Animal Behavior and the Four Themes of AP

BiologyChapter 51

Behavior• Behavior can be fuzzily defined as “actions an animal takes,” but there’s no one definition that makes everyone happy. Phenomena studied by behavioral ecologists include:– The function of peacock tail symmetry– How a songbird came to sing a particular tune

– The circumstances under which a moth produces pheromones

What’s happening?

Oh, dude, Oh, dude, lunch…lunch…

Doo de doo de Doo de doo de doo dAAAH doo dAAAH ZEUS ON A ZEUS ON A POGO STICKPOGO STICK

Behavior

• And it’s important to avoid what I just did, anthropomorphization - the attribution of human characteristics to non-human subjects

Questions about Behavior

• Ethologist Niko Tinbergen outlined four questions that can be asked about any behavior, and a full understanding of the behavior therefore demands multiple approaches.– Two search for proximate causes of the behavior• “How” questions that probe the mechanism

– Two search for ultimate causes• “Why” questions that probe the reasons for it

Tinbergen’s Four Questions

• 1. What are the genetic/developmental mechanisms? (Proximate cause)

• 2. What are the anatomical/physiological mechanisms? (Proximate cause)

• 3. What historical pathways led to the current behavioral trait? (Ultimate cause)

• 4. What selective processes shaped the behavioral trait? (Ultimate cause)

Sources of Behavior• Behaviors can be:

– Innate - has a genetic basis•Instinct, “born with it”•Example: fixed action patterns, sequences of unlearned, unchangeable behaviors– Kelp Gull chicks peck at a red spot if they see one, even just on the end of a stick. Here’s what their mother’s head looks like:

• Another example: Male stickleback fish will attack a fake fish of any weird size or shape, if it has a red underside. A perfectly-shaped fake fish that doesn’t have a red underside goes unmolested.

Sources of Behavior• Another example, imprinting.– Ethologist Konrad Lorenz found, in studying Greylag Geese, that 13-16 hours after hatching, goslings would “imprint” on whatever was predominately moving nearby, and thereafter mimic its behavior.

– In the wild, this is almost always the mother. In the case of Lorenz’s incubators …

Sources of Behavior– Learned - Acquired as a consequence of experience•1999, researchers trained some ravens how to open a trick box with food, then released them into their flock. Soon, many untrained members of the flock had learned to copy the trick and could easily open the boxes themselves.

Sources of Behavior• Behaviors can, and often do, have both genetic and environmental factors– An example from humans: alcohol and drug addiction. Predisposition to addictive behavior vis-a-vis variations in the brain’s dopamine reward pathways - genetic, the presence of traumas and high stresses - environmental, and the likelihood of developing addiction is a complex interplay of multiple variables.

Types of Behaviors• Behaviors can be broken down into (broad, not all-inclusive) categories such as:– Antipredation– Foraging– Habitat selection/territoriality– Migration– Communication– Mating– Parental care– Sociality

Adaptation• A trait that is adaptive is one that gives its bearer a reproductive advantage.– This is conceived of in terms of number of successful descendants. For instance, number of healthy great-grandchildren.

• A trait that is maladaptive is one that confers a reproductive disadvantage.

Not Discussion

• What does an organism need to be, to do, or to have in order to successfully produce great-grandchildren?

Optimality in Behavior• Focusing on one of Tinbergen’s ultimate causes, the adaptive nature of behavior

• Behavioral adaptations can be summed up as a “quest for optimality”– Traits that maximize benefits while minimizing costs to the greatest extent possible are considered optimal

Optimality in Behavior• Think of it like efficiency.

– It’s time for your first car! Are you a Formula One Racing enthusiast? How about an F1 Ferrari, then?

What would be the benefits?

What would be the costs?

Optimality in Behavior• Beware: don’t conflate adaptive optimality with intention!– Example: Great Black Backed Seagulls prefer to eat the rare Jonah Crab over the more common Green Crab. There are competing hypotheses as to why, including:• Deriving greater nutritional benefit from a Jonah than a Green Crab

• Competitive displacement, many other seabirds are already hunting Green Crabs

• Jonah Crabs may be easier to crack open than Green Crabs

• Jonah Crabs may be less likely to be carrying harmful parasites

Optimality• The majority of the time, what we’re looking at is optimizing free energy. Energy optimization is at least tangentially involved in nearly any adaptive behavioral study.– What, specifically, do organisms need free energy for that makes it so important for understanding the origins of behaviors?

Optimality• Free energy is necessary for

– Baseline cellular operation and maintenance, and extra energy beyond that can be invested in•Good health and defense•REPRODUCTION

Parental Investment• Pre-zygotic sources of investment

– Producing numerous and healthy gametes– Search for a mate– Competition for the mate– Act of mating and complications– Risk of parasites/disease– Establishing a nesting site

• Post-zygotic sources– Labor/egglaying– Defending nest territory and young– Providing food and water for young– Educating young (time away from foraging)

Optimality• There are many ways to optimize, to attempt to obtain maximum energy at minimum cost. We’ll look at just a few examples:

– Migration– Mate choice– Signalling

Migration

• Migration is a form of dispersal, the annual movement away from and return to the same location.– Seen in animals ranging from crabs to whales

Migration• Costs– Physically demanding, requires excess free energy

– Difficulty finding shelter from adverse weather– Exposure to predation– Exposure to different pathogen profile

• Benefits– Avoid harsh seasonal changes– Resource availability

Optimizing Migration• Example: Red-eyed vireo

– Migrates from Eastern U.S. to Central & South America

– Two possible routes:•Directly across Gulf of Mexico. Shorter distance, nonstop flying, absolutely no food, but no predators either.

