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Ulva lactuca thallus
A thallus is a plantlike multicellular
body lacking any
vascular tissue
(xylem or phloem).
http://bio59000.free.fr/Photosbio59000/Biovegetale/Algues/Ulva%20lactuca.gif
Ulva life cycle There are three isomorphic thalli:
Some species of Ulva
are anisogamous.
isogametes syngamy
+
–
1N 2N
Gametophytes
+
zygote
settles on
substrate
Sporophyte
–
settle on
substrate
+
–
Since they are
motile, they are also
meiosis
+
–
called zoospores.
The meiospores made
by the sporophyte are of
two mating types.
holdfast
sporocyte
The life cycle is:
diplohaplontic
diplontic
haplontic
Codium
http://massbay.mit.edu/exoticspecies/exoticmaps/images/codium_big.jpg
The life cycle is:
diplohaplontic
diplontic
haplontic
Codium Life Cycle
syngamy
zygote
1N 2N
Sporophytes
anisogametes
2 sexes
holdfast
sporangium
sporocytes
meiosis
zoospores
Oedogonium thallus
http://www.plingfactory.de/Science/GruKlaOeko/Teichleben/Algen/Oedogonium%20sp..jpg
Oedogonium
Here the filaments are out of focus.
The asexual zoospore is in focus.
http://www.botit.botany.wisc.edu/images/130/Chlorophyta/Oedogonium_Images/Zoospore_MC.low.jpg
Oogonium
http://www.rbgsyd.nsw.gov.au/__data/page/1810/Oedogonium.gif
Oedogonium
This is the zoospore, or maybe it
is the sperm. Both have the same
look!
http://www.biologie.uni-hamburg.de/b-online/fo44/18.jpg
When both
oogonium and
antheridium
appear on the
same filament the
alga is
homothallic.
http://www.csupomona.edu/~jcclark/classes/bot125/resource/graphics/g/chl_oedogonium.jpg
Oedogonium Life
Cycle
Since antheridia
and oogonia are sperm
on the same
filaments, this
species is
chemotaxis
homothallic.
Vegetative
zoospores can
clone the
gametophyte
Zoospores settle
down with a holdfast
and grow into a
filament.
syngamy
zygote
empty
antheridia
egg
(hypnospore)
(in oogonium)
1N 2N
(in
oogonium)
The zygote
divides
meiotically to
release 4
zoospores.
meiosis This life cycle is ?
Evolution of Gametes for Syngamy:
Isogametes - Anisogametes - Oogametes
+
–
Evolution of Life Histories: multicellularity and sex
Unicellular (neither truly diplontic nor truly haplontic…but taking
both “shortcuts” maybe with asexual reproduction
added on diploid and/or haploid sides)
Diplontic (no multicellular haploid)
Haplontic (no multicellular diploid)
Diplohaplontic (both haploid and diploid multicellular forms)
Sequence unclear: elaborations vs reductions?
Multiple pathways in different groups?
SYNGAMY
gametes
zygote
germination
mitosis
differentiation
mitosis
gametangia
differentiation
Gametophyte1N
2N
Sporophyte
differentiation
differentiation
mitosis
germination
sporangium
mitosis
spores
sporocyte
MEIOSIS
The flowering plant is a multicellular diploid sporophyte.
The sporophyte encloses the multicellular haploid gametophyte.
The life history is thus diplohaplontic.
The gametes are oogamous but the sperm lack flagellae.
Gender expression has moved from gametophyte to sporophyte.
http://www.bakerlite.co.uk/pics/Wales/South%20Wales/Vale/Trees/Tree-8.jpg
Life Cycle of Flowering Plants