Speciation Flashcards
Species-
group of individuals capable of interbreeding and reproducing the same type of offspring
Reproductive isolating mechanisms
prevent interbreeding (and gene flow) between two different species even though they may live in the same area
Prezygotic barriers-
reproductive isolating mechanisms that prevent fertilization from taking place
Temporal isolation-
the two species reproduce at different times of the day, season, or year
Habitat isolation-
two related species that live in the same area but live and breed in different habitats
Behavioral (sexual) isolation-
animal species exchange distinctive signals before mating. Another species would not recognize these signals and therefore would not mate
Mechanical isolation
structural differences (incompatible genital organs) prevent successful mating if it is attempted
Gametic isolation-
even if mating does occur
the egg and sperm of different species are incompatible
Postzygotic barriers-
if fertilization does take place between closely related species, this increases likelihood of reproductive failure
Hybrid inviability-
Postzygotic barrier. genes of different species do not interact properly and embryo spontaneously aborts
Hybrid sterility-
Postzygotic barrier. if a hybrid animal does survive, gametes are often abnormal
Hybrid breakdown-
if two hybrid animals survive and mate with each other, their offspring might not be able to reproduce
Speciation
formation of a new species
Allopatric speciation
Population is divided by a geographic barrier so that 2 populations cannot interbreed
Sympatric speciation
formation of new species without the presence of a geographic barrier
Causes of speciation
Polyploidy, Hybridization, Ecology
Polyploidy
possession of more than the normal 2 sets of chromosomes
polyploidy in plants–why does it happen?
Takes place because of nondisjunction of all tetrads during meiosis (or spontaneous doubling of chromosomes before meiosis); therefore diploid organisms produce diploid gametes.
Where does polyploidy often occur?
Occurs often in plants- can be triploid (3n), tetraploid (4n), or higher.
what can polyploid plants reproduce with?
These new species can only reproduce with other members of its group but not with its parents
Hybridization-
two different forms of a species from different areas mate + produce offspring. This mating only occurs (and offspring can only survive) in a small overlap area called a hybrid zone.
hybrid zone
a geographically overlapping area where two different forms of a species can mate and reproduce.
Ecology-
can cause 2 different species to form
Balanced polymorphisms–>speciation
can lead to speciation in which each polymorphism each variety splits off into a different species