Lecture 17: Species PDF

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 ◆ 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