speciation - 8.2 Flashcards
what is a species
- all members of a population that can interbreed under natural conditions
- individuals of different species are reproductively isolated
methods of speciation definition
for a new species to form, individuals from the original species must evolve to become reproductively isolated from the remainder of the population (establishing a new interbreeding population)
what are reproductive isolating mechanisms
factors that prevent 2 populations from interbreeding
2 reproductive isolating mechanisms
prezygotic
postzygotic
prezygotic definition
prevents species from mating and prevents fertilization (no zygote is created)
postzygotic definition
these mechanisms DO NOT prevent mating (sperm may fertilize the egg and create a zygote), but maturation and reproduction in offspring are prevented
5 examples of prezygotic mechanisms (isolation)
behavioural isolation
temporal isolation
ecological isolation
mechanical isolation
gametic isolation
behavioural isolation
different courtship and mating rituals
eg. birds of paradise
temporal isolation
mating at different times of year
eg. american toad mates in early summer while the fowler’s toad mates in late summer
ecological isolation
occupy different habitats
eg. one cricket species lives in sandy soils while the other lives in loamy/grassy soils
mechanical isolation
differences in morphology = incompatibility
eg. dragonfly claspers
gametic isolation
sperm cannot fertilize the egg of another species
eg. red and purple sea urchins are chemically incompatible :(
3 postzygotic mechanisms
zygotic mortality
hybrid inviability
hybrid infertility
zygotic mortality
zygote is unable to develop
eg. sheep x goat
can mate but but fertilized egg doesn’t continue to divide (unable to create another being)
hybrid inviability
offspring develops but dies before birth or cannot survive
eg. leoger (lion x tiger)
very rare, usually dies before birth
hybrid infertility
healthy but sterile
eg. mule, infertile
4 types of speciation
allopatric speciation
sympatric speciation
peripatric speciation
parapatric speciation
allopatric speciation definition
the formation of a new species (as a result of evolutionary changes) following geographical isolation
allopatric speciation; explain
genetic information is no longer shared in allopatric speciation, so mutations aren’t shared either
- natural selection causes the species to become less and less alike
allopatric speciation examples
mountain formation
continental drift
migrating to a remote island
sympatric speciation definition
the evolution of populations within the same geographical area into separate species
sympatric speciation; explain
individuals WITHIN a population become isolated from other members
polyploidy
polyploidy
a mutation which causes the number of chromosomes to double (results in sympatric speciation)
sympatric speciation example
hawthorn flies and apple maggot flies, apple maggot flies evolved when apple trees were introduced in an area with only Hawthorn trees
(some stayed with the Hawthorn trees, some went to the apple trees)
peripatric speciation
a small population at the PERIPHERY of a large population breaks off and becomes an isolated niche
parapatric speciation
a small population enters a niche which is not isolated and adjacent to the population(s)
