Social Insects

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Social Insects

• Sociality evolved multiple times in insects
• Much of Earths fauna consists of social insects
• They play major roles in entire ecosystems
• Proliferation of ants and termites associated
  with change from solitary to social lifestyle

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Subsocial

• More widespread
• 13 orders of insects
• no reproductive division of labor

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Eusocial

• Three traits
• Some individuals in colony reproduce, others
  sacrifice reproduction
• Cooperation in tending young
• Overlap of generations within colonies
• Ants, termites, some bees and wasps

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Aggregations as subsocial behavior

• Food exploitation
• bark beetles
• Roosting
• Aposematism
• monarch butterflies
• ladybird beetles
• Chemical defenses
• Sawflies
• Parental care

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Aggregations as subsocial behavior

• Food exploitation
• bark beetles
• Roosting
• Aposematism
• monarch butterflies
• ladybird beetles
• Chemical defenses
• sawflies
• Parental care

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Parental care

• What parental care do all insects provide?
• Post hatching attention, provision and protection
  of food
• Without nesting
• Tending eggs and young
• Care of nest
• Can involve feeding
• Blattodea, Orthoptera, Dermaptera, Hemiptera,
  Coleoptera and Hymenoptera

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Membracid nannies

• Parental care by ants.
• Ants obtain honeydew from treehoppers

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Nesting as social behavior

• Eggs laid in structure and parents tend young
• Types of nests
• New construction
• Pre-existing
• Types of care
• Vigilence
• Nutrition

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Nesting as social behavior

• Solitary nesting
• No reproductive division of labor
• Examples ground nesting crickets, earwigs, some
  beetles, Hymenoptera
• What orders? Nesting is not known in other orders.

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Nesting as social behavior
Most nesting subsocial Hymenoptera are parasitoid
wasps.
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Communal nesting

• Nests shared among individuals
• Parents clean, provision, defend nests
• Conflicts among nest mates common
• Halictinae, Megachilinae, Andreninae

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Subsocial aphids thrips

• Aphids
• Behavioral and morphological differences
• Soldiers
• All first instar
• molt into normal feeding individuals
• Reproduction delayed if molt is delayed
• Special caste of soldiers

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Subsocial aphids thrips

• Aphids
• Behavioral and morphological differences
• Soldiers
• All first instar
• molt into normal feeding individuals
• Reproduction delayed if molt is delayed
• Special caste of soldiers

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Subsocial aphids
Soldier nymphs
Remain at 2nd instar without molting and
growing. Sclerotized cuticle Sterile Attack
natural enemies competitors Perform
housekeeping.
Adults
Differences likely attributable to differences in
gene expression between the castes POLYPHENISM
Genetically identical clones by parthenogenesis
Molt and grow. Soft cuticle. Contribute to
reproduction. Perform neither defense nor
house-keeping.
Reproductive (normal) nymphs
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Subsocial aphids

• Soldiers injecting venom into predatory lacewing
  larva

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Subsocial aphids thrips

• Thrips
• Behavioral and morphological differences
• Dispersers soldiers in colony in gall
• Soldiers defend gall against other thrips species
  and usually reproduce less than dispersers

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Subsocial thrips
Dispersers are highly fecund, participate in
extensive brood care, and are adept and
initiating and growing new galls.
Soldiers have low fecundity and are involved
primarily in defense of the gall from
kleptoparasites. They cannot initiate or grow
galls.
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Quasisociality Semisociality

• Communal nest- Members of same generation
  cooperate in brood care
• Quasisociality- All females can reproduce
• Semisociality
• Division of reproductive labor
• Workers are sisters to queens
• No morphological difference between queen and
  workers

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Eusociality

• Multigenerational colonies
• Polyphenism morphological differences between
  queen and workers
• Polyethism behavioral differences
• Caste system
• Reproductives
• Workers
• Soldiers
• Subcastes
• Found only in Hymenoptera and ALL Isoptera

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Natural selection Eusociality

• Why would some individuals NOT be involved in
  reproduction?

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Natural selection Eusociality

• W.D. Hamilton gave us the tools to solve one of
  Darwins greatest challenges.
• The evolution of altruism.

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Eusocial Hymenoptera

• Why are there so many origins of Eusociality in
  the Hymenoptera?
• How are r and B maximized with respect to C?

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Super-relatedness in Hymenoptera

• What sex-determination system do all Hymenoptera
  have?
• So, what is the genetic relatedness between
  sisters?
• How could this result in a maximization of r?
• What benefits might there be of this extensive
  social behavior?

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Eusocial Hymenoptera

• Which is/are the male(s) in the above figure?
• Which is/are the female(s) in the above figure?
• Feeding quality substance yields polyphenism in
  diploids, which are all ____________.

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Hymenoptera

• Numerous origins of eusociality from
  subsociality.
• Primitively eusocial
• Females morphogically similar
• Colonies usually annual
• Advanced eusocial
• Ants, some wasps, many bees
• Behavioral and morphological differentiation
• Workers different than queens

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Primitive eusocial Hymenoptera

• Numerous transitional lineages, e.g.
• Polistine Wasps, a few others
• gt1 female forms colony
• Colony lasts 1 yr
• Variable reproductives
• Bumblebees, Halictinae
• gt1 female forms colony
• winning female reproduces and is aggressive
• Sexual retardation reversed if queen dies

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Bumblebees

• Colony foundation by one or more females
• Pheromones used to modify worker behavior
• Ovarian development in late season workers
• Queen may be driven from nest
• Workers produce male offspring parthenogenetically

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Advanced eusocial Hymenoptera

• Many bees and some wasps, ants
• Females dimorphic
• Specialization of workers
• Wasps
• Queen founds first brood of workers
• Subsequent generations include males, then
  reproductive females

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Eusocial honeybees (Apidae)

• Colony develops and may found new colonies during
  summer
• Nest made of wax secreted by bees
• Castes queen (larger), worker (smaller), drone
• Old workers hive Young workers field

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Extreme eusociality ants (Formicidae)

• All ants are eusocial
• Workers may be polyphenic
• Trophogenic
• Feeding
• Predatory
• Seed and grain harvesters
• Mutualists with plants
• Honey dew specialists
• Fungus harvesters
• Parasites (slave-makers usurpers)

Amblyopone are specialist predators of centipedes
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Extreme eusociality ants (Formicidae)

• All ants are eusocial
• Workers may be polyphenic
• Trophogenic
• Feeding
• Predatory
• Seed and grain harvesters
• Mutualists with plants
• Honey dew specialists
• Fungus harvesters
• Parasites (slave-makers usurpers)

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Extreme eusociality ants (Formicidae)

• All ants are eusocial
• Workers may be polyphenic
• Trophogenic
• Feeding
• Predatory
• Seed and grain harvesters
• Mutualists with plants
• Honey dew specialists
• Fungus harvesters
• Parasites (slave-makers usurpers)

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Eusocial Isoptera

• What sex determination system do termites have?
• Uh-oh, zup?
• Perhaps something about maximizing B when
  feeding on wood?
• What else happens to wood-feeding insects in
  their population structure (remember Normark
  paper)?

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Eusocial Isoptera

• In what way does this caste determination
  structure differ from Hymenoptera?

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Termites

• Lower termites
• Wood-digesting endosymbionts
• Loose castes, all workers immature
• Morphology and caste may change after molting
• Queen similar to workers

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Termites

• Higher termites Termitidae
• No symbiotic flagellates
• How do they digest wood?
• Rigid caste system
• Queen differs from workers

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Termite mounds