Adaptations & Traits 4 Flashcards
hermaphroditic (2)
- having both male and female sex organs or other sexual characteristics
- majority of plants; minority of animals
dioecy (2)
- having the male and female reproductive organs in separate individuals
- minority of plants; majority of animals
hermaphroditism: advantages (4)
- easier to find mate; “reproductive insurance”: due to selfing, guaranteed mating
- less genetic mixing when selfing
- all of the population is compatible
hermaphroditism: disadvantages (3)
- trade-offs: may not be well specialized for specific male/female reproduction
- inbreeding depression if selfing occurs
- limited to those around them
dioecy: advantages (3)
- more genetic mixing
- specialization of male/female reproduction
- avoids inbreeding depression
dioecy: disadvantages (2)
- susceptible to extreme sex ratio fluctuations at small N
- only 50% of the population is compatible
sexual reproduction
- mating with another individual, leading to the production of genetically mixed offspring
asexual reproduction (2)
- production of offspring without mating or genetic mixing
- via tillers, budding or fission, or asexual seeds/eggs
despite the diversity in organism reproductive systems, what do the majority of eukaryotes practice (2)
- majority reproduce sexually at least every once in a while
- all living eukaryotes descended from an sexual ancestor that already had the genetic tools for sex
asexuality: advantages (4)
- reproduce faster by investing in only one sex
- all of the parent’s genes are passed to the offspring
- no competition for mates
- better able to maintain adaptations
sexual reproduction: advantages (2)
- more diverse offspring
- faster adaptation due to higher variance
evolutionary enigma of sex
- sexual reproduction evolved early and has been maintained across most eukaryotes, despite substantial costs of sex
costs of sex (5)
- cost of producing males
- destruction of favourable gene combinations
- cost of finding a mate
- risk of not finding a mate
- risk of disease transmission during mating
enigma of sex: cost of producing males
- by dividing resources between daughters and sons, sexual females should be quickly outcompeted by asexual variants that can invest resources only into reproducing females (all else being equal)
enigma of sex: destruction of favourable gene combinations (2)
- mom and dad have good gene combinations as they have lived to produce
- sexually produced offspring could contains mixture of genes from mom and dad that is disadvantageous; why break up good gene combinations?
what advantages pay the cost of sex
- sex can generate variation needed by selection through recombination and segregation
what are two exceptions to this statement: sex generates variation needed by selection
- sex need not increase variation
- not all variation helps selection
in what scenario can sex decrease variation (3)
- selection occurs that favours homozygous individuals
- after selection, there are fewer heterozygous individuals
- where asexuality would preserve this variation, sex reduces the variation in the trait by restoring the frequency of heterozygous individuals
in what scenario does variation not help selection (2)
- selection occurs that favours heterozygous individuals
- sex restores the frequency of homozygotes, increasing variance in a direction that opposes selection (variation produces low fitness offspring)
segration load/recombination load
- the reduction in fitness from sex and recombination unravelling the genetic associations built by past selection
modifier genes
- genes that alter a trait of interested
- there are modifier genes for sex and recombination
negative epistasis hypothesis for sex (2)
- in fitness interactions (epistasis) among genes were predominantly negative: extreme genotypes would be less fit and less frequent, decreasing genetic variance in fitness through disequilibrium
- sex could restore genetic variance and improve response to selection
negative epistasis hypothesis for sex indicate that sex/recombination is favoured only when: (3)
- epistasis is negative, but weak
- little variance in epistasis
- sex/recombination is rare
does the negative epistasis hypothesis for sex explain why we have sex?
- no, there are too many limitations
Red Queen hypothesis for sex
- sexual reproduction has evolved to increase the rate of adaptation in the face of changing interactions with other species
challenge of the Red Queen hypothesis for sex (2)
- as long as there is ample genetic mixing within a population and selection is not too strong, the frequency of sex decreases as a result of the Red Queen
- this is because sex mainly breaks apart the fit gene combinations that allowed the parents to survive species interactions (high segregation/recombination load)
Red Queen hypothesis for sex indicate that sex/recombination is favoured only when: (3)
- epistasis is weak
- sex/recombination is rare
- there is strong selection per locus
