Lecture 17: Species PDF
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Uploaded by AdventuresomeMridangam
University of Maryland, College Park
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Summary
This biology lecture discusses species concepts, reproductive isolation, and different types of speciation. It covers important topics like pre- and postzygotic barriers and how isolation plays a key role.
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Species No de nition that applies in all cases Biological Species constant - BSC = Limitations â—‹ Most used species concept â—‹ All members have potential to interbreed under natural conditions and produce viable, fertile offspring â—‹ Dif cult to apply â—† Not clear who has the potential to interbreed â—† N...
Species No de nition that applies in all cases Biological Species constant - BSC = Limitations ○ Most used species concept ○ All members have potential to interbreed under natural conditions and produce viable, fertile offspring ○ Dif cult to apply ◆ Not clear who has the potential to interbreed ◆ Not apply to asexual organisms or fossils ○ Species Complex ◆ Boundaries between species are unclear ○ Emphasizes reproductive isolation Morphological species concept ○ practical substitute, structural features Phylogenetic species concept ○ Smallest group on tree (lineage) Ecological ○ Terms of niche Separates Species Prezygotic barriers ○ Prevent formation of zygote or fertilized egg Postzygotic barriers ○ Prevent development of viable or fertile offspring Prezygotic barriers 1. Habitat isolation ○ Potential to hybridize, but prefer different habitat so they never mate ○ Maggot y 2. Temporal isolation ○ potential to interbreed, but are ready at different times fl fi fi ○ Timing! 3. Behavioral Isolation ○ Don’t mate because of differences in courtship or other behaviors ○ Bird songs ○ Fire y blink patterns 4.Mechanical Isolation ○ Lock and Key 5. Gametic Isolation ○ Gametes dont recognize due to different receptors Postzygotic Barriers 1. Reduced Hybrid Viability ○ Hybrid offspring dont develop ○ Don’t survive as well 2. Hybrid Infertility ○ Sterile/ weak offspring 3. Hybrid Breakdown ○ Low hybrid adult viability ○ 1st gen hybrids fertile, but 2nd gen hybrids are sterile/weak Differences arise 1. Allopatric speciation ○ Physical barrier divides population (canyon) 2. Sympatric Speciation ○ No physical barrier separating diverging populations Allopatric Speciation Adaptive Radiation ○ evolution of many diverse adapted species from common ancestor ○ Speciation on islands Populations differences due to ○ founder effect through genetic drift ○ Natural selection under different conditions, physical/behavioral differences that inhibit breeding even if contact s restored fl 1. Re-contact may reinforce differences acquired in isolation ○ Reinforcement = Hybrid offspring have lower survival, selection favors assortative mating ○ Hybrids gradually cease to form 2. Re-contact may overwhelm differences acquired in isolation ○ Fusion ◆ Large areas of hybridization & highly t hybrids may fuse the two species back into one = Hybrid vigor ◆ Hybrid Vigor = Hybrid has higher tness than parents Sympatric Speciation 1. Autopolyploidy = same species ○ polyploidy can lead to new species ○ Duplicate chromosome # reproductively isolates offspring from parent population ○ Common in plants (80%) ○ Self-fertilize 2. Allopolyploidy ○ Hybridization and errors in meiosis lead to polyploidy offspring with chromosomes from 2 different species ○ Key force in plant speciation = new species fi fi ◆ Hybrid vigor
