What are the factors which lead to speciation? Describe them. (5marks)
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Based on the biological species concept, the key property of a species is that it is a reproductively isolated group of organisms.
The various mechanisms responsible for the creation of new reproductive barriers between groups of organisms, which must happen in order for speciation to occur, are called reproductive isolating mechanisms.
Barriers to reproduction come in two main categories.
1. Prezygotic Barriers
Barriers that either prevent mating or else hinder fertilization if mating does occur.
2. Postzygotic Barriers
Barriers that prevent a hybrid zygote from developing into a viable, fertile adult.
Prezygotic barriers include
1. Temporal Isolation
Breeding of individuals in the two species occurs at different times (different times of the day, different seasons, etc.)
2. Behavioral Isolation
Courtship rituals and other species-specific behaviors allow individuals to recognize as mates those of their own species.
3. Habitat Isolation
Individuals of two species living in the same area occupy different habitats, so they rarely encounter one another.
4. Mechanical Isolation
Mating is attempted but morphological differences between the two species prevents its successful completion.
5. Gametic Isolation
Sperm of one species cannot fertilize the eggs of another species.
Postzygotic barriers include
1. Hybrid Inviability
Hybrid offspring are not viable: their development or ability to survive is impaired and they do not reach reproductive age.
2. Hybrid Sterility
Hybrid offspring are viable and reach reproductive age, but they cannot reproduce.
3. Hybrid Breakdown
Hybrid offspring are viable and can reproduce, but their own offspring are not viable or are sterile.
The various mechanisms responsible for the creation of new reproductive barriers between groups of organisms, which must happen in order for speciation to occur, are called reproductive isolating mechanisms.
Barriers to reproduction come in two main categories.
1. Prezygotic Barriers
Barriers that either prevent mating or else hinder fertilization if mating does occur.
2. Postzygotic Barriers
Barriers that prevent a hybrid zygote from developing into a viable, fertile adult.
Prezygotic barriers include
1. Temporal Isolation
Breeding of individuals in the two species occurs at different times (different times of the day, different seasons, etc.)
2. Behavioral Isolation
Courtship rituals and other species-specific behaviors allow individuals to recognize as mates those of their own species.
3. Habitat Isolation
Individuals of two species living in the same area occupy different habitats, so they rarely encounter one another.
4. Mechanical Isolation
Mating is attempted but morphological differences between the two species prevents its successful completion.
5. Gametic Isolation
Sperm of one species cannot fertilize the eggs of another species.
Postzygotic barriers include
1. Hybrid Inviability
Hybrid offspring are not viable: their development or ability to survive is impaired and they do not reach reproductive age.
2. Hybrid Sterility
Hybrid offspring are viable and reach reproductive age, but they cannot reproduce.
3. Hybrid Breakdown
Hybrid offspring are viable and can reproduce, but their own offspring are not viable or are sterile.
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4
Speciation is the production of new species by existing ones.
Natural selection- during the life cycle of any organism many genetic changes occur, some of them are not sufficient enough to create variations but some are capable. These variations and changes may be helpful for organism or not, if by any means they support the organism and make it better adapted in the nature they are passed on to the next generations, that is, they are selected naturaly.
Geographical isolation- if by any geographical barrier like river, mountain or any natural catastrophes geographical barrier are created between the groups of species making them different populations of the species so that the gene flow between the different populations is prevented and different populations start evolving as separate entities.
Genetic drift- drastic change in the frequency of particular genes and the prevention of gene flow between the different populations is also taken into account. Here mutations also plays an important role to create sudden shift in gene frequencies.
Reproductive isolation- all the above forces ultimately creates enough variations in the organisms that these organisms of different populations becomes incompatible for reproduction resulting in the complete blockage of the species.
Natural selection- during the life cycle of any organism many genetic changes occur, some of them are not sufficient enough to create variations but some are capable. These variations and changes may be helpful for organism or not, if by any means they support the organism and make it better adapted in the nature they are passed on to the next generations, that is, they are selected naturaly.
Geographical isolation- if by any geographical barrier like river, mountain or any natural catastrophes geographical barrier are created between the groups of species making them different populations of the species so that the gene flow between the different populations is prevented and different populations start evolving as separate entities.
Genetic drift- drastic change in the frequency of particular genes and the prevention of gene flow between the different populations is also taken into account. Here mutations also plays an important role to create sudden shift in gene frequencies.
Reproductive isolation- all the above forces ultimately creates enough variations in the organisms that these organisms of different populations becomes incompatible for reproduction resulting in the complete blockage of the species.
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