Behavioral Plasticity in Cichlids

• A dominant male cichlid fish courts and breeds with females, and confronts other males – dominance is indicated by bright coloration and a dark eye bar

• A subordinate male cichlid flees dominant males, does not court or breed, and has a drab coloration

• Removal of a dominant male initiates cascade of changes in gene expression in a subordinate male that rapidly transforms its behavioral and physical phenotype to dominant

Dominant Male Cichlids

Epigenetic Effects

• Epigenetic mechanisms cause heritable changes in behavior without altering DNA sequence

• Example: Lack of tactile stimulation early in a female rat’s life causes methylation of its DNA, resulting in changes in gene expression that suppress oxytocin’s effects

• The methylated DNA is passed on from generation to generation, disrupting oxytocin’s influence and negatively affecting female parental behavior

Take-Home Message:How does the environment affect behavior?

• With behavioral plasticity, environmental factors influence an individual’s behavior during its lifetime.

• The environment can also cause heritable changes in behavior through epigenetic modifications of DNA.

43.5 Movements and Navigation

• All animals are motile during some part of their life cycle

• An innate directional response is called a taxis

• Example: Planarians are negatively phototactic and positively geotactic

• Kinesis is a response that causes an animal to increase or decrease its movements without regard for direction

• Example: Planarians are photokinetic

Migration

• During a migration, an animal interrupts its daily pattern of activity to travel in a persistent manner toward a new habitat

• Migration most often involves seasonal movement to and from a breeding site

• Some animals (e.g. birds) migrate every year; others (e.g. eels) migrate only once to spawn and die

Navigation and Migration

• Some animals have an innate magnetic compass – they use variations in Earth’s magnetic field to determine direction

• Example: A European robin “sees” directional differences in Earth’s magnetic field with its right eye

• Some animals navigate by the sun and stars

• A migrating animal may gauge its progress relative Earth’s magnetic field, or to visual or olfactory landmarks

Vision-based Magnetic Compassin European Robins

Take-Home Message:What factors influence animal movements?

• Innate responses to specific stimuli can influence the rate or direction of animal movements.

• Some animals migrate between habitats. Navigating to a specific site requires an ability to determine compass direction and a mental map.

43.6 Communication Signals

• Communication signals transmit information between members of the same species• Chemical signals such as bee pheromones• Acoustical signals such as prairie dog barking• Visual signals such as threat displays• Tactile signals such as honeybee dances

• Bird courtship often involves both visual and acoustic signals

Prairie Dog Barking a Warning

Courtship Display in Albatrosses

Threat Display: Male Collared Lizard

Tactile Display: Honeybee Dances

Stepped Art

When bee moves straight up comb, recruits fly straight toward the sun.

When bee moves straight down comb, recruits fly to source directly away from the sun.

When bee moves to right of vertical, recruits fly at 90° angle to right of the sun.

ANIMATED FIGURE: Honeybee dances

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Communication

• Chemical and acoustical signals typically are effective over longer distances than visual or tactile ones – also, they are more effective in the dark

• The same signal may function in more than one context

• Example: In dogs and wolves, a play bow indicates that any seemingly aggressive signals that follow, such as growling, should be interpreted as play behavior

A Wolf’s Play Bow

Eavesdroppers and Counterfeiters

• Predators can benefit by intercepting signals sent by their prey

• Example: Frog-eating bats locate male tungara frogs by listening for their mating calls

• Counterfeit signalers can also pose a threat

• Example: A predatory beetle imitates the flash of a female firefly to lure a male firefly close enough to eat him

Take-Home Message: What are the benefits and costs of communication signals?

• A communication signal transfers information from one individual to another individual of the same species. Such signals benefit both the signaler and the receiver.

• Signals have a potential cost. Some individuals of a different species benefit by intercepting signals or by mimicking them.

43.7 Mates, Offspring, and Reproductive Success

• Males and females behave in ways that maximize their own reproductive success• Males compete for females and seek many mates• Females select for quality of a mate, not quantity

• Microevolutionary process favor characteristics that provide an advantage in obtaining and keeping mates

Mating Systems

• Promiscuity: Members of both sexes mate with multiple partners

• Polygamy: One sex has multiple partners

• Monogamy: A male and female mate only with one another

• Members of a species may vary in their behavior, and formation of pair bonds does not preclude extrapair matings

Sexual Selection

• When one sex is the limiting factor for the other’s reproduction, sexual selection occurs

• Examples:• Female hangingflies mate only with males that supply food• Female fiddler crabs judge a male’s burrow-building skill

before selecting a mate• Male sage grouse display at a lek to be chosen by

females• Male bison fight to hold a territory with access to females

Male Hangingfly Bearing Food

Male Fiddler Crab with Large Claw

Male Sage Grouse at a Lek

Male Bison Defending Territory

Parental Care

• Parenting requires time and energy• Increase in survival of young may outweigh costs

• Examples:• In mammals, females are typically sole caregivers• Male midwife toad cares for eggs• Cooperative care of young by both parents occurs most

frequently in birds

Female as Sole Caregiver

A Male Caregiver

Cooperative Care

Take-Home Message: What factors affect mating systems and parental care?

