Organisms are well adapated to their environments

4 examples

1. protective colorations: bird has white feathers in winter and brown in summer

         a. to avoid detection by predators or their prey

   2. Bird feet: water birds have paddle feet; perching birds have scrawny feet

   3. Desert plants: convergences btw plants that live in deserts from around the world

         a. minimizes SA leaf, waxy cuticle, thick trunk, spines, thorns prevent access to stored H20; bright flowers attract pollinators in bloom

         b. these groups have no genetic contact but has same soln to common problem

   4. adaptive radiation: common ancestor was shared but NS created new species, each species is adapted to special kind of habitat

         a. Darwin’s finches—different islands, different variants of finches

               i. different beaks for different feeding niches

1. The ability of a population to expand is infinite but the ability of the environment to support populations is finite

         a. some limitation on population expansion

   2. organisms within populations vary, and this variation affects ability of organism to survive and reproduce

         a. when (1) applied, individuals w/in populations has different reprod. success

   3. Variations are transmitted from parents to offspring

         a. variations can be transmitted

àWhen these conditions hold, natural selection produces adaptation

Example of Natural Selection with 3 postulates

1. Environmental constraints: drought makes large seeds abundant

2. some individuals have large beaks and so survive and reproduce more

3. beak size is inherited

-->characteristics of populations changed=adaptation

     -mean beak sized increased

-Implausible: simple random undirected process cannot create complexity

    a. random mutations

    b. selective retention

-->result: small improvements, beneficial changes retained, complexity

Evolution by variation and selective retention (4)

  1. Produces complex adaptions

   2. No planning or design

   3. Can produce rapid change or maintain stasis

   4. Acts mainly on individuals

     a. correlated characteristics

     b. disequilibrium

     c. genetic drift

     d. local vs. global optima

     e. external forces

Correlated Characteristics (mechanism of inheritance)

1. Beak depth and widths are correlatedàdeep=wide beak

       a. correlations arise when one gene affects multiple traits (pleiotropy)

  2. When traits are correlated, selection on one trait affects both

       a. deep beaks advantageous; shallow-beaked birds die; beaks get deeper, but will also get wider

   3. Pleiotropy can create maladaptations

       a. shallow beaked birds die

       b. wide beaked birds die

       c. selection on depthàdeeper beaks

       d. selection on width-->thin beak

       e. pleiotrophy means beaks can’t be deep and thin

       f. selection on depth >width, even though thin beak is advantageous

       g. beaks get deeper and wider

ànot best beak, but best selection can produce

1. At equilibrium population will be stable

      a. change in any direction will be disadvantageous

      b. evolution will maintain status quo

   2. If change was recent, population won’t be well-adapted

   3. On Galapagos, drought followed by el nino

        i. dry seeds (small) then wet conditios=larger seeds

   4. birds need to catch up to new conditions

 1. Small samples less accurate than large ones

   2. Genetic drift produces random patterns of change

   3. Genetic drift can cause difference to arise btw small populations

           a. founder effects

                i. People from Holland went to S. Africa; 1-2 people cannot produce melotonin (cannot go outside)àpeople in S Africa has this trait in high frequency

                ii. This population in SAfrica has different alleles than founding population b/c sample from smaller population

           b. loss of beneficial traits

                i. random sampling from larger population=loss of good traits

a. Fitness landscape is like a topographic map

      b. population can be at local peak

      c. population can’t reach global peak without dripping into valley

      d. selection avoids valleysàyou are stuck on local peak

      e. population will not always reach global peak

         a. selection has no design, working with what you got within range

         b. evolution of eyes illustrates local optima: insects with compound eyes not have best design, but can’t get to where we are

 a. why can’t elephants flyàheavy animals need strong bones, which are heavy and can’t fly

  b. why can’t male mammals lactateàhormones that facilitate milk production inhibit testosterone production

 1. Traits evolve if they are good for the group

   2. Natural selection is very slow process

   3. NS always produces change

Natural Selection usually works at level of individual (NOT SPECIES!)

   1. example: population regulation

       a. species of finches on islandàapproach limit of environmental resources

       b. species benefit if individuals limit reproductionàwill reproductive restraint evolve?

           i. whole species will go extinct b/c not enough resources for all to survive=crash

-Consider the fate of a “restraint” allele

  1. Imagine that mutant allele generates reproductive restraint

  2. trait is transmitted from parents to offspring

  3. Birds with restraint trait produce fewer offspring than birds without trait

  4. proportion of individuals w/ restraint trait will decline

  5. frequency of trait in population will drop

  6. reproductive restraint trait will not evolveàfreq allele decline b/c outcompeted

       a. good for population but disadvantage to individàDarwin’s Postulate: traits not advantageous to individual=no evolve

       b. selection enhances ability of individuals to survive and reproduce

Change can be rapid: artificial selection

  1. wolves were domesticated about 15,000 yrs ago in Asia

       a. dogs are all one species, but lots of variability within that species

  2. common rock pigeon created new species

-Can evolution (not artificial manipulation) produce rapid change?

