lecture 11/12

Question 1

allopatric speciation

Answer 1

• speciation resulting from physical isolation (vicariance)

- consequences: gene flow? genetic drift? selection? mutation?

Question 2

allopatric speciation and biological species concepts

Answer 2

• determines “distinctiveness” of species in sympatry, and use the same degree of separation as a yardstick for use in allopatry.
• but “distinctiveness” seems arbitrary and what if there’s no sympatric species? (giraffes, elephants, chimps?)

Question 3

peripatric speciation

Answer 3

• speciation resulting from the isolation of a small peripheral population, usually by dispersal or colonization.
• consequences: founder effect and comparing to allopatric speciation: genetic drift? selection?
• founder effect

Question 4

parapatric speciation

Answer 4

• speciation within a continuous geographic area, usually across a habitat transition.
• selection vs gene flow
• what happens to the probability of speciation when gene flow is greater than selection? selection is greater than gene flow?

Question 5

sympatric speciation

Answer 5

• when populations become isolated by preferences for different habitats or mates, even though they are not physically isolated.
• rarer than the other types of speciation; allopatric is most common

Question 6

animals vs plants

Answer 6

• polyploidization is a major mechanism of speciation in plants
• polyploids retain extra sets of chromosomes

Question 7

autopolyploids

Answer 7

duplicate chromosomes from the same species; selfing/cloning

Question 8

allopoloyploids

Answer 8

combine chromosomal sets from different species

Question 9

secondary contact

Answer 9

• when previously isolated populations reconnect
• outcome depends on how much the populations diverged while in allopatry
• possibilities: gene flow, hybridization, reproductive isolation (prezygotic: offspring never form, postzygotic: offspring inviable, sterile, or low fitness), reinforcement

Question 10

secondary contact and hybrid zones

Answer 10

• hybrid zones are areas where previously isolated populations meet, mate, and produce offspring

Question 11

what causes postzygotic isolatiokn?

Answer 11

• Dobzhansky-Muller incomptability: an ancestral population splits into two species and a new mutation arises to fixation in both that are not compatible with each other so when the two species breed, the offspring hybrids have lower fitness.

Question 12

reinforcement

Answer 12

• hybrid offspring have low fitness

- natural selection leads to assortative mating and the prezygotic isolation of populations

Question 13

What happens when hybrid offspring have increased fitness?

Answer 13

• hybrid speciation
  1. Polyploid advantages over parents: Extreme phenotypic traits, instant reproductive isolation
  2. Homoploid hybrid advantages over parents: Few initial advantages, BUT…
• Recombination will produce extremely high genetic variances
• Phenotypes more extreme than either parent
• Burst of variation can help attain new adaptive peaks far from parental optima

Question 14

sexual selection

Answer 14

• occurs when individuals in a population differ in their ability to attract mates (nonrandom mating)
• it targets genes that code for mate choice traits and favors individuals with heritable traits that enhance their ability to obtain mates.
• produces changes in allele frequencies

Question 15

How is sexual selection different from natural selection?

Answer 15

• asexual or selfing population:
  survive + grow + reproduce = fitness
• outcrossing sexual population:
  survive + grow + find a mate + reproduce = fitness

Question 16

What Are the Consequences of Sexual Selection?

Answer 16

• Sexual dimorphism: sexually selected traits can differ sharply between the sexes.
• Sexual selection violates the assumptions of the Hardy-Weinberg principle by causing certain alleles to increase or decrease in frequency and resulting in evolutionary change

Question 17

selection trade offs

Answer 17

males (or the sex that attracts the mates) often sacrifice their fitness in order to have a higher rate of success attracting mates (bright colors are not good for camouflage, but attract females)

Question 18

The Fundamental Asymmetry of Sex

Answer 18

• Females usually invest more in their offspring than males.
  “Eggs are expensive, but sperm are cheap”
• Female fitness is limited by an ability to gain the
  resource required to produce eggs and rear young. 

• Male fitness is limited by the ability to attract mates.

Question 19

what are females choosing?

Answer 19

• good genes: greater size, enhanced color, louder/more complex vocalization, large ornaments reflect general health and vigor
• sexy sons: female increases her fitness (= no. of grandchildren) disproportionately by producing attractive sons
• in each generation, the female preference applies strong directional selection on the male trait to become more exaggerated, even if the trait has no adaptive value.