speciation when does an evolutionary branch become a new species?
TRANSCRIPT
SPECIATIONWhen does an evolutionary branch become a new species?
WHAT IS A SPECIES? Historically, scientists have used morphology to classify organisms eg. a monkey and tiger look different so they are different species
BUT a Chihuahua and German Shepherd look different and are both of the same species (Canus lupus)
WHAT IS A SPECIES?
Species – (according to Oxford dictionary) a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding to produce reproductively
viable offspring.*
SPECIATION
The process by which members of the same species split into 2 (or more) new species is called SPECIATION
It’s hard to tell when a new species has evolved because…
a) it’s a long, gradual process
b) not all evolutionary changes result ina new species
SPECIATION For speciation to occur, members of an ancestral species must become isolated from each other
This isolation prevents the flow of genes between gene pools
Selective forces may effect each gene pool differently
TYPES OF SPECIATION
ALLOPATRIC SPECIATION
Speciation that results when a population is separated by a physical barrier (this is the most common form of speciation)
The formation of Panama 3.5 mya by tectonic shifts caused pockets of isolation of the predominant lobster species at the time
These small gene pools gave rise to new species of South American lobsters
Nene geese evolved when, 5mya, Canadian geese migrated to the Hawaiian islands and never returned
Nene geese have adaptations for surviving on volcanic terrain
PERIPATRIC SPECIATION
Speciation that results when a small group of members inhabiting a peripheral region of the range become reproductively isolated (very similar to allopatric)
Polar bears evolved due to glaciation that cut-off a small group of brown bears from the main population
Members of the community acquired traits such aswhite fur, extreme temperature tolerance and theability to swim long distances
PARAPATRIC SPECIATION
Speciation that results from partial separation of 2 diverging species
Individuals of each developing species may come into contact occasionally but selection for behaviours/mechanisms prevent interbreeding
The Bullock’s and Baltimore orioles evolved from a common species that spanned the USA
Over time western and eastern orioles came to rely on different songs to call mates and this ledto speciation
SYMPATRIC SPECIATION
Speciation in which a new species evolves while living in the same location as the original one
>200 species of Cichlids in East Africa arose from a shared common ancestor that dwelt in the same lake system 113mya
Behavioural preferences such as mating depth, colouration, etc.within the same population led to speciation
REPRODUCTIVE ISOLATION
The inability of 2 species to mate anymore is called REPRODUCTIVE ISOLATION (sometimes called ‘pre-zygotic isolation’)
There are 5 types of reproductive isolation:
1. Spatial isolation Species can’t mate because they live in different areas
REPRODUCTIVE ISOLATION
The inability of 2 species to mate anymore is called REPRODUCTIVE ISOLATION (sometimes called ‘pre-zygotic isolation’)
There are 5 types of reproductive isolation:
2. Temporal isolation Species can’t mate because they look for mates at different times of
year
REPRODUCTIVE ISOLATION
The inability of 2 species to mate anymore is called REPRODUCTIVE ISOLATION (sometimes called ‘pre-zygotic isolation’)
There are 5 types of reproductive isolation:
3. Mechanical isolation Species can’t mate because their reproductive organs are
incompatible eg. Bush babies
REPRODUCTIVE ISOLATION
The inability of 2 species to mate anymore is called REPRODUCTIVE ISOLATION (sometimes called ‘pre-zygotic isolation’)
There are 5 types of reproductive isolation:
4. Behavioural isolation Species can’t mate because their mating rituals are too different
REPRODUCTIVE ISOLATION
The inability of 2 species to mate anymore is called REPRODUCTIVE ISOLATION (sometimes called ‘pre-zygotic isolation’)
There are 5 types of reproductive isolation:
5. Gametic isolation Species can’t mate because their gametes can’t fuse