Transcript Outcomes of Evolution

OUTCOMES OF
EVOLUTION
Selection
acts on
Variation
Genetic
variation
Directional
Disruptive
Stabilizing
Directional Selection
■ Favors one of the
extreme variations
of a trait
■ Can lead to rapid
evolution of a
population
Disruptive Selection
■ Favors both extreme variations of a trait
■ Eventually results in no intermediate forms of the trait
■ Leads to the evolution of two new species
Stabilizing Selection
■ Favors average individuals
■ Reduces variation in a population
SPECIATION
■ The evolution of a new species from previously
existing species
■ Isolating Mechanisms lead to speciation
CRASH COURSE:
SPECIATION
https://www.youtube.com/watch?v=2oKlKmrbLoU&list=PL3EED4C1D68
4D3ADF&index=15
What can lead to speciation?
■ Geographic Isolation
– A new species can evolve when a
population has been GEOGRAPHICALLY
ISOLATED.
– Physical barriers divide a population
■ Reproductive Isolation
– Occurs when formerly interbreeding
organisms can no longer mate and produce
fertile offspring
■ Genetic information becomes too
different (mutations)
■ Behaviors become too different (mating
seasons)
On the Origin of Species
■ Darwin did not publish his ideas on evolution until 1859.
■ He published On the Origin of Species by Means of Natural Selection
Darwin’s ideas have been updated
■ Genes are responsible for
inherited traits.
Darwin’s ideas have been updated
■ Isolation leads to species
formation.
■ Isolation: the condition in which
two populations of the same
species cannot breed with one
another.
■ Populations of the same species
living in different locations tend to
evolve differently.
http://williamcalvin.com/bk3/img/kaibab.gif
Kaibab Squirrel
Aberts Squirrel
Species:
■ Group of organisms that are
genetically similar and can
produce fertile offspring.
13: Processes and outcomes of evolution
■ Challenge: How do evolutionary processes
biodiversity?
■ Vocab:
– Adaptations
– Macroevolution
– Microevolution
– Speciation
lead to changes in
#1
■ Microevolution refers to the evolution of very small organisms, such as bacteria.
– FALSE
Microevolution is evolution on a small scale that changes the gene pool of a
population or species
Microevolution
■ Results in changes in the frequency of alleles (like we saw in the mice in activity 12)
■ Four main factors:
– Mutations
– Natural selection
– Genetic drift
– Gene flow
#2
■ The evolutionary fitness of an organism is related to its physical strength or size.
– FALSE
Evolutionary fitness is related to the probability of survival and reproduction
#3
■ Adaptations result only from natural selection.
– TRUE
Adaptations are inherited characteristics that favor survival or reproduction and are
the result of natural selection
Adaptations
■ Inherited traits that increase an organism’s fitness (survival and rate of
reproduction)
■ Results from natural selection
– Organisms cannot CHOOSE to adapt
– Organisms don’t adapt out of NEED. Either they have traits that will help them
survive, or they die!
– INDIVIDUAL organisms cannot adapt in their lifetime
#4
■ Geographic Isolation results from either changes in the land or migration of a group
of organisms to a distant location.
– TRUE
Geographic Isolation can occur when rivers or canyons form, or if a population
moves far away from others of the same species.
#5
■ When gene flow continues between two populations, they are likely to remain the
same biological species.
– TRUE
When populations share a common gene pool they exchange genes through sexual
reproduction and share any genetic changes
#6
■ The evolution of many species from one ancestral species is proposed as a
mechanism for the evolution of the 13 species of Galapagos finches.
– TRUE
Scientists think that the different species of finches evolved from a small population
that was blown off course from mainland South America
Speciation
■ If enough small changes accumulate in a population (microevolution), this could
lead to speciation (macroevolution)
■ Occurs most often when gene flow is restricted or cut off
■ Examples:
– adaptive radiation of Darwin’s finches
– changes in birds seen in the computer simulation
#7
■ Until human populations grew and began to change the environment, there were
very few extinctions.
– FALSE
Extinctions have occurred throughout earth’s history for many reasons, including
disease and natural disasters. Human activities have increased the rate of
extinctions
#8
■ Macroevolution refers to any evolutionary changes at or above the species level.
