Ch24 - Origin of Species
Identification of species
molecular features
ecological factors
evolutionary relationships
morphological traits
ability to interbreed
physical characteristics
drawbacks
how many traits to consider?
some traits are continuously varied
what degree of dissimilarity to use?
members of the same species can look very different, whereas members of different species can look very similar
reproductive isolation prevents interbreeding of species
drawbacks
difficult to determine in nature
some organisms can interbreed but do not
does not apply to asexual or extinct species
similarities to look for:
- DNA sequences inside genes
- gene order
- chromosome structure
- chromosome number
may be difficult to draw a line when separating species
factors related to a species habitat can be used to differentiate between one species and the other
can be unreliable because some bacterial strains (for example) exhibit similar optimum conditions when it comes to habitat
reproductive isolation mechanism
interspecies hybrid
when two different species produce offspring
pre-zygotic barriers
post-zygotic barriers
habitat isolation
temporal isolation
behavioral isolation
gametic isolation
mechanical isolation
size or compatibility of genitalia
mate choice depends on behavior (e.g., song choice)
geographic barrier prevents interbreeding
reproduction at different times of the year
gametes unable to unite successfully
hybrid inviability
hybrid sterility
hybrid breakdown
zygote formed, cannot survive and progress
interspecies hybrid is viable but sterile and cannot reproduce
viable & fertile but inherited genetic abnormalities
speciation
what is it?
two types
mechanisms