1. Behavior is everything an animal does and how it does it. Behavioral has both proximate and ultimate causes.
a. Proximate questions are concerned with the environmental stimuli that trigger a behavior, as well as the genetic, physiological, and anatomical mechanisms underlying it. Proximate questions are referred to as “how?” questions.
i. Proximate mechanisms produce behaviors that evolved because they increase fitness in some way.
b. Ultimate questions address the evolutionary significance of a behavior and why natural selection favors this behavior. Ultimate questions are referred to as “why?” questions.
2. Four questions must be answered to fully understand any behavior. The first two, which concern mechanism and development, are proximate questions, while the second two are ultimate, or evolutionary, questions.
a. What is the mechanistic basis of the behavior, including chemical, anatomical, and physiological mechanisms?
b. How does development of the animal, from zygote to mature individual, influence the behavior?
c. What is the evolutionary history of the behavior?
d. How does the behavior contribute to survival and reproduction (fitness)?
3. A fixed action pattern (FAP) is a sequence of unlearned behavioral acts that is essentially unchangeable and, once initiated, is usually carried to completion.
a. A FAP is triggered by an external sensory stimulus called a sign stimulus.
i. In the red-spined stickleback, the male attacks other males that invade his nesting territory. The stimulus for the attack is the red underside of the intruder.
ii. A male stickleback will attack any model that has some red visible on it.
(1) A proximate explanation for this aggressive behavior is that the red belly of the intruding male acts as a sign stimulus that releases aggression in a male stickleback.
(2) An ultimate explanation is that by chasing away other male sticklebacks, a male decreases the chance that eggs laid in his nesting territory will be fertilized by another male.
b. Imprinting is a type of behavior that includes learning and innate components and is generally irreversible.
i. Imprinting has a sensitive period, a limited phase in an animal’s behavior that is the only time that certain behaviors can be learned.
ii. An example of imprinting is young geese following their mother.
(1) A proximate explanation for young geese following and imprinting on their mother is that during an early, critical developmental stage, the young geese observe their mother moving away from them and calling.
(2) An ultimate explanation is that, on average, geese that follow and imprint on their mother receive more care and learn necessary skills, and thus have a greater chance of surviving, than those that do not follow.
4. Behavioral traits, like other aspects of a phenotype, are the result of complex interactions between genetic and environmental factors. In biology, the nature-versus-nurture issue is not about whether genes or environment influence behavior, but about how both are involved. All behaviors are affected by both genes and environment.
a. In some cases, the behavior is variable, depending on environmental experience.
b. In other cases, nearly all individuals in the population exhibit identical behavior, despite internal and external environmental differences during development and throughout life.
i. Behavior that is developmentally fixed is called innate behavior.
ii. Such behaviors are under strong genetic influence.
iii. The range of environmental differences among individuals does not appear to alter innate behavior.
5. Many animal movements are under substantial genetic influence.
a. A kinesis is a simple change in activity or turning rate in response to a stimulus.
b. A taxis is an automatic, oriented movement toward or away from a stimulus.
c. Migration is the regular movement of animals over relatively long distances.
6. Much of the social interaction between animals involves transmitting information through specialized behaviors called signals.
a. In behavioral ecology, a signal is a behavior that causes a change in another animal’s behavior.
b. Some features of animal communication are under strong genetic control, although the environment makes a significant contribution to all communication systems.
c. Many signals are efficient in energy costs.
d. Animals communicate using visual, auditory, chemical, tactile, and electrical signals. The type of signal is closely related to an animal’s lifestyle and environment.
i. For example, nocturnal species use olfactory and auditory signals.
ii. Birds are diurnal and have a poor olfactory sense. They communicate primarily by visual and auditory signals.
iii. Humans are more attentive to the colors and songs of birds than the rich olfactory signals of many other animals because of our own senses.
e. Many animals secrete chemical substances called pheromones, chemicals which alter the behavior of other animals.
