Lecture 12: Origin of Species Flashcards
What is a species?
a taxonomic rank (the most specific unit)
a biological classification of individuals based on a set of characters
What is speciation?
The creation of a new species with absent or limited gene flow between the populations
What are the mechanisms of change in speciation?
Change in gene flow
Mutation
Genetic drift
Natural Selection
What are the factors that may cause a population to separate and stop exchanging genes?
Geographic/physical barriers (mountains, rivers, deserts, etc)
Courtship behaviours (different mating rituals)
Breeding seasons (summer vs winter)
periods of activity (diurnal vs nocturnal)
What is natural selection?
Organisms with advantageous traits are more likely to survive and reproduce, passing on those traits to future generations
What is genetic drift?
Based on probability, the frequency of different genes in a population can change over time, even when not under selection pressure.
What is mutation?
Random change that happens when DNA is replicated. Most are NOT adaptive. But some create new characters!
What are the three ways we define a species?
Morphological
Biological
Phylogenetic
What is the morphological species concept?
Two populations that have distinguishable phenotypic characteristics are classified as different species
What are the limitations of morphological species concept?
Sorting species by appearance is a very rough way of differentiating groups
Does not take into account modern genetics
Less accurate than using ecological or molecule evidence to determine species
What is the biological species concept?
Defines a species as members of populations that can breed produce fertile offspring
What are some issues with biological species concept?
assumes all reproduce sexually –> asexual reproduction in animals is rare but does occur
We cant test the ability of mating between every pair of species
What is the phylogenetic species concept?
species are groups of individuals that share a unique common ancestor by showing that the individuals share unique traits.
What are the ways in which populations evolve to become new species?
allopatry
paraptry
sympatry
What is allopatric speciation?
geographic isolation/barriers prevent gene flow between populations (ex: isthmus of panama forming and separating fish populations) –> primary speciation mechanism
What is parapatric speciation?
When a new species arises within a continuous population, without geographical isolation, but due to differences in selection pressures across the population’s range
What is the main way for parapatric speciation to occur?
New niches opening and populations move in and evolve different
What is sympatric speciation?
The evolutionary divergence of a new species from a surviving ancestral species, where both populations continue to inhabit the same geographic region
What is the difference between sympatric and parapatric speciation?
Sympatric speciation occurs within the same geographical area, while parapatric speciation happens at the edge of a species’ range, where adjacent populations diverge
What are hybrids?
Organisms that we consider to be different species that interbreed can produce a hybrid –> usually sterile but occasionally fertile
Why don’t we see more hybrids?
Ranges usually do not overlap *
May have different courtship rituals
- due to climate change polar bear and grizzly territory
Why are hybrid plants special?
Plants readily hybridize and hybrid offspring are usually fertile –> even if infertile, they can reproduce asexually to spread
What is despeciation?
When two distinct species become one through hybridization.
