Major Evolutionary Transitions Flashcards
Describe a major evolutionary transition
- a change in the way information is passed from generation
- coined by Maynard-Smith and Szathamry
What can a major evolutionary transition lead to?
a transition in individuality: a new kind of individual from a group of previously independent individuals
Major evolutionary transitions comprise a
disruption to the gradualism of evolution.
Describe some major evolutionary transitions
- independent genetic replicators to chromosomes
- prokaryotic to eukaryotic cells
- sexual reproduction from asexual clones
- multicellularity from protists
- eusociality
- language
Describe the production of the heterotrophic protoeukaryote
- invagination of the plasmamembrane to create the endomembrane system of the endoplasmic reticula, nuclear envelopes and nucleus
- endosymbiogenetic acquisition of a free-living facultatively anaerobic alphaproteobacterium by an anaerobic archaeon host
Describe the protoeukaryote
cells working together to achieve a common goal
Describe the formation of the ancestral autotrophic eukaryote was formed
- secondary acquisition of a photosynthetic cyanobacterium
- conversion of this into a photosynthetic plastid
Describe the major evolutionary transition of sexual reproduction from asexual clones
- allows the separation of the germline from the somatic cells
- allows for crossing over and recombination
- sterilises some cells
- requires a mated pair
Describe the major evolutionary transition of multicellularity from protists
- capable by plants, fungi and animals
- ancestors undergo clonal group formation
- e.g. animals, fungi, red algae, gren plants, volvocine algae, brown algae, ciliates. cyanobacteria, actinobacteria and methanobacteria
Describe subsocial multicellularity
- stay with their parent
- clonal relatedness
- e.g. Homo sapiens
Describe semisocial multicellularity
- cells formed are potentially non-clonal
- relatedness <1
- facultatively multicellular
- slime moulds
- Portuguese man o’war
Describe semisocial slime moulds
- spore forming (reproduction and dispersal)
- stalk (sterile, evolutionary dead-end)
- not multicellular organisms
- not obligate: can exist as unicellular amoeba
Describe semisocial Portuguese man o’war
- cell colony and differentiated to a degree
- not clonal
- tentacles have a different genetic lineage
Describe complex multicellularity
- obligate
- requires subsocial development, alongside a single celled stage.
Describe the 5 non-clonal “multicellular” lineages
facultative multicellular organisms.
Describe the 12 clonal multicellular lineages
- 3 facultative
- 9 obligate
Describe eusociality in Blattodea
- Hymenopteran social cockroaches
- formation of nests, containing a ventilation shaft, chimney, fungus combs, nursery galleries and the royal cell
- individuality has transformed from solitary to colony living
Describe the process of a major evolutionary transition
- solitary individuals coming together to form a cooperative group
- cost
- occurs at all levels of group complexity
- groups sometimes manage to achieve a new higher level of individual
Describe sociality in Suricatta suricatta
- colonial living
- co-operative lifestyle creates high promiscuity; low intragroup relatedness of siblings
- as promiscuity increases from 1-20, sibling relatedness falls from 0.5 to 0.26
- decreases the r parameter of Hamilton’s rule
- less benefit (less selection towards) acting co-operatively
- eusociality is not achieved
How is promiscuity measured?
number of mates
Describe a driving factor towards the achievement of a major evolutionary transition
Number of mates
How did the Hymenopterans achieve eusociality?
intragroup selection (that is governed by Hamilton’s rule) has been eliminated
Describe the elimination of intragroup selection
can occur by either the alignment of genetic interest through sufficient relatedness, or through the repression of competition
How is competition repressed?
- selection against mutants: genetic clonality eliminates selection
- intertwining fates of cells: e.g. parliament of genes repressing transposons
co-operative group formation mechanism is
a crucial and profound factor in selection elimination, and major evolutionary transition.
Describe subsocial colonies
- nests form from queens
- daughter offspring of 0.5 relatedness are the first helpers
- siblings stay in the group
- sibling relatedness is the same as offspring relatedness
- depend on promiscuity
Describe honeybee (Apis mellifera) colonies
- queen has multiple mates
- secondary order of workers are sterile
- ancestors were monogamous: polygamy evolved later (sterile ancestors could not reinnovate fecundity)
Describe semisocial colonies
- siblings of relatedness <0.5, or unrelated individuals of negligible relatedness come together to forma nest
- relatedness of nephews and nieces is less than the relatedness of offspring
Describe the major evolutionary transition to eusociality with respect to subsocial and semisocial colony development
- only ever occurred in lineages with a strictly monogamous ancestor
polygamous ancestor have remained solitary.
Sphecid, Polistine and vespine wasps, and the Halictine and Corbiculate bees,
