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PHYCOLOGICAL SOCIETY OF AMERICA
Delesseria
decipiens Reproduction
and Life History
Delesseria, like the other members of the Division Rhodophyta, has a triphasic life history consisting of three independent life stages. Delesseria also has an isomorphic life history, meaning that it has a morphologically similar gametophyte and tetrasporophyte. Click on the picture for more information on each life stage.
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Gametophyte The gametophyte is
the stage of sexual reproduction in Delesseria, with gametes
being produced from dioecious (separate
sexes) haploid algae. The male gametophyte produces non-motile sperm
called spermatia in
reproductive structures called spermatangia that
are located all over the blade of the alga. Spermatangia, which range
from 5 to 10 mm in size, can often be yellow or colorless due to a lack
of chloroplasts and pigments, but are often difficult to find in many
red algae. Although unable to control their movement, spermatia have
approximately the same specific gravity as seawater, allowing them to
float for a short period in their attempt to reach a female gametophyte.
Delesseria decipiens
has an oogamous reproductive
strategy, with a large, non-motile female gamete, which is housed within
the female reproductive structure, the carpogonium.
The carpogonium is an elongate cell with long protrusion on the end, called
the trichogyne that
is the site of 
spermatia attachment. The wall of the trichogyne is thought
to be somewhat
sticky, perhaps with mucus, helping the spermatia
to form an attachment while fertilization occurs.
The carpogonium of the female gametophyte forms from
a
division of a pericentral
cell of a fertile leaflet, forming a cell known as the supporting cell.
This cell will divide further to form the carpogonial branch, on the end of
which the carpogonium will form. The carpogonial branch of Delesseria always
has exactly four cells. Each fertile leaflet will form only one cystocarp,
although it may produce many carpogonia.
Carposporophyte
The carposporophyte is
the only non-free living stage of the Delesseria life
cycle, living embedded in the blade of the female gametophyte
after fertilization. While the carposporophyte itself
is diploid, it is enclosed by a pericarp,
haploid tissue from the female gametophyte. The combination
of the pericarp and the carposporophyte is called the cystocarp.
The carposporophyte forms
after fertilization when
the newly formed 
diploid nucleus is transferred from
the carpogonium to
an auxiliary cell,
which is formed only after fertilization occurs. In
genus Delesseria, this transfer happens directly
with no intermediate cells in between. The carposporophyte
continues to divide in the auxiliary cell, forming carpospores which
when released, settle and grow into the next life stage,
the tetrasporophyte.
Carpospores in the carposporophyte
Tetrasporophyte
The
diploid tetrasporophyte represents
the second asexually reproducing life stage of Delesseria and
results in meiosis and the formation of haploid tetraspores.
These tetraspores, when dispersed, will settle and
grow into both male and female gametophytes, completing
the reproduction cycle. Tetraspores are formed in the tetrasporangia,
enlarged cells with dense cytoplasmic contents 
that
can be seen grouped around the midrib in D. decipiens as
in the picture on the left. Tetraspores will generally
form on only the last and next to last orders of branching
on a particular blade. The tetrasporangia then divide
to form four tetrahedrally orientated tetraspores,
which look similar to the logo for a Mercedes-Benz. 
Tetraspores on the surface of a tetrasporophyte
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