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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