Speciation is defined as the gradual process by which ___ _______ arise: formation of _____________.
Speciation is defined as the gradual process by which new species arise: formation of biodiversity.
Population divergence is driven by _______ _________ or _____ between environments.
Population divergence is driven by natural selection or drift between environments.
When is speciation considered to have occurred?
Speciation occurs when both species have become so genetically divergent (through the accumulation of fixed differences) that mating between the two populations fails to produce any viable offspring.
What is allopatric speciation?
- Speciation that occurs due to a vicariance event: a physical barrier that divides a geographic range
- Gene flow ceases and the separate populations evolve independently.
Even if the physical barrier is removed, species that have diverged allopatrically may/may not remain distinct (provided enough time has elapsed to allow for significant divergence).
Even if the physical barrier is removed, species that have diverged allopatrically may remain distinct (provided enough time has elapsed to allow for significant divergence).
Speciation occurs when:
Speciation occurs when the two populations are unable to produce viable, fertile offspring.
What is sympatric speciation?
Sympatric speciation occurs when two species diverge from a single ancestor without the presence of a physical barrier. It can only occur when reproduction isolation occurs.
What is polyploidization?
Polyploidization occurs when meiosis fails, leaving a gamete with twice the number of chromosomes (2n instead of n).
Polyploidization results in _____________ _________.
Polyploidization results in reproductive isolation.
Polyploidy can cause ______ __________.
Polyploidy can cause sudden speciation.
Prezygotic mechanisms occur before/after fertilization while postzygotic mechanisms occur before/after fertilization.
Prezygotic mechanisms occur before fertilization while postzygotic mechanisms occur after fertilization.
Prezygotic mechanisms prevent ______ or ____________.
Prezygotic mechanisms prevent mating or fertilization.
Postzygotic mechanisms prevent zygote ____________ or ____________.
Postzygotic mechanisms prevent zygote development or reproduction.
What are the various types of prezygotic barriers?
- habitat isolation
- behavioural isolation
- temporal isolation
- mechanical isolation
- gametic isolation
What causes habitat isolation?
Species live in different habitats and rarely encounter each other.
What causes behavioural isolation?
Different mating rituals/behaviours that do not attract members of other species.
What causes temporal isolation?
A lack of overlap between the reproductive timing of two species.
What causes mechanical isolation?
The inability to mate due to differences in reproductive anatomy.
What are the three types of postzygotic barriers?
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
What characterizes hybrid viability?
- Fertilization can occur and development begins
- Offspring typically die in early development and do not reach maturity.
What characterizes hybrid breakdown?
- Hybrids are fertile and are capable of mating
- Pattern of gene flow is strongly unidirectional, the hybrid is poorly adapted to live certain environments = lower fitness
What characterizes reduced hybrid fertility?
Hybrids are viable but are sterile and incapable of reproduction (evolutionary dead-end).
Morphological species concept: species are ___________ organisms characterized by unique ___________ traits.
Morphological species concept: species are discrete organisms characterized by unique morphological traits.
Biological species concept: species are groups who are actually or potentially _____________ natural populations that are ______________ ________ from other such groups.
Biological species concept: species are groups who are actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
