Social Insect Biology lecture notes 1-13 PDF

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Lecture 1: IntroductionNews and Views Article (20%)  Its not to summarise the paper - pick out the key message of the paper, why is it important?  Pick one of the five research papers given - either health or disease Exam (2 hours) - part a: answer 4/6 questions), part b: 1/2 (80%)Is no text book ...

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Lecture 1: Introduction News and Views Article (20%)  Its not to summarise the paper - pick out the key message of the paper, why is it important?  Pick one of the five research papers given - either health or disease Exam (2 hours) - part a: answer 4/6 questions), part b: 1/2 (80%) Is no text book for additional reading - use current literature Read: Nowak et al., 2010. The evolution of eusociality Aphids are viviparous - give birth to live young Why are we fascinated with social animals? Humans have been studying social animals (in particular insects) for 2000+ years  Aristotle – the philosopher studied bees Scientists are modern day philosophers  Charles Darwin – very interested in social insects, because they were the one special difficulty in his theory of evolution by natural selection - he was worried because the ant workers all support the queen, and this didn't fit with his theory f natural selection.  W.D Hamilton - changed the course of eusocial research theory  E.O Wilson  Richard Dawkins No one knows how eusociality evolved, so need to make our own minds up Why do we study social animals?  Biodiversity  Ecological importance  Economic importance - pollination support 600 million to the food, anually globally  Learning and memory  Sensory physiology  Self-organisation  Interactions with the environment Which animals are eusocial?  Bees  Termites  Ants  Naked mole rats  Snapping shrimp  Social aphids What do we mean by “eusocial”? Comes from the Greek word “eu” meaning good or truly, and the Latin word “socius” = companion We are so interested in eusociality because it reflects the highest level of organisation of an animal society that we know about Term was introduced by S. Batra in 1966, but she has since retired

E.O. Wilson found this term and defined it in 1971, so he is often credited with coming up with this term of eusociality Definition: Eusociality To be eusocial you have to have:  A reproductive division of labour  Cooperative brood care  Overlap of generations capable of caring for brood/young o Humans would be seen as eusocial if there was reproductive division of labour – e.g. a mother had 3 daughters and 1 daughter was born sterile every time. Over the years other people have tried to come up with other definitions of eusociality: Highly restricted:  “On the basis of castes, with eusocial taxa having non-totipotent sterile and reproductive castes” o Which means the society is divided up into different castes, some of which aren’t totipotent – so sterile, and others which are reproductive.  “Restrict to ‘highly complex’ societies, with reproductive division of labour, cooperative foraging and food-sharing”  Greatly expanded  “As a continuum based on reproductive skew, species with obligatory sterile workers having high skew” o Which means reproductive skew – high in bees for example because only the queen reproduces, but the skew is low in primitive societies because most females will reproduce.  Good definition  “No general definition possible” o Wcislo 1997 TREE Therefore, there has been a lot of debate about eusociality But the definition we are going to stick to in this course is the one by E.O. Wilson Social does not mean eusocial There are lots of examples of behaviours in the natural world that are social e.g. things like aggression, altruism, cooperation. E.O. Wilson proposed Sociobiology. 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 organisms evolutionary success is measured by the extent to which its genes are represented in the next generation. Social behaviours are actually quite common in animal kingdom All eusocial animals have Communal living Very common in invertebrates Also seen in vertebrates (e.g. humans, lions) Benefits  Increased mating success (don’t have to leave the group to find a mate)  Access to resources/foraging efficiency – e.g. often find lionesses hunting together  Problem solving  Protection from predators

E.g. birds flying in formation E.g. Sociable weaver makes nests in trees, all the nests have small holes at the top where lots of individuals live W.D. Hamilton came up with the selfish herd hypothesis Concentrated groups arise because prey selfishly attempt to place their conspecifics between themselves and the predator, so the conspecifics are eaten first o Causing an endless cycle of movement toward the centre of the group Examples: Weevil larvae (coleoptera) – huddle together so keeping an eye out of predators and in doing so look bigger than they are Desert locust – have a gregarious phase where they all swarm together Forest tent caterpillar – huddle together Leads to the formation of communal nests Nests sites are only shared within a generation e.g. birds lay eggs, these eggs hatch, grow up and then find somewhere else to make a nest to lay their own eggs to create new offspring, although there are some exceptions Communal living is a preadaptation to eusociality The key question: When you have a communal nest, is there an overlap of generations in that nest capable of caring for brood? o If there is then that is an organism that is potentially eusocial