– TRUE
Macroevolution includes speciation and extinction, which change earth’s biodiversity.
Most species that have lived on earth are now extinct, perhaps as high as 99%
Activity 10: What is a Species?
■ Challenge: How do new species separate from
■ Page 472 -- Introduction
existing species?
Background Information- pg 473
■ The biological species concept is a method of defining a species based on whether
the organisms can breed with each other in nature to produce fertile offspring.
■ Gene flow results from this interbreeding, as genes move between populations
■ Members of the same species share a common group of genes called a gene pool
■ This method of classification does not always fit:
(species that reproduce
asexually, some plants
that can crossbreed, extinct fossil organisms)
Part A: Procedure
Claims about the process of species separation:
• Early means they are still one species
or have just begun separation.
• Mid means they are separating.
• Late means they are at the end of
separation, they are most likely two
species.
Part A: Procedure
■ Read the examples from the textbook, pages 475-479
Species Separation
■ Complete a chart for each of your assigned examples
Example number/
organism name
Claim
Evidence to support the
claim
Reasoning
Ex. 1: Red and Purple Sea Urchins
Species Separation
Example number/
organism name
Example 1: Red and purple sea urchins
Claim
Late
Evidence to support the
claim
Eggs can only be fertilized in a lab, embryos do
not survive
Reasoning
Even though eggs can be artificially fertilized, the
offspring don’t survive, so there is no exchange of
genes or a common gene pool. They have most
likely split into two different species
Procedures
■ Example #1 as a class
■ Group 1– examples 4, 5, 8
■ Group 2 – examples 3, 6, 9
■ Group 3 – example 2, 7, 10
Part A: Procedure
Dogs
and
wolves
Northern & California
Spotted owls
Blue
& red Cichlids green
lacewings
Copper
resistant/tolerant
monkeyflowers
Eastern/Great
Plains frogs
Midas cichlid
Red sea urchins
Horses
Orchids
Arrow cichlid
Purple sea urchins
Donkeys
Orchids
Part B: Procedure
■ Steps 13-15 (Scientific Groupings)
■ Analysis questions 2 & 3
Procedure Step 15– Reproductive
■ Behavioral Isolation- different mating signals/rituals
Barriers
–
Meadowlarks, fireflies, blue/red cichlids
■ Habitat Isolation- same area, different habitat
–
Garter snakes, insects
■ Temporal Isolation- different breeding times
–
Lacewings, orchids
■ Mechanical Isolation- physically incompatible
–
Flowering plants, damselflies
■ Gametic Isolation- sperm and eggs can’t interact
–
Purple/White Sea urchins
■ Hybrid Sterility- offspring are infertile
–
Horses/donkeys
■ Reduced Hybrid Viability- offspring don’t live long
–
Frogs
■ Geographical Isolation- live in different locations
–
Lions/tigers, squirrels
So what happens next?
■ Reproductive barriers prevent gene flow between populations
■ Mutations and adaptations that evolve in one population can’t be shared with the
other if there is no gene flow
■ Over time, populations can become so genetically different that they are no longer
the same species (speciation)
Analysis Question 2
■ Explain how geographic isolation can lead to speciation.
– If two populations do not meet in nature, than there is no gene flow between
the populations. There genes will continue to mutate and evolve separately,
since the populations will have different gene pools.
Analysis Question 3
■ Lions and tigers do not overlap in range and do not breed in nature. In
captivity, a male lion may mate with a female tiger and produce offspring.
Although more rare, a male tiger may also mate with a female lion to
produce offspring. In both cases, the male offspring are sterile, while the
females might or might not be fertile. Explain where lions and tigers are on
the speciation continuum, according to the biological species concept.
Support your answer with evidence and reasoning.
– Very late in the process of speciation, but not totally separate, since
male offspring are infertile but females might still be able to produce
offspring of their own.
Human Species
■ DNA evidence suggests that modern humans (Homo sapiens) could interbreed with
Homo neanderthalis
■ There is newly discovered evidence of another human ancestor, “Denisova” that
might have bred with humans as well
■ One current hypothesis is that all three species evolved from Homo heidelbergensis
along parallel paths at the same time. Denisovans and Neanderthals went extinct.
Homo sapiens survived.