Monterey Bay Aquarium Research Institute
Marine Botany

Antithamnion defectum

Life History

life cycle cartoon

Antithamnion defectum has a typical three stage red-algal life history. The three stages are the tetrasporophyte which is diploid, the dioecious gametophyte stage which is haploid, and the carposporophyte stage which is diploid and grows on the female gametophyte as can be seen in the cartoon above. Therefore, the sporophyte and gametophyte are isomorphic, meaning they appear identical except for their reproductive structures.

tetrasporangia The diploid tetrasporophyte undergoes meiosis creating tetraspores, which are oval shaped, red, cruciately divided and pedicellate, which can be seen in the picture to the right. Released spores settle and grow into haploid male and female gametophytes. Male gametophytes have unpigmented spermatangia which grow from the adaxial side of the inner cells of branchlets as seen in the picture. The three pictures below are actually of spermatia on A. dendroidem, but they would look similar in A. defectum. One study investigating the spermatangial development in Antithamnion found that spermatangial vesicles within the spermatia (something common in red algae) may be responsible for making spermatial attachments. Spermatial attachments are long, thin filaments which aid in the binding of the spermatia to the trichogyne by extending the surface area of the spermatia and by having ligands which preferentially bind to particular carbohydrate receptors on the trichogyne. [7]

spermatiaspermatia spermatia
apical branch The female gametophyte has 4-celled carpogonial branches which grow from the basal cells of apical branches. The picture shows a typical apical section of A. defectum, although no carpogonial branches are present. Syngamy is oogamous, as the non-swimming (flagella-lacking) spermatia attaches to the trichogyne of the procarp. Only one carposporophyte develops per carpogonial branch. After fertilization, the auxiliary cell is cut off from the supporting cell. The auxiliary cell divides to form a lower foot cell and an upper gonimoblast cell which eventually forms the carposporophyte. The carposporophyte is diploid