Chapter 10 Social Behaviors Lecture PowerPoint PDF

Rick Relyea · Robert Ricklefs The Economy of Nature 7th edition Lecture PowerPoint Chapter 10 Social Behaviors © 2014 by W. H. Freeman and Company  Chapter 10 concepts 1 Living in groups has costs and benefits. 2 There are many...

Rick Relyea · Robert Ricklefs The Economy of Nature 7th edition Lecture PowerPoint Chapter 10 Social Behaviors © 2014 by W. H. Freeman and Company  Chapter 10 concepts 1 Living in groups has costs and benefits. 2 There are many types of social interactions. 3 Eusocial species take social interactions to the extreme.  Chapter 10 concepts 1 Living in groups has costs and benefits. 2 There are many types of social interactions. 3 Eusocial species take social interactions to the extreme. 1 Social behaviors Social behaviors: interactions with members of one’s own species, including mates, offspring, other relatives, and unrelated individuals. Social behaviors have a genetic basis and are subject to natural selection. Selection has favored cohesive groups and constrained antagonism. Many organisms other than animals exhibit social behaviors. Examples: Bacteria and protists can secrete chemicals to sense each other and react in “friendly” or “aggressive” ways. Damaged plants emit volatile chemicals that warn other plants. 1 Group benefits Predator Detection/evasion: A group may be able to fend off predators better than an individual. Dilution effect: the reduced, or diluted, probability of predation to a single animal when it is in a group. Probability of death = 1/group size Vigilance-Group Size Effect: More individuals watching for predators allows each individual to spend less time watching, and more time feeding. Example: As flock size of European goldfinches increases, the total amount of time the group spends watching for predators increases. The individual amount of time an individual spends watching decreases. 1 Group benefits Food location: Many individuals searching for food may be able to find rare food more easily. Probability of prey capture may increase in a group. Mate finding: Being social makes it easier to find potential mates because large groups attract the attention of females. Lek: the location of an animal aggregation to put on a display to attract the opposite sex. Example: Larger leks of ruffs (a wading bird) attract more females, resulting in an increased percentage of successful male copulations. 1 Group costs Conspicuousness: Groups of animals are more conspicuous to predators. Disease Transmission: The risk of parasites increases in groups; high densities can increase the rate at which diseases spread. Risk of disease spread is particularly problematic in aquaculture or livestock operations, where animals are kept at high densities. Example: Tropical fish that live in higher densities on reefs that are not fished (i.e., protected) also have more parasites. 1 Group costs Competition: Larger groups are better able to locate food, but that food must be shared among all members. Example: Large flocks of the European goldfinch consume seeds in an area much faster than small flocks. Large flocks have to spend more time flying between patches of seeds. Each bird has to spend more time and energy looking for food. 1 Group costs Aggression: Living in groups can lead to aggression among members. Example: Chickens are well-known for fighting when raised under crowded conditions. When one chicken receives an injury that causes a spot of blood on its feathers, other chickens will peck at the spot, causing more injury, more spots of blood on other chickens, and more group fighting. Allowing only best-performing social groups (i.e., those that exhibit less fighting) selects for chickens that behave better in groups and that have a greater lifetime egg production. 1 Alternative outcomes Territory: any area defended by one or more individuals against the intrusion of others. Defending a high-quality territory generally assures greater resources (e.g., food, nest sites). Territories can be transient or relatively permanent. Territoriality common: mobile species, limited resources Uncommon: high pop density, unpredictable resources (C Or rearranged… C/B < r For altruism to evolve, the cost-benefit ratio must be < than r (red area in graph). 2 Why does altruism exist? Example: Male turkeys display to females alone or in a coalition. When a coalition displays together, only the dominant male gets to breed. Coalitions are mixtures of full (r = 0.5) and half brothers (r = 0.25); average r is 0.42. Males that displayed alone (i.e., not in a coalition) sired an average of 0.9 offspring. Dominant males in a coalition sired an average of 6.1 offspring. Indirect fitness benefit of subordinate male in a coalition: B x r = 6.1 x 0.42 = 2.6 This is greater than 0.9, so selection should favor altruism and coalition breeding. 2 Kin Selection – Tiger Salamanders—can develop predatory morphology under high density (and cannibalistic) – BUT delay that when raised with siblings, delayed development of predatory morphology 2 Cooperation in extended families depends on relatedness  Chapter 10 concepts 1 Living in groups has costs and benefits. 2 There are many types of social interactions. 3 Eusocial species take social interactions to the extreme. 3 Eusocial animals Eusocial animals are distinguished by four 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 Among insects, eusocial species are limited to Hymenoptera and Isoptera, including bees, ants, wasps, and termites. Other than insects, the only two animals known to be eusocial are the naked mole rat and the Damaraland mole rat. https://youtu.be/OdLwAA5fHHc?si=P5dpXkWBtzkG_04O 3 Ants, bees, and wasps Caste: individuals within a social group sharing a specialized form of behavior. Queen: the dominant, egg-laying female in eusocial insect societies; typically mate once during their lives. Sons are made by laying unfertilized eggs and daughters are made by laying fertilized eggs (i.e., a haplodiploid system). Haplodiploid: a sex-determination system in which one sex is haploid and other sex is diploid. Nonreproductive progeny of a queen gather food and care for developing brothers and sisters. 3 Ants, bees, and wasps Societies include sterile, female workers; reproductive drones; and future queens. Daughters are diploid and are produced when a queen’s haploid gamete is fertilized by a drone’s haploid gamete. Drones (i.e., sons) are haploid and are produced when a queen’s gamete remains unfertilized. 3 Ants, bees, and wasps r between mothers and daughters = 0.5 r between daughters = 0.75 r between brothers and sisters = 0.25 Since relatedness between daughters is greater than between mothers and daughters, caring for a sister provides more benefit than caring for offspring. 3 Ants, bees, and wasps Since r between brothers and sisters is lower than r between daughters, it benefits females to take care of sisters instead of brothers. This may explain why broods of reproductive individuals usually favor females to males 3:1. 3 Termites Termite colonies can be massive structures dominated by a mated pair called the king and queen. The king and queen produce sons and daughters by sexual reproduction; both types of offspring serve as workers. Offspring remain sexually immature unless the king or queen dies. Many species have a cast of soldiers, which have very large heads and help to defend the nest. 3 Mole rats A single queen and several kings are responsible for all reproduction. All individuals are diploid, but workers forego reproduction in favor of caring for younger siblings and the colony. Research suggests offspring are not willingly subordinate. The dominant female harasses offspring, which increases stress, reduces levels of sex hormones, and makes them less motivated to breed. 3 Origins of eusociality Eusociality has independently evolved many times. Being haplodiploid favors the evolution eusociality; it is not required for its evolution. Eusocial behavior could evolve if the cost of leaving a colony is high due to a low likelihood of surviving; this reduces the cost of foregoing reproduction. Example: Some naked mole rats leave the home colony to form new colonies. Most of these colonies do not persist for more than a year, leading to a reduced direct benefit. Under these conditions, a large r is no longer required to favor eusociality.