  1. Cichlid fish have diversified in E. African lakes

       a. Lake Victoria 12,400 kyaàsingle ancestral species=now 500 spp

       b. lake Tanganyika 6-12myaà1 ancestor=250spp

       c. Lake Malawi .7-4myaà1 ancestor=1000 spp

            i. have very minute habitat specializations

Evolution can maintain traits across time (needs selection—stabilizing—to maintain status quo)

  1. Coelacanths persisted for 300my yrs

  2. cockroachs

      a. no change does not mean no selection; need NS for status quo

-Natural selection can produce stasis

1. ultimateàwhy a particular trait favored or preserved by NS (long processes)

     Eg. Why elephant has long trunkàreach high branches; descended from ancestor with traits

      a. phylogeny (evolutionary history of traits)

      b. function (adaptive value)

  2. Proximateàshort term, here and now

    Eg. In us, certain traits appear with puberty or as we mature=development trajectory

      a. ontogeny (development trajectory)

      b. mechanism (hormones, physiology, genes)

1. circular reasoning: adaptive traits evolve, so traits that evolve are adaptive

       a. see trait (eg peacock), NS maintain it so must be adaptive

           i. now, we know that tails help female know he has good genes

   2. plausibility is not proof: adaptive just so stories

   3. adaptationist reasoning ignores constraints, devel. Interactions, chance, etc

       a. male not lactate=not adaptation (optimal) but best they can do (testosterone)

àtrait we see might not be adaptive

Eg. Female baboons are really interested in other baboon’s babies

a.       hormone w/ babies makes you good mom? Being indifferent=worse

1. complex design

2. convergence

3. phylogeny

4. experiments

Complex design: eye vs telescope

Grand Canyon

a. Grand Canyon or telescopes: not alive but complicated

      b. eye: living and complicated

           i. iris reg. entry, light sensitive cells in retina convert image to nerve impulses, nerve impulses provide info to color and intensity, optic nerve carries info to brain, brain interprets image

      c. nature of complexity differs: parts must be put together in just right way for eye to function; improbable that parts come together by change

          i. many different conformations and combinations of elements can exist in Canyon, but similar kinds of canyons in the other parts of Southwestàlots of ways to build canyon

     d. eye is produce of blind variation and selective retention; change not directed with goal in mind; change is gradual in small steps

          i. trace evolution of eye from simpler to more complex forms

     e. telescopes are product of foresight and planning; innovations are directed, novel features

 1. convergent evol=species from different evol. Lineages living in same enviro evolve similar traits

   2. evidence that traits have been shaped by selective forces

         e.g. cactus, nectar feeding birds, spines+quills, anteaters, high altitude adapations

1. Trait A is adaptive response to environmental conditions, then closely related species living in different conditions will not show trait A (same evol history but different habitats)

2. Need information about

      a. evolutionary relationships among species (phylogeny)

      b. distribution of traits

-Example: blacked headed gulls mob predators

1. adaptive hypothesis: mobbing distracts predators, reduce chance predator finds eggs

2. But mobbing is dangerous costly behavior

      a. dangerous to approach predator

      b. energetic expense

àwon’t do it if has another alternative that works better

 1. gulls vary in nesting habitats

          a. black headed nest on ground and so nest vulnerable to predators

          b. close relatives won’t nest on ground, not vulnerable and won’t mob predators (eg live on cliff)

   2. Use phylogeny to test functional hypothesis: mobbing evolved as defense against ground predation

          a. predict: kittiwakes nest on cliffs, won’t mob

   3. difference among closely related species allows us to test functional hypothesis

-Example: nest parasitism in cowbirds

   1. eg. Bronzed cowbird puts eggs in others’ nest

-Why is nest parasitism adaptives?

   1. raising chicks is hard work

   2. parents who outsource infant care can produce more offspring than parents who raise offspring on their own

-How did nest parasitism evolve?

   1. Outgroup is non-parasitic cowbird (not parasitic)

   2. First nest parasitie specialized on one species

   3. More generalized parasitism evolved

-Example:African assain bug

1. covers back with debris (carcasses of dead insects), dust and sand

2. hypothesis: corpse camouflage protects bug from predators

3. test: present bugs with and without cover to predators

     a. naked=likely attacked; more stuff=ignored

-Example: Chicks begins signals

1. chicks use gape signal to beg for food

2. bright red coloration is conspicuous

3. Coloration is from carotenoid pigments in blood

4. carotenids are associated with immune function

-Develop hypothesis

1. function of red coloration to signal health and vigor to parents

2. parents who preferentially feed healthier offspring will have higher fitness

3. Predict

      a. infant health will affect gape color

      b. gape coloration will affect response to begging

-Experimental manipulation of gape color affects parental feeding behavior

1. treatment: drop food coloring into chicks’ mouth to alter colors

      a. control: yellow dye and water

      b. only those treated with red dye had increased feedings per hour

1. focus on adaptative problem

    a. example: avoid predation, find mate

    b. analyzes range of adaptations in nature

         -camouflage, mimicry, grouping…

         -male courtship, male competition

2. Focus on adaptive systems

    a. example: hose-parasite evolution, ant-acacia mutualism (feed ants, ant protect from herbivores), detailed analysis of single system

       -eg life cycles of hosts and parasites, orchids and pollinators, etc