Natural selection (Lucy) Flashcards
What were the 3 inferences Darwin made about natural selection?
1 - Fierce struggle for existence
2 - Hereditary constitution of the surviving individual
3 - Continue gradual change of population
Who was Alfred Russel Wallace?
British naturalist, biologist etc
Best known for independently concieving the theory of evolution thru natural selection - his paper on the subject was jointly published w some of Charles Darwin’s writings
Prompted Darwin to publish origin of species
What did Darwin hypothesise about natural selection?
(Common ancestory of all living things)
He hypotheseized that all species have descended from on of few common ancestors
New species do not arise from independent acts of creation or spontaneous generation but from pre-existing species
Branching pattern of ancestry that connects all life
How did Darwin’s ideas compare to Lamarck’s?
Lamarck suggested independent progression whereas Darwin proposed the branching tree of life
What are the 3 components of natural selection?
- Variation
- Inheritance
- Differential reproductive success
What is variation?
Individuals in a pop differ from one another
What is inheritance?
Some of these differences are inherited from their parents
What is differential reproductive success?
Individuals w certain traits are more successful than others at surviving & reproducing in their environment
Give an example of variation, inheritance & differential reproductive success causing natural selection:
Ladybirds:
- Variation = members of the pop vary in the traits they display, some are RED while others appear ORANGE
- Inheritance = offspring tend to resemble their parents
- Differential reproductive success = BRIGHTER bettles are BITTER –> predators learn to avoid them - SO - bright beetles more liekly to survive so more likely to reproduce
- Result = evolution by natural selection –> proportions of different variants in beetle pop will change over time
How do mutations affect natural selection?
Mutations = major source of variation on which natural selection acts
Mutations are random - no respect to needs of organism, independent of selection, most are random & harmless
Does natural selection act on genotypes or phenotypes?
Phenotypes –> this is bc gene codes for a trait but it only appears under set conditions
Give an example of phenotype depending on both genotype & environment:
Yarrow plants (Achillea millefolium)
Depends on its genotype & the altitude at which it is raised
(Rest of description):
Pops of yarrow plants grown in gardens at three sites that were at different altitudes: high, medium, and low elevation. For example, the green screen behind the plants of genotype 1 shows that these plants grow tall at high and low elevations, but are short at medium elevation. The blue screen behind the plants of genotype 4 shows that these plants respond very differently to elevation. This genotype grows tallest at medium elevation and shorter at high and low elevations. Adapted from Clausen, Keck, and Hiesey (1940, 1948).
What are levels of selection?
Consistent differences in fitness among phenotypically (and genetically) different individuals w/in pops
Selcetion acts on genes, cell types, individuals, (pops & species)
Give examples of levels of selection:
e.g. selfish genes, transponsons
e.g. segregation, distortion, meiotic drive - do not follow Mendel’s laws; mouse t allele kills sperms that carry normal T allele, so 90% of sperm carry t –> tt. individuals die/are sterile
What is fitness? (Components of natural selection)
The ability of an individual (genotype) to survive (viability) & to reproduce (fertility)
What is viability?
Probality of survival to reproductive age
What is fertility?
Avg number of offspring per individual that survive to reproductive maturity
What are the 2 divisions of fitness that we look at?
- Absolute fitness
- Relative fitness
What is absolute fitness?
Represents the avg number of offspring (reproductive success) produced by individuals of a particular genotype
What is relative fitness?
(More important in an evolutionary context)
Represents the avg no. offspring (reproductive success) produced by individuals of a particualr genotype relative to other members of the pop
What was the first way which natural selection was measured in a wild population?
Beak size in Geospiza fortis
Birds arrived on Galapagos ~ 3 million yrs ago then rapidly diversified into different forms
Why was measuring finches on the Galapagos islands an ideal study?
On Daphe major –> relatively untouched island, no goats, no farming & can measure every type of seed finches each
How was natural selection mearured in finches (Geospiza fortis)?
1 - Beak size is heritable & size of beak makes a difference between life & death
2 - Drought in 1977 - spurge plants all died, so no small seeds availble
3 - In subsequent years, beak size was 8-11mm (9.2avg), afterwards it was 9.7mm = 15% bigger
4 - 5 yrs later - much rains, spurge seeded again, beak size dec again
What was the lesson from the study on finches (Geospiza fortis) on the galapogus islnmads
NS is variable (e.g. had they arrived at diff time, would have seen diff effects)
- NS can occur at surprising speed
- The nature of NS can change over time
Gave an example od phenotypes affecting natural selection:
Oldfield - beach mouse coat colour
Peromyscus polionotus lives in 2 different habitat inland on the dark soil of the oldfield (majority of its habitat) & on the beach (sandy), they show 2 colour patterns nicely matching their environments. The remarkable thing is that the Florida beaches and Islands where these mice are living are only 4000 to 6000 years old.
Hopi discovered considerable phenotypic variation in coat colour, both within and between populations. Also discovered considerable genetic variation at the Mc1R locus associated with coat colour
What development was made from the coat colour study on mice?
Links phenotyes to genotypes –> Natural selection not only require variation but it requires inheritance. TWO PIGMENTS RESPONSIBLE OF COAT COLOR
Thru discvoery of Mc1R gene (Melacortin-1receptor)
What does the Mc1R gene do?
Known to influence coat color in many species of mammals and birds, depending of its interaction with other genes this gene switches back and forth between producing a dark pigment eumelanin or a light pigment phaeomelanin
What is triggering the switch is a protein alpha-MSH (Alpha melanocyte stimulating hormone) when it triggers the production of eumelanin
But another protein can also bind to the MC1R receptor it is called ASP Agouti signal protein where the system switch to the production of phaeomelanin
SO we have a fantastic system and equilibrium between a receptor and two activators between two circulating molecules. It is a co-dominant system
SO ANY MUTATION CHANGES THE BINDING BETWEEN THE RECEPTOR AND THE ACTIVATOR WILL IMPACT THE EQUILIBRIUM leading to coat color polymorphism
What is the most famous example of evolution by natural selection directly observed in the wild?
& give examples of this
Industrial melanism in the peppered moth
(A) The pale gray “typical” form and the melanic form on a tree trunk darkened by air pollution (left) and on a normal, nonblackened trunk (right).
(B) The decline in the frequency of the melanic form in three British localities, indicated by dots of different colors, as air pollution decreased during the late twentieth century. (B after [11].)
Slide 28
ffff