7. Mating and parental behavior by male prairie voles (Microtus ochrogaster) are under strong genetic control.
a. Prairie voles and a few other vole species are monogamous, a social trait found in only 3% of mammalian species.
b. Male prairie voles help their mates care for young, a relatively uncommon trait among male mammals. Male prairie voles form a strong pair-bond with a single female after they mate, engaging in grooming and huddling behaviors.
c. Mated males are intensely aggressive to strange males or females, while remaining nonaggressive to their mate and pups.
d. Arginine-vasopressin (AVP), a nine-amino-acid neurotransmitter released in mating, mediates both pair-bond formation and aggression in male prairie voles.
i. In the CNS, AVP binds to a receptor called the V1a receptor.
ii. There are significant differences in the distribution of V1a receptors between the brains of monogamous prairie voles and related promiscuous montane voles.
iii. When the prairie vole V1a receptor gene was inserted into laboratory mice the mice developed the same distribution of V1a receptors as the prairie voles and also showed many of the mating behaviors of the voles.
iv. Thus, a single gene appears to mediate much of the complex mating and parental behavior of the prairie vole.
8. Environment, interacting with an animal’s genetic makeup, influences the development of behavior.
a. Diet plays an important role in mate selection by Drosophila mojavensis, which mates and lays its eggs in rotting cactus tissues.
i. The food eaten by male flies as larvae strongly influenced mate selection by female flies.
(1) The proximate cause in the female mate choices was in the exoskeletons of the flies, assessed by the sense of taste in female flies.
(2) When males from the other population were “perfumed” with hydrocarbons extracted from males of the same population, they were accepted by female flies.
b. The California mouse (Peromyscus californicus) is monogamous and, like male prairie voles, male California mice are highly aggressive to other mice and provide considerable parental care.
i. Unlike prairie voles, even unmated California mice are aggressive.
ii. Researchers placed newborn California mice in the nests of white-footed mice (and vice versa).
iii. White-footed mice are not monogamous and provide little parental care.
iv. This cross-fostering changed the behavior of both species.
(1) Cross-fostered California mice provided less parental care and were less aggressive toward intruders when they grew up and reared their own young.
(2) Their brains had reduced levels of AVP, compared with California mice raised by their own parents.
(3) White-footed mice reared by California mice were more aggressive as parents than those raised by their own parents.
9. One of the most powerful ways that environmental conditions can influence behavior is through learning, the modification of behavior based on specific experiences.
a. Habituation involves a loss of responsiveness to unimportant stimuli or stimuli that do not provide appropriate feedback.
i. For example, some animals stop responding to warning signals if signals are not followed by a predator attack (the “cry wolf” effect).
ii. In terms of ultimate causation, habituation may increase fitness by allowing an animal’s nervous system to focus on meaningful stimuli, rather than wasting time on irrelevant stimuli.
b. The fitness of an organism may be enhanced by the capacity for spatial learning.
i. It may be advantageous for animals to modify their behavior based on experience with the spatial structure of their environment, including the locations of nest sites, hazards, food, and prospective mates.
(1) Digger wasps found their nest entrances by using landmarks, or location indicators, in their environment.
ii. Because some environments are more stable than others, animals may use different kinds of information for spatial learning in different environments.
(1) Sticklebacks from a river learned a maze by learning a pattern of movements.
(2) Sticklebacks from a more stable pond environment used a combination of movements and landmarks to learn the maze.
(3) The degree of environmental variability influences the spatial learning strategies of animals.
iii. Some animals form cognitive maps, complex arrangements of spatial relationships of objects in their environment.
c. Associative learning is the ability of animals to learn to associate one stimulus with another.
i. For example, a mouse may have an unpleasant experience with a colorful, poisonous caterpillar and learn to avoid all caterpillars with that coloration.
ii. Classical conditioning is when an animal learns to associate a meaningless stimulus with a significant one.
iii. Operant conditioning is also called trial-and-error learning. An animal learns to associate one of its own behaviors with a reward or a punishment. Note that this refers to voluntary behavior.
