Sexual reproduction Algae

Volvox

1) triggered by environmental stress (heat/drought)

2) large nonmotile egg in oogonium

3)small motile male sperm packets

colonies may dioicious or monoecious

4) zygote forms, ungerdoes meiosis

5)haploid embryo becomes new daughter cell

hypnozygote

resting cyst resulting from sexual fusion

Oogamy

large, nonmotile female

small, motile male

Coleochaetophyceae

Charophyceae

Chlorophyceae - Oedogonium

Charophyceae oogamy

oogonia/antheridia in axil of whorls

may be mono/diocious

sperm finds eggs via pheromones

zygote may survive dormant period

Oedogonium oogamy

Chlorophyceae

macrandrous:lacking dwarf males

antheridia develop directly from vegetative cells

each produces two spermatozoids that fertilise an egg cell

oogonium with pore in wall for sperm access

Isogamy

gametes identical, may be homo or heterothallic

conjugation zygnematophyceae

1) induced by N availability

2) compatible cells/filaments near and share common mucus coat

3) opposing cells connect, often via conjugation canal

4) entire protoplast emerge as gametes

5) only 1 gamete formed

conjugation desmidiales

1)asexual division

2)compatiable mating types found via phermones, trigger gamete formation and passive/active behaviour, conjugation canal

3) 2 zygospores formed

4)first zygote cells look like Cosmarium

5) another division lobes form new semi cells

Prasinophyta Isogamy

Nephroselmidophyceae: Nephroselmis olivacea

fusion produces zygote

after meiosis releases 2 cells

heterothallism

Dasycladales isogametes

biflagellated with CCW orientation of flagellar bases

Halimedinae release of male and female gametes (5)

Bropsidales

simultaneous in many representatives (Halimeda, Caulerpa, Penicellus, Udotea)

like corals

in night, entire protoplasts migrate to the apical parts of thallus, in morning approximately 5 % of popultion of one species begins to release gametes simultaneously

whole process takes up to 15 minutes, during which time the visibility in water decreases to about 1 m

after fusion, zygotes formed, which sink to sediment

Chlorocystis sexual life cycle (3)

male and female gametophytes produce two-flagellated gametes that are morphologically different (anisomagy) and fuse to form a four-flagellated zygote.

zygote then sheds its flagella and forms a diploid codiol stage that is attached to a solid substrate.

After meiosis, it produces four-flagellated zoospores that attach to the apical part, shed their flagella and give rise to a new coccal stage

Ulothrix sexual production (7)

protoplast turns into biflagellate isogametes

fertilisation produces tetraflagellate zygote

attaches and forms the codiolum stage

after meiosis, releases tetraflagellate zoospores

give rise to filament

when spring ends, all protoplasts turn into gametes and only empty cell walls remain from the cells

population in stream suddenly disappears, alga in codiolum stage, waiting until next season when it cools again

Spongomorpha sexual reproduction

Ulvophyceae

isogamic

gametes produced by the transformation of protoplast and their multiplication

4-flagellated zygotes adheres and forms the petrocelis stage

then produces tetraflagellated zoospores, give rise to new thalli

petrocelis stage

described as a separate genus of red-algae Petrocelis

Ulvales gamete formation occurs in

marginal parts of gametophyte thallus

Ulvales fusion of gametes

orms zygote

attaches to substrate

immediate sporophyte growth

Ulvales zoospore morphology

haploid tetraflagellate

Ulvales zoospore (2)

by meiotic division

gives rise to gametophyte

Pediastrum sexual reproduction

isogamic, gametes tend to be smaller than zoospores and, unlike them, have a stigma.

Hydrodictyon reticulatum sexual reproduction Chlorophyceae

isogamic

After the fusion of isogametes, a zygote is formed, reduction division occurs and four haploid zoospores are released, which give rise to a hypnozygote of polyhedral shape, and

then it is the same as in the case of asexual reproduction.

Sphaeroplea annulina sexual reproduction (4) Chlorophyceae

oogamie– the cytoplasm of the oogonia divides into several egg cells,

into which biflagellated spermatozoa penetrate.

After fertilization, they are formed orange hypnozygotes with a two-layer wall, covered with winged processes.

Hypnozygotes are able to survive adverse conditions and then germinate

Chlamydomonas sexual reproduction (9)

isogamic

The vegetative cell divides into gametes, which are smaller than the mother cell.

The gametes then collide and touch each other with the tips of their flagella, which contain specific proteins for recognizing compatibility.

When a suitable partner is found, the flagella of both gametes stick together along their entire length, bringing the cells closer together until their contents fuse.

A motile planozygote with four flagella and two chloroplasts. It then sheds the flagella and forms a resistant cell wall containing algenan.

Mature wall hypnozygote

It is thick, reddish-brown in color and has a distinctly structured surface.

After a dormant period in the sediment, reduction division occurs and four new cells emerge from the ruptured zygospore.

Under unfavorable conditions, palmellar stages can also form in the slime

hyponozygote

non-motile, dormant resting zygote (resting cyst) formed during the sexual reproduction of certain aquatic microorganisms

planozygote

A mobile zygote

Prasiola sexual reproduction

oogamic

diploid vegetative thalli form mosaic of light and dark parts

dark parts: meiotic division occurs to produce eggs

light parts: spermatozoa formed

after fertilisation: zygote formed, germinates into diploid thallus

Trebouxiophyceae