Chapter 2- The evolution of behavior Flashcards
Artificial selection
When humans want to increase the probability of a trait being expressed in the species. The species undergoes an artificial breeding program so this trait will occur more frequently. In Darwin’s The Origin of Species he described how pigeons were able to be bred artificially to increase the frequency of certain traits, like with breeding homing pigeons. Also occurs with plants and many other animals
Natural selection
The evolutionary process where traits increase in frequency over time if they give an individual a reproductive advantage. Darwin came up with this theory even before Mendel’s work on genetics.
Ultimate questions
Usually focuses on evolutionary forces, asks “why” questions, like why an animal has a specific behavior.
Artificial selection in dogs
This process began with wolf populations about 15000 years ago. We now have many different dog breeds, although the qualities selected for in each breed is different. Companionship or herding behavior could be selected for in a breed. The artificial selection process answers the question of why we see the herding breeds of dogs we see today.
Silver fox domestication experiment
Researchers only allowed the most docile foxes to breed in their fox population in Siberia. These foxes could eventually be held and petted by humans, and would even seek out human contact. This is an example of artificial selection
Domestication syndrome
Many domesticated species display a distinctive combination of traits- includes mottled coloration, floppy ears, curly tails, and more juvenile characteristics. It’s possible that domestication syndrome traits are genetically linked to the traits leading to tameness, and are a byproduct of selection for tame behavior. Tameness may have an effect on neural crest cell development, leading to the traits leading to domestication syndrome.
Phenotype
The observable properties of an organism
Genotype
The genetic makeup of an organism
Natural selection for group hunting
For some animals, hunting in groups increases the likelihood that they will capture prey. Greater access to food can give them a reproductive advantage. Even if this advantage is slight, the trait will have a large increase in frequency over time. A fitness benefit of 1% would mean that the trait would have almost 100% frequency after 1060 generations
Allele
A variant of a gene- one of two or more alternative forms
3 prerequisites required for natural selection
- Different varieties of the trait
- Fitness consequences of the trait- one version of the trait must impact reproductive success differently than the other
- A mode of inheritance for the trait
Approaching novel objects in birds
Approaching a novel object can be dangerous if it turns out to be a predator, but it can be beneficial if the object is a potential food source. For the trait to vary, the birds in the population must have different approach scores. Birds that are reluctant to approach a novel object were less likely to add new food sources to their diet. Therefore, they had less reproductive success.
Genetic variation
Behavioral variation in approach score that correlates with genetic differences between animals in our population
Mutation
Any change in genetic structure. This can generate genetic variation in a population.
Addition and deletion point mutations
Occur when a single nucleotide is added/deleted from a stretch of DNA. Genes usually code for the production of proteins, so these mutations usually result in an inactive enzyme that can affect an animal’s behavior.
Base mutations
Occurs when one base in a nucleotide replaces another. These proteins can affect protein function, so they can have an impact on an individual’s reproductive success, sometimes may impacting behavior. Some base mutations, called silent mutations, don’t cause changes in amino acids.
Genetic recombination
Another source of genetic variation. During meiosis, when pairs of chromosomes line up during cell division, sections of a chromosome can cross over and switch positions with sections of the other chromosome. The swapping creates the new genetic variation and therefore variation in behavioral traits.
Migration
One way of genetic variations entering the population via a nongenetic pathway. This is when individuals from other populations introduce genetic diversity by bringing new trait variants to the population.
Fitness consequences
Refer to the effect of a trait on an individual’s lifetime reproductive success. One example is the difference in reproductive success associated with slow versus fast approach behavior in birds. A trait must have fitness consequences for natural selection to act on it, although it is very unlikely that two behavioral variants will have the same exact effect on reproductive success.
Reproductive success
Refers to the mean number of reproductively viable offspring an individual produces
Narrow-sense heritability
A measure of the proportion of variance in a trait that is due to additive genetic variance. Differences in a trait can come about in many different ways- genetic or environmental differences. Can be measured through a truncation selection experiment or through parent-offspring regression.