Parental care Essential for euscociality. Very common in insects e.g. Demaptera, Blatteria, Hemiptera and Coleoptera In its most simple form, parental care can consist of the mother depositing a waxy coating on its eggs to protect them from the environment. But parental care can range to complex behaviours: Range of behaviours:  Defending of the egg  Egg attendance/brooding  Food provisioning  Offspring attendance – so could be providing to offspring throughout its life  Offspring brooding Examples:  Borrower bug  European beewolf: stung and paralysed a honey bee for its offspring to eat  European earwig  Burying beetle  Wood-feeding cockroach: the mother feeds its offspring by allowing them to feed off her haemolymph (blood)  Treehopper These examples are mostly solitary species, so you can have these parental care behaviours without being eusocial Presocaility to eusociality Can think of it like on a continuum scale  Presocial

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Communal Quasisocial Semisocial Eusocial

Reproductive division of labour Some temporarily or permanently sterile individuals work, while other individuals reproduce. This is shown by some species with parental care and communal nests and cooperative brood care – so are semisocial Webspinner - not a eusocial species but does display behaviours Highly eusocial: Honeybees, termites, leaf cutter ant  High number of individuals  Complex division of labour  Worker polymorphism may be present  Queen-worker dimorphism is high Eusociality has evolved multiple times throughout history: Chordates Naked mole rat – from sub-Saharan Africa  Feed on underground tubers  There is limited dispersal - so  Queen beats her workers into submission (the workers can reproduce, but they don’t) Damaraland mole rat  Limited dispersal – also inbreeding  Reproductive suppression of workers by the queen – the male and female workers have underdeveloped ovaries and testes. So when you remove the dominant female the workers will develop mature gonads and will reproduce. Eusocial crustaceans Snapping shrimp  There are 5 species that are eusocial – only one breeding female  Live inside sponges – so there is limited dispersal and high relatedness

Eusociality in insects Found in:  Isoptera (termites)  Thyasanoptera (thrips)  Hemiptera (aphids)  Coleoptera (beetles)  Hymenoptera – most commonly found in o Particularly in the aculeate (parasitic wasps, solitary wasps, bees, ants, eusocial wasps).

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9 origins of eusociality

Has evolved independently in separate insect orders

Lecture 2: The Main Characters Don’t need to know about the specific species names in the lecture - more important to know about their lifestyles/histories Eusociality is found within 5 orders:  Isopteran (termites)  Thyasanoptera (thrips)  Hemiptera (aphids)  Coleoptera (beetles)  Hymenoptera (mainly aculeata – bees, ants and some wasps)

Termites Eusociality evolved once at the base of the termite lineage.  Phylogenetics has now taught us that termites are essentially social cockroaches – so their DNA is very similar  All appox 2800 species of termites are eusocial - high complexity in the eusociality they posses E.g. Macrotermes – this is an example people like to show because you can see the big differentiation between the termite queen and the worker morphology. The queen is filled eggs – can lay 30,000 eggs a day and can have up to 2 million workers in a colony at any one time. The queen and king mate for life - the workers constantly feed the queen throughout her life Termite mound structure and colony Video – termites BBC world The air around termites underground gets stale - so have a ventilation system. Hot stale air from the mound rises up through the chimney. The walls of the mound are all porous to allow cooler ambient air to mix with the hot stale air in the chimney - creating an internal air current. Termite life history strategies Termites are divided into higher termites and lower termites  this has nothing to do with eusociality, both groups have highly complex social species  Found in mostly tropical areas  Are hemimetabolous – don’t go through pupal life stage,  Males and females are diploid (have sets of chromosomes) Lower termites  Which is ancestral, so the original eusocial termite was a lower termite  All have association with bacteria/protozoa in the hindgut that helps digest cellulose  Protozoa passed onto the offspring via anal feeding, so can pass on the symbiont to generations. Higher termites  Have lost this ability  But have gained the ability to become gardeners – they culture fungi or bacteria which digest the cellulose externally and then feed on the digested cellulose  Make up 75% of all termite species Example: Zootermposis life history stages Is a lower termite

