Lecture 9 Flashcards
what was the confusion about the link between micro and macroevolution?
can processes of microevolution lead to macroevolution?
taxonomic (morphological) species concept
based primarily on distinct measurable differences
biological species concept
based on inter-fertility among individuals
why is it so hard to define a species?
concepts vary among groups of organisms and among scientists. There is no universal species concept.
- geographic isolation alone is NOT sufficient
- isolation does NOT have to be absolute (what cutoff?)
Darwin’s definition of a species
groups of organisms that are sufficiently similar in phenotype
Ernst Meyer’s view on distinguishing species
reproductive isolation as key to distinguishing species
what species does the BSC not apply to?
does not apply well for bacteria, asexuals, highly self-fertilising species…or fossils
allopatric speciation
often called geographic speciation
- due to involvement of geographical isolation
- much more common and easier to evolve
stages where reproductive isolation can occur
pre-zygotic:
- finding a compatible mate and mating
- fertilisation
post-zygotic:
- development and growth of zygote (F1)
- adult survival & reproduction
- growth, survival, reproduction of offspring (F2)
pre-zygotic barriers
prevent mating or fertilisation so no zygote is formed:
- geographical, ecological
- temporal, behavioural (mate recognition)
- mechanical (genital stricture compatibility)
- cellular (sperm-egg compatibility)
use Rhagoletis pomonella (Apple Maggot Flies) as an example of pre-zygotic isolation
- host shift after arrival of domesticated applies in 1800s
- differences in timing of host planting fruiting (apple vs hawthorn)
- different timing of fly mating on preferred host plant)
- reduces fly gene flow by 94% in sympatry (same region)
describe pre-zygotic isolation in abalone
binding of sperm lysin protein to egg vitelline envelope receptor (VERL) required for fertilization (molecular lock and key)
Lysin/VERL interaction has coevolved
– Different evolutionary changes in different species
– Causes reproductive isolation due to fertilization
incompatibility
post-zygotic barriers
prevent proper functioning of zygotes
once they are formed
* Caused by combinations of genes with low fitness in the
hybrid
* Arise as an indirect byproduct of evolution acting
separately in different populations (cannot be directly
favored by natural selection)
intrinsic post-zygotic barriers vs extrinsic post-zygotic barriers
Intrinsic Post‐zygotic Barriers:
* Inviability, sterility, or abnormal development of hybrids
Extrinsic Post‐zygotic Barriers:
* Ecological mismatch of hybrid phenotype to environment
example of intrinsic post-zygotic isolation
Mule is a sterile hybrid cross of:
* Male donkey (62 chromosomes)
* Female horse (64 chromosomes)
Hinny is a sterile hybrid of:
* Male horse (64 chromosomes)
* Female donkey (62 chromosomes)
relation between genetic distance and post-zygotic isolation in fruit flies
- The more that fly pairs are genetically differentiated,
the more likely they are to be reproductively isolated
example of extrinsic post-zygotic isolation
aposematic helicons butterflies
Hybrids have aberrant colour patterns
* Higher predation risk
* Lower mating success
local adaptation by different populations can lead to
reproductive isolation and speciation
distinct evolutionary responses happen due to
different selective pressures
is local adaptation necessary for speciation?
Local adaptation not absolutely necessary, but accelerates population divergence and
evolution of RI
describe sticklebacks in marine and freshwater environments
In marine environment:
– Bony armor protects against large fish predation
In freshwater:
– Loss of armor increases growth rate
– Greater winter survival
– Earlier breeding
so, can microevolution lead to macroevolution?
yes - as populations diverge genetically as a result of evolutionary forces
(mutation, natural selection, genetic drift), they become reproductively
isolate
define and describe adaptive radiation
The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
– Originates from a single common ancestor
– The process results in an array of many species
– The species differ in traits allowing exploitation of a range of habitats and resources
Four features commonly identify an adaptive radiation
1) Recent common ancestry from a single species
2) Phenotype‐environment correlation
3) Trait utility
4) Rapid speciation
define ecological opportunity
the absence (or reduction) of competition for resources
two things that cause adaptive radiation
ecological opportunity and high propensity for speciation
how does ecological opportunity come about?
Colonization of competition‐free regions (e.g., islands, lakes, or continents)
Extinction (which can eliminate competitors)
Key innovation (evolution of a trait that provides access to new resources)
high propensity for speciation
RI evolves more readily in some clades than others
define hybridisation
The exchange of genes between species as a result of occasional inter‐species mating
– Sometimes can reverse speciation process to merge two groups into one
how does hybridisation vary across the tree of life?
common in plants and fish, rare in mammals
how can hybridisation result in complex patterns of variation?
Can be evolutionarily significant for speciation, especially by polyploidy
define polyploidy
Describes an organism, tissue, or cell with more than
two complete sets of homologous chromosomes
define and describe allopolyploidy
Allopolyploidy (e.g. AA x AA -> AA AA)
– Arises from duplicated karyotype following
hybridization between species
– Commonest type of polyploidy
define and describe autopolyploidy
Autopolyploidy (e.g. AA -> AA AA)
– Arises from duplicated karyotype within a species
(e.g. non‐disjunction)
describe how allopolyploid hybridisation comes about
- Two species mate and produce an F1 hybrid
offspring (genotype AA*) - F1 hybrid offspring produces unreduced diploid
gametes (genotype AA*) due to meiotic
nondisjunction - Diploid gametes combine to produce tetraploid
F2 offspring - Tetraploid is fertile, but is reproductively
isolated from parental species
evolutionary significance of polyploidy
Polyploids are reproductively isolated from their
diploid parents
– Hence a form of sympatric speciation
* Polyploids exhibit novel phenotypes
– Allows exploitation of new habitats
* Polyploids often show hybrid vigor due to
heterozygosity, particularly in allopolyploids
* Polyploid origin for ~50% of flowering plants
– Many crop plants & invasive species
Evolutionary Significance of Hybridization© BIO120 Fall 2024
draw the speciation continuum
