sign in sign up
<<
Home , Eusociality

Social

Insect Social Insects

• evolved multiple times in insects • Much of Earth’s fauna consists of social insects • They play major roles in entire ecosystems • Proliferation of and associated with change from solitary to social lifestyle Social Insects

• Consistent trend: • Numerous forms of subsocial in numerous lineages – Aggregations TO – TO – Parental care & nesting TO – Communal nesting TO • Increasing division of labor and reproduction in fewer lineages TO • Primitively eusocial in fewer lineages TO • Advanced eusocial fewer lineages Subsocial

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

• Three traits – Some individuals in reproduce, others sacrifice reproduction – Cooperation in tending young – Overlap of generations within colonies • Ants, termites, some and Aggregations as subsocial behavior

• Food exploitation – bark • Roosting Aggregations as subsocial behavior

• Aposematism – monarch butterflies – ladybird beetles • Chemical defenses – sawflies • Parental care 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 – Can involve feeding – , Orthoptera, Dermaptera, , Coleoptera and Membracid nannies

• Parental care by ants. • Ants obtain from treehoppers Nesting as social behavior

• Eggs laid in structure and parents tend young – Types of • New construction • Pre-existing – Types of care • Vigilence • Nutrition Nesting as social behavior

• Solitary nesting – No reproductive division of labor – Examples: • ground nesting crickets, • earwigs, angel insects • some beetles, • Hymenoptera – What orders? – Nesting is not known in other orders. Nesting as social behavior

Most nesting subsocial Hymenoptera are parasitoid wasps. Communal nesting

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

• Aphids – Behavioral and morphological differences 1. Soldiers • All first instar • molt into normal feeding individuals • Reproduction delayed if molt is delayed 2. Special caste of soldiers Social aphids

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

Reproductive (normal) nymphs Social aphids

Soldiers injecting venom into predatory lacewing larva Social aphids & thrips

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

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

• Communal nest- adults cohabit a single nest, but each care for their own young. • Quasisociality- adults cohabit a single nest, and cooperate in brood care. • Semisociality – Division of reproductive labor – Workers are sisters to queens • =caste system • No morphological difference between queen and workers – No overlap of adult generations 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 Natural selection & Eusociality

• Why would some individuals NOT be involved in reproduction? Natural selection & Eusociality

• W.D. Hamilton gave us the tools to solve one of Darwin’s greatest challenges. • The of . Eusocial Hymenoptera

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

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

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

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

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

• All ants are eusocial • Workers may be Amblyopone polyphenic are specialist predators of – Trophogenic centipedes – Feeding • Predatory • Seed and grain harvesters Extreme eusociality: ants (Formicidae)

• All ants are eusocial • Workers may be polyphenic – Trophogenic – Feeding • Mutualists with plants • Honey dew specialists Extreme eusociality: ants (Formicidae)

• All ants are eusocial • Workers may be polyphenic – Trophogenic – Feeding • Fungus harvesters

Extreme eusociality: ants (Formicidae)

• All ants are eusocial • Workers may be Polyerges polyphenic Slave-maker – Trophogenic – Feeding • Parasites (slave-makers & usurpers) Slave

A queen Polyergus slave-raiding attended to by a Formica worker. Parasitic queens such as Polyergus emit pheromones that are attractive to host ant workers Extreme eusociality: ants (Formicidae)

• All ants are eusocial • Workers may be Polyerges polyphenic Slave-maker – Trophogenic – Feeding • Predatory Formica • Seed and grain Slave harvesters • Mutualists with plants • Honey dew specialists • Fungus harvesters • Parasites (slave-makers & usurpers) A queen Polyergus slave-raiding ant attended to by a Formica worker. Parasitic queens such as Polyergus emit pheromones that are attractive to host ant workers 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 the Normark paper)? Eusocial Isoptera

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

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

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