10. Varying degrees of genetic and environmental factors contribute to the learning of complex behavior.
a. Animal cognition is the ability of an animal’s nervous system to perceive, store, process, and use information gathered by sensory receptors. It connects behavior with nervous system function.
i. Chimpanzees learn to solve problems by copying the behavior of other chimpanzees.
ii. The development of songs by birds has revealed varying degrees of genetic and environmental influence on the learning of complex behavior.
(1) For instance, New World flycatchers that are reared away from adults of their own species will sing the song characteristic of their own species without every having heard it.
(2) Individual white-crowned sparrows reared in silence perform abnormal songs, but if recordings of the proper songs are played early in the life of the bird, normal songs develop.
11. Because of the influence of genes on behavior, natural selection can result in the evolution of behavioral traits in populations.
a. When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution.
b. Experiments have provided evidence for behavioral evolution.
i. e.g., a polymorphism in a gene for foraging in Drosophila melanogaster. The gene is called for, and it has two alleles.
(1) One allele, forR, results in a “rover” phenotype in which the fly larva moves more than usual.
(2) The other allele, fors, results in a “sitter” phenotype in which the fly larva moves less than usual.
ii. Researches reared Drosophila at high and low population densities for 74 generations.
iii. The fors allele increased in low-density populations, while forR increased in high-density populations.
(1) At low densities, short-distance foraging yielded sufficient food.
(2) At high densities, long-distance foraging helped the larvae to move beyond areas of food depletion.
c. Natural selection favors behaviors that increase survival and reproductive success. Two of the most direct ways that behavior can affect fitness are through influences on foraging and mate choice.
i. Foraging includes not only eating, but also any mechanisms that an animal uses to recognize, search for, and capture food items.
(1) Optimal foraging theory views foraging behavior as a compromise between the benefits of nutrition and the costs of obtaining food, such as the energy expenditure and risk of predation while foraging.
(a) Natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits.
(2) Researchers have carried out a cost-benefit analysis of feeding behavior in crows in BC.
(a) Crows search tide pools for snails.
(b) A crow flies up and drops the snail onto the rocks to break its shell.
(c) If the drop is successful, the crow eats the snail’s soft body.
(d) If it is not successful, the crow flies higher and tries again.
(e) The research predicted - and found - that crows would, on average, fly to a height that would provide the most food relative to the total amount of energy required to break the snail shells.
(3) Risk of predation is one of the most significant potential costs to a forager.
(a) Mule deer are preyed on by mountain lions throughout their range.
(b) Researchers studied mule deer populations in Idaho to determine if they forage in a way that reduces their risk of falling prey to mountain lions.
(c) The researchers found that food available to mule deer was fairly uniform across the potential foraging area. Risk of predation varied greatly, however.
(i) Mountain lions killed most mule deer at forest edges.
(ii) Few were killed in open areas and forest interiors.
(d) Mule deer feed predominantly in open areas, avoiding forest edges and forest interiors. When deer are at the forest edge, they spend significantly more time scanning their surroundings than when they are in other areas.
ii. Mating behavior, which includes seeking and attracting mates, choosing among potential mates, and competing for mates, is the product of a form of natural selection called sexual selection.
(1) In many species, mating is promiscuous, with no strong pair-bond or lasting relationships.
(2) In species where the mates remain together for a longer period, the relationship may be monogamous (one male mating with one female) or polygamous (one individual mating with several partners).
(3) Polygamous relationships may involve a single male and many females (polygyny) or a single female and many males (polyandry).
(4) Among monogamous species, males and females are often so much alike morphologically that they are impossible to distinguish based on external characteristics.
(5) Polygynous species are generally dimorphic, with males being larger and more showy.
(6) In polyandrous species, females are ornamented and larger than males.
iii. The needs of young are an important factor constraining the evolution of mating systems.
(1) Parental investment refers to the time and resources expended for the raising of offspring.
(a) Most newly hatched birds cannot care for themselves and require a large, continuous food supply that a single parent cannot provide. In such cases, a male will have more successful offspring if he helps his partner to rear their chicks than if he goes off to seek more mates. This is why most birds are monogamous.
