BI111 Lecture Notes - Lecture 4: Medium Ground Finch, Selective Breeding, Divergent Evolution

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9 Feb 2017
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Evolutionary Theory before Darwin
Lamarck's contributions to evolutionary thought
Species change with time(are not fixed points)
Changes pass on from one generation to the next(parents look like their offspring)
Organisms respond to environmental conditions(sensitive to their local environment)
Hypothesized mechanism(Principle of use and disuse and principle of inheritance of acquired
characteristics)
o The traits during an individuals lifetime would be passed on to ones offspring
Epigenetics: how different genes are turned on/off based on the environment parents
experienced (based on expression)
Darwin's Observations and Inferences
Observation 1: Populations have great capacity to grow, but are ultimately limited by resource
availability(lots of population growth, but must be competition for resources)
Inference: Competition between individuals in a population for resources
Observation 2: individuals vary within populations in heritable traits related to competitive success
(ultimately survival)
Inference: some individuals more likely to survive and reproduce than others
Observation 3: Individuals ay also vary within populations in heritable traits related to REPRODUCTIVE
competitive success
Inference: Some individuals more likely to reproduce than others
Adaptive Evolution: A populations characteristics change over time, as advantageous traits become
more common
Changes in allele frequencies over time
Evolution encompasses all types of changes brought about by selection processes and chance
events
Charles Darwin suggested mechanism of adaptive evolution(natural selection), and used
domesticated species to first illustrate concept of artificial selection: change associated with
exaggeration of desirable (from human perspective) rather than improved survival or reproductive
abilities
Domesticated species and adaptation
Depending on environment, different phenotypes are adaptive or deleterious
Traits(with genetic basis) that might otherwise put individuals at a competitive disadvantage may
be desirable to humans and thus become favoured by selective breeding
E.g.: Change from dehiscence(shed ripped grains) to indehiscence (Hold on to ripened grains)-
weakening of tissue at the base of the individual seeds
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Tomatoes are mutations from different domesticators
Peppered moth (Biston betularia)
Two major phenotypes- Morpha typica(peppered moth) and morpha carbonaria(black moth)
Difference is due to a single dominant mutation- Makes moth black and one salt and pepper
appearance
Salt and pepper has phenotypic advantage(camouflage)
Industrial Revolution
In Manchester, had huge consequences polluted everything with thick black smoke
The trees were covered in thick black soot which then gave the black moths an advantage and the
peppered moth would stick out
Endemic: meaning they are found in one place but no where else
Darwin's Pigeons (in England)
Artificial selection is an analogous process to Natural Selection
Darwin's Finches
Adaptive radiation caused by divergent selection to utilize alternate food resources
Different island have different resources, leading to speciation
Allopatric-isolation
Disruptions in beak depths: A change in the weather
Year 2: Drought
o Total rainfall for the entire year: 24mm
o In a normal year, 130mm of rain would fall (134.7mm in Year 1 of study)
Seed production (availability) changed
o Year 1 June: 10+ grams of seeds per m2
o Year 2 June: 6 grams of seeds per m2
o Year 2 December : 3 grams of seeds per m2
Finches produced no eggs in year 2, most born in year 1 died
What was there to eat?
A variety of seeds are produced on the island, but Finches prefer the softest seeds, (the easiest to
open)
Hardest seed on the island is produced by the Caltrop
o It takes a medium ground finch with a beak at least 11mm long to open one
o Ground finches with beaks that are 10.5mm long or less haven't even been seen trying to
eat them
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