Lecture 1
Phenotypic plasticity and the evolution of eusociality
how animals are affected by their environment
you have 1 DNA- which makes 2 phenotypes
queen bee and worker bee
queen bee- lives for 4 years, abdomen, large active ovaries, lay 200 eggs a day, leaves once in her
lifetime to mate on a mating flight- come back lays eggs,
worker bee- live 6 weeks in summer, do all the work in the hive, in charge of the hive, if the queen
isn't laying high quality eggs workers will kill her and make a new queen
same dna- both females
what they ate during larval development is what makes them different - queen developed eating
royal jelly
queen produced a pheromone- queen mandibula pheromone - workers respond to environmental
stimulus- this changes behaviour - groom queen and worker ovaries stay at small state
queen ovary is large and fills the whole abdomen
worker ovary are more string like- 2 in abdomen each made up of a couple strings
Why are we fascinated by social animals?
charles darwin
social insects are the 1 special difficulty in theory of evolution by natural selection
female castes that don't reproduce
all animals should want to reproduce
all driven by fitness or passing genes onto next generation
WD Hamilton rule
why you get sterile castes in insects
social insects- they're related to queen
support queens reproduction
indirect fitness- share genes with queen- passed onto next regeneration
kin selection
criticised by EO Wilson
ant biologist
Why do we study social animals?
• Biodiversity-social insects dominate the areas in which they inhibit, biodiversity they contribute, at
as ecosystem engineers
• Ecological importance
• Economic importance- 1/3 of food we eat rely on pollination, this contributes billions of pounds
globally to the economy - food supply
• Good biological models for
• Learning and memory
• Sensory physiology
• Self organisation
• Interactions with the environment
Which animals are eusocial?
Mammals:
naked mole rats- not insects
ants, wasps, aphids, bees, termites, snapping shrimp (crustacean)
depends on definition
,What do we mean by “eusocial”?
Comes from the Greek word “eu” meaning good or truly and the Latin word “socius” =
companion.
Reflects the highest level of organisation of an animal society.
• The term was introduced by Suzanne Batra in 1966
– Batra S.W.T. (1966) Indian J. Entomol 28 375-393.
• Defined by E. O. Wilson in 1971
– Wilson E.O. (1971) The insect societies, pp 4-6
Definition(s)
Eusociality
– Reproductive division of labour- some usually females reproduce and some don't
– Cooperative brood care- ones that don't reproduce look after the brood of those who do
– Overlap of generations capable of caring for brood.
Humans are not as we don't have reproductive division of labour
No caste system- some individuals are not allowed to reproduce
Cooperative brood care- preschool
Overlap of generations- grandparents caring for grandchildren
Other definitions of eusociality
Highly restricted
– “On the basis of castes, with eusocial taxa having nontotipotent sterile and reproductive castes”
• Crespi & Yanega 1995 Behav Ecol; Crespi 2005 Ann Zool Fennici
– “Restrict to ‘highly complex’ societies, with reproductive division of labor, cooperative foraging
and food-sharing”
• Crespi & Yanega 1995 Behav Ecol; Crespi 2005 Ann Zool Fennici
• Greatly expanded
– “As a continuum based on reproductive skew, species with obligatory sterile workers having high
skew”
• Sherman et al., 1995 Behav Ecol; Lacey & Sherman et al., Ann Zool Fennici
We have deiced what this is based on behaviour
Social ≠ eusocial
• Sociobiology = The extension of population biology and evolutionary theory to social
organisation.
- Study of the evolutionary mechanics behind social behaviours (e.g. altruism, aggression).
- The fundamental principle of sociobiology: an organism's evolutionary success is measured
by the extent to which its genes are represented in the next generation.
• E.O. Wilson (1975) Sociobiology: The new synthesis.
• Social behaviours are actually quite common in the animal kingdom
• Some of these behaviours may be important preadaptations for the evolution of eusociality.
Communal living
• Very common in invertebrates
• Seen in vertebrates (e.g. humans)
• Benefits
- Increased mating success
- Access to resources / foraging efficiency
, - Problem solving
- Protection from predators
Selfish herd hypothesis
Concentrated groups arise because prey selfishly attempt to place their conspecifics between
themselves and the predator
– causing an endless cycle of movement toward the centre of the group
Communal nests
Key question:
Is there overlap of generations capable of caring for brood?
No
Parental care
Very common in insects e.g. Dermoptera (earwigs), Blattaria (cockroaches), Hemiptera (true bugs)
and Coleoptera (beetles).
water bug- place eggs on back- walks around- hatch from there and wonder off
burying beetles- collect corpse of a mouse, drag it back, remove intestines and fur, make meat ball,
bury in dire, bury eggs around it, larvae eat this, parental care - food provisioning
offspring attendance- when larvae hatch from eggs parents are tending to them
burrower bug
european bee wolf
burying beetle
treehopper
Range of behaviours
– Defending the egg
– Egg attendance / brooding
– Food provisioning
– Offspring attendance
– Offspring brooding
Parental care: Defence
Presociality to eusociality
Solitary • Female mass provisions brood (dies before they hatch)
Subsocial • Parental care, progressive provisioning.
Communal • Members of same generation live together Presocial
• No brood care
Quasisocial • Members of same generation live together
• Cooperative brood care
Semisocial • Members of same generation live together
• Cooperative brood care
• Reproductive division of labour
Eusocial • Overlapping generations Eusocial
• Cooperative brood care
• Reproductive division of labour
