module7 lecture print - university of san diego home...
TRANSCRIPT
Social Insects
• Sociality evolved multiple times in insects
• Much of Earth’s 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
Social Insects
• Consistent trend: • Numerous forms of subsocial
in numerous lineages – Aggregations TO – Parental care 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
Eusocial
• Three traits – Some individuals in
colony reproduce, others sacrifice reproduction
– Cooperation in tending young
– Overlap of adult generations within colonies
• Ants, termites, some bees and wasps
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 nest – Can involve feeding – Blattodea, Orthoptera,
Dermaptera, Hemiptera, Coleoptera and Hymenoptera
Nesting as social behavior
• Eggs laid in structure and parents tend young – Types of nests
• 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.
Communal nesting
• Nests shared among individuals
• Parents clean, provision, defend nests
• Conflicts among nest mates common
• Halictinae, Megachilinae, Andreninae
Social aphids & thrips
• 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
Adults
Soldier nymphs Remain at 2nd instar without molting and growing.
Sclerotized cuticle
Sterile
Attack natural enemies & competitors
Perform housekeeping.
Reproductive (normal) nymphs
Molt and grow.
Soft cuticle.
Contribute to reproduction.
Perform neither defense nor house-keeping.
Genetically identical clones by parthenogenesis
Differences likely attributable to
differences in gene expression between
the castes POLYPHENISM
Social 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
Social thrips
Dispersers are highly fecund, participate in extensive brood care, and are adept at 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.
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
• W.D. Hamilton gave us the tools to solve one of Darwin’s greatest challenges.
• The evolution of altruism.
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
• Bumblebees, 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 • Pheromones 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 (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
Extreme eusociality: ants (Formicidae)
• All ants are eusocial • Workers may be
polyphenic – Trophogenic – Feeding
• Predatory • Seed and grain
harvesters
Amblyopone are specialist predators of centipedes
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
polyphenic – Trophogenic – Feeding
• Parasites (slave-makers & usurpers)
Polyerges Slave-maker
Formica Slave
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
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)
Polyerges Slave-maker
Formica Slave
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)?
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