Midterm 2 Flashcards
Adaptation
- short term change within a species (aka microevolution); example moth wings change colour
Evolution
Long term changes that results in the appearance of new species (aka macro evolution)
Natural selection
How species change over time
- the primary mechanism of biological change over time (adaptation and evolution)
- proposed by Darwin
- the differential survival and reproductive success in each parental generation which leads to a change in frequency of traits from one generation to the next (adaptation/ evolution)
Natural selection 3 fundamental Observable facts
- variation
- inheritance
- overproduction
Variation from..
- random mutations
- random genetic recombination
- non- random mate choice
Inheritance
- Variation passed from parents to offspring
- principles not known when Darwin wrote “on the Orion of species”
Overproduction
- there are always more offspring born that can or do survive to adulthood (competition)
Who survives to adulthood?
- those who happen to have variation (morphology or behaviour) that helps them survive
- the environment naturally selects some variants over others
Important point to understanding evolution by natural selection:
- not survival alone but survival and reproduction
Fitness
- An individual’s ability to reproduce successfully compared to other members of the same species
- Low fitness= low reproductive success
- high fitness = high reproductive success
How does natural selection work?
- traits possessed by individuals with high survival and reproductive success will be passed to future generations at higher rates
- the environment naturally selects some variations over others to survive and reproduce
- the population over time becomes better adapted to local environments
A change in the frequency of traits from one generation to the next
Adaptation/ evolution
Traits that are well suited to the environment..
- give individuals an advantage in survival and reproductive success
- will appear in increased frequency in future generations
The traits that are not well suited to the environment..
- put individuals at a disadvantage in survival and reproductive success
- will appear in decreased frequency in future generations
Peppered moth
- example of natural selection producing adaptation
4 points about natural selection (peppered moth demonstrates):
- Evolution (change) operates on the population- no individual moth ever changed colour. Individuals do not “evolve”
- Natural selection operates in the individual. Individuals survive and reproduce or not
- Variation had to be there in the first place
- There is no such thing as an absolutely better variant- depends on the environment
Sociobiology (developed in 1960s and 1970s)
- applying evolutionary principles, specifically natural selection, to behaviour
- trying to understand how behaviour might be naturally selected/ adapted/ evolved
- asking how behavioural variations give individuals an advantage in survival and reproduction
3 main components of sociobiology
- Kin selection
- Reciprocal altruism
- Parental investment
Popular definition of altruism
Helping and selfless behaviour; opposite if selfish behaviour
Biological definition of altruism
- behaviour that potentially improves the survival and reproductive success of the recipient while potentially endangering the actor
Altruism examples
- predator alarm calls
- defending a group member from a predator
- helping another individual in a fight (coalition)
- feeding/ caring for an infant
Why is altruism hard to explain ?
- natural selection states the behaviour that increases the survival and reproductive success of the actor will be passed on at a higher rate to next generation and
- behaviour that decreases the survival and reproductive success of the actor will not
Group selection
- originally altruistic behaviour was thought to evolve because it was for the good of the group
Problem with group selection- Wynne- Edwards 1962
- defined as natural selection acting in the group rather than the individual
- for it to work, groups with altruists would have to have higher fitness that those without (but altruists may have decreased RS, while selfish individual would have better RS)
- the altruists wouldn’t be passing on their genes
- rejected: natural selection only makes sense if it acts on the individual (each individual striving to maximize own reproductive success)
What questions was the origin of sociobiology?
“how could altruism have evolved?”
Altruism evolved not by ___, but by _____
Not by group selection, but by kin selection
Kin selection: based on recognition that…
- Each individual shares generic material with their relatives
- Even if you never reproduce, it is possible to have some of your genes represented in the next generation if your relatives are reproductively successful (helping inclusive fitness by helping kin)
Natural selection can operate on ___ rather than individuals
Genes
Inclusive fitness
Individual fitness plus the effect upon the fitness of relatives
Hamiltons rule
c< bxr
1) the cost (c) to the actors fitness
2) the benefit (b) to the recipients individual fitness
3) the degree of relatedness (r) between the actor and the recipient (the proportion of genes shared by common descent)
Does altruism ever occur between non-relatives?
