PATTERNS OF EVOLUTION 2

PATTERNS OF EVOLUTION 2

1. CONVERGENT EVOLUTION

   • superficially similar features formed by different developmental pathways
     • eg eyes of vertebrates & squids have lens & retina but their many profound differences indicate independent evolution
   • MIMICRY
     • features of one species specifically evolved to resemble those of another species
       • example of convergent evolution
         • eg Batesian & Mullerian mimicry - defences against predators by resemblance to unpalatable or dangerous animal

2. PARALLEL EVOLUTION

   • parallelism - involves similar developmental modifications that evolved independently, often in closely related organisms
     • eg differences in feeding parts in crustaceans

3. evolutionary reversals

   • return from an 'advanced' or derived character state to more 'primitive' or ancestral state
     • eg winged insects evolved from wingless ancestors but many lineages have lost wings in subsequent evolution
   • DOLLO'S LAW
     • once complex characteristics lost they're unlikely to be regained
       • however, evidence of regaining of acquatic larval stage in dusky salamanders potentially disprove this

4. homoplasious features often adaptations by different lineages to similar environmental conditions

   • eg long thin beak evolved independently in at least 6 different lineages of nectar-feeding birds

5. MOSAIC EVOLUTION

   • evolution of different characters at different rates within a lineage
     • incorrect to consider 1 living species more 'advanced' than another
   • one of most important principles of evolution
     • species evolve piecemeal rather than as a whole
       • important exceptions: features that function together may evolve in concert

6. GRADUALISM

   • evolution by small successive changes

7. SALTATION

   • evolutionary jump usually of large magnitude

8. homologous characters may differ greatly among taxa because form evolved as function changed

   • eg sting of wasp or bee modification of ovipositor used by other members of species to insert eggs into plant hosts