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.
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.
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