Bio 207 Organismal Evolution
February 2, 2022
Dr. Manos Lecture 11 Notes
I.
II.
III.
Introductory Comments
a. Brown algae are an independent lineage from the land plants, despite their
large size and photosynthetic ability
b. BLT - an example of the tree of life’s diversity and how that diversity
benefits humans
c. Land Plant Invasion Overview
i. Early land plants came from freshwater, leading to ancient land
plants - the Bryophytes
1. Bryophytes = mosses and relatives
ii. Many challenges for first land plants:
1. Drought
2. UV radiation
3. Temperature
iii. A number of transitions occurred to achieve the multicellular
flowering plants of today
iv. Evolutionary baggage (from aquatic ancestors) posed challenges too
Slide #95: Life Cycle Summary/Review
a. Ploidy - haploid (a single set of chromosomes - N) or diploid (two sets of
chromosomes - 2N)
i. Sex cells are haploid
ii. Animals and diatoms are diplontic (diploid dominant)
1. Haploid phase is short-lived
iii. Algae, fungi, dinoflagellates, and others are haplontic (haploid
dominant)
1. Diploid phase is short-lived, often resting and single-cellular
iv. Kelp, macroalgae, and land plants are diplohaplontic - alternation of
generations
1. One generation is haploid; one is diploid
2. Brown algae uses haploid phase to be mobile (since diploid
phase is anchored to seafloor)
Multicellularity
a. Cells working together with some degree of specialization of cells (e.g.,
tissues, organs, organ systems, etc.)
b. Very little differentiation/specialization in the multicellularity of brown
algae
c. Slide #96a: Advantages of Multicellularity
i. Cell Partitioning
IV.
V.
1. Organism persists beyond just the gamete phase, often for
long periods of time
2. Gametes and haploid phases both have separate selective
pressures acting on them
3. Large size requires support systems, such as skeletons (endo,
exo)
ii. Cell Specialization
1. Organ systems
2. Meristems in plants allow for multiple points of growth
a. Brown algae meristems only produce more leaves,
unlike flowering plants, whose meristems can produce
different tissue types (e.g., flowers)
iii. Isolate Damaged Areas
1. Plants are able to section off wounded areas and heal those
areas
a. Contrast with bacteria: a puncture to the cell
wall/membrane could be lethal to the whole organism
iv. Life Span Increases
1. Larger control over resources (space, light, food) and greater
reproductive ability/spread
d. Slide #96b: Other Approaches to Getting Large
i. Coenocytes - develop one very large cell
1. Ex: plasmodial slime molds, siphonous green algae
a. Slime molds are in the supergroup amoebozoa (fungi
and animals are opisthokonts)
i. Opistho = behind
ii. Konts = one flagellum
iii. Opisthokonts = single flagella on the back
b. Slime molds popularized by The Blob movie
2. Can be multinucleate (but still unicellular)
ii. Colony Formation - one clonal organism (identical genotypes) made
of many cells with division of labor
1. Different from multicellularity: each individual cell could
survive on its own
2. Ex: algae, corals, bacterial biofilms (weak division of labor)
iii. Filamentous Growth - body grows through filaments
1. Ex: fungi, algae
Archaeplastids
a. Red and green algae are sister groups
Land Plants - Embryophytes - all have embryos
a. First phase of land plants are liverworts, hornworts, and mosses
i. Arise from algal organisms, gaining terrestrial adaptations and losing
evolutionary baggage
ii. Most primitive features of land plants are found here
b. Green algae are not a clade - non-monophyletic/paraphyletic - because land
plants (as a separate group) arise from them
c. Green algae are more diverse than red or brown algae
d. Slide #97: Green Algal Diversity
i. 10x as many species in green algae compared to red/brown
ii. Very good at spreading across landscapes
iii. Very good at forming symbiotic relationships
1. Symbiosis enables organisms to expand the number of habitats
they can exist in (e.g., tree bark)
2. Lichens = green algae + fungi
3. Anemone is in symbiosis with green algae
a. Anemone provides a habitat in exchange for
photosynthetic energy
4. Salamanders are in symbiosis with green algae
a. Algae enters salamander eggs, providing oxygen and
energy in exchange for habitat
b. Highly specialized algal species: Oophila amblystomatis
iv. Key features:
1. Chlorophyll a & b, and carotenoids
2. Store food in chloroplasts as starch
3. Cell walls made of cellulose
v. Ernst Haeckel (1904) - scientific illustrator, proponent of evolution
vi. Green algae have expanded into many unique areas (e.g., symbiosis)
1. Microbiotic crusts in the desert - dirt-like structure filled with
algae, cyanobacteria, and other animals
a. Critical for ecosystem function through nitrogen-fixing
cyanobacteria
vii. Many green algae are unicellular
1. Chlamydomonas
a. Slide #98: Haplontic Life Cycle of Green Algae
i. Diploid phase is a unicellular zygospore
viii. Some are colonial
1. Volvox - thousands of swimming cells chained together with a
number of specialized cell types coordinating flagella
movement in order to allow whole-organism movement
2. Hydrodictyon - use a filamentous net to hold together
3. Pediastrum - highly symmetrical
ix. Coenocytes are green algae
x. Charophytes thought to be transitional form to land plants
1. Green algae have symmetrical or asymmetrical flagella
a. Also have mixture of life cycles
2. Land plants have exclusively asymmetrical flagella
a. Also have exclusively alternation of generations
3. Charophytes have haplontic life cycle
4. Mosses, hornworts, and liverworts have alternation of
generation (gametophyte dominant)
5. Tracheophytes have alternation of generation (sporophyte
dominant)
6. Charophytes, e.g. Chara, have 3D bodies, apical growth
(meristems), leaf-like structures, sex organs (moss-like),
a. These features suggest transitional form
7. Only diploid phase is zygote, which will divide meiotically to
become haploid
Notes Written by Trevor Gannalo
Feel free to email with questions, concerns, or suggestions: trevor.gannalo@duke.edu