BIOL 3445 Lecture Notes - Lecture 25: The Hummingbirds, Coevolution, Marsupial
BIOL 3445.001 | Lecture #25 | 4/17/2018
Coevolution
ANNOUNCEMENTS
➢ Exam #3 (04/19)
o Only covers material from study guide (through 04/12)
o Practice quiz and study guide online
➢ Final Exam
o Basically, just exam #4 - Not cumulative
o Today’s lecture will be on the final
OBJECTIVES
― Explain why the geographic mosaic theory of coevolution explains so much of
the variation we see in nature
― Why does selection between antagonists lead to a coevolutionary arms race?
― Why might there be selection against virulence in pathogens?
― Explain why mutualisms are vulnerable to cheaters
― What is the difference between Mullerian and Batesian mimicry?
― Explain why endosymbiosis is a type of mutualism
WHAT IS COEVOLUTION?
― Coevolution: reciprocal evolutionary change between interacting species driven
by natural selection
o Reciprocal Selection: each species imposes selection on the other
― EXAMPLE: Hummingbirds and Flowers
o The hummingbirds’ beak is the right shape to fit into the flower and draw
out the nectar
o The flowers’ colors and shapes are attractive to the birds
o There is no landing pad or pollen pad for insects to land
o There is room for the hummingbirds’ wings to flap
o Only a hummingbird’s beak is long enough to pollinate the flower and
only the flower is the right shape for the hummingbird beak
find more resources at oneclass.com
find more resources at oneclass.com
BIOL 3445.001 | Lecture #25 | 4/17/2018
Geographic Mosaic of Coevolution
― Geographic structure of populations influences the coevolution dynamic
between species
― Direction and intensity of coevolution varies
from population to population
― Co-evolved genes from different populations
mix as a result of gene flow
― The geographic mosaic is made up of hotspots
and coldspots:
o Hotspots: areas where selection is very
intense between two species
o Coldspots: areas where selection is less
intense or nonexistent
o Interactions between species can be
antagonistic or mutualistic
― Group Exercise: How does geographic mosaic
theory of coevolution explain why some places
have higher levels of biodiversity than others?
o Biodiversity often leads to speciation
o The more species interact, the more likely they are to be influenced by
natural selection
ANTAGONISTS
― Antagonists: two species that interact in a negative way
o Predators and prey
o Parasites and hosts
o Either both are harmed, or one is harmed while one benefits
― Two species that are antagonists often generate negative-frequency
dependent selection on each other
o The rarer genotype of either the host/prey of the parasite/predator is
favored
o The uncommon trick/surprise has an advantage until it becomes common
Coevolutionary Alteration
― Coevolutionary Alteration: when predators or parasites shift to a different species
of prey/host as they counter-adapt
― EXAMPLE: Cuckoos vs Hosts
o Cuckoo parents do not raise their own children
▪ They find an unattended nest of host species and replace an
original egg with one of their own
▪ The host species will raise the baby cuckoo as its own
o Cuckoos are large and will kick out the other young
o Cuckoo hosts have evolved defenses (mainly egg recognition) against
cuckoos
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exam #3 (04/19: only covers material from study guide (through 04/12, practice quiz and study guide online. Final exam: basically, just exam #4 - not cumulative, today"s lecture will be on the final. Explain why the geographic mosaic theory of coevolution explains so much of the variation we see in nature. Explain why mutualisms are vulnerable to cheaters. Explain why endosymbiosis is a type of mutualism. Coevolution: reciprocal evolutionary change between interacting species driven by natural selection: reciprocal selection: each species imposes selection on the other. Geographic structure of populations influences the coevolution dynamic between species. Direction and intensity of coevolution varies from population to population. Co-evolved genes from different populations mix as a result of gene flow. The geographic mosaic is made up of hotspots and coldspots: hotspots: areas where selection is very intense between two species, coldspots: areas where selection is less intense or nonexistent. Interactions between species can be antagonistic or mutualistic.
