Sex!
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Why are males costly?
• Cost 50% of female reproductive output • Asexual females leave more offspring • Males have high levels of competivity • Cost of finding a partner • Loss of genes each generation
Define sex
• Meiotic sex is usually the fusion of haploid gametes to form a diploid cell in offspring • Bacterial sex involves the mixing of genetic material
Give an example of an asexual organism that still relies on sex
Poecilia formosa (fish) • all-female species • mates with males of other species to instigate parthenogenic egg production (doesn’t use sperm, just needed to start development) • Males now are evolving discrimination
What other mechanisms can a female eliminate the input of a male?
Some asexual species show paternal genome elimination
Why is a lack of genetic variation thought to be ‘bad’?
• Can expose deleterious recessives - Slow rate of evolution means an inability to track changing environments and pathogens
What did the study of the parthenogenic/sexual snail Pomatopgyrus antipodarum show?
Frequency of males depends on • Snail density (ability to find a partner) • Level of infection (need for genetic diversity)
What is one of the main advantages of sex?
Allows independent benificial combinations to be combined much more quickly than in asexuals
Why is sex more common with larger genomes?
As deleterious mutation rates are usually more common and sex can be used to avoid these
Why is the flatworm schmidtea polychroa not completely asexual?
Sometimes has ‘sneaky’ sex
What are the 3 plant breeding systems?
• Monoecious - male & females on the same plant • Dioecious - male & females on different plants • Plygamous - both
What is androdiecy?
When there are both hemaphrodite plants and male plants in the population (very rare)
What is gynodiecy?
When there are both hemaphrodite plants and female plants in the population
What is the genetic model for the evolution of gynodiecy?
1 + k >2 (where k is the female advantage) Essentially females must produce double of the seed of a hemaphrodite in order to succeed 1 + k > 2 (1- ssigma) takes into account inbreeding depression and reduced seed quality
What is the genetic model for the evolution of androdiecy?
1 + K >2 (1-ssignma)/(1-s) (where K is male advantage) This takes into account the preemption of access to ovules in hemaphrodites due to selfing
What selection was found in the plant sagittaria latifolia in monoecious and dioecious populations?
Higher rate of selfing in monoecious, however in both populations there was a strong selection against inbred offspring. Both populations also had similar diversities, however both grew in individual clusters
Why is it possible that dioecious plants are less species rich than the rest of the groups?
Either a lower speciation or higher extinction rate - could be as higher genetic diversity is maintained resulting in less divergence
Why can sexually dimorphic flowers be detrimental to a dioecious plant species?
• In times of abundant pollinators males are more evolve elaborate floral displays • Becomes problematic when there is lower pollinator abundance as they are less likely to visit female flowers