sp2 - Reproductive Isolation Flashcards
what does reproductive isolation do?
- reduces gene flow/ or prevents/reduces interbreeding btwn sets of populations
placing limits on gene flow, facilitates adaptation
- maintains the separation of species, even if initial barrier gone
- defines the reproductive community, within which interbreeding brings about species cohesion
Are things same species if can produce viable offspring in captivity?
Not necessarily!!
Reproductive isolation
reduction of gene exchange btwn populations due to a range of isolating barriers
Isolating barrier
a specific mechanism acting at a specific stage to reduce or prevent gene flow
Interbreeding
aka interspecific mating or hybridization
compare success to success within species
Examples of Isolating Barriers
mating season diffs
geographical separation
mating behaviour
incompatible anatomy
different chromosome numbers
inviable zygotes
different adaptations
barrier loci
hybrid sterility
different ploidy
gametic incompatible
Different Times Isolating Barriers could occur
Pre-mating barriers
Post-mating/prezygotic
Postzygotic barriers
Pre-mating barriers
reduce likelihood that individuals exchange gametes
Post-mating barriers
aka prezygotic barriers
reduce the likelihood that individuals which mate produce a zygote
Postzygotic barriers
reduce the likelihood that zygotes will live or reproduce
Geographic isolatiom
pre-mating isolating barrier
seemingly permanent
Why does the order of action of isolating barriers matter?
The order affects which barriers are most important to overall reproductive isolation
The order affects the amount of resource that is squandered when individuals of different species interact
behaviour isolation
pre-mating isolating barrier
even if overlapping in range, don’t recognize mating behaviours
mechanical isolation
pre-mating isolating barrier
genitalia of diff species may not fit
*** female and male structures coevolved
failure of fertilization
post-mating/prezygotic barriers
sperm may not have correct protein to fertilize eggs
ex. sea urchins that differ in amino acid seq. of sperm-egg recognition protein (bindin) cannot interbreed
important note about measurement of postzygotic isolation
relative disadvantage. of hybrid relative to non-hybrid
hybrid viability
relative likelihood hybrids will survive
hybrid sterility
ability of hybrids to produce viable gametes and offspring
intrinsic barriers
act on offspring independantly of environment
extrinsic barriers
vary in expression depending on environment
intrinsic hybrid inviability
hybrids more likely die at early lifestages regardless of environment
intrinsic hybrid sterility
viable but reduced or no fertility indep. of environment
extrinsic hybrid inviability
more likely to die early, but dependent on environment. do worse in environment of one or both parents, because food sources they specialize in are rare or absent
extrinsic hybrid sterility
viable but reduced fertility bc of environmental factors
ex prod normal gametes but flower reduced in certain environments
Range of RI
from 0 to 1
HOWEVER never truly 1, could be 0.999999999
Pollinator Isolation
Not ONE trait, influenced by many floral traits
pollinators not selecting hybrids = extrinsic hybrid sterility
Importance of early isolating barriers
prevent the loss of reproductive effort
How to determine Total Isolation (IT)
(1 - IT) = (1 - I1)*(1-I2)…(1 - In)
I1, I2 etc = amount isolated by a barrier, ex if only 20% of individuals can get past geographic barrier I1 = 0.8
what is (1-IT)
amount of gene flow possible given the action of a set of isolating barriers
contribution of barrier to total reproductive isolation
overall effect of action barrier not in relation to others * acting on percent of remaining pop
ex. if 20%, but only 64% of population remaining
contribution - 0.2 * 0.64
