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14.1 Sociality evolves when the net benefits of close associations exceed the costs From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: reduced search times for food in minnows • Research question: What foraging benefits are associated with sociality? (Pitcher, Magurran, & Winfield 1982) • Hypothesis: Sociality reduces search time for food because multiple individuals simultaneously search • Prediction: As group size increases, the search time for an individual to find hidden food declines From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: reduced search times for food in minnows • Methods: – Minnows (Phoxinus phoxinus) – Placed hidden food in 1 of 84 ice cube tray wells – Manipulated the number of fish in a group (2, 4, 6,12, or 20) – Uniquely marked one focal fish in each group and recorded its time to find food From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: reduced search times for food in minnows • Results: – The time to find food for the focal fish declined as group size increased • Conclusion: – One advantage of group living is that it takes less time for an individual to find food From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: increased diet breadth in coyotes • Research question: How does sociality affect predator feeding behavior? (Gese, Rongstad, & Mytton 1988) • Hypothesis: Sociality increases diet breadth because larger hunting groups can more effectively capture large prey items • Prediction: Coyotes in large groups will consume more large food items than individuals in small groups; diet breadth increases with group size From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: increased diet breadth in coyotes • Methods: – Coyotes (Canis latrans) – Observed groups biweekly for 33 months – Noted group size and collected fresh scats to determine their diets – Divided food eaten into three sizes: small (< 0.5 kg), medium (0.5 –10 kg), and large (> 10 kg) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Foraging benefits: increased diet breadth in coyotes • Results – Individuals in larger groups had a greater volume of large prey items in their scat • Conclusion: – Larger groups had a greater diet breadth because they consumed a greater amount of large prey items From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Antipredator benefits in honeycreepers • Research question: Do individuals in mixedspecies groups obtain antipredator benefits? (Hart & Freed 2005) • Hypothesis: Individuals in mixed-species groups experience lower predation risk than individuals not in groups • Prediction: Individual vigilance rate will decline as group size increases; individuals in a flock will display lower vigilance than those not in a flock From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Antipredator benefits in honeycreepers • Methods: – Akepas (Loxops coccineus) – Used focal animal sampling to record the vigilance rate, social status (in a flock or not), and total flock size From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Antipredator benefits in honeycreepers • Results: – Vigilance rate was lower in larger groups – For males, vigilance rate was higher when not in a flock – Female vigilance was not affected by social status • Conclusions: – Individuals benefit from sociality via reduced vigilance – Males benefit more than females, perhaps because they are more obvious to predators From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Aerodynamic benefit: reduced cost of movement in pelicans • Research question: Why do large birds fly in a Vformation? (Weimerskirch et al. 2001) • Hypothesis: This formation reduces the cost of flying • Birds in formation will have a lower wingbeat frequency and heart rate than solitary birds From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Aerodynamic benefit: reduced cost of movement in pelicans • Methods: – White pelicans (Pelecanus onocrotalus) – Placed heart rate monitors on trained birds – Videotaped flight formations and collected data on wingbeat frequency, noting location of each bird in formation • Flying pelican video From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Aerodynamic benefit: reduced cost of movement in pelicans • Results: – Birds in formation behind the leader had a slower wingbeat frequency and lower heart rate • Conclusion: – Large birds have reduced flight costs by flying in formation From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press The costs of sociality • Sociality entails costs; these costs can limit sociality and group size • Competition occurs when one individual negatively affects the fitness of another • Competition for resources can increase with the size of a group From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Competition in schooling fish • Research question: What limits sociality? (Herczeg, Gonda, & Merilä 2009) • Hypothesis: Competition is an important cost of sociality • Prediction: The growth rate of fish raised in groups will be lower than that of solitary fish From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Competition in schooling fish • Methods: – Nine-spined sticklebacks (Pungitius pungitius) – Reared juveniles either alone in a 1.4 L tank or in a school of 100 fish in a 140 L tank – All fish had access to unlimited food – Measured standard length of all fish at 12 and 20 weeks to calculate growth rate From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Competition in schooling fish • Results: – For both populations studied, individuals