•West to Texas, then down through Mexico. Shelter and some food available, longer distance, predators present.

Optimizing Migration• Researchers caught vireos in Alabama, measured their body fat, then measured which direction they flew off.– Vireos with < 5 g body fat showed a mean orientation toward the west-northwest

– Those with ≥ 5 g body fat showed a mean orientation toward the south!

Mate Choice• Reframing in terms accurate to actual selection processes:– “Good Genes” hypothesis: Individuals predisposed towards mates with physical characteristic A, where physical characteristic A correlates with survival success, will have greater reproductive success themselves because their kids will inherit those survival-conferring genes. That predisposition becomes more common over time.

– But there’s more than that…

• “Healthy Mate Hypothesis” - Predisposition towards mates with characteristics that…– Correlate with foraging success, so that s/he can feed you and the kids

– Correlate with high parental investment, so you don’t have to risk as much taking care of things yourself

– Correlate with low parasite load, so they don’t pass on parasites/diseases to you and/or the kids

• There’s also runaway sexual selection, but that’s a topic for another day

Mate Choice - Discussion

• Classic example: Peacocks

Discussion• Classic example: Peacocks

– Studies showed that female preference for males placed the highest value on the symmetry of their tail spots• Could this be a case of the “Good Genes” hypothesis? If this hypothesis is true, what could spot symmetry have to do with optimizing reproductive success?

• Could this be a case of the “Healthy Mate” hypothesis? If this hypothesis is true, what could spot symmetry have to do with optimizing reproductive success?

• What tests could you do to determine which hypothesis is most accurate?

Signaling• Animals use visual, audible, tactile, electrical, and chemical signals to indicate dominance, find food, establish territory, and achieve reproductive success.

• Signaling can significantly help optimize an animal’s resources!– Generally by minimizing costs

Signaling

• Visual - the peacock’s tail is an example– It enhances reproductive success, advertises suitability as a mate

– Other examples?

Signaling• Audible - from bird calls to whale songs to cricket chirps– Example: male elephant seals bellow to establish their territorial dominance• Carries a cost: maintaining that proboscis, and the act of the bellow

• But it can avoid the even greater cost of a fight

Signaling• Tactile - signaling by touch.– Primates grooming each other

– Hermaphroditic worms aligning to indicate mating interest

Signaling

• Electrical and chemical– Electric eels communicate with pulsing electrical fields

– Pheromone production to signal mating availability

Signaling

• Ants use chemical signals to find food– Here, fire ants follow a chemical trail laid down by scientist E.O. Wilson

Signaling• And one of the coolest examples - the waggle dance!– Direction of the waggle relative to the hive shows the direction of the food

– Duration of the waggle part of the dance indicates distance to the food

– http://www.youtube.com/watch?v=-7ijI-g4jHg

Fig. 51-8cWaggle dance (food distant)(c)

30°

Beehive

A

B

C

Location Location Location

30°

BA C

Signaling• Elaborate signaling systems are particularly to be expected in species like ants and bees, and also termites.

• Eusociality is the highest level of social organization.– Individuals are born to social roles, vary physically and genetically depending on social role

– Work highly cooperatively– Most individuals do not reproduce themselves

Social Behavior• Eusociality is just the most rigid and elaborate form of sociality.

• Some level of sociality, various cooperative behaviors, are present in a wide variety of species.

Social Groups• Social grouping - Think packs of wolves, pods of dolphins, prides of lions– Feature dominance hierarchies - members of group ranked according to social status, a “pecking order”

– Group has order and stability, reduced aggression•Other benefits? Drawbacks?

Cooperative Behavior• Cooperative behavior can tend to be conflated with altruism, a selfless act for another’s benefit, but this isn’t the case.– There is reciprocal altruism, in which an individual helps another because it expects to gain something in return•For instance, searching for food for a few hours in the morning with the expectation that another member of the group will search at night

Inclusive Fitness• And there is the concept of inclusive fitness, which is your direct + indirect fitness.– Direct fitness is your reproductive success because you reproduced.

– But fitness isn’t truly about the number of your grandkids three generations from now… it’s about the amount of your genetic information in the gene pool three generations from now.• How can you pull that off without involvement of direct fitness?

Inclusive Fitness– Indirect fitness is your reproductive success because someone related to you reproduced.•Some of their genes are yours too!

Inclusive Fitness• This can be quantified! William Hamilton proposed a measure for predicting when natural selection would favor altruistic acts among related individuals

• Three key variables in an altruistic act:

– Benefit to the recipient (B)– Cost to the altruist (C)

– Coefficient of relatedness (the fraction of genes that, on average, are shared; r)

Fig. 51-28

Parent A Parent B

OR

Sibling 1 Sibling 2

1/2 (0.5)probability

1/2 (0.5)probability

Inclusive Fitness• Hamilton’s Rule: Natural selection

favors altruism when rBB > rCC

• Kin selection is the natural selection that favors this kind of altruistic behavior by enhancing reproductive success of relatives

Inclusive Fitness• Example:• If an altruistic act resulted in the loss of one’s own offspring (C = 1, rC = .5 genetic units, because half of its DNA was yours), but led to the survival of three nephews (B = 3, rB = .25), will altruism be favored by natural selection in this instance?

Inclusive Fitness• This has held in a number of fascinating studies, such as:– Ground squirrels are more likely to make alarm calls rather than hide proportional to their relatedness to the burrow residents near the intruder.

– Seychelles Warblers become helpers at their parents’ nests proportional to the likelihood of being able to obtain a nest of their own that year.