CH. 7 (Origin of Species) Flashcards
What did Darwin not explain?
How the continuous process of evolution produced discrete groups—speciation
Problems with the morphological species concept
- Some species are sexually dimorphic (would we classify males and females as separate species? no)
- Sometimes members of the same species look different (humans)
cryptic species
Species that are morphologically identical but still different from each other ex. Drosophila and Anopheles Gambiae (mosquitoes)
reproductively isolated
distinct gene pools that do not intermingle
Ernst Mayr and Theodosius Dobzhansky
first to realize differences in gene pool meant different species.
biological species concept
a species is a group of interbreeding natural populations that are reproductively isolated from other such groups (genetic difference that arose by their behaviour, appearance, physiology)
What organisms do not fit under BSC
There has to be potential for gene flow thus asexually reproducing organisms (bacteria, funghi) do not fit criteria. We also can’t apply this theory to fossil remains.
pre-mating barriers
different mating displays, pheromones, habitats, different pollinators (flowers)`
Post-mating barriers
pollen doesn’t germinate, fetuses die before birth, hybrids are sterile if they do survive
sister species
species that are each others closest relatives—often separated in nature by geographical barriers (close to each other ex. flowering species of plants found in east Asia and eastern USA)
geographic barriers
different evolutionary forces causing natural selection to work in different ways leading to different species
if genomes are differentiated enough…
the hybrid will die
Theory of Geographic Speciation
evolution of genetic isolation first requires that they be geographically isolated. Species cannot possibly split if they retain the opportunity to interbreed.
Where are “radiations” often found and why?
Archipelagos. As species move from island to island they become isolated (Anolis lizard, finches of Galapagos)
What characterizes reproductive isolation?
mating discrimination between pairs, sterility of hybrid, inviability of hybrid
sympatric speciation
speciation without geographic isolation
Why is it hard to find evidence for sympatric speciation?
Even if you find two related species in the same area how would you know they arose in the same area rather than just moving together?
allopolyploid speciation
hybridization of 2 different species that live in the same area (most common with plants). Usually requires that the two species have different numbers of types of chromosomes. The hybrid will be sterile because it wont have the proper pairing of chromosomes when it attempts to make pollen or ovules.
- HOWEVER double chromosome allopolyploids can reproduce because they have double the alleles and can pair
autopolyploidy
When chromosomes of single species are doubled. Doesn’t require hybridization. They can mate with each other but not with parent species (immediate speciation)
What does polyploid speciation necessitate?
The rare event of formation and union of sperm and eggs with abnormally high numbers of chromosomes. This must happen in two successive generations.
What proportion of species of flowering plants were formed via polyploidy?
Quarter of all flowering species. Polyploid speciation is found in nearly every group of plant except trees.
Example of animal polyploid
Red viscacha rat of Argentina (animal polyploids are very rare—mostly fish, insects, worms)
Polyploid speciation
changes in the chromosome numbers rather than the genes themselves meaning speciation occurs much faster. Genomes are inherently incompatible.
How can we check to see if wild species have hybridized?
artificially resynthesize the wild hybrid (will often have same phenotype)
