Social Insects & Insects Behaviour (Part 1) PDF

Topic 5: SOCIAL INSECTS & INSECTS BEHAVIOUR  Outline Social Insects (Part 1) - Introduction - Degrees of Sociality - Characteristics - Examples: termites, honey bees, ants Insects Behaviour (Part 2) - Tactile - Chemical - Acoustic - Visual  Introduct...

Topic 5: SOCIAL INSECTS & INSECTS BEHAVIOUR  Outline Social Insects (Part 1) - Introduction - Degrees of Sociality - Characteristics - Examples: termites, honey bees, ants Insects Behaviour (Part 2) - Tactile - Chemical - Acoustic - Visual  Introduction of Social Insects Social insects (ants, bees, wasps and termites) are among the most diverse and ecologically important organisms on earth.  Degrees of sociality (after Michener 1969) ◼ Solitary: independent ◼ Subsocial: the adults care for their own young for some period of time (e.g.cockroaches) ◼ Communal: insects use the same composite nest without cooperation in brood care (digger bees) ◼ Quasisocial: use the same nest and also show cooperative brood care (Euglossine bees) ◼ Semisocial: in addition to the features in quasisocial, also has a worker caste (Halictid bees) ◼ Eusocial: in addition to the features of semisocial, there is overlap in generations (Honey bees): offspring assist parents  What are the eusocial insects? Defining characteristics: cooperative brood care overlap of adult generations reproductive division of labor (= sterile castes)  Characteristics of insect societies ◼ They live in groups of closely related individuals ◼ Individuals are usually faithful to their “family” ◼ Often live in a confined locality (“nest, hive”) In eusocial insects ◼ Overlapping generations: parents live with offspring ◼ Members collaborate in raising the offspring ◼ Sterility of a large number of individuals of the colony (e.g. “workers”, “soldiers”): reproductive division of labour  Reproductive division of labour ◼ In bees and ants, for example, the queen typically lays all the eggs ◼ Sterile individuals (workers, soldiers etc.) do all the other work, i.e. nest construction, feeding the young, collecting food, nest defence etc. – in short, they help the queen with maximising its fitness, while foregoing to produce their own offspring. What are the benefits of sociality?  The social insects have royalty! ◼ Social Hymenoptera (ants, wasps, bees) have a queen. ◼ Social Isoptera (termites) have a king & queen. ◼ The queens (and kings) are typically long lived (15 years in termites, 4 years in honeybees). ◼ Their sole task is often reproduction (while other individuals are often sterile and don’t reproduce). Western drywood termite, Incisitermes minor Honeybee Apis mellifera queen Queen, king, soldiers and workers in termites This slide will be further discussed during our synchronize lecture (Webex meeting) This slide will be further discussed during our synchronize lecture (Webex meeting) 12 Life cycle: egg to larva to pupa to adult bee  Queens are not genetically different from workers! ◼ The question of whether a female individual turns out as a queen or worker is dependent on the food that she receives as a larva. ◼ In honeybees, larvae turn to queens when food nectar contains more than 35% hexose, and workers when there is less than 10% hexose ◼ Workers feed “queens to be” with a mandibular gland secretion called “royal jelly” which ensures that bee queens live for 2-4 years (rather than 7-8 weeks as in workers) ◼ In addition, the queen is much larger, has bigger ovaries, and spermatheca ◼ Can lay 1500 eggs / day! HEXOSE= A monosaccharide, or simple sugar, containing (C6H12O6). The hexoses are by far the most abundant simple sugars.  Size of insect societies ◼ In honeybees, one queen and up to 40,000 workers ◼ In bumblebees, one queen and 20-500 workers ◼ In wasps, 1 to 1000s of queens and 1000s to millions of workers ◼ In ants, 1 to over a million queens; up to many million workers ◼ One Japanese red wood ant colony contains 307 million ants, including some 306 million workers and about 1.1 million queens. ◼ In Hymenoptera, the workers are invariably female; the males are good only for one thing: mating. Termites also have male workers  Haplodiploid sex determination in all Hymenoptera ◼ Haploid male bee copulates with diploid female -> haploid sperm is stored in female bee’s spermatheca ◼ When female “wants” to produce son, she lays an unfertilised (haploid) egg -> male offspring ◼ To produce female offspring, mother needs to add sperm to egg as it passes down oviduct ◼ Only 2 chromosomes shown here The queen can decide on the sex of her offspring! ◼ In honey bee combs, large cells are for drones (males) and small ones for workers (females) – the queen puts only haploid (unfertilised) eggs into large cells, and only diploid (fertilised) ones into small cells. Fire ant: efficient use of sperm by the queen ◼ Like in honeybees, the queen of fire ants can also actively determine the sex of her offspring ◼ On average, only 3 sperm are used to produce one fertilised egg (female offspring) Coercion – are workers forced not to reproduce? ◼ In many species (of bees), workers can lay (unfertilised) eggs, which are haploid and will turn into males ◼ Queens “control” the reproduction of their workers by pheromones, physical “bullying” and actively eating eggs by workers Basic info: From the eggs laid by the queen, THREE (+ 1) different types of bee emerge, depending on the modes of fertilization and feeding (and homo-heterozygous). This slide will be further egg of discussed during our mother queen synchronize lecture (Webex meeting) egg fertilized egg NOT by sperm fertilized by sperm light heavy feeding feeding + royal jelly unferilized? fertilized = Therefore it diploid should not daughter develop at all! worker, queen But still gets a drone son! Why? + 1 ??? worker daughter queen 18  this part first What is “Haplodiploidy” ? Why is it important in honeybees? egg of Egg of haploid diploid) diploid diploid (hemizygous, X (homozygous, XX) (heterozygous) (homozygous) The father bee (drone) is haploid (a set of 8 chromosomes eg X, This slide will be further discussed during our while the mother bee (queen) is diploid “(2 sets eg XX, XY, YY still 8 chromosomes in each set. synchronize lecture (Webex meeting) Haplodiploidy: A haplodiploid species is one in which one of the sexes has haploid cells (cells containing one copy of each chromosome) and the other sex has diploid cells (cells containing two copies of each chromosome). Most commonly, the male is haploid and the female is diploid. The male then develops from unfertilized eggs, with only one set of chromosomes, while the female develops from fertilized eggs ( the sperm provides a second set of chromosomes when it fertilizes the egg). 