BIOL1130 Lecture Notes - Lecture 12: Sympatric Speciation, Dna Barcoding, Polyploid
7 Jun 2018
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Speciation
• What are species?
o Species represent a fundamental unit in biology
o Generally accepted as real
• Ways of defining species
o Morphological taxonomic species concept – members of a
species are morphologically alike
▪ Used widely, but appearances can often be deceiving, e.g.
caterpillar and adult of the monarch butterfly or sexual
dimorphism of the common pheasant
o Biological species concept – groups of interbreeding individuals
that are reproductively isolated from other such groups
▪ Does not consider asexually-reproducing species or fossils
▪ Morphological diversity and reproductive isolation do not
go hand-in-hand
▪ Applies to populations not individuals
o Recognition species concept – species are groups sharing a
common mate recognition system
o Evolutionary species concept – a species is a lineage of
populations delineated by common ancestry and able to remain
separate from other species
o Ecological species concept – defines a species as a set of
individuals with shared ecological attributes
• Species concepts
o All models emphasize the restriction of gene flow between
populations so that divergence between them can occur
o Reproductive isolation is important from an evolutionary
perspective because it allows different species to evolve in their
own ways
• Reproductive isolation
o Pre-zygotic barriers (before fertilization)
▪ Ecological – species occupy the same geographic area but
do not hybridise because they occupy separate habitats
▪ Temporal – differences between species in the timing of
reproduction
▪ Behavioral – differences between species in courtship
behaviours
▪ Mechanical – physical restrictions to mating
▪ Gametic – gametes of different species do not interact
o Post-zygotic barriers (after fertilization)
▪ Zygotes dies early during embryogenesis
▪ F1 hybrid survive but are sterile
▪ Backcross or F2 hybrids are inviable or sterile
o How does it arise?
▪ Post-zygotic isolation cannot be the direct results of natural
selection because it is impossible to select for inviable
offspring
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