What is dioecy?
female or male
plants can be too. eg. yews
What animals can be asexual?
ostropods eg.daphnia - alternate between sexual and asexual =cyclic parthogenesis.
amphibians
vertebrate
reptiles
NOT mammals
asexual animals have recently derived from a sexual ancestor. they are found on the tips of trees. evolves fairly often in plants and animals, but is an evolutionary dead end
What is parthenogenesis?
asexual reproduction where offspring develop from unfertilised egg.
-particularly common in arthropods and rotifers.
- seen in some fish, amphibians, reptiles.
daphnia = cyclic parthenogenesis
What is gynogenesis?
special case of sexual reproduction in which insemination neccesary but head of sperm penetrating ovum doesn’t transform it. No genetic transformation.
What is hybridogenesis?
hemicolonial- half genome is passed intact to next generation- other half is discarded.
- occurs in hybrid of 2 species animals and some live bearing fish.
What are the methods of reproduction in flowering plants?
Obligate Sexuality arises in around 1%
Vegetative Propagation - multicellular structures become detatched and develop into new individuals.
Apomixis - eggs or seeds are produced by mitosis, no fertilisation, genetically identical.
What is the advantage of being asexual?
Asexuals have a 2 fold advantage. as they donate twice as much genetic material as sexual individual.
-sex is also costly, due to traits needed to access mate and disease risks.
Why is sexual reproduction the most prolific form of reproduction?
as natural selection works more efficiently in sexuals so they can adapt faster to changing environments and remove deleterious mutations faster
sexuals can restore optimal genotype by recombination
asexuals cant restore except by back mutation which is rare.
What is one situation a constant selection pressure is maintained on a species?
coevoltuion with parasites.
-parasites have shorter generation time.
-advantage over host in evolutionary arms race
-sex shuffles immune gene combos.
=moving target for parasites.
What is mullers ratchet?
process by which genes of an asexual population accumulate deleterious mutations in an irreversible manner. =fittness declines
How is speciation in asexuals different to sexuals?
As they dont need to evolve reproductive isolation, speciation is easier in asexuals.
however they adapt slower to changing environment so speciation is slower than sexuals.
What are some ancient asexuals?
Bdelloid rotifers.
- 480 species described
- typified by their rotary aparatus and leech like locomotion
- super abundant in damp habitats, moss, puddles, soil etc.
- adults undergo anhydrobiosis in harsh environments and dispersal.
- no males, no meiosis,
Describe the bdelloid genome
- no homologous chromosomes.
- homologous regions clotted around
- lack major catagories of retrotransposons
- lack some meiosis and sperm otogenis gnes but not others.
- asexual 60myrs.
Describe the genus rotaria
- 9 species.
- geometric morphometrics of feeding morphology
- seperated by clear morphological differences
- ecologically distinct
- found on different parts of the same insect
- have speciated into more species but are less distinct than sexual rotifers. (monoganauts)
Why haven’t Bdelloids gone extinct? (theories)
- special mechanism to compensate for lack of sex
- suited to harsh environment
- not real asexuals (discrete)
- THEY PICK UP FOREIGN DNA
