordinated.  Minor workers of the American ant Pheidole dentata forage singly for food outside the nest.  When they discover a food particle too large to carry home, they lay an odor trail back to the nest.  The trail chemical is carried in the poison gland and released through the sting when the tip of the abdomen is dragged over the ground.  The trail attracts and guides both the other minor workers and members of the soldier caste, all of whom then assist in the cutting up and transport of the food.  Qualities of Sociality 9. Information flow:  Norbert Wiener said that sociology, including animal sociobiology, is fundamentally the study of the means of communication.  The magnitude of a communication system can by measured in three ways :  The total number of signals.  The amount of information in bits per signal.  The rate of information flow in bits per second per individual and in bits per second for the entire society.  Qualities of Sociality 10. Fraction of time devoted to social behavior:  The allocation of individual effort to the affairs of the society is one fair measure of the degree of sociality.  R. T. Davis and his coworkers (1968) detected a rough correlation with these several traits within the primates.  Lemurs (Lemur catta ) , generally regarded to have a somewhat simple social organization, devote approximately 20 percent of their time to social behavior.  While pigtailed macaques (Macaca nemestrin ) and stumptailed macaques (M. speciosa ), which by other criteria are relatively sophisticated social animals, invest about 80 and 90 percent of their time, respectively, in social acts.