Lecture 6: Sex, Reproductive systems, and Evolution

Question 1

What are the two types of reproductive modes?

Answer 1

Asexual and sexual

Question 2

What are the two types of sexual reproduction?

Answer 2

Dioecious and hermaphrodite

Question 3

Dioecious

Answer 3

Male and female reproductive organs exist in different individuals

Question 4

Hermaphrodite

Answer 4

Organism that has complete reproductive organs. Produces gametes normally associated with both the male and female sex

Question 5

What are the two mating systems that involve hermaphrodites?

Answer 5

Cross-fertilization (two hermaphrodites) and self-fertilization

Question 6

Can members of similar species have different reproductive systems?

Answer 6

Yes, water fleas (daphnia) reproduce sexually in warmer, more turbulent water and reproduce asexually in cooler, calm water.

Question 7

Many perennial plants reproduce…

Answer 7

.. through both sexual and clonal reproduction

Question 8

Tangled bank hypothesis

Answer 8

Theory that suggests benefits of sex. With a wide assortment of organisms competing for light and food in a heterogenous environment, diversity is favoured. Capable of using broader range of available resources.

Question 9

Red Queen hypothesis

Answer 9

Related to the co-evolution of predator and prey. Sexual reproduction produces more variation and thus allows for faster evolution (avoidance of extinction)

Question 10

What is the advantage of sex in evening primrose?

Answer 10

Studies conducted suggested that sex eliminated harmful mutations (stopped deleterious mutations from accumulating).

Question 11

What’s another word for clonal propagation? Which species is it more common in?

Answer 11

Asexuality. More common in plants and invertebrates. Very rare in vertebrates.

Question 12

What is the evolutionary potential of asexual species?

Answer 12

They have low evolutionary potential because they lack significant genetic variation. Asexual species are usually found at tips of phylogenies.

Question 13

What are the Bdelloid rotifers?

Answer 13

Asexual species that has diversified to over 300 species without sex. Males are unknown.

Question 14

Outbreeding

Answer 14

mates are less closely related than random

Question 15

Inbreeding

Answer 15

mates more closely related than random.

Question 16

Factors that lead to inbreeding

Answer 16

• small population

- hermaphroditic individuals (most plants and some animals have potential to self-fert)

Question 17

Inbreeding avoidance strategies for flowering plants

Answer 17

flowers attract pollinators, timing of male and female reproduction is offset, various genetic/ morphological mechanisms to avoid selfing

Question 18

Inbreeding avoidance strategies for animals

Answer 18

dispersal, kin recognition, delayed maturation, extra pair copulation (mating outside monogamous pairing)

Question 19

Inbreeding depression

Answer 19

Reduction in fitness of inbred offspring in comparison with outcrossed offspring

• genotypic frequencies change
• heterozygosity reduced by 50% per generation with self-fertilization
• homozygosity for deleterious recessive alleles results in inbreeding depression.

Question 20

Why has selfing evolved many times despite inbreeding depression?

Answer 20

Associated with extensive phenotypic variation. Beneficial when pollinators are lacking or flowers are far apart (pollen would be wasted). Selfers have a transmission advantage and if inbreeding depression is low selfing can spread via natural selection.

Question 21

Proportion of selfing and outcrossing plants/animals?

Answer 21

20% of plants = hermaphroditic plants and animals are highly selfing,
10-20% = highly outcrossing

Question 22

What does selfing in Capsella yield?

Answer 22

Selfer (rubella) produces Smaller flowers and has lower DNA diversity compared to animal pollinated outcrosser capsella (grandiflora). Higher proportion of deleterious mutations in the selfer.

Question 23

What are the long-term effects of selfing?

Answer 23

low diversity and inefficient selection possibly leading to higher extinction.