Social Insects Psychology 3107
Introduction • Many Insects live in hives, nests or what have you • Definite roles for different castes, usually only one female that lays eggs • Other females are ‘sterile’
An Example • The life history of the Bumblebee • Mated females emerge in spring after 8 months of hibernation • Mated the previous autumn • Colony in which she was hatched is all dead • Up to 100 or so females left the colongy • First she forages for pollen
The flight of the Bumblebee! • Pollen provides • Fat, minerals and vitamins for egg formation • Later on she forages for nectar • Provides carbohydrates • Stores nectar in wax containers • Lays eggs in the ‘Hall of Pollen’ • First brood are sterile females • forage
Bzzzzzzzzzzzzz • Second brood are also sterile females • Cared for by the first brood • Third brood are fertile females and males • Cared for by first and second brood • Third brood leaves, males mate and die, females mate and hibernate • The colony is really just a reproductive factory
Eusociality • For Eusociality we need • Overlapping generations • Cooperative care of the young • Sterile castes • In insects, euscociality occurs in: • Hymenoptera • Ants • Bees • wasps
Eusociality • Isoptera • Termites • Homoptera • Aphids • Some say that these two are not truly eusocial, but if you look at that definition, you could, under certain circumstances, say bees were not eusocial!
Haplodiploidy • Eusociality has evolved 11 separate times just in Hymenoptera! • Why? • Sterile females are usually very closely related • Basically, it does not pay to have young, it pays more to take care of your sisters, as they are more closely related to you than any potential offspring!
Haplowhatoidy? Daughter Son Mother Father .5 .5 .5 .5 female 1.0 0 1 0 male Sister Brother .75 .25 female .50 .50 male
Males are just clones of half of female chromosomes So you see, sisters are either 75 % related, or 100% related or 50% related, averages out to 75 %
So, what’s the deal with….. • Termites • They aren’t haplodiploid • They are eusocial • There is a king too • Queen is an egg laying machine
While you’re at it, explain • Naked mole rats • Mammals • ‘Penises with teeth’ • Both with the termites and the NMR we have cases of eusociality, but also normal diploid reproduction
Conclusion • Social insects are a great example of the predictions of genetics and evolution at work. • Termites and naked mole rats show that eusociality is not simply due to haplodiploidy • Gene environment interaction baby!