BIOL 203 Lecture 10: Social Behaviours - Fall 2024 PDF

Lecture 10 Social Behaviours BIOL 203 October 30th, 2024 1 Learning objectives 1. Describe how living in groups has costs and benefits 2. Illustrate the four types of social interactions 3. Explain how eusocial species take social interactions to the extreme 4....

Lecture 10 Social Behaviours BIOL 203 October 30th, 2024 1 Learning objectives 1. Describe how living in groups has costs and benefits 2. Illustrate the four types of social interactions 3. Explain how eusocial species take social interactions to the extreme 4. Describe the social interactions of plants 2 Key Concept Living in groups has costs and benefits 3 Living in groups has costs and benefits Social behaviours are individual interactions with mates, offspring, other relatives, and unrelated conspecifics Shaped by both genetic and environmental factors Subject to natural selection Usually associated with mate selection or intraspecific competition for food or territory Both costs and benefits to social interactions 4 Benefits of living in groups Living in groups can increase survival Groups of individuals can be better at fending off attacks from predators than individuals (e.g., muskox) Dilution effect = probability of predation of individuals is reduced while in a group Increased vigilance (e.g., meerkats) 5 Increased vigilance Individuals can spend less time watching predators, more time feeding E.g.) European goldfinch (Carduelis carduelis) 6 Benefits of living in groups Living in groups can also help animals locate and consume resources More conspecifics means more eyes for finding food Can increase probability of capturing prey 7 Benefits of living in groups Living in groups can also make it easier to find mates Animals aggregate in large groups to attract mates by making calls/displays; location is called a lek E.g.) ruff (Philomacus pugnax) 8 Costs of living in groups Groups of animals are more conspicuous to predators High population densities can increase rate of spread of disease/parasites E.g.) parasitism in coral reef fishes 9 Costs of living in groups Living in groups also increases competition for food Larger groups might be better at finding food, but food must be shared among individuals E.g.) European goldfinch 10 Balancing costs and benefits Natural selection should favour group sizes that balance costs/benefits for each species E.g.) yellow baboons (Papio cynocephalus) Live in groups of 20-100 individuals Medium-sized groups (50-75) have lowest stress levels due to less competition for food (less travel), ability to defend against other groups/predators 11 Many species establish territories Territory = area defended by one or more individuals from others Usually contain resources (e.g., food, limited nest type) Transient to permanent Defence ensures greater resources and more mates E.g.) roe deer (Capreolus capreolus) 12 Dominance hierarchies When benefits of group living override benefits of defending a territory, species form dominance hierarchies = social ranking among individuals Often determined through combat or contests of strength/skill Once established, subsequent contests resolved via ranking 13 Concept check How is the dilution effect a benefit in group living? Why are optimal group sizes often a compromise between the costs and benefits of group size? Use an example to explain. 14 Key Concept There are four types of social interactions 15 Types of social interactions Most social interactions can be described as an action by one individual (donor) directed towards another individual (recipient) Every interaction can affect fitness of both individuals; either positive/negative Four main types of interactions 16 The four types of social interactions Cooperation = both donor/recipient increase fitness Selfishness = donor experiences fitness advantage at expense of recipient Spitefulness = interaction reduces fitness of both donor/recipient Altruism = recipient has increased fitness at expense of donor 17 Altruism and kin selection Altruistic behaviour is interesting because it does not lead to increase in direct fitness = fitness an individual gains by passing on copies of its genes to offspring (favoured by direct selection) Altruism can increase fitness of a relative Since share a common ancestor, indirectly passes genes to offspring = indirect fitness (favoured by indirect selection a.k.a. kin selection) Inclusive fitness = sum of direct and indirect fitness 18 Coefficient of relatedness Probability any gene shared by relatives = coefficient of relatedness Value depends on degree of relatedness in diploid species 19 Calculating indirect fitness Indirect fitness is the fitness benefit gained by a recipient relative (B) multiplied by the coefficient of relatedness between donor/recipient relative (r): 𝐼𝑛𝑑𝑖𝑟𝑒𝑐𝑡 𝑓𝑖𝑡𝑛𝑒𝑠𝑠 = 𝐵 × 𝑟 An individual gains the highest probability of indirect fitness by promoting fitness of closest relatives and no possibility of indirect fitness with non- relatives 20 Evolution of altruistic behaviour makes sense when examining costs/benefits Genes for altruistic behaviour will be favoured when the fitness benefits of the recipient (B) times the recipient’s coefficients of relatedness to donor (r) is greater than the direct fitness cost to the donor (C): 𝐵 × 𝑟>𝐶 Cost-benefit ratio must be less than the coefficient of relatedness: 𝐶 Τ𝐵 < 𝑟 21 Evolution of altruistic behaviour makes sense when examining costs/benefits If inclusive fitness of altruistic behaviours exceeds inclusive fitness of selfish behaviours, altruism is favoured by natural selection Altruism is favoured when: Cost to the donor is low Benefit to the relative is high Donor/recipient are closely related 22 Kin selection in wild turkeys (Meleagris gallopavo) Male turkeys display at leks, either alone or in groups In group displays, only dominant male copulates with females Why do subordinate males display in leks if they do not breed? 