19 Haplodiploidy (for more explanation www.animalbehavioronline.com/haplodiploidy.html) Hymenoptera, the Order of insects that includes the bees, ants and wasps, has an interesting and unusual genetic method of sex determination. Males are haploid--they have only one copy of each chromosome--while females are diploid--two copies of each chromosome. Female bees (workers and queens) are created in the usual way, with a sperm from a male fertilizing a female's egg. One set of chromosomes comes from the father, the other from the mother, yielding a diploid daughter. Males, however, have a mother but no father. Males develop from an unfertilized egg, making them haploid. The queen, being a female just like the workers, can have sons even if she never mates! The worker, also a female just like the queen, can also have sons when forced by absence of queen hormone in the hive (laying workers), even if she never mates. Sex determination of this kind --haploid males and diploid females-- is called haplodiploidy. This model (genetic theory) is called “the complementary allele model” Let us trace the set of chromosome, eg set X and set Y, each 16 chromosomes sperm of egg of Queen Queen father, X mother measures measures queen, Y width of width of cell. If cell. If Egg fertilized by sperm = egg NOT drone worker XY fertilized by sized, then sized, then (heterozygous diploid) sperm, Y Y only XY , (heterozyg light heavy feeding ous) feeding + royal jelly unfertilized? Y fertilized = XY is all his diploid mother’s daughter drone, Y characteristics worker XY daughter (male) (mother’s boy) worker, queen (female) queen, XY But how is it that “homozygous diploid male” can happen? 1. Gender (jantina) in bees, is actually determined by a single gene (Beye et al. 2003). 2. If there is only one copy of this sex gene (because the animal is haploid, eg Y), then the bee develops as a male. 3. If there are two copies of the sex gene (representing two chromosomes, because the animal is diploid, eg XY) and they also differ in their DNA sequences, then the animal develops into a female. 4. In other words, a bee which is heterozygous diploid, eg XY for the sex determination gene, is a female. 5. But a bee which is a homozygous diploid animal eg XX, YY, develops as a sterile male. 6. In honey bees, the homozygous diploids are killed by their heterozygous sisters (older worker bees) whilst still in the larvae stage. In beekeeping, this represents considerable waste to the colony. 7. This means that inbreeding (XX, YY) in the bee colony is costly (losing killed larvae) instead of increasing population, and bee breeders must avoid inbreeding. This slide will be further discussed during our synchronize lecture  But what happens if the father drone was also a Y set individual (a relative) ? Let us trace the set of chromosome, eg set X and set Y. Queen measures width of sperm of egg of cell. If worker sized, then XY father, Y mother queen, Y egg NOT Egg fertilized by fertilized by sperm = YY sperm, Y The nurse bees will automatically kill This slide will be further the homozygous light heavy feeding discussed during our dipoid larva. The feeding + royal jelly synchronize lecture latter stage is (Webex meeting) seldom reached. ‘worker’ YY, homozygous dipoid He (“mother’s “worker” is no more female but boy”) is a normal now actually a male!! If ‘he’ is haploid Y male, allowed to live, he grows growing in a large squeezed in a small worker cell drone cell drone, Y daughter queen, YY  SUMMARY: From basic info, now advanced info. From the eggs laid by the queen, FOUR different types of bee emerge, depending on the 1. modes of fertilization and 2. feeding 3. homozygous or heterozygous sets of chromosomes. This slide will be further discussed during our synchronize lecture 1. (Webex meeting) 2. 3. hemizygous (= heterozygous heterozygous haploid) drone homozygous worker queen 24 drone Queen/worker dimorphism allows coercion (Tom Wenseleers) Bombus terrestris Apis mellifera Nannotrigona melanocera Vespula vulgaris Atta cephalotes Dorylus wilverthi In 3 seconds only, WHICH ONE IS THE QUEEN? 1, 2, 3 stop, time is up! 26 2.5 Castes of honeybee: 2.5.1 types of castes and their functions, 2.5.2 age factor affecting changes in duties, 2.5.3 social organization in a stable colony, an unstable colony, a swarm colony. Drone Bee Queen Bee Worker Bees drone being expelled 27 by workers revision, DUTIES OF THE WORKER BEE start immediately after emergence We have seen the individual castes separately(2.4). Here are some revision pictures. The Main Stages in the Lives of Worker Bees First Stage: DUTIES OF THE WORKER BEE start immediately after emergence Cleaning Brood Cells emergence Cleaning Brood Cells Second Stage: A worker bee's second job is tending larvae. Third Stage: Construction Fourth Stage: Guarding the Hive Fifth Stage: Foraging 28 Temperature Regulation in the Hive Queen bee Drone Bee Worker Bee 29  Review Social Insects (Part 1) - Introduction - Degrees of Sociality - Characteristics - Examples: termites, honey bees, ants Insects Behaviour (Part 2) - Tactile - Chemical - Acoustic - Visual