Lecture 23B and 23C Flashcards
speciation
formation of distinct species by genetic divergence leading to reproductive isolation
what is the first steep of speciation
*genetic isolation due to separation in space time or behavior(allopatric or sympatric)
what is the second step of speciation
genetic makeup of each population changes through selection, genetic drift, or mutation
What is the third step speciation
reproductive isolating mechanisms evolve (results in a new species)
can speciation still occcur if without spatial separation?
yea! it would be sympatric speciation meaning: they evolve without a geographic barrier
what’s the most common mode of speciation in animals?
allopatric speciation(population becomes geographically divided)
what can drive sympatric speciation
polyploidy
behavioral isolation
ecological specialization
temporal isolation
what can drive allopatric speciation
geographic barriers
dispersal
vicariance
adaptive divergence
founder effect
differential selection pressures
in allopatric speciation evolution can proceed independently through
mutation
genetic drift
natural selection
sexual selection
vicariance
physical splitting of a habitat
sympatric speciation
speciation without geographic separation
1st step to sympatric speciation
individuals coexisting
2nd step to sympatric speciation
mutation occurs that restricts or stops gene flow
3rd step to sympatric speciation
2 populations are isolated in sympatry
the initial gene flow in sympatric speciation is
biological:
-genetic(chromosomal change, aneuploidy resulting in nondisjunction)
-ecological(host shift)
-behavioral( changes in mate preferences)
sympatric
sympatric speciation by autopolyploidy occurs when there are
errors in meiosis
Errors during meiosis causes
extra sets of chromosomes in khanates and offspring(polyploidy)
Prezygotic Isolating Mechanisms
prevent mating and or fertilization
posyzygotic isolating mechanisms
fertilization occurs but hybrid fails to reproduce or live
prezygotic isolating barriers
behavioral, ecological/spatial, temporal, mechanical, gametic
PRZI- behavioral
species use different courtship signals
PRZI- ecological/spatial
species live in same area but use different habitats so they rarely encounter eachother
PRZI- temporal
species breed at different times
PRZI-mechanical
anatomical differences between individuals prevent mating
PRZI-gametic
gametes of two species meet, but do not fuse
POSTZY: hybrid incompatibility/and inavailability
hybrid embryos die
POSTZY: Hybrid sterility
offspring lives but unable to reproduce
what are the favorite that determine how fast a new species can form
*gene-flow
*size of geographic barrier separating two populations
*dispersal
*natural selection
*size of populations
what’s the average time required for speciation
2 to 3 million years
new species more commonly form instantaneously in
plants
Adaptive radiation
fast speciation
describe the two types of adaptive radiations
1) single ancestral species rapidly diversified jnto many descendant species
2) descendant species diverge into genetically different forms that occupy diff habitats
