EV6 - 8.1 Other Types of Selection

EV6 ­ 8.1 Other Types of Selection
December 13, 2013
Natural Selection
Friday, December 13th
1) Other Types of Selection
­ note
2) Consequences of Human Influence
* Unit Test will be Wednesday!
Types of Selection:
1) Directional Selection
• favours individuals with a more
extreme variation of a trait
• i.e- common in artificial breeding,
where individuals with an enhanced
trait are often selected.
Strawberries have been selected for
larger and sweeter fruits, chili
peppers for hotter flavour, and
thoroughbred horses for running
speed.
3)Disruptive Selection
• Favours individuals with variations at
opposite extremes of a trait over
individuals with intermediate variations
• Sometimes environmental conditions
favour more than one phenotype. For
example, two species of plants with
different sized flowers (small and large)
may be available as a food source for the
hummingbird population. Birds with long
and short bills will be more successful and
will contribute more offspring to later
generations
• Evolution occurs when natural selection
acts on the genetic variability within
populations.
• Genetic variation arises by chance through
genetic mutations and recombination.
• The process of natural selection, however,
does not occur by chance. The
environment favours certain individuals
over others. Just as human breeders
select for specific traits in plants and
animals, the environment selects
individuals that are better suited for
their environment.
2) Stabilizing Selection
• occurs when the average phenotype
within a population is favoured by the
environment.
• i.e. - hummingbirds with medium sized
bills living in an environment with medium
sized flowers with be more successful at
getting food and reproducing than those
with very short or long bills.
• i.e. - average birth weights in human
babies have a better chance of survival
over babies that are premature(low
weight) or heavier - could threaten the
life of mother and baby.
4) Sexual Selection
Definition:
• Favoring of any trait that specifically enhances the mating success of an individual. Common Forms of Sexual Selection
1) Female Mate Choice:
Females choose mates based on physical traits such as bright coloration or behaviors.
EV6 ­ 8.1 Other Types of Selection
December 13, 2013
Bird shows off to Attract Female
http://youtu.be/gqsMTZQ­pmE
Moonwalking Bird
http://www.youtube.com/watch?v=M8pqH6zXDE0&feature=fvwrel
Birds of Paradise ­ Acrobatics Display
2) Male vs. Male Competition
Males evolve physical attributes such as antlers that are often used in direct competition.
Losing or Success Can mean the difference between territories, harems etc. Ram Rumble http://www.youtube.com/watch?v=1g5IK66O2qU
http://www.youtube.com/watch?v=pZ8x3apg4Lw&feature=relmfu
The Lyre ("Liar") Bird
http://www.youtube.com/watch?v=VjE0Kdfos4Y&feature=relmfu
The Mating Dance (Planet Earth)
FYI ­ Successful male elephant seals may mate with dozens of females each year & hundreds in their lifetime. A weak male may live a longer life, but produce no offspring.
http://www.youtube.com/watch?v=bEhAbwCYc1c&feature=fvwrel
Sexual Selection Often Lead to Sexual Dimorphism
Traits such as bright coloration can be favored by sexual selection, but can be a disadvantage when it comes to longevity.
Good health enhances reproductive success but finding a mate is even more important.
Sexual selection often leads to the males and females of a species evolving appearances and behaviours that are quite different from each other (sexual dimorphism).
FYI: Fringe lipped bats locate the male Tungara frog by listening to their mating calls ­ Male frogs that call frequently are likely to get eaten, male frogs that don't call = unable to attract a mate
Sexual dimorphism of the polygamous Northern elephant seal Female (left) and male Common Pheasant illustrating the dramatic difference in both color and size between sexes
EV6 ­ 8.1 Other Types of Selection
December 13, 2013
Plants & Sexual Selection
Colorful flowers and scents are sexual features of plants. Attract pollinators
Evolutionary Change without Selection
Genetic Drift
1) Genetic Drift: A change in the genetic make­up of a population resulting from chance
p.550-554
Very common in small populations
http://www.youtube.com/watch?feature=player_embedded&v=tHBEokBPaU0
2) Bottleneck Effect
• a dramatic, often temporary reduction in population size, usually resulting in significant genetic drift
• caused by over­hunting, severe weather disasters, disease, severe pollution, habitat loss
• a very small sample of alleles survives to establish a new population
Can lead to fixation of alleles, thereby increasing the incidence of homozygous individuals. Why is this bad?
It reduces genetic diversity of a population!!
Northern Elephant
Seal
­subject to over­hunting in the 1890's to 20 seals!
­today, have increased to over 127,000
­seals are genetically similar
Cheetah
­believed to have suffered bottleneck 10,000 ya
­cheetah's have low genetic variability, low reproductive rates and are vulnerable to disease http://www.youtube.com/watch?feature=player_embedded&v=C_7nTs7lSgo
http://www.youtube.com/watch?feature=player_embedded&v=­JP7XxdziWs
EV6 ­ 8.1 Other Types of Selection
3) Founder Effect
• a few individuals from a large population leave to establish a new population
• For example, a small number of finches from the coast of South America established a founding population on the Galapagos Islands
• seen in self­pollinating plants
• seeds being carried by wind or water to distant islands • migrating birds that don't return to the main population
December 13, 2013
Complete worksheet:
Consequences of Human Influence