Has had its genome sequenced, that’s why its so popular The larvae go through an incomplete metamorphosis, so the egg hatches into a dependent instar larvae, which then moults to become a final instar larvae – which is the worker stage of Zootermposis (incomplete developed larval stage) and they can stay in this stage for a long period of time. The change in pheromones in the hide cause this larvae to differentiate into either a: o Neotenic (secondary queen) – which can then become a new queen. A neotenic will then mate and leave the hide to find a new colony. o A nymph which can then further develop into a Alate (immature reproductive) – which is a flighted queen o Soldier – which is specialised in defence So the ability to be any of these different phenotypes with different morphologies and behaviours is encoded in the DNA of the first instar larvae and is regulated by pheromones. Termite worker castes Termites have multiple worker castes, so the workers and soldiers may be males or females, this differs fro the hymenoptera where the workers are always females.  The worker caste does most of the work in the nest, such as foraging, food storage, and brood and nest maintenance.  The soldier caste are purely for defence E.g. the Macrotermes givus major soldier has large head with very large mandibles Reproductives The king and queen mate for life Different termite species have different eusocial complexity  In some species there is low reproductive skew; offspring will eventually become reproductives, E.g. Zootermopsis some of the females will go off to found their own colonies and become queens  In some species there is a high reproductive skew; offspring are sterile, E.g. Macrotermes all of the reproduction is done by the queen. In some species the primary king and queen are replaced by secondary neoteinics, which are reproductive that wait around in the nest to take an opportunity to take the place of the king or queen. - E.g. Kalotermitidae In some species workers (which are called pseudergates) can become reproductive as well. This is reasonably uncommon in termite species. So how did eusociality evolve in the termites? Eusociality in the termites is the oldest example of eusociality we have, so it evolved the longest period of time ago. It is thought that the ancestral termite required symbiosis with a microorganism in order to digest cellulose. The symbiont was then passed from mother onto the offspring by anal feeding, which necessitates the offspring remaining close to the mother. This created conditions with limited dispersal and inbreeding, causing high relatedness. Once established the benefits of eusociality outweighed the costs and it has been stabilised over evolutionary time.

Eusocial thrips (Thysanoptera)  

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Only 4 species out of about 5000 are eusocial. Thrips are haplodiploid – meaning the females are diploid and males are haploid, so males are produced by unfertilised eggs The eggs develop in a gall, where the insects causes an outgrowth of the plant tissue around it and protects it from the environment. But it also encases the insects in a wall of plant tissue and prevents the offspring from dispersing, so creates an opportunity for limited dispersal, inbreeding and high relatedness. Sub-fertile soldiers defend the gall containing their mother and siblings from invasion and takeover by kleptoparasitic thrips and other insect invaders that want to take advantage of the gall. An interesting paper that came out last year – the main morphological difference between the soldiers and workers is that that the soldiers have these long forearms. So scientists always said that: of course they have longer arms, they are the soldier caste so they use them for defence and fighting. But it turns out when carrying out experiments, the soldier caste don’t fight any more than the workers do. The forearms arms contain an antimicrobial peptide, that is used for healing. So it goes around and helps members of its own nest survive after an attack.

Hemiptera (aphids)      

The only eusocial species in the hemiptera are the aphids And in the aphids only 50 eusocial species out of 4000 known species Likely to have been 17 independent origins, so in 17 different species there has been conditions that have been right for the evolution of eusociality In eusocial aphids sterile soldiers are smaller than the workers, but they defend the colony against predators e.g. lace wing. All eusocial aphid species inhabit galls – bits the plant that protect them from the environment Limited dispersal in every caste They reproduce clonally, so that every daughter is 100% genetically identical to the mother (genetic relatedness = 1) o Interested in, why are only 50 of them eusocial then??

