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Lecture 19

BGYB51H3 Lecture 19 Notes Nov 12

Biological Sciences
Course Code
Maydianne Andrade

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BGYB51H3 Lecture 18/19 Notes
-host race is a subgroup that specializes on a particular host or have habitat requirements
-the specialization evolved due to selection
-variation in emergence time in hawthorn flies, which can lead to speciation
-disruptive selection occurs in apple and hawthorn flies in which hawthorns that emerge
between both peak periods do less well than other hawthorns
-flies show strong preference for one fruit type
-incipient species are populations that have diverged but are not isolated, which indicates
there is some gene flow
-a difference in colour can be caused by a single nucleotide substitution in a gene regulating
-if one population occupies a niche, selection leads to adaptation to that niche and new
environment, causing divergence
-sexual selection concentrates on the phenotypic variation among individuals in their ability
to obtain mates
-sexual selection affects mating success and gene flow and can result in divergence of species
-reproductive isolation can lead to divergent traits that
x prevent interbreeding
x interbreeding leads to poor hybrids
-female choice or incompatible genitalia can prevent interbreeding
-hybrid fitness determines if speciation is maintained
-poor hybrid fitness maintains speciation, equal hybrid fitness renews gene flow and
homogenization, higher hybrid fitness causes gene flow and potential loss of parent species
-reinforcement may cause pre-zygotic isolating mechanisms such as
x mate choice
x incompatible genitalia
x timing of mating
-speciation requires that there is a loss of gene flow initially
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