(b) Birds with young that can feed and care for themselves from birth, such as pheasant and quail, have less need for parents to stay together. Males of these species can maximize their reproductive success by seeking other mates.
(2) In mammals, the lactating female is often the only food source for the young, and males play no role in caring for them in most mammal species.
(a) In some mammal species, males protect many females and their young.
(b) Certainty of paternity can influence mating systems and parental care.
(c) If the male is unsure if offspring are his, parental investment is likely to be lower.
(i) Males in many species with internal fertilization engage in behaviors that appear to increase their certainty of paternity, including guarding females, removing sperm from the female’s reproductive tract before copulation, and introducing large numbers of sperm to displace the sperm of other males.
(ii) Certainty of paternity is much higher when egg laying and mating occur together, in external fertilization.
(iii) Parental care in aquatic invertebrates, fishes, and amphibians, when it occurs, is as likely to be by males as females.
(iv) Male parental care occurs in only 7% of fish and amphibian families with internal fertilization and in 69% of families with external fertilization.
iv. Sexual selection is a form of natural selection.
(1) Sexual dimorphism within a species results from sexual selection, a form of natural selection in which differences in reproductive success among individuals are a consequence of differences in mating success.
(2) Sexual selection can take the form of intersexual selection, in which members of one sex choose mates on the basis of particular characteristics of the other sex - such as courtship songs, or intrasexual selection, which involves competition among members of one sex for mates.
(3) Mate preferences by females may play a central role in the evolution of male behavior and anatomy through intersexual selection.
(a) An experiment showed whether imprinting by young zebra finches on their parents influenced their choice of mates when they matured.
(b) A red feather was taped to the head of both parents, male parent only, or female parent only, before the young chicks opened their eyes. Control zebra finches were reared by unadorned parents.
(c) When the chicks matured, they were given a choice of ornamented or unornamented mate finches.
(d) Males showed no preference, but females reared by ornamented fathers preferred ornamented mates.
(e) These results suggest that females imprint on their fathers and that mate choice by female zebra finches has played a key role in evolution of ornamentation in male zebra finches.
(4) Males compete with each other by (often ritualized) agonistic behaviors that determine which competitors gain access to resources. The outcome of such contests may be determined by strength or size.
12. Game theory evaluates alternative strategies in situations where the outcome depends on each individual’s strategies and the strategies of other individuals. It can be used to model behavioral strategies.
a. There are three different male phenotypes in populations of side-blotched lizards (Uta stansburiana): orange throats, blue throats, and yellow throats.
i. Orange-throat males are the most aggressive and defend large territories with many females.
ii. Blue-throat males are also aggressive but defend smaller territories with fewer females.
iii. Yellow-throat males are nonterritorial and use sneaky tactics to mimic females and sneak copulations.
b. Frequency of the three types of males varies from year to year.
c. Modeling showed that the relative success of different males varies with the abundance of other types of males.
i. When blue-throat males are abundant, they can defend their few females from the sneaky yellow-throat males.
ii. However, they cannot defend their territories against the aggressive orange-throat males.
iii. Orange-throat males take over large territories but cannot defend large numbers of females against the sneaky yellow-throat males.
iv. Yellow-throat males then increase in numbers but are defeated by the blue-throat males.
v. The cycle continues.
13. Most social behaviors are selfish, meaning that they benefit the individual at the expense of others, especially competitors. Behavior that maximizes an individual’s survival and reproductive success is favored by selection, regardless of its effect on other individuals. The concept of inclusive fitness can account for most altruistic behavior.
a. Altruism is defined as behavior that appears to decrease individual fitness but increases the fitness of others.
i. Belding’s ground squirrel lives in some mountainous regions of the western United States.
ii. The squirrel is vulnerable to predators such as coyotes and hawks.
iii. If a squirrel sees a predator approach, it often gives a high-pitched alarm call, which alerts unaware individuals.
iv. The alerted squirrels then retreat to their burrows.
v. This conspicuous alarm behavior calls attention to the caller, who has a greater risk of being killed.
b. If related individuals help each other, they are, in effect, helping keep their own genes in the population.
c. Inclusive fitness is defined as the effect an individual has on proliferating its own genes by reproducing and by helping relatives raise offspring.
i. Hamilton’s rule states the conditions under which altruistic acts will be favored by natural selection. The three key variables are as:
(1) The benefit to the recipient is B.
