Serial endosymbiosis as the basis for algal diversity Flashcards
What is the hypothesized primary endosymbiont and and example
Started with an ancestral cyanobacterium with a protective sheath (to protect against being ingested by a predator) –> so it could have been potentially intact if ingested by a predator and the cell itself would remain viable
- ex. Gloeocapsa
Describe the origin of the chloroplast in Algae
Primary endosymbiosis involved a phagotrophic eukaryote engulfing a cyanobacterium in a food vacuole membrane, resulting in a double layered plastid or chloroplast containing chl a and phycobilins
With primary endosymbiosis how many membranes are around the chloroplast
2 - there was the original membrane around the chloroplast and then the membrane of the food vacuole that took it in
Describe Glaucophytes
- these were evolutionary products of primary endosymbiosis
- are extant
- they contain chloroplasts called cyanelles that looked like structurally reduced cyanobacterial cells (they had an inner cyanobacterial membrane and DNA and also had phycobilisomes in its thylakoid membrane like cyanobacteria tend to have)
Describe the single primary endosymbiosis hypothesis in terms of the algal lineages
- major algal lineages evolved from a specific heterotrophic flagellate that varied in its primary cyanobacterial endosymbionts
- you have the glaucophytes which have a chloroplast similar to cyanobacterial cell
- you have red algae which had cyanobacteria with the capacity to produce phycorythrin to give that red color
- and you have green algae and land plants which had the 2 layer membrane chloroplast, but the chloroplast looks different than cyanobacteria and it can produce chlorophyll b which cyanobacteria don’t produce
What is the missing link to the primary endosymbiotic event leading to the different algal lines
prochlorophytes –> these marine cyanobacterium contained both chlorophyll a and b and must have been the endosymbiotic origin of the green algal chloroplast
What is the alternate hypothesis to the single primary endosymbiosis event that gave rise to the different algal lineages
- an alternate hypothesis is that different heterotrophic flagellates each contain a distinct endosymbiont
- so there isn’t a common ancestor between the algal who appear to be more polyphyletic - so maybe they came from different ancestors
–> there are multiple origins
Which hypothesis helps explain why the algae are polyphyletic
the multiple origins hypothesis - that different heterotrophic flagellates each contain a distinct endosymbiont
describe red algae as evolutionary products of primary endosymbiosis
- they may have had non flagellated ancestor or had loss of flagella b/c red algae have no flagella anywhere in their life history
- they had a cyanobacterial endosymbiont that was able to produce high concentrations of phycoerythrin to get that red color
- they also have a two layer membrane around their chloroplast
describe secondary endosymbiosis
here you get the addition of a remnant food vacuole of the secondary phagotroph so you now have three membranes around the chloroplast
- in certain algae you can see the reduced nucleus (nucleomorph) of the eukaryotic endosymbiont (so the reduced nucleus is within the primary endosymbiote which was consumed)
Euglenoids are evolutionary products of what endosymbiosis event
- secondary endosymbiosis
- so they have three layered chloroplasts and they contain both chlorophylls a and b but do not produce starch
cryptophytes are the evolutionary produce of what endosymbiosis event
- secondary endosymbiosis event
- they are biflagellate like euglenoids but they differ in their external morphologies and cryptophytes also contain a nucleomorph (the reduced nucleus of the primary endosymbiote)
dinoflagellates are the product of what endosymbiosis event
tertiary endosymbiosis
what’s similar between cryptophytes and euglenoids
both are bi flagellate
what do dinoflagellate nuclei look like
they are continuously condensed