I.  Sterile castes in social insects.
 
 

  A queen of the army ant Eciton burchelli.  As in all ants, the queen is responsible for all the reproduction in the nest and may lay between 100,000 and 300,000 eggs in a three-week period.  (From E. O. Wilson.  1971.  The Insect Societies.  Belknap Press, Cambridge MA.)
 
 
 
 
 
 
 
 
 
 

   Castes in the ant Pheidole kingi.  The queen is the lower right individual.  Immediately above the queen is a male.  Other individuals are sterile workers.  (From E. O. Wilson.  1971.  The Insect Societies.  Belknap Press, Cambridge MA.)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

      A nest of the paper wasp, Polistes fuscatus.  Workers are of two types: secondary foundresses and workers proper.  Secondary foundresses have the physiological capability to reproduce and are inseminated, but when they join the nest of a primary foundress, their ovaries regress and they fail to reproduce.  Workers proper are the progeny of the queen and are not inseminated.   (From E. O. Wilson.  1971.  The Insect Societies.  Belknap Press, Cambridge MA.)
 
 
 
 
 
 
 
 
 
 

  Adult castes in the hornet, Vespula maculata.  Top picture: worker.  Bottom picture: queen.  Workers are sterile.   (From E. O. Wilson.  1971.  The Insect Societies.  Belknap Press, Cambridge MA.)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

    Queen, male, and workers in a nest of the termite Amitermes hastatus.  Workers are kept permanently in a juvenile state
    by pheromones emitted by the queen, and thus do not reproduce.  (From E. O. Wilson.  1971.  The Insect Societies.
    Belknap Press, Cambridge MA.)

II.  Alarm calls in mammals
 

    Female Belding's ground squirrel (Spermophilus beldingi) emitting an alarm call.  Alarm calls are given to warn other individuals about the presence of a nearby predator and are usually directed toward close kin.  It is believed that giving an alarm call increases the chance that the predator will attack the caller. (From J. W. Bradbury and S. L. Veherencamp.  1998.  Principles of Animal Communication.  Sinauer, Sunderland, MA.)
 
 
 
 
 
 
 
 
 

III.  Division of Labor in Coelentrates
 
 

  The Portugese man-of-war, Physalia physalis, is a colonial coelentrate.  What appears to be one individual is really a colony of individuals that perform different functions (see next picture).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

   A. and B.  Colony of the coelentrate Muggiaea showing the functional specialization of individual zooids.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

IV.  Helpers at the nest in Florida Scrub Jays
 
 

   Drawing of mated pair, nestlings, and helper (left) at a nest of the Florida Scrub Jay (Aphelocoma coerulescens).  (From E. O. Wilson.  1975.  Sociobiology: The New Synthesis.  Belknap Press, Cambridge, MA.)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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