(2) The cost to the altruist is C.
(3) The coefficient of relatedness is r, which equals the probability that a particular gene present in one individual will also be inherited from a common parent or ancestor in a second individual.
ii. The rule is rB > C
(1) The more closely related two individuals are, the greater the value of altruism.
iii. Kin selection is the mechanism of inclusive fitness, where individuals help relatives raise young.
d. Some animals behave altruistically toward others who are not close relatives.
i. Such behavior can be adaptive if the aided individual can be counted on to return the favor in the future.
ii. This exchange of aid is called reciprocal altruism and is commonly used to explain altruism between unrelated humans.
iii. Reciprocal altruism is limited to species with stable social groups in which individuals have many opportunities to exchange aid and where there would be negative social consequences for those who “cheat” and refuse to return favors to those who have helped them in the past.
iv. However, because cheating may provide a large benefit to cheaters, behavioral ecologists have questioned how reciprocal altruism could arise.
v. To answer this question, behavioral ecologists have turned to game theory.
(1) It’s been found that reciprocal altruism can evolve and persist in a population where individuals adopt a behavioral strategy called tit for tat.
(2) In this strategy, an individual treats another individual the same way it was treated the last time they met.
(3) Individuals are always altruistic, or cooperative, on the first encounter, and will remain so as long as their altruism is reciprocated.
(4) When it is not, they will retaliate immediately but will return to cooperative behavior as soon as the other individual becomes cooperative.
14. Social learning, learning through observing others, forms the roots of culture, which can be defined as a system of information transfer through social learning or teaching.
a. Cultural transfer of information has the potential to alter behavioral phenotypes and influence the fitness of individuals.
b. In many species, mate choice is strongly influenced by social learning.
c. Mate choice copying, a behavior in which individuals in a population copy the mate choices of others, has been extensively studied in the guppy Poecilia reticulata.
i. Female guppies prefer to mate with males having a high percentage of orange coloration.
ii. However, if a female sees another female engaging in courtship with a male with relatively little orange, she will choose a male with little orange herself.
iii. Below a certain threshold of difference in mate color, mate choice copying by female guppies can mask genetically controlled female preference for orange males.
iv. The advantage for females is that mating with males that are attractive to other females may increase the probability that her male offspring will also be attractive and have high reproductive success.
d. Vervet monkeys (Cercopithecus aethiops) in Kenya produce a complex set of alarm calls.
i. Distinct alarm calls warn of leopards, eagles, or snakes, all of which prey on the small vervets.
ii. Vervets react to each alarm differently, depending on the threat.
iii. Infant vervets give alarm calls but in an undiscriminating way.
(1) For example, they call “eagle” for any bird.
(2) With age, they improve their accuracy.
iv. Vervets learn how to give the right call by observing other members of the group and by receiving social confirmation for accurate calls.
15. Human culture is related to evolutionary theory in the discipline of sociobiology, whose main premise is that certain behavioral characteristics exist because they are expressions of genes that have been perpetuated by natural selection.
a. The spectrum of possible human social behaviors may be influenced by our genetic makeup, but that is very different from saying that genes are rigid determinants of behavior.
b. Just as individuals vary extensively in anatomy, so we should expect variation in behavior.
c. Because of our capacity for learning, human behavior is probably more plastic than that of any other animal.
d. Over our recent evolutionary history, we have built up a diversity of structured societies with governments, laws, religions, and cultural values that define acceptable and unacceptable behavior, even when unacceptable behavior might enhance an individual’s Darwinian fitness.
e. In human behavior, as in other animals, genes and environmental factors build on each other.
f. Perhaps it is our social and cultural institutions that provide us with the only uniquely human feature.