Week 2: Evolution by natural selection Flashcards
Field crickets
Male crickets produce species-specific calling songs
Each species have their own “song” created by the “file” and “scraper” on their wings rubbing together.
Female preferences for male cricket calling songs
They prefer fast song over slow song
And slow song over no song
Oceanic field crickets (Teleogryllus oceanicus)
Are found across Oceania and in coastal Australia.
Typically inhabit on soil ground hiding in fissures or holes in the terrain.
Were introduced to Hawaii by humans
Parasitic fly (Ormia ochracea)
A female fly is attracted by the song of the male cricket and deposits larvae on or around him
The larvae quickly burrow into the host and emerge about 7-10 days later, killing the host
The parasitic flies were introduced to Hawaii from North America.
Crickets on Hawaiian islands develop silent wings in response to the parasitic attack.
No male crickets sing in Hawaii, but they are in high abundance.
Flatwing crickets
Males have no sound-making structures.
These mutant males are silent like females
The silent wing trait is caused by a mutation to a single gene located on the crickets’ X chromosome
Rapid evolution in cricket mating behavior
Predation pressure –> silent males
Between the late 1990’s and 2003, in just 20 or so cricket generations, Kauai’s cricket population had evolved into an almost entirely silent one.
Female crickets generally won’t mate with a silent male, but an experiment introducing a female from a pre-mutation and post-mutation population, show that they have a lax standard when it comes to choosing a mate and low resistance to silent males. Gave the silent mutation a chance to gain a foothold.
Evolution definition
Heritable change in the characteristics of a population over generations
Evolution by natural selection
- Variation: Members of a species differ in some of their characteristics.
- Inheritance: Parents are able to pass on some of their distinctive characteristics to the offspring
- Differential reproductive success: Some individuals have more surviving offspring than others in their population, thanks to their distinctive characteristics.
To understand how natural selection operates, the first thing any ethnologist must do is to be specific about which behavior is being studied.
Variation
Variation in a trait can be caused by either environmental or genetic factors
Genetic variation
For natural selection to act, there must be variation in the trait under investigation.
No variation, no natural selection
Sources of genetic variation
Mutation: any change in genetic structure
Genetic recombination
Migration: individuals coming from other populations can introduce new trait variants
Inheritance
For NS to act on a trait, that trait must be passed down from one generation to the next.
Without a mode of inheritance, any differences that exist within one generation are washed away.
Because genes are passed down from generation to generation, they are the primary mode of transmission.
Fitness
The number of offspring produced by an individual
The contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals in the population
Fitness consequences of a trait
Refer to the effect of a trait on an individuals reproductive success.
Adaptation
A characteristic that makes an organism better able to survive and reproduce
A characteristic that confers higher fitness to individuals than any other existing alternative exhibited by other individuals within the population
Adaptive value definition
The contribution that a trait or gene makes for greater fitness
Adaptationist
A behavioural biologist who develops and tests hypotheses about the possible adaptive value of a particular trait
Adaptationist approach
Observation –> ask wether the behavior is adaptive –> form hypotheses (how the trait is used, why individuals possessing the trait have higher fitness than individuals lacking it)
Forces of evolution
- Mutation
- Migration (=gene flow)
- Genetic drift
- Selection
1-3 are random processes
4 is nonrandom bc selection operates on fitness difference
Charles Darwin
An English naturalist and geologist
On the Origin of Species (1959)
The Descent of Man, and Selection in Relation to Sex (1871)
Proposed the theory of evolution by natural selection
The founder of modern evolutionary theory
Most of his focus was on South America and the Galapagos Islands
Malthusian Theory of population
Population tend to increase geometrically.
Subsistence increases only arithmetically.
The growth of populations is continuously checked.
Charles Darwin applied Malthusian theory to the natural populations
A better-adapted organism would acquire more resources and leave more offspring.
Nature “selects” individuals with traits that allow them to flourish and reproduce. This idea came to be known as survival of the fittest.
Charles Darwins Natural Selection
Over long periods of time, natural selection leads to adaptation.
Over an evolutionary time span, a population’s characteristics change to make its members better suited to their environment
Darwins two main conclusions
- All organisms are descended with modification from common ancestors.
- All prominent scientists of the day were convinced of this point within 20 years. - The mechanism for evolution was natural selection.
- This was not fully accepted until the late 1920s, partly because of a widespread belief in blending inheritance, in which the traits of the parents were thought to be blended in the offspring.