raised in groups had the lower growth rate • Conclusions: – Competitive interactions in groups reduce growth rate; a cost of sociality From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Group size and competition in primates • Research question: Does competition affect the size of social groups? (Chapman & Chapman 2000) • Hypothesis: Competition for food limits group size • Prediction: Low-resource environments should have smaller group sizes than high-resource environments From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Group size and competition in primates • Methods: – Red colobus (Procolobus pennantii) and red-tailed guenons (Cercopithecus ascanius) – Characterized diets at four sites – Each month, recorded the density of food trees on transects and the average group size of each species From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Group size and competition in primates • Results: – Average group size was positively correlated with the density of food trees • Conclusions: – Competition for food appears to limit group size From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Sociality and disease transmission in guppies • The transmission of infectious diseases is an important cost of sociality • Disease transmission rates increase with group size From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Sociality and disease transmission in guppies • Research question: How does sociality affect disease transmission? (Richards,Van Oosterhout, & Cable 2010) • Hypothesis: Tighter spacing between individuals enhances disease transmission • Prediction: Disease transmission rates will be higher in tighter social groups From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Sociality and disease transmission in guppies • Methods: – Guppies (Poecilia reticulata) – Created single-sex schools of six fish – Recorded average nearest neighbor distance in each school – Infected a single fish in each school with 100 G. turnbulli parasitic worms – Recorded the spread of parasitic worms to other school members after three days From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Sociality and disease transmission in guppies • Results: – Nearest neighbor distance was smaller in female than male groups – Females spent more time shoaling than males From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Sociality and disease transmission in guppies • Results: – A higher proportion of females became infected than males • Conclusion: – Disease transmission is affected by degree of sociality; this is a cost of group living From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Applying the Concepts Applying the Concepts 14.1 Group size of social species in captivity – Many social species suffer stress when forced to live in captivity with an inappropriate number of conspecifics – The size of groups in the wild is rarely the best group size in captivity – Institutions should create environments with greater structural complexity so that animals can modify their proximity to others From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 14.2 Dominance hierarchies within groups reduce aggression • Dominance hierarchy – An organized social system with dominant and subordinate members • Linear dominance hierarchy – An individual is dominant to each member below it and subordinate to all members above it in rank From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Dominance hierarchies and crayfish • Research question: Do dominance hierarchies affect aggression? (Herberholz, McCurdy, & Edwards 2007) • Hypothesis: Dominance hierarchies reduce aggression between individuals • Prediction: Level of aggression will be high during hierarchy formation but will then decline From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Dominance hierarchies and crayfish • Methods: – Crayfish (Procambarus clarkii) – Created groups of three juvenile crayfish – First recorded aggressive and submissive interactions for 30 min (no resource present) – Then allowed the crayfish access to a large piece of food and again recorded number of aggressive and submissive behaviors – Recorded all physical contact with food From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Dominance hierarchies and crayfish • Results: – First observed > 5 aggressive and submissive acts/min in the absence of food but then recorded < 2 aggressive and submissive acts/min in the presence of food – Crayfish formed a linear dominance hierarchy; the alpha individual had the greatest access to food • Conclusions: – Once formed, dominance hierarchies reduce aggression From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Stable dominance hierarchies in baboons • Research question: How do dominance hierarchies affect stress levels? (Bergman et al. 2005) • Hypothesis: The formation of a dominance hierarchy reduces aggression and stress in individuals • Prediction: Aggression level and stress hormones such as glucocorticoid will be lowest when stable dominance hierarchies exist From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Stable dominance hierarchies in baboons • Methods: – Chacma baboons (Papio hamadryas ursinus) – Noted periods when stable dominance hierarchies existed and other periods when changes occurred in the dominance hierarchy (e.g., when a new male became dominant) – Collected fecal samples and characterized glucocorticoid levels of individuals From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Stable dominance hierarchies in baboons • Results: – Aggression was lowest during stable