BIOL 1082 Lecture Notes - Lecture 4: Allele Frequency, Natural Selection, Polyploid
Ch. 22 LO
Speciation Reading: Concepts 22.1 & 22.3-22.4
1. Compare and contrast the different species concepts used by biologists, describing the
strengths and weaknesses of each.
• Biological Species Concept: a group of populations whose members have the potential
to interbreed in nature and produce citable offspring
o Limitations: no way to evaluate barriers in fossils, does not apply to asexually
• Morphological species concept: distinguishes a species by body shape and other
structural features
o Limitation: relies on subjective material that is debatable
• Ecological species concepts: defines a species in terms of its ecological niche
o Limitation: still interbreed
• Phylogenetic species concept: smallest group of individuals that share a common
ancestor.
o Limitation: determining the degree of different required to indicate separate
species
2. Describe the various kinds of pre- and post-zygotic barriers to gene flow between populations,
and their relationship to the biological species concept.
• Pre-Zygotic Barriers
o The barriers between two unrelated species to reproduced viable offspring.
These barriers validate that the biological species concept can be used as a
means to prove speciation.
o Pre-zygotic barriers happen before the zygote even develops. It blocks
fertilization.
o Habitat Isolation: when two species may not even encounter each other because
they live in different habitats of a population.
o Temporal isolation: species that breed during different times of the day,
different seasons or different years
o Behavioral isolation: If two species have different courtship rituals then they will
not reproduce. They enable mate recognition.
o Mechanical isolation: mating is attempted but morphological (body)
differences prevent its successful completion.
• Post- Zygotic Barriers
o Post-zygotic barriers happen when a sperm cell overcome the pre-zygotic
barriers & when two different species successfully fertilize a zygote
o Reduced Hybrid Viability: the genes of a different parent may interact in ways
that impair the hybrid's development or survival in it's environment.
o Reduce Hybrid Fertility: Even if the hybrid offspring lives, they may still be
sterile.
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Document Summary
These barriers validate that the biological species concept can be used as a means to prove speciation: pre-zygotic barriers happen before the zygote even develops. Once this happens or any other geographic separation, the two population may diverge so does the gene pool. Natural selection, mutations and allele frequencies may influence & occur within these species for so long that the two populations that were once one may become reproductive isolated: ex: the populations of the mosquitofish. If reinforcement is occurring then hybrids gradually cease to be formed: barriers to reproduction between species should be stronger for sympatric populations than for allopatric populations. Usually females can differentiate the males of their species with another. This is why it"s stronger: explain the possible outcomes when populations that are partially isolated become sympatric, fusion occurs: If the reproductive barriers are weak in a population, gene flow can happen between the 2 species and thus creating offspring.
