Speciation Flashcards
(34 cards)
Define morphological convergence.
Species evolve to look the same but are only distantly related.
Morphological convergence creates cryptic variation. Define cryptic variation.
That which is undetectable in the phenotype and only evident from genetic studies.
Both extinct and extant species need to be taken into account when assessing diversity. True or false?
True.
Define speciation.
Whereby populations become reproductively isolated from each other, gene flow is stopped. These populations then diverge and accumulate differences, forming a new species.
What is the species continuum?
A scale ranging from high to low species diversity.
There are 3 different concepts of what a species is. What are they?
- Morphological concept
- Phylogenetic concept
3, Biological concept
Explain the morphological concept of a species.
Species are groups of organisms that look similar.
Explain the phylogenetic concept of a species.
Species are the smallest sets of organisms sharing a common ancestor.
Explain the biological concept of a species.
Species are groups of interbreeding organisms that are reproductively isolated from other groups.
What is an advantage to the biological concept of a species?
It does not rely on morphology which can be misleading.
What are disadvantages to the biological concept of a species? List 4.
- It cannot be applied to asexual species
- Does not account for temporary geographical boundaries
- It cannot be applied to the fossil record
- It does not account for hybridisation
Which of the 3 concepts of a species is the most widely accepted?
The biological concept.
Species can become reproductively isolated at 2 major stages. What are they?
- Pre-zygotic: before mating
2, Post-zygotic: after mating
Pre-zygotic isolation can occur for geographic reasons. Give an example of this.
If two organisms live either side of a physical barrier, they will never meet and won’t mate.
Pre-zygotic isolation can occur for a) behavioural or b) mechanistic reasons reasons. Give an example of each.
a) Spawning times are different, e.g. in corals, so gametes never meet
b) Genitalia are not compatible
Post-zygotic isolation can occur for genetic reasons. Give an example.
Chromosome rearrangements mean that chromosomes are unable to recombine at meiosis and hybrids are unviable.
What does the Dobzhansky-Muller model show?
Explains that when two species diverge from a common ancestor, they acquire and fix different mutations. This means the chromosomes of both species are unable to recombine at meiosis.
What is Haldane’s rule?
The heterogametic sex in F1 hybrids, the progeny of 2 different species, is often sterile.
Explain how Haldane’s rule works.
The maladapted traits of sex chromosomes are not masked in the homozygous state, thus mutations accumulate that often lead to infertility.
Post-zygotic isolation can occur for ecological reasons. Give an example.
Hybrids are less fit and thus are outcompeted.
Define allopatric speciation.
Where a physical boundary forms between populations, causing them to diverge.
Give an example of allopatric speciation.
The Isthmus of Panama: the Caribbean and Pacific plates collided and volcanoes created the land mass of Costa Rica and Panama. Speciation of marine life occurred in the Caribbean sea and Pacific Ocean, an example species being the Alpheus snapping shrimp.
Define peripatric speciation.
The formation of islands.
Why are populations split by allo or peripatric speciation susceptible to genetic drift?
They are much smaller.