periods – Fecal glucocorticoid levels were lowest during stable periods • Conclusions: – Aggression and stress levels are lowest during periods when dominance hierarchies are stable From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Social queuing in dominance hierarchies in clownfish • Research question: Why do subordinates stay in social groups? (Buston 2004) • Hypothesis: Subordinates can move up the dominance hierarchy over time, a process known as social queuing • Prediction: Subordinates will obtain future reproductive benefits by staying in their group From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Social queuing in dominance hierarchies in clownfish • Methods: – Clownfish (Amphiprion percula) – Observed 97 social groups – Noted any recruitment of new individuals and changes in breeding status – Experimentally manipulated 16 groups by removing the breeding male – Observed changes in social status From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Social queuing in dominance hierarchies in clownfish • Results: – No reversals in dominance rank were observed – When breeding female was lost, the breeding male changed sex and became the breeding female; the next-highest-ranking nonbreeder in the group became the sexually mature male – Removal of breeding male resulted in the next-highestranking nonbreeder becoming a reproductive male – Any new recruits always entered the group as the most subordinate member • Conclusion: – Subordinate group members can eventually achieve dominant reproductive status via social queuing From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 14.3 Helping behavior, or altruism, is often directed toward close kin • Altruism – Any behavior that increases the fitness of another (the recipient) and involves a cost to the altruist • Inclusive fitness – An individual’s genetic success (offspring produced) plus the genetic success of its relatives • An altruist can increase its inclusive fitness by helping a close relative (kin selection) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 14.3 Helping behavior, or altruism, is often directed toward close kin • Hamilton’s rule and kin selection – For altruism to evolve, the additional benefit (B) obtained by the recipient must be greater than the cost to the altruist (C), adjusted for the degree of relatedness (r) between the individuals – Helping behavior can evolve when B x r > C From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 14.3 Helping behavior, or altruism, is often directed toward close kin • The degree of relatedness varies among pairs of individuals • Close relatives have the highest degree of relatedness From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Belding ground squirrel alarm calls • Research question: Can kin selection explain the evolution of alarm-calling behavior in ground squirrels? (Sherman 1977) • Hypothesis: Alarms calls help close relatives avoid predation; the production of alarm calls is costly (they increase the risk to the caller of being killed by a predator) • Prediction: Individuals near close relatives will most often produce alarm calls From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Belding ground squirrel alarm calls • Methods: – Belding’s ground squirrels (Spermophilus beldingi) – Studied a population of marked individuals – Juvenile females remain close to their natal burrow at maturity while juvenile males disperse – Females are near close kin while males are not – For all occasions when predators were nearby, noted the first individual to produce an alarm call From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Belding ground squirrel alarm calls • Results: – Adult females produced the most alarm calls – Adult males and juveniles produced the fewest alarm calls • Conclusion: – Kin selection can explain the variation in alarm-calling behavior observed From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Cooperative breeding and helpers at the nest • Some social groups exhibit cooperative breeding • Some adults in the group reproduce while others help to care for their offspring • These “helpers at the nest” are exhibiting altruistic behavior From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism and helping at the nest in birds • Research question: Why do some adults within a social group help other adults to raise their offspring? (Russell & Hatchwell 2001; Hatchwell et al. 2004) • Hypothesis: Kin selection explains the evolution of helpers at the nest • Prediction: Helpers are close relatives of the adult breeders From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism and helping at the nest in birds • Methods: – Long-tailed tits (Aegithalos caudatus) – Known pedigrees and genetic data provided information about relatedness – Noted instances of helping behavior and long-term survivorship of nestlings (recruitment into a social group the following year) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism and helping at the nest in birds • Results: – Helpers assisted pairs that contained at least one relative; in 90% of cases, they helped a close relative – The probability of recruitment of a young the following year increased with the number of helpers at their nest • Conclusion: – Kin selection explains helping behavior; helpers benefit by increasing their inclusive fitness From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism in turkeys • Male turkeys may form social coalitions (a pair of males) and display together to attract females – Only the dominant male mates • Solo males