Week 6.1

Social Behaviour

Overview of Animal Behaviour

  • Course Code: BIO3436

  • Professors: Fajar Andriyanto/Solent

European Bee-Eater (Merops apiaster)

Description

  • The European bee-eater is a bird species known for its vibrant colors and social behavior.

    • nest in big colonies, often sharing the burrows they excavate in sandy banks, which provide protection from predators and harsh weather conditions.

    • not just parents that take care of offspring… helpers at nest help take care of babies from other parents. This communal rearing behavior enhances the survival rates of the young, as multiple adults contribute to feeding and protecting the chicks.

Migration Behavior

  • when nest fails: females leave find somewhere else, males stay and help to raise the remaining young or assist in the care of the communal nest until the next breeding season.

  • Females Migration: During migration, females will leave the colony if their nest fails.

  • Males' Role: Males remain in the colony to assist at other nests, displaying a cooperative social structure.

Altruism in Animal Behavior

Definition of Altruism

  • Altruism: Any behavior that benefits others at a cost to the altruist, reflecting a selfless nature in social interactions among animals.

    • alarm calls… beltings ground squirrels alarm calls are a prime example of altruism, as these squirrels warn their peers of potential threats, sacrificing their own safety in the process.

    • same thing with european bee-eaters → benefits the colony at the sacrifice of themselves

Group Selection Theory

Background

  • Proposed by V.C. Wynne-Edwards (1962).

  • The theory posits that altruistic groups persist longer than selfish groups.This suggests that the success of a species may depend not only on the traits of individuals, but also on the cooperative behaviors and dynamics of the groups they form.

Requirements for Group Selection

  • Isolated groups

    • if groups aren’t isolated they can’t act as individuals

  • Low rate of immigration

  • High rate of group extinction

    • no selective pressure… no competition then the groups may not evolve distinct traits that could help them thrive in their respective environments.

Questioning Altruism

  • If group selection is not the only explanation, then why do animals exhibit altruistic behavior?

Evidence in European Bee-Eaters

  • All helpers at nests are male.

    • helpers typically at nest of close male kin (father, brother…)

    • only males have kin in the colony

    • when they reach adult hood females disperse and males stay in the colony they were born in -→ this prevents inbreeding possible evolutionary solution

  • Helpers are typically assisting close male relatives (philopatric males), while females migrate and disperse to neighboring colonies.

Alarm Calls in Belding's Ground Squirrels

Observational Study

  • Alarm calls are classified based on the reproductive status and kin relations among female Belding's ground squirrels.

    • researchers observed two groups to see which group was making more alarm calls… all individual making alarm calls are female… reproductive females make way more alarm calls than non reproductive females

    • alarm call made by reproductive female and residents of the colonie… their kin will benefit even if they are sacrificed

Data Summary

  • Frequency of Calling to Predators:

    • Reproductive Females (No Kin): Alarm calls were significantly low (

    • Reproductive Females (Mother or Kin): Alarm calls were higher than expected. → kin will benefit for vocalization

    • Reproductive Residents vs. Nonresidents: Significant differences exist in alarm calls when compared across categories:

    • Reproductive Residents: p < 0.05

    • Nonresidents: p < 0.03

  • Relative Calls: Calls by females are influenced by their presence or absence of kin, with relatives showing higher call frequencies.

Concept of Nepotism in Altruism

  • Both European bee-eaters and Belding's ground squirrels exhibit nepotistic behavior where assistance is provided preferentially towards relatives.

Inclusive Fitness

Definition and Formula

  • Inclusive Fitness: Altruism evolves when behaviors increase the frequency of genes related to altruism.

  • Formula for Inclusive Fitness: ext{Inclusive Fitness} = ext{Direct Fitness} + r imes ext{Indirect Fitness}

    • Direct Fitness: An individual's own reproduction.

    • Indirect Fitness: The effect one has on the reproduction of related individuals.

      • genes are going on but not by direct input but by their kin reproducing

    • Coefficient of Relatedness (r): The probability that a gene is shared by common ancestry. Values of r range between 0 and 1.

Heinrich Hamilton's Theorem

  • Hamilton's Rule states altruism can evolve through natural selection when: rB - C > 0

    can predict when an animal is going to help another animal

    • Where:

    • r = coefficient of relatedness

    • B = benefit to the receiver of altruism

      • fitness benefit

    • C = cost to the altruist

Gene Sharing Calculation

  • Example Calculation of r: r = (0.5)^2 + (0.5)^2 = 0.5

    • Meaning individuals share 50% of their genes with direct offspring.

