18. Speciation Flashcards
Define Ernst Mayr’s biological species concept
“…groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.”
Define allopatric speciation and provide an example
Allopatric Speciation – speciation occurs in geographic isolation. Change occurs when populations live in different areas
population ranges are entirely separate thus selective pressures are different in each environment.
trees that are seperated by a ravine or large river.
Define sympatric speciation
Sympatric Speciation – speciation within a population where all individuals are potential partners. Change occurs within a population in the same location
is the genetic divergence of a population from a single parent species inhabiting the same geographic region.
Use the example of polyploidy to explain how reproductive isolation can occur within a population in the same geographic location
Polyploidy: whole extra sets of Chromosomes
Common in plants; and rarely in some animals (grey tree frog, some fish)
Instantly organisms becomes genetically isolated.
Distinguish between allopatric and sympatric speciation
In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation. In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation.
Describe the mechanisms that may lead to genetic divergence of isolated populations
when populations are geographically separated, they will diverge from one another, both in the way they look and genetically. These changes might occur by natural selection or by random chance (i.e., genetic drift), and in both cases result in reproductive isolation.
Name the types of reproductive barriers that must be overcome for speciation to occur and give examples of each
pre-zygotic
-Geograohical, temporal, behavioral isolation
post- zygotic
-Gamete Incompatibility
-Zygote Mortality
Distinguish between prezygotic and postzygotic reproductive barriers
Prezygotic isolation – occurs before fertilisation can occur (no offspring are produced)
Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
Describe five prezygotic reproductive barriers and give an example of each
1. Habitat Isolation- Two species that occupy different habitats within the same area many encounter each other rarely, even though they are not isolated by obvious physical barriers. EX. Garter Snakes one on land, one on water.
2. Temporal Isolation- Species that breed during different times of the day, different seasons or different years cannot mix their gametes. EX. Spotted Skunk.
3. Behavioral Isolation- Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. EX. Blue Footed Boobies.
4. Mechanical Isolation- Mating is attempted, but morphological differences prevent its successful completion. EX. Shells of 2 snails.
5. Gametic Isolation- Sperm of one species may of be able to fertilize the eggs of another species. EX. Sea Urchins.
Explain how hybrid breakdown maintains separate species even if fertilization occurs
It maintains separate species because the hybrid offspring is not able to reproduce (sterile) thus is unable to populate a new species.
Describe the proposed mechanism for the evolution of eukaryotic cells, referring to both the endosymbiotic theory, and infoldings of mesosomes
Describe adaptive radiation
Adaptive radiation is a rapid increase in the number of species with a common ancestor, characterized by great ecological and morphological diversity.
Describe the effects of genetic drift on a population
Genetic drift can result in the loss of rare alleles, and can decrease the size of the gene pool. Genetic drift can also cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.
Explain how genetic drift and natural selection can lead to speciation
when populations are geographically separated, they will diverge from one another, both in the way they look and genetically. These changes might occur by natural selection or by random chance (i.e., genetic drift), and in both cases result in reproductive isolation.