also display to females as solitary individuals From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism in turkeys • Research question: Why do subordinates help the dominant male? (Krakauer 2005) • Hypothesis: Kin selection explains helping behavior in male turkeys • Prediction: For a subordinate male, B x r > C From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism in turkeys • Methods: – Turkeys (Meleagris gallopavo) – Captured and marked individuals and collected blood samples for genetic analysis – Determined degree of relatedness among coalition males – Determined reproductive success of males in coalitions and solo males From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Altruism in turkeys • Results: – Coalition males were close relatives (r = 0.42) – On average, dominant males sired 6.1 more offspring than solo males = B – Solo males sired on average 0.9 offspring = C – (B x r) > C [(6.1 x 0.42) > 0.9] • Conclusions: – Kin selection and Hamilton’s rule explains helping behavior by subordinate male turkeys From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 14.4 Some species exhibit extreme altruism in the form of eusociality • In eusocial species, a social group contains: 1. Overlapping generations 2. Cooperative brood care by nonparents 3. A reproductive division of labor; some adults reproduce while others do not reproduce (they are sterile) and care for the young of others • Castes – Behaviorally distinct individuals within eusocial groups From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Applying the Concepts Applying the Concepts 14.2 Are naked mole rats eusocial? • Naked mole rats satisfy most of the criteria of eusocial species, but variation in body size is continuous rather than discrete as in eusocial insects • O’Riain el al. (2000) found a discrete morphological trait – the length of lumbar vertebrae L5 was much larger in queens • Naked mole rats do have discrete morphological castes From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Eusociality and haplodiploidy • Haplopdiploid genetic system – Haploid males develop from unfertilized eggs – Diploid females develop from fertilized eggs From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Eusociality in ants • Research question: Can kin selection explain eusociality in the ant Formica fusca? (Bargum, Helanterä, & Sundström 2007) • Hypothesis: Hamilton’s haplodiploidy hypothesis states that sterile females can obtain high fitness by helping a close relative to raise additional offspring • Prediction: The degree of relatedness among sisters within a colony will be 0.75 From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Eusociality in ants • Methods: – Ant (Formica fusca) – Collected queens and workers from 56 colonies – Genotyped individuals to determine degree of relatedness From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Eusociality in ants • Results: – For two-thirds of the colonies, degree of relatedness was 0.70, not significantly different than 0.75 – For one-third of the colonies, the degree of relatedness was 0.30, lower than predicted • Conclusions: – Two-thirds of colonies had single queen, resulting in a high degree of relatedness (supports haplodiploidy hypothesis) – One-third of colonies had multiple queens, resulting in a lower degree of relatedness (does not support haplodiploidy hypothesis) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Evolution of eusociality and kin selection in Hymenoptera • Research question: Can kin selection explain the evolution of eusociality in Hymenoptera? (Hughes et al. 2008) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Evolution of eusociality and kin selection in Hymenoptera • Methods: – Mapped female reproductive behavior of 267 species of eusocial bees, wasps, and ants onto phylogeny – Identified behavior as either monandry (female mates with only a single male) or polyandry (mates with multiple males) – Identified females as low polyandry (mates with fewer than two males on average) or high polyandry (mates with more than two males on average) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Evolution of eusociality and kin selection in Hymenoptera • Conclusions: – Monandry appears to be the ancestral trait – Polyandry appears to be a derived trait, especially in species with high polyandry – Kin selection (the haplodiploidy hypothesis) likely played an important role in the initial evolution of eusociality in Hymenoptera – Polyandry evolved in several species later From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Figure 12-21 Multi-level selection model Figure 12-37 PNAS 2005 In this new assessment of the empirical evidence, an alternative to the standard model is proposed: group selection is the strong binding force in eusocial evolution; individual selection, the strong dissolutive force; and kin selection (narrowly defined), either a weak binding or weak dissolutive force, according to circumstance. Close kinship may be more a consequence of eusociality than a factor promoting its origin. . . . Eusociality in ants and termites in the irreversible stage is the key to theirecological dominance and has (at least in ants) shaped some features of internal phylogeny. Their colonies are consistently superior to solitary and preeusocial competitors, due to the altruistic behavior among nestmates and their ability to organize coordinated action by pheromonal communication. From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2013 by Oxford University Press “Ants rule the world” -- Amelia Loew