    • r = proportion and probability = correct

    • full sibling share both parents

      • getting approx 50% of genes going from one individual to the next

      • connects the two siblings to see how related they are… 0.5 for every line

      • Half-siblings share one parent, resulting in an approximate gene sharing of 0.25.

      • This genetic sharing is influenced by the random assortment of alleles during reproduction.

      • Understanding these proportions helps in genetic counseling and ancestry research.

      • The closer the genetic relationship, the more similar the traits and characteristics are likely to be.

      • This concept is crucial in studies involving heritability and evolutionary biology.

    • two bottom cousines

      • trace lines that connect cousins to grandparents, 4 lines through one grandparent and 4 lines through other so → (0.5)^4 + (0.5)^4 = 0.125 → 12.5% related

Understanding Evolutionary Implications

Difference Between Inclusive Fitness and Group Behavior

  • The concept that animals increase their inclusive fitness contrasts with the idea that they act for the good of the species or group.

Multilevel Selection Theory

  • Defines selection mechanisms at various levels:

    • Selection among groups within a population.

    • Selection among individuals within a group.

    • Selection among genes within an individual.

Requirements for Group Selection in Multilevel Selection

  • Isolated groups,

  • Low immigration rates (< 1 per generation),

  • High group extinction rates.

  • above instances are incredibly rare

Relationship Between Individual and Group Behaviors

  • Always prioritize inclusive fitness for calculating allele frequencies.

  • Individual replication is the fundamental level; thus, group behavior influences gene frequencies equivalently to individual behavior.

  • the individual even if embedded in the group individual is still the unit of selection even with group pressure but at the end it is still individual pressure

Altruistic Behaviour and Genetic Self-Interest

  • Altruism can statistically evolve through individual self-interest, even in high altruistic behavior contexts that increase inclusive fitness.

Eusociality as a Social Behavior Case

Characteristics of Eusociality

pinnacle of social behaviour

  • Overlapping generations.

    • parents and offspring are alive at the same time… grandparents sometimes

  • Cooperative care of the young.

    • like the bee eaters w extra help at the next

  • A division of reproductive labor among individuals.

    • some individuals are responsible for reproduction but others are not

  • occurs mostly in hymenoptera (wasp, bees, andts, termites, and naked mole rates)

    • ants building bridge with bodies so other ants can get to otherside to get food for whole colonie

    • bee dance

    • bee killing wasp by vibrating and heating up wasp

Genetic Structures: Haplodiploidy in Hymenoptera

  • Males are haploid (having one set of chromosomes).

    • single cet of chromosomes identical to gather

  • Females are diploid (having two sets of chromosomes).

    • standard meiosis generates a cet of dif gametes each w one chromosome

    • one set of chromosomes for every gamete is completely identical because of gather… sisters share 50% genetic makeup with mother and 50% with father… father shared 100% DNA with daughters

    • can increase relatedness … hightened sociality

  • Example genetic relationship in sister-sisters yielding high genetic relatedness (75% on average).

Issues with the Haplodiploidy Hypothesis

  • Despite many bees being haplodiploid, approximately 20,000 species remain solitary.

    • most bees are social

  • Eusocial behavior is observed in species like termites and naked mole rats which do not follow this structure.

    • some species arent haplodiploid

Monogamy Hypothesis in Eusociality

  • When haplodiploidy fails to account for eusociality, relatedness via kin selection becomes crucial.

  • Lifetime monogamy facilitates a high degree of relatedness among siblings, encouraging the evolution of sterile workers and eusocial systems.

  • altruism related to high relatedness

Eusocial Groups and Monogamous Behavior

  • Assessment of monogamy in Hymenoptera shows variance in relatedness.

  • Many eusocial species engage in polyandry, which complicates predictions regarding eusociality and monogamy.

  • phylogenetically what was their mating system

    • black line indicate monogamy red lines polyamory

    • having monogamy as ancestral trait established a sterile work force and once establised reproductive are able to become polandrou

Examples of Eusociality Among Insects

  • Various classifications of eusocial insects include groups of Hymenoptera, Sphecid wasps, and Halictine bees.

Concluding Topics

  • The complexities of sociality and eusociality will be discussed in the subsequent session.