What do we Mean by a Species?

Thoughts

1. Gog and Magog, are they different species from humans?
2. Therefore, by definition, humans all belong to the same species.
3. Have Gog and Magog specialized and becomes a different species than humans due to isolation?
4. What about isolated communities like in Siwa, Nubia and other more isolated ones such as in Islands (belonging to India for instance where contact has been attempted yet unsuccessfully).
5. Hybridization in American population, what does it lead to.
6. Inadvertent hybridization of F1 hybrids with other forms of the same species or hybridization among different cultivars of a plant may result in unfavorable results in offspring.
7. What is a cultivar? (A form of ecotype?)
8. Isolated communities of humans, like Siwa and Nubia, have imposed cultural rules of not marrying from outside their communities.
9. Donkeys and horses produce infertile mules when they mate. This fits them perfectly within the definition of being two distinct species (two distinct biospecies).

Hybridization against forces of natural selection

Digest

• Speciation, the forming of distinct species, is a process not a sudden event
• Hybridization and natural selection are two opposing forces
• According to the Mayr-Dobzhansky test, two organisms belong to the same biospecies if they could breed together in nature to produce fertile offspring
• Allopatric speciation vs sympatric speciation
• Ecological speciation is speciation driven by divergent natural selection in distinct subpopulations according to Dolph Schluter (2001)
• Stages of speciation (in the most orthodox view of ecological speciation):
1. Two subpopulations become geographically isolated and natural selection drives genetic adaptation to their local environments
2. Reproductive isolation (pre-zygotic or post-zygotic) builds up between the two subpopulations
3. The two subpopulations re-meet in a phase of secondary contact
4. The hybrids between individuals from the different subpopulations are now of low fitness. Natural selection will then favor any feature in either subpopulation that reinforces reproductive isolation preventing the production of low fitness hybrid offspring. These breeding barriers then cement the distinction between what have now become separate species.
• In northern Europe, the lesser black-backed gull and the herring gull are now two distinct species. They do not hybridize and are therefore true biospecies.  Their 'ancestors' still hybridize freely after spreading east and west from Siberia.

European herring gull (top) and lesser black-backed gull (bottom)

Questions

1. So, what exactly is a species?
2. So, ecotypes are different forms of the same species? Also different forms, like peppered moths (melanic and nonmelanic) belong to the same species?
3. How come species are classified by scientists then reclassified later on in a different way?

Geographic Variation within Species: Ecotypes

Digest

• ecotypes: geographic variation within species
• local adaptation can occur within the same species
• there are experiments that can be done to check if two populations of a species at different environments have undergone local adaptation
• examples of plants that have been locally adapted (populations at high and low altitudes) and plants that have not been locally adapted (dispersed at distances starting from 0.1 to 2000 km apart)
• experiments are done by transplanting members of both populations under investigation at the same environment then measuring to see if differences between them appear
• there can exist a balance between local adaptation and hybridization: "local selection by no means always overrides hybridization"

Ecotype experiment

Questions

• Which of the two are considered to be ecotypes?
• Are the different ones still considered of the same species?

Questions

1. How can experiments be made to test the interaction between hybridization and specialization (divergence)?
2. What are ecotypes?

Specialization within Species

Thoughts

The idea of mobility makes me think about people of Upper Egypt and how their mingling with Egyptians from the Nile Delta area creates a sort of hybridization which is healthy. On the other hand, people who live in Siwa and have been more or less in isolation from the external world for thousands of years have been forced to adapt more to their environment. Also people who live in Aswan in Egypt and are Nubians might have less genetic variation and are more adapted to their environment.

Digest

• The term species will be defined in the next section.
•  An ecotype was coined in 1922 by Göte Turesson for plant populations "to describe genetically determined differences between populations within a species that reflect local matches between the organisms and their environments."
• Only if the forces favoring divergence are strong enough to counteract the mixing and hybridization of individuals from different sites and  there is sufficient heritable variation on which selection can act evolution then forces the characteristics of populations to diverge from each other.
• Immobile organisms become differentiated most notably while mobile organisms are less exposed to the forces of natural selection and therefore do not have to match themselves to a fixed environment as much as immobile organisms have to.

Questions

1. Why is there no continuum of species along a spectrum of variation among organisms?
2. What is the definition of a species?
3. What about variation within the same species according to the environment they live in?