Truncation selection experiment
- Measure the approach score of every bird in the population when it reaches twelve months of age to find a mean value (X0)
- Truncate (cut off) the population level variation in approach scores by allowing only those individuals with approach scores greater than some value to breed. Then calculate the mean approach score of those individuals (X1). Use these values to calculate S.
- Raise the offspring produced by the generation 1 birds that were allowed to breed under conditions identical to those experienced by their parent. Approach scores measured at 12 months, mean is X2.
Selection differential (S)
The difference between X1 and X0. It is the maximum amount we could expect natural selection to change approach scores, or the amount of change we could expect if all the variation in approach score was genetic variation upon which natural selection could act.
Response to selection (R)
The difference between X2 and X0. It’s a measure of how much truncation selection has changed approach scores across generations 1 and 2.
In a truncation selection experiment, heritability is defined by
Heritability is defined by R/S. If the heritability is 10/30, then one third of all the variance in approach is due to genetic variance upon which natural selection can act. Many traits show low to moderate heritability
Parent-offspring regression
Another way to measure narrow-sense heritability. When narrow-sense heritability is high, behavioral variation in offspring should map onto behavioral variation observed in parents, since offspring are inheriting genes from their parents. There is lower narrow-sense heritability when there is a greater role of environmental variance in determining variance in behavior. These factors include diet, location, and others.
Additive genetic variance
Refers to the deviation from the mean phenotype due to inheritance of a particular allele and this allele’s relative (to the mean phenotype of the population) effect on phenotype
Brown and Brown cliff swallow study
This is a species where group size affects survival by affecting rates of parasitic infection. They found that the group size in which an individual lived was similar to the group size in which their parents lived, regardless of habitat. The correlation did not seem to be due to environmental variation, so group size is likely a heritable trait. Statistically, there was a strong correlation between parent and offspring colony size.
Cross-fostering experiment for group size preferences in birds
Another experiment by Brown and Brown. They used nestlings from two large and five small colonies. Half of the nestlings in large colonies were removed and replaced with the nestlings from small colonies so that offspring from both large and small colonies were placed in the same nest. There was a positive correlation with the group-size preferences of the offspring’s genetic parents (their foster parents did not seem to influence group size preference). This indicates narrow-sense heritability for the complex behavioral trait of group size preference.
Sociobiology
The study of the evolution of social behavior
“Selfish gene” approach to ethology
The idea that genes associated with behavior are the units on which natural selection acts. Genes can be considered “selfish” because natural selection favors alleles that increase the reproductive success of an individual and that allele will increase in frequency. So natural selection often (not always) produces genes that appear to be selfish.
Conservation biology
Goal is to detect populations under risk in order to minimize damage to those environments. One approach is to look for traits that indicate the ability to respond to changing conditions in the environment. One trait (symmetry on both sides of the body) has been identified as one indicator that animals are able to handle developmental stress.
Lens symmetry study
Lens proposed that conservation biologists can use asymmetry as a warning system for detecting populations under risk. They studied a population of thrushes in a Kenyan forest. They found decreased rates if survival as they moved from areas with low amounts of damage to areas with high amounts of damage. Symmetry of the tarsus bone decreased as damage to the forest increased. This indicates that population biologists should pay more attention to populations with high measures of asymmetry.
Adaptations
Traits that natural selection shapes to allow an organism’s traits to match its environment. Adaptations are traits associated with the highest relative fitness in a given environment. Natural selection is the main process that produces adaptations.