23 Kin selection in wild turkeys (Meleagris gallopavo) Subordinates usually full or half- brothers (average r = 0.42) Dominant males sire ~6.1 offspring Solitary males sire ~0.9 offspring Indirect fitness = B x r = 6.1 x 0.42 = 2.6 24 Alternatives to kin selection Although common, kin selection not the sole explanation for cooperative breeding E.g.) white-winged trumpeters (Psophia leucoptera) Unrelated females join groups to help raise offspring (do not breed; indirect fitness = 0) Why does this occur? 25 Alternatives to kin selection Not possible to protect territory as a single mated pair Also, when breeding female dies, young female takes place as breeder Trade current fitness for potential of future fitness 26 Concept check Why can altruism not be explained by direct fitness alone? In the kin selection explanation for the evolution of altruism, why is the benefit to the recipient (i.e., relative) weighted by its coefficient of relatedness (r) to the donor? 27  Eusocial species take Key Concept social interactions to the extreme 28 Eusocial species take social interactions to the extreme Eusocial species (i.e., “truly” social species) display the following characteristics: 1. Several adults living together in a group 2. Overlapping generations of parents and offspring living together in the same group 3. Cooperation in nest building and brood care 4. Reproductive dominance by one or a few individuals, and the presence of sterile individuals 29 Eusocial species take social interactions to the extreme Almost all eusocial species are insects, limited to Isoptera (termites) and Hymenoptera (bees, wasps, ants) Two mammal species; naked mole rat (Heterocephalus glaber) and Damaraland mole rat (Fukomys damarensis) 30 Eusocial species take social interactions to the extreme Most individuals don’t sexually mature, specialize in tasks = castes Range from simple societies (e.g., honeybees) to complex (e.g., leaf-cutter ants) 31 Eusociality in ants, bees, and wasps Eusociality common in Hymenoptera (bees, ants, wasps) Typically dominated by one egg-laying female (or a few) = queen(s) Mate only once in lifetime, store enough sperm to produce all offspring (>1 million offspring over 10-15 years in some ants) Non-reproductive progeny gather food and care for offspring How does this evolve? 32 Eusociality in ants, bees, and wasps Eusociality in hymenopterans facilitated by haplodiploid sex- determination system Queen has same relationship to sons/daughter (r = 0.5) All females have same genes from father, 50% probability of shared genes from mother (r = 0.75) Brother-sister have r = 0.25 33 Eusociality in ants, bees, and wasps If female helps raise young of fertile sister, gets fitness benefit x 0.75 If a female raises her own young, gets fitness benefit x 0.5 Indirect fitness benefit of caring for sister exceeds caring for daughter Cooperation usually favoured in all female castes 34 Eusociality in termites Termites are diploid, so evolved differently than hymenopterans Colonies dominated by mated king/queen, produce sons/daughter via sexual reproduction Most offspring act as workers, can become sexually mature if king/queen dies Second non-reproductive caste = soldiers 35 Eusociality in mole rats Live in colonies of up to 200 individuals All reproduction via a single queen and several kings All diploid individuals Workers capable of reproduction, but queen harasses them, become stressed, lowers sex hormones and drive to reproduce 36 Origins of eusociality Evolved independently multiple times Haplodiploidy seems to favour eusociality, but some haplodiploid species not eusocial, some eusocial species diploid (e.g., mole rats) Could be due to minimal cost in direct fitness E.g.) Some naked mole rats leave and start small new colonies, often do not persist past 1 year (so low direct fitness either way) Origins still actively debated 37 Concept check What are four characteristics of eusocial species? 38 Key Concept Social interactions also exist in plants 39 Social interactions also exist in plants Many species other than animals also exhibit social behaviour Bacteria/protists can sense individuals through chemical secretions, can react “friendly” or “aggressive” Free-living slime molds can aggregate to form large fruiting bodies Plants can also chemically communicate with each other 40 Social responses to herbivory Plants can warn other plants about herbivory E.g.) alder (Alnus glutinosa) Researchers manually removed leaves on one shrub, then examined herbivory on nearby shrubs 41 Social responses to herbivory Plants closer to shrubs with leaves manually removed experienced lower levels of natural herbivory Plant releases chemicals when attacked, nearby plants detect and increase defences However, possible not a social behaviour 42 Social responses to competition Plants also can distinguish between relatives and nonrelatives E.g.) American sea rocket (Cakile edentula) When grown near relative, develops less dense root mass (less competition) Near non-relative, dense root mass (more competition) 43 Concept check If one plant can increase its defences when another plant is attacked by a herbivore, does this represent altruism? Explain. 44 Next class Population distributions (Chapter 10) Seminar #1: Modelling Population Growth and Regulation (bring a laptop!) Lab notebook and Pine demography due next seminar Midterm II – Wednesday, Nov. 6th 45