Serial endosymbiosis as the basis for algal diversity

Question 1

What is the hypothesized primary endosymbiont and and example

Answer 1

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

Question 2

Describe the origin of the chloroplast in Algae

Answer 2

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

Question 3

With primary endosymbiosis how many membranes are around the chloroplast

Answer 3

2 - there was the original membrane around the chloroplast and then the membrane of the food vacuole that took it in

Question 4

Describe Glaucophytes

Answer 4

• 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)

Question 5

Describe the single primary endosymbiosis hypothesis in terms of the algal lineages

Answer 5

• 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

Question 6

What is the missing link to the primary endosymbiotic event leading to the different algal lines

Answer 6

prochlorophytes –> these marine cyanobacterium contained both chlorophyll a and b and must have been the endosymbiotic origin of the green algal chloroplast

Question 7

What is the alternate hypothesis to the single primary endosymbiosis event that gave rise to the different algal lineages

Answer 7

• 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

Question 8

Which hypothesis helps explain why the algae are polyphyletic

Answer 8

the multiple origins hypothesis - that different heterotrophic flagellates each contain a distinct endosymbiont

Question 9

describe red algae as evolutionary products of primary endosymbiosis

Answer 9

• 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

Question 10

describe secondary endosymbiosis

Answer 10

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)

Question 11

Euglenoids are evolutionary products of what endosymbiosis event

Answer 11

• secondary endosymbiosis
• so they have three layered chloroplasts and they contain both chlorophylls a and b but do not produce starch

Question 12

cryptophytes are the evolutionary produce of what endosymbiosis event

Answer 12

• 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)

Question 13

dinoflagellates are the product of what endosymbiosis event

Answer 13

tertiary endosymbiosis

Question 14

what’s similar between cryptophytes and euglenoids

Answer 14

both are bi flagellate

Question 15

what do dinoflagellate nuclei look like

Answer 15

they are continuously condensed

Question 16

How can dinoflagellates get their chloroplast

Answer 16

they can reduce the endosymbiont to a chloroplast or steal the chloroplast from a digested cryptophyte –> this is called kleptoplastidy

Question 17

what is kleptoplastidy

Answer 17

this is when dinoflagellates steal the chloroplast from a digested cryptophyte