Yes- cannot be explained by kin selection, alternative explanation proposed is reciprocal altruism
Reciprocal Altruism (Trivers 1971)
- helping behaviour between non relatives
- individuals help others so that they will get help in the future when they need it, individuals will cease to help “cheaters”
2 requirements for reciprocal altruism
1) sociality: individuals must have the opportunity for repeated interactions
2) “helping” individuals are of similar abilities (rank, size, etc.)
Does “helping” behaviour ever occur between non-kin without evidence of reciprocal altruism?
Yes- these types of behaviours could also evolve through mutualism
Mutualism
- interaction between two organisms where each gains a fitness benefit
- these interactions can look like co/operation (or bee pollinating flower, males in coalition)
- not altruism because there is no overall cost to the actor helping
Natural selection operates on
Individual & genes
Evolution acts on the
Population
Grooming between two un-relayed females of similar rank is best explained by:
Reciprocal altruism
Sexual selection
- mechanism proposed by Darwin to explain secondary sex characteristics
- realized that some traits possessed by (mostly) males were impossible to explain with natural selection
- instead of aiding males in survival, these traits seemed detrimental
Secondary sexual characteristics
- features of sexual dimorphism
- male/ female distinctions that appear at puberty and go beyond basic reproductive differences
- examples: differences in size, coloration, weaponry, shape, ornamentation.
Sexual dimorphism examples among mammals
- peacock
- birds of paradise
- deer
- lions
- Irish elk (antlers)
Sexual dimorphism primate specific examples
- hamadryads (canines)
- geladas (red chest)
- uakaris (red face?)
Why was another mechanism needed to explain secondary sexual characteristics?
- They are not easily explained by natural selection (not apparently beneficial, and sometimes even detrimental, to survival
- They do not appear until adulthood
According to Darwin, there are two mechanisms leading to the evolution of secondary sexual characteristics:
- Male- male competition
2. Female mate choice
While secondary sex characteristics do not provide ___, they can give males a _______ advantage
Do not provide survival advantage, can give males reproductive advantage
Male male competition
- intra- sexual selection
- secondary sexual characteristics give males a reproductive advantage through competition. With other males
Types of Male- male competition (Anderson 1994)
- Contests- physical attacks or threats
- Scrambles- early search & detection if females that determines the order of contact
- Endurance rivalry- time and energy spent seeking, attracting, and defending mates, as well as being reproductively active
Female choice
- inter- sexual selection
- secondary sexual characteristics give males a reproductive advantage by making them more attractive to females
“Good genes” models
“-Handicap” models
- “viability indicator” models
“Handicap” models
- purpose that ornamentation reduces average male survival, enabling females to assess individual males ability to survive despite his burdensome ornament
Viability indicators
- females asses male characters because they specifically indicate a secondary less apparent trait determining male fitness
- examples testosterone levels, parasite load, body size, fighting ability, age, tenure stage
Sexually selected traits
- behavioural displays
- acoustic displays
- ornaments
- weapons
- pelage/ plumage
- skin coloration
- chemical signals
Behavioural Displays as indicators
- stiff leg display- colobus monkeys
- males vary in expression of these behaviours (ex high ranking males display more than low ranking males)
- male displays decreases in vigorous over time
- displays were targeted to other groups and males
Acoustic displays as indicators- wahoo
Wahoo - Yellow baboons
- rate and duration are correlated with a males competitive ability. High ranking males:
- call more often and at faster rates
- call for longer bouts
- give wahoos with higher fundamental frequencies (FO)
- give longer ‘hoo’ syllables
- FO decline, hoo syllables shortened and forming dispersion decreases
with age
- the acoustic features of contest wahoos thus potentially allow listeners to assess a males competitive ability