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BSC 196 (51)
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Lecture 10

BSC 196 Lecture 10: lecture 10

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Biological Sciences
BSC 196

when hybrids are less fit, selection should favor barriers to reproduction barriers should be stronger for sympatric than allopatric species For example, in species of flycatchers, males are more similar in allopatric populations than sympatric populations If hybrids are as fit as parents, there can be substantial gene flow between species selection may favor hybrids in novel environment e.g., pollution in Lake Victoria has resulted in turbid (i.e., murky) water this has reduced the ability of female cichlids to distinguish males of different species Reinforcement = strengthening reproductive barriers to gene flow different mechanisms promote reinforcement: reproductive isolating mechanisms Reproductive Isolating Mechanism = characteristic that prevents gene exchange 1) Prezygotic - prevent mating or fertilization efficient 2) Postzygotic - prevent hybrid from reproducing inefficient Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown How long does it take new species to form? Speciation can occur rapidly or slowly and can result from changes in few or many genes Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 mill
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