Proximate and ultimate questions Two basic types of questions asked in Animal Behavior Proximate (focus on mechanics of behavior). Ultimate (focus on advantages of the behavior)

Proximate questions Questions about physical mechanisms. Focus on the genetic-developmental aspects and the sensory-motor aspects of the behavior. Focus on things that cause or enable the animal to perform the behavior.

Proximate questions Examples of proximate questions: How mechanically does the behavior take place? What factors in the environment stimulate the behavior? How do the nerves and muscles generate the behavior? How do the animal’s genes affect the behavior?

Ultimate questions Ultimate questions are questions about the evolutionary reasons for a behavior. They are questions about the selective processes that shape the behavior.

Ultimate questions Examples of ultimate questions: What is the purpose of the behavior? In what way does the behavior increase an individual’s reproductive success? Does the behavior increase an individual’s prospects of survival?

How do we answer behavioral questions? Examples from Niko Tinbergen’s work.

A proximate question. How do beewolves find their way home?

Beewolves (type of wasp) nest in sandy areas.

Beewolf homing When leaving nest to hunt bees, female beewolf covers nest entrance with sand. How does she relocate it?

Beewolf homing Beewolves circle next before leaving. Do they remember landmarks? How would we test this?

Beewolf homing Tinbergen cleared objects from around nest after beewolf left and found she struggled to relocate it.

Tinbergen also set up landmarks around nest for wasp to use.

. Then moved landmarks. Result: wasp searched where landmarks suggested nest should be. .

Beewolf homing Tinbergen’s second experiment is more powerful than his first because it makes a more specific prediction.

An ultimate question: Why do Black-headed gulls remove eggshells from their nests?

Gull egg removal Tinbergen hypothesized that broken eggshells draw attention to the nest and attract predators. Removing the eggshells should reduce predation risk.

Experiment Place broken eggshells at different distances from intact gull eggs. Does presence of egg shells affect chance of intact eggs being found?

Yes! Distance from Pct eggs eaten eggshell to egg 15 cm 42% 100 cm 32% 200 cm 21%

Gull egg removal Conclude that Black-headed gulls remove egg shells because this behavior reduces egg losses to predators (and ultimately increase the bird’s reproductive success).

How did egg removing behavior evolve? Genetic mutation made a gull more likely to remove egg shells from its nest. This gull had higher reproductive success than others in population, so gene became more common and ultimately became fixed in the population as alternative genes became extinct. This is the process of natural selection.

A couple of things to think about Why haven’t gulls evolved eggs that are comouflaged on the inside? What color would you expect the eggs of birds that nest in trees to be?

The logic of natural selection Charles Darwin published the origin of species in 1859.

Evolution by natural selection In “The Origin”, Darwin outlined the mechanism by which evolution mainly occurs. This mechanism is Natural Selection.

The process of natural selection Natural selection is a simple process that is based on a number of observations from which a series of inferences can be made.

Population growth rate Observation: Populations have high birth rates and so populations have the potential to increase exponentially, but they don’t. Generally, populations remain stable over time. Observation: Resources are limited.

Struggle for existence Observation: More young are born than survive to reproduce. Inference: There must be what Darwin called “a struggle for existence” or more appropriately “a struggle to reproduce” i.e., competition between individuals for limited resources.

What determines the winners in the struggle? Variation.

Variation among individuals Observation: There is variation among individuals Some birds remove eggshells from their nests, but others don’t. [or organisms differ in how well camouflaged they are; or how quickly they can run, etc.)].

Variation affects reproductive success Inference: Variation (i.e., differences between organisms) influences their survival and reproduction. Allele “for” egg removal exists. Organisms with the allele on average produce more offspring. In general, organisms that are better adapted to their environment are more likely to survive and reproduce.

Variation has a hereditary basis Observation: Variation has a genetic basis and traits can be inherited. Allele for egg removal is inherited. Remember: Variation can be affected by both genes and environment, but for evolution to occur the variation must be heritable.

Differential reproductive success results in evolution Inference: Differences between individuals in their reproductive success alter the frequencies of alleles from one generation to the next. Allele “for” egg removal causes organisms with the allele to lose fewer eggs/young to predators. Therefore, on average they produce more offspring than those without the allele. That allele then becomes more common in the next generation.

Definition of evolution Because of natural selection evolution is inevitable. What is definition of evolution?

Definition of evolution Evolution is change in the genetic structure of a population from one generation to the next. E.g. Allele for eggshell removal becomes more common each generation. Eventually, allele becomes fixed in population.

Always look for the advantage a behavior confers Natural selection underpins all ultimate questions in animal behavior. One should always look for the advantage a behavior confers. The advantage of a behavior is measured in terms of how much it increases the organism’s reproductive success.

Infanticide in Hanuman langurs

Langurs live in groups of one male, several females and their young. Males fight to control groups of females.

When new male takes over group, infants often killed by the new male.

Why does infanticide take place? Why does the male risk serious injury from females to kill babies? How can this behavior be favored by natural selection? Shouldn’t it be selected against because babies are killed?

Possible explanations for infanticide? Overcrowding. Males in high density populations become hyperaggressive and so attack babies. But, infanticide occurs in low density populations too.

Possible explanations? Darwinian: Male kills young so females come into oestrus (become fertile) sooner. Male increases his reproductive success. The behavior favors the spread of “infanticide genes” even though it may have a net negative effect on a langur population.

Infanticide in Hunuman langurs Darwinian explanation is probably correct. Infanticide found in other animals too under similar ecological circumstances.

Lions: males taking over a pride try to kill all young < 9 months old.

25% of cubs in some lion populations killed by males.

Jacanas: Polyandrous (one female mates with several males). Female taking over territory kills any chicks of previous female. Frees up male to tend new female’s eggs.

Group Selection In “Animal dispersion in relation to social behaviour” Wynne-Edwards 1962 proposed an alternative to natural selection. Vero Copner Wynne-Edwards (1906-1997)

Group Selection Unrestrained reproduction and overpopulation lead to starvation and extinction of groups. Groups that limit reproduction more likely to survive than groups that don’t. Traits that restrain reproduction and increase survival of group favored.

Group Selection Wynne-Edwards suggested that mass assemblies of organisms e.g. at roosts (“Epideictic Displays”) used by population to estimate appropriate reproductive effort. Claimed restraint shown by breeders.

Group selection explanation for langur infanticide Killer males reduce population growth Population does not destroy food supply. Therefore, less likely to die out.

Group selection explanation for langur infanticide Males risk injury by attacking babies. But, groups with baby killers less likely to become extinct. Baby killing selected for by group selection.

Group selection explanation for langur infanticide But natural selection acting too. Males that don’t kill babies less likely to be injured and die. “Cheater” genes for not attacking babies spread through population.

Two major flaws of group selection Cheater genes can invade and spread. In nature too much gene flow between populations for group selection to be effective.

For next Friday week (the 3rd of February) read chapters 1-3 of Dawkin’s The Selfish Gene. Be prepared to write brief synopsis/analysis in class and discuss chapters in class.