NATURAL SELECTION, ADAPTATION AND MICROEVOLUTION

NATURAL SELECTION, ADAPTATION AND MICROEVOLUTION

1. 1) STUDYING ADAPTATION

   • why do organisms live the way they do?
   • how has past evo shaped a trait or an orgnsm?
   • why can't nat sel. fashion perfect orgnsm?
     • correlated traits mutation allele lack of variation, can't change

2. 5) LIFE HISTORY EVO BY NAT SEL

   • LH traits can evolve rapidly
   • The factors driving evo can be tested
   • Translocation exp- guppy
     • guppy popn in low and high predation area
       • *selection can act on multiple co-adapted traits
       • *the adaptiveness of traits & the drivers of evo can be tested
       • * adapted traits are subjected to ongoing natural selection as environmental conditions change & continue to evolve
       • Microevolution can lead to appreciable change that occurs rapidly on ecological timescales

3. 2) ADAPTIVE TRADE-OFFS

   • if fitness is abt survival & reproduction? why can't they continuously produce high quality offspring and live forever?
     • some orgnsm close to perfect, but only SOME of the traits (e.g.thrips egg mite, brown kiwi)
   • a) time & E an orgnsm can harvest is finite
   • b) biological processes take time
   • c) fundamental trade-offs in the set of traits.
   • d) increase fitness in one trait can reduce a fitness of another trait

4. 3) ADAPTATION & THE EVOLUTIONARY STRATEGIES

   • 1) An evolutionary strategy
     • a set of co-adapted traits which allow an organism to survive & adapt to their ecological niche
   • 2) Life history strategy (LHS)
     • an orgnsm's investment in growth, maturation, reproduction, survival

5. 4) LIFE HISTORY STRATEGIES

   • LH traits are associated w fitness and are polygenic traits
   • Key qs in LH analysis
     • Why live as long as they do?
     • Why some reproduce once and others have many reproductive attempts during their lifespan?
     • Why vary in the number of offspring they produce?
     • Why vary in the time they take to become sexually mature?
   • 1) Trade-offs: Fecundity vs Lifespan
     • e.g. rotifiers
       • - produced lots of young, early in their life – had a shorter life
       • - produced less young per day, lived longer and produced more young over their lifespan
     • * High reproduction on one day decreases chances of survival to the next day
     • * Reproduction is deleterious to future survival
   • Trade-offs: Current vs future reproduction
     • e.g. Meadow grass
       • the number of inflorescences per plant - produced in the 1st year or 2nd yr
         • produce more in 1st yr, produce less in its 2nd yr
     • e.g. collared flycatchers Ficedula albicollis
       • some produce young in first yr, smaller clutch size, but their lifetime reproductive succesful is higher
       • increase clutch size in the 1st year, the clutch size reduces with age
       • young that was produced in bigger clutch size will have less clutch size itself
   • Predictable & unpredictable Env
     • rm = reproductive rate

6. 6) MICROEVO AS A SOURCE OF LARGE SCALE CHANGE

   • * genetic drift causes random changes in allele/traits- popn can drift in diff directions and diverge.
   • * selection leads to adaptation to local conditions, & differences btwn popn can accumulate
   • * Limited gene flow + drift/selection can cause popns to diverge
   • * Low levels of gene flow help to maintain diversity & connection of popns & still allow adaptation to local conditions, high levels of gene flow may swap local selection
   • RING SP - two reproductively isolated forms are connected by a chain of intermediate populations
     • Bridge between microevolution and speciation/ macroevolution
       • Show the history of divergence of 2 sp & demonstrate how microevolutionary changes can accumulate into differences btwn sp.
       • Show how geographical differentiation to the level of sp can occur in the face of ongoing gene flow
     • e.g. Siberian Greenish warbler Phylloscopus trochiloides
       • 2 populations that are not interbreeding - different morphology and song
       • Interbreeding in intermediate popns around the ring

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