Cycle 8: Life on Earth, Species and Speciation and Cycle 7: All About Sex

Question 1

Asexual Reproduction in plants.

Answer 1

New individuals are genetically identical (bulbs, corms, tubers, rhizomes, adventitious roots)

Question 2

Asexual Reproduction in animals.

Answer 2

• Fragmentation
• Budding
• Parthenogenesis: females produce offspring without fertilization from sperm
  Thelytoky: female offspring are produced
  Arrhenotoky: male offspring are produced

Question 3

Thelytoky

Answer 3

female offspring are produced

Question 4

Arrhenotoky

Answer 4

male offspring are produced

Question 5

Sexes in plants.

Answer 5

• Monoecious (flowers of both sexes in plant)
• Dioecious: male and female flowers are on different plants
• Hermaphrodites: the flower has male and female parts (but not much selfing occurs)

Question 6

Sexes in animals.

Answer 6

• Monoecious hermaphrodite:
  Species with male and female sex organs
• Sequential hermaphrodite
• Dioecious: individuals of separate sexes
  Some will not exhibit sexual dimorphism (when sexes look different)

Question 7

Sequential hermaphrodites.

Answer 7

Change from male to female or female to male based on a series of cues (olfactory, visual, auditory, tactile)

Question 8

Size advantage model.

Answer 8

Protrandry: male to female
Protogyny: female to male

Question 9

Why sex?

Answer 9

Cons: time spent, male-male competition, courtship, rejection, natural enemies, STDs

Pros: Diversity of offspring (chances for gaining beneficial alleles, and losing negative ones) through sexual reproduction

Question 10

Monogamy.

Answer 10

one partner

Question 11

Polygamy.

Answer 11

Polygyny: male mating with many females
Polyandry: female mating with many males

Question 12

Courtship behaviour and mating

Answer 12

Visual, auditory, chemical, and tactile
Habitat influences which cues are used during mating.

Question 13

Sexual Selection

Answer 13

Females are generally the choosier sex (but there are exceptions)
The sex that invests more in offspring (higher parental investment) is the choosier sex.
Can also be dependent on ecological situations (role reversal)

Question 14

When and how do females choose partners?

Answer 14

WHEN FEMALES CHOOSE:
Male strategy: Mate as often as possible (best strategy to leave his genes)
- Male-male competition:
- A cost of sexual reproduction
- Post-mating sperm competition
- Second mating increases reproductive success of female
- Second male may not sire any progeny (competition can dependent on sperm quality)
- Could be that female chooses ( has not been ruled out)
- Evolution of adaptations to reduce sperm competition
- Increased ejaculate size
- Remove sperm from previous mating
- Mate guarding

HOW DO FEMALES CHOOSE?
- Visual signals (e.g. size)
- Nuptial gifts
- Good gene hypothesis and symmetry (more symmetrical implies better genes)
- MHC (group of genes on cell surfaces)
- Different MHC genes (fitness against parasites varies based on MHC genes)
- Goal is to obtain a diversity of MHC genes for protection of progeny against disease.

Question 15

Ecological Concept

Answer 15

Populations that are adapted to specific niches in the environment
E.g. Mosquitoes feeding on humans vs birds may evolve differently

Advantages
- Explains role of environment in speciation

Disadvantages
- Unable to explain existence of same species in different environments

Question 16

Morphological Concept

Answer 16

Individuals of species share measurable traits that distinguish them from other species

Advantage
- Easy to classify physical traits to recognize species

Disadvantage
- Does not reveal much about evolutionary history
- Cannot distinguish different species with similar physical characteristics

Question 17

Biological Concept

Answer 17

• Interbreeding populations that don’t reproduce with other species
• All individuals in a species can successfully mate and produce viable, fertile offspring
  Genetic Cohesiveness: populations of same species experience gene flow that mixes their genetic material
  Genetic Distinctiveness: different species can’t exchange genetic info

Advantage
Testable and describes gene flow of species

Disadvantage
Does not apply to asexual and extinct organisms

Question 18

Phylogenetic Concept

Answer 18

• Populations that share recent evolutionary history
  Independent branch on phylogenetic tree = species
• Common morphological ancestry for sexually reproducing organisms
  Implies reproductive isolation, but does not prove

Advantage
Applies to all groups of organisms (asexual, extinct)

Disadvantage
Does not describe gene flow

Question 19

Clinal Variation

Answer 19

Gradient of traits in a geographic range
Varying environment conditions favour different traits → evolution within a species

Question 20

Ring Species

Answer 20

Population migrates around geographic barrier → two adjacent populations that cannot interbreed
Considered same species due to shared alleles + gene pool through intermediates

Question 21

Prezygotic Isolating Mechanisms

Answer 21

Temporal Isolation: Mating at different times
Ecological Isolation: Different habitats
Mechanical Isolation: Different reproductive structures
Behavioural Isolation: Different mating signals (courtship displays)
Gamete Mortality (Gametic Isolation): Incompatibility between sperm and egg

Question 22

Postzygotic Isolating Mechanisms

Answer 22

Hybrid Inviability: Conflicting genes prevents development
- Fertilization occurs but hybrid is frail or has has early death
Hybrid Sterility: Survives but unable to produce functional gametes
Hybrid Breakdown: Hybrid develops and can mate with other hybrids + parent species
- Second generation will have higher fatality, lower fertility
- Long-term reproductive isolation rather than immediate

Question 23

Allopatric vs Sympatric Speciation

Answer 23

Modes of speciation based on species isolated by location
Allopatric: Two populations that are geographically separated potentially causing evolution of reproductive isolating mechanisms
Sympatric: Reproductive isolation that evolves between subgroups that arise with one population

Question 24

Allopatric Speciation

Answer 24

Two populations that are geographically separated potentially causing evolution of reproductive isolating mechanisms
Examples:
- Physical barrier that subdivides a large population
- Small population becomes separated from a species main geographical location
- Natural disasters

Question 25

Secondary Contact

Answer 25

Two previously isolated populations reunite
Not required for speciation to occur

Potential Outcomes
Reinforcement:
increases the rate of speciation
If reproductive isolation occurs, there is speciation
When the two species are back in contact, they can’t interbreed

Fusion:
slows down the rate of speciation
Populations successfully interbreed, they can “fuse” back together
Gene flow can continue → remains one species

Question 26

Autopolyploid Mutations on Speciation

Answer 26

Autopolyploidy mechanism:
- Chromosomes fail to separate in cell division = no reduction of number of chromosomes = gamete is a different ploidy than parent
Offspring species can’t interbreed with original parent species

Question 27

Evolutionary Myths

Answer 27

1) Why the idea that “humans are descended from chimps are incorrect”

We just share a common ancestor that doesn’t mean chimps are our ancestors

2) Why some traditional groupings of organisms do not reflect evolutionary relationships

Just because some organisms are grouped together does not mean they are as closely evolutionary related as they seem
Also, shared similarities might not always reflect shared ancestry, it could be convergent evolution

3) “Pedigree Collapse”
The idea that some of your ancestors are not ALL unique individuals
eg. great x13 aunt on mom’s side and great x9 grandmother on dad’s side are the same person