Lecture 6: Sex, Reproductive systems, and Evolution Flashcards
What are the two types of reproductive modes?
Asexual and sexual
What are the two types of sexual reproduction?
Dioecious and hermaphrodite
Dioecious
Male and female reproductive organs exist in different individuals
Hermaphrodite
Organism that has complete reproductive organs. Produces gametes normally associated with both the male and female sex
What are the two mating systems that involve hermaphrodites?
Cross-fertilization (two hermaphrodites) and self-fertilization
Can members of similar species have different reproductive systems?
Yes, water fleas (daphnia) reproduce sexually in warmer, more turbulent water and reproduce asexually in cooler, calm water.
Many perennial plants reproduce…
.. through both sexual and clonal reproduction
Tangled bank hypothesis
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.
Red Queen hypothesis
Related to the co-evolution of predator and prey. Sexual reproduction produces more variation and thus allows for faster evolution (avoidance of extinction)
What is the advantage of sex in evening primrose?
Studies conducted suggested that sex eliminated harmful mutations (stopped deleterious mutations from accumulating).
What’s another word for clonal propagation? Which species is it more common in?
Asexuality. More common in plants and invertebrates. Very rare in vertebrates.
What is the evolutionary potential of asexual species?
They have low evolutionary potential because they lack significant genetic variation. Asexual species are usually found at tips of phylogenies.
What are the Bdelloid rotifers?
Asexual species that has diversified to over 300 species without sex. Males are unknown.
Outbreeding
mates are less closely related than random
Inbreeding
mates more closely related than random.
Factors that lead to inbreeding
- small population
- hermaphroditic individuals (most plants and some animals have potential to self-fert)
Inbreeding avoidance strategies for flowering plants
flowers attract pollinators, timing of male and female reproduction is offset, various genetic/ morphological mechanisms to avoid selfing
Inbreeding avoidance strategies for animals
dispersal, kin recognition, delayed maturation, extra pair copulation (mating outside monogamous pairing)
Inbreeding depression
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.
Why has selfing evolved many times despite inbreeding depression?
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.
Proportion of selfing and outcrossing plants/animals?
20% of plants = hermaphroditic plants and animals are highly selfing,
10-20% = highly outcrossing
What does selfing in Capsella yield?
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.
What are the long-term effects of selfing?
low diversity and inefficient selection possibly leading to higher extinction.