Eusocial beetles (Coleoptera) 

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Only one eusocial species is known – ambrosia beetle, Austroplatypus incompertus  Found in Australia and inhabits live eucalyptus trees  It is diploid, but there are really only females as part of the nest  It is thought they became eusocial to overcome the toxic tree resin – but this is not known for sure A recent publication has found one primitively eusocial, Xyleborinus saxeseni  Haplodiploid – females have two sets of chromosomes, males have one set  But the reproduction division of labour is incomplete in this species – meaning why its primitively eusocial All ambrosia beetles farm fungi to eat So the environments which they inhibit means they’ve limited dispersal, inbreed and so have a high relatedness. But all ambrosia beetles all have these conditions, so eusociality have only evolved once

Hymenoptera Is where we see the highest number of eusocial species Hymenoptera can be split into 3 groups: 1. Symphyta – sawflies and woodwasps  Around 7000 species and none of these are eusocial  Some of the species are often pests of agriculture and forestry 2. Apocrita – parasitic wasps  55,000 species and they are all parasitoids or parasites of plants  Some are used in biocontrol of other species - but no  None of the species are eusocial - but interesting  However, a couple have really interesting behaviours – whereby sibling larvae develop within a host cooperate and have sterile soldiers o So there is reproductive division of labour because the soldier castes are sterile o There is cooperation in brood care because half the brood become soldiers and half become reproductive brood o But there is no overlap of generations – so don’t classify as eusocial E.g. in Copidosoma floridanum, a parasitoid of moths They only lay 1-2 eggs per host (1 male, 1 female), these eggs are interesting because they are polyembryonic, which means the eggs will divide repeatedly to form a brood of multiple individuals – some of the individuals will become either: - Soldiers - Workers The larvae are genetically the same, but they are very morphologically different. The soldiers will develop earlier and hatch first, and then they will kill relatively unrelated opposite sex siblings – so protecting their genetically identical brothers or sisters. 3. Aculeata – parasitic wasps, solitary wasps, bees, ants, eusocial wasps  54,000 species and many are eusocial – there are 9 independent origins of eusociality  Defines the aculeata: the ovipositor is not used to lay eggs, its used as a sting Why is eusociality so common in the aculeata? - Why have they been able to evolve eusociality so successfully? It is thought that it comes down to the preadaptations:  Aculeata have parental care  Mothers build nests to rear offspring  Nests can be reused between generations, associate kin, increase relatedness  Progressive provisioning of the nest - Bees provision larvae with pollen - Wasps provision larvae with prey - This cooperation results in assured fitness return  Haplodiploidy hypothesis (increased relatedness) – this hypothesis relies on the fact that females have two sets of chromosomes and males have one set, so its easier to increase relatedness amongst individuals because there is a decrease in the genetic variability. Wasps – not all species are social  Wasps are sort of the ancestral state of the Aculeata

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Not all wasps are social, but a lot are parasitic E.g. the cuckoo wasp is a kleptoparasite – it lays its eggs in the nests of other insects, its eggs hatch first, eat the eggs of the other insect and then move on, which is quite an evolved lifestyle E.g. jewelled/emerald cockroach wasp – stings a cockroach twice, the first sting disables its front legs, the second delivers venom directly into the cockroaches brain, which paralyses it. The wasp leads the roach to her burrow and lays a single egg on it. When the egg hatches the grub will burrow into the roaches body and its out its organs. There is around 4200 species of wasps and out of this 860 are eusocial They are all predators and all make nests from paper, but some do this in different ways – e.g. chew up wood and make nests Eusociality has evolved twice over 65 mya Stenogastrinae – hover wasps Tropical Tend to be primitively eusocial - Tend to have small colonies founded by a single female - Castes are not morphologically distinct - Daughters stay to help raise brood then leave to found their own nests - So in general there is less than 30 indvs per nest Polistinae Diverse group - around 300 species Tropical or temperate regions Form small to large colonies Primitive to advanced eusociality - Colonies founded by a single female - Distinct queen in some, but not in others - Gynes (future reproductives) have higher fat stores than worker individuals Vespinae – hornets and yellowjackets There are 4 genera - Vespa (hornets) - Provespa (night hornets) - Dolichovespula (wood wasps) - Vespula (yellowjacket wasps) Mainly temperate - common in the UK and NZ Small to large colonies - depending on the species Distinct queens

Ants      

All ants are in the Formicidae and all ants are eusocial Eusociality evolved once in t...