• The positive effects of genetic diversity among offspring make monogamy rare.

• In many species, a few males monopolize mating opportunities either by enticing females to choose them or by defending a territory with many females.

• Parental care evolves only when the benefit of parental care outweighs the costs in lost opportunity for more offspring.

43.8 Living in Groups

• Animals that live in social groups may benefit by cooperating in predator detection, defense, and rearing the young

• Such groupings evolve only if benefits of close proximity to others outweigh the costs

Defense Against Predators

• In some groups, cooperative responses to predators reduce the net risk to all• Alarm calls (e.g. birds, monkeys)• Presenting a united front (e.g. sawfly caterpillars)

• A selfish herd forms when animals hide behind one another to avoid predators

Group Defenses: Sawfly Caterpillars

Group Defenses: Musk Oxen

Improved Opportunities

• Many mammals live in social groups and cooperate in hunts, but cooperative hunters are not always more successful than solitary ones

• Groups are more successful at fending off scavengers, caring for young, protecting territory

• Group living also allows transmission of cultural traits, or behaviors learned by imitation, such as termite “fishing” among chimpanzees

Cooperative Hunting in Wolf Packs

Chimpanzees Fishing for Termites

Dominance Hierarchies

• Many animals that live in permanent groups form a dominance hierarchy

• Dominant animals get a greater share of resources and breeding opportunities than subordinate ones

• Example: Wolves cooperate in hunting, caring for young and defending territory, but only the alpha male and alpha female breed

Regarding the Costs

• In most habitats, the costs of living in large groups outweigh the benefits• Large groups attract predators• Increased competition for space and food• Increased vulnerability to disease and parasites• Risk of being killed or exploited by others

• Example: Penguins form dense breeding colonies in which competition for space and food is intense

Penguin Breeding Colony

Take-Home Message:

Benefits and costs of living in a social group

• Living in a social group can provide benefits, as through improved defenses, shared care of offspring, and greater access to food.

• Costs of group living include increased competition and increased vulnerability to infections.

43.9 Why Sacrifice Yourself?

• Extreme cases of sterility and self-sacrifice have evolved in only a few groups • Insects such as honeybees, termites, and ants • Two species of mammals (mole-rats)

Eusocial Animals

• A eusocial animal lives in a multigenerational family group with a reproductive division of labor

• Permanently sterile workers care cooperatively for the offspring of just a few breeding individuals

• In some species, sterile workers are highly specialized in form and function

Specialized Workers: Honeypot Ant

Specialized Workers: Soldier Ant

Specialized Workers: Soldier Termite

Honeybees

• Queen honeybee• The only fertile female in her hive; she secretes a

pheromone that makes all other females sterile

• Worker bees• Females that develop from fertilized eggs; they collect

food and maintain the hive

• Drones• Stingless males that develop from unfertilized eggs; they

mate with a virgin queen and die

Termites

• Termites live in huge family groups with a queen who specializes in egg production – a king supplies sperm

• Unlike the honeybee hive, a termite mound holds sterile males and females

• Winged reproductive termites of both sexes develop seasonally

Mole-Rats

• Mole-rats are the only eusocial mammals

• A reproductive mole-rat queen mates with one to three kings

• Their nonbreeding worker offspring feed the clan, dig burrows, and protect against predators

Queen Honeybee

Queen Termite

Queen Naked Mole-Rat

Evolution of Altruism

• Altruistic behavior• Behavior that enhances another individual’s reproductive

success at the altruist’s expense

• Theory of inclusive fitness• Altruistic behavior is perpetuated because altruistic

individuals share genes with their reproducing relatives

Take-Home Message: How can altruistic behavior be selectively advantageous?

• Altruistic behavior may be favored when individuals pass on genes indirectly, by helping relatives survive and reproduce.

• Mechanisms that increase relatedness among siblings may encourage the evolution of eusocial behavior.