2 examples of adaptation
- Antipredator behavior in guppies
- Cooperative behavior in naked mole rats
Natural selection for physical traits in guppies
Guppies can be found both upstream and downstream of waterfalls. Waterfalls act as a barrier to predators, so guppies downstream of waterfalls face severe predation and guppies upstream face weak predation. There isn’t much gene flow between these sites, so natural selection should favor different traits in each guppy population- research has found genetic signatures that are indicate of natural selection favoring different sets of alleles linked to behavioral traits at each site. Guppies at high predation sites mature faster, produce more broods of smaller offspring, and use more resources for reproduction. This is because size of these fish is irrelevant with so many predators, so simply producing more offspring increases the changes of some surviving. Low predation sites favor larger guppies because larger guppies can’t be targeted by the main predator in the area
Schoaling
A measure of group cohesiveness in guppies. This is a type of antipredator behavior
Predator inspection
Refers to the tendency for individuals to move toward a predator to determine more information about the danger involved
Antipredator behavior in guppies
Includes shoaling and predator inspection. Researchers predicted that guppies in high predation sites would shoal in larger numbers, and that they would inspect a predator more cautiously and more often than low predation guppies
Antipredator behavior in guppies study Magurran
Guppies were transferred from a high predation site to a low predation site. The descendants of guppies from the high predation area exhibited shoaling and predator inspection behaviors that were more similar to those of guppies at low predation sites. However, over time, the guppies moved back toward a high predation area and exhibited antipredator behavior characteristic of a high predation area. Natural selection could either have maintained this behavior or shifted back toward high predation traits over time.
Eusociality
An extreme form of sociality that is present in many social insect groups and also in naked mole rats
3 characteristics associated with eusociality
- A reproductive division of labor in which individuals in certain castes reproduce and individuals in other castes do not
- Overlapping generations- individuals of different generations are alive at the same time
- Communal care of young
Kinship theory
Suggests that the more genetically related individuals are, the more cooperation they will show with each other. Naked mole rats in a colony are genetically related and therefore highly cooperative with each other.
DNA fingerprint
One naked mole rat study used 3 DNA probes to isolate 3 distinct DNA fragments from the rats. Each had around 29 distinct bands, and the pattern of bands represents the DNA fingerprint of the mole rat. The more closely the fingerprints of individuals match, the more closely related those individuals are. Mole rats have a high level of genetic relatedness and are on average more closely related than genetic siblings
Phylogenetic trees
Show the evolutionary history of a group of species and the phylogeny of the groups of organisms, time flows from left to right. Species with a common ancestor tend to have more traits in common due to a shared set of alleles. This is a hypothesis of the evolutionary history of groups of species, and additional evidence is usually required to determine that the tree is correct.
Nodes
The points where a phylogenetic tree split. They represent common ancestors to whatever groups come after the branching point. A common ancestor is not identical to a currently living species due to evolution occurring over time
Root
The base of a phylogenetic tree. It’s a common lineage from which all species indicated on a tree are derived
How are phylogenetic trees constructed?
Traits are measured in groups of organisms- they can be structural, development, molecular, behavioral, or based on related anatomical structures. Homologous traits are used to build trees because they indicate a common ancestor, but homoplasies are not used
Homology
A trait shared by two or more species because they share a common ancestor. Used in phylogeny building because they reflect shared evolutionary histories
Homoplasy (analogous traits)
A trait shared by two or more species, but not because they share a common ancestor. They occur because natural selection has acted independently on each species. They can distort relationships when building a phylogenetic tree. Convergent evolution leads to analogous traits
Polarity
The direction of historical change in a trait. To create a phylogenetic tree, it must be determined which version of a trait appeared first. Fossil records are sometimes used to determine this, but molecular genetic data is used more commonly. DNA sequences are compared to each other at the nucleotide level
Parsimony analysis
The idea that the phylogenetic tree that requires the least number of evolutionary changes is the most likely to be correct. Researchers usually end up creating many possible phylogenetic trees for a taxon- this is one technique used to distinguish between them.
How do ethologists use phylogenetic trees?
In some cases researchers can use behavioral data to build phylogenies, but this is rare
1. To examine the evolutionary history of mating systems- researchers would find an established phylogenetic tree for the taxa and then superimpose the existing behavioral data onto the tree
2. To make inferences about natural selection- researchers can use phylogenetic data to determine whether co-occurrence of traits is a result of common ancestry or if it’s independent of phylogenetic history
Comparative method
One set of traits may seem to co-occur. One interpretation of the data could be that natural selection has independently favored this combination of traits, repeatedly. However, it’s also possible that evolutionary changes caused these traits- there could be shared evolutionary history among the species. When the evolutionary history of the traits is compared on a phylogenetic tree, we can see whether the traits were independently favored or due to shared evolutionary history (if both of the traits evolved at one time along one branch)
Capellini sleep and cognitive function study
Capellini analyzed the phylogenetic history of multiple species of mammals and found no evidence for the correlation between the brains and REM sleep. However, she found a positive correlation between relative amygdala size and nREM sleep. The study provides some evidence for the link between cognitive function and sleep in mammals
Sleep and the immune system study (Preston and Nunn)
Examined the hypothesis that sleep strengthens the immune system. They hypothesized that WBC count and sleep would be positively correlated, while WBC and platelet count and sleep would not be correlated. The data supported this hypothesis. Species that slept longer also had reduced parasite loads.
4 states of parental care systems in animals
- No paternal care
- Maternal care
- Paternal care
- Biparental (maternal and paternal) care
Evolution of parental care systems in fish study (Mank)
Researchers used morphological and molecular genetic data to build a phylogenetic tree of families of ray-finned fish. They used the tree to make inferences about the evolution of parental care by categorizing the species based on their parental care systems and then examined the order in which these systems appeared over evolutionary time. It was found that there were 22 independent occurrences of a shift from no parental care to paternal care in a descendant species. No evidence was found for the stepping stone model, in which parental care systems evolved in a specific order. There were multiple origins of all parental care systems.
Stepping stone model
The idea that parental care systems evolved in fish in the order of no parental care, paternal care, biparental care, and then maternal care in the case of male desertion. Other data has not supported this idea.
Mating strategy of Poeciliiade fish study
Researchers examined which mating strategy of the fish was the ancestral mating strategy and which was the derived mating strategy. They built a phylogeny using sequences of a mitochondrial rRNA gene and then mapped male mating strategy onto their phylogeny. They found that gonadopodial thrusting was the ancestral state, meaning that display of a male’s bright coloration was a derived mating strategy
Evolution of the peppered moth
Initially, moths in England in the 1800s were mostly white, with 3-4% being dark. Due to pollution, the white moths were more vulnerable to predators. Over time, dark moths increased in frequency in the population
Selective advantage of a trait
Natural selection will increase the frequency of a trait if the trait is heritable and if the trait increases reproductive success.
Why is it difficult to determine if a behavior is heritable?
Behavior can be transmitted through culture. It can also be difficult to observe.
Which variable in birds could be a predictor for future reproductive success? (3)
- Male sparrows sing to attract mates- males who were able to sing a greater variety of songs were more likely to attract mates and therefore had greater reproductive success.
- Territory size also predicts mating success, but it’s independent from song repertoire
- Body mass and length of offspring primary feather growth are other predictors
Gull phylogeny
Evolution of nesting on cliffs- some gulls nest on cliff ledges or on trees. Gulls have a communication system to avoid conflicts
Bank swallow antipredator behavior
They have the same antipredator behavior of the kittiwake- we can compare the evolution of both species
What development changed the study of phylogeny?
1970s advances in molecular genetics changed the study of phylogeny. DNA sequences could now be used to answer questions about phylogeny
Lizard behavior study (Losos)
*Goal- to examine the short term and long term effects of the introduction of predators on prey (brown anole lizards) behavior and morphology
*Background- these lizards reside on rock islands where predators are absent
*Method- predators were introduced experimentally. Brown anoles were observed on similar islands, without predators, as a control.
*Results- the population of brown anoles decreased. However, brown anoles quickly responded behaviorally by moving to higher branches. There was also strong evidence for natural selection acting on morphology. Larger females and males with longer legs were selected for to escape from predators.
*Explanation- the introduction of predators resulted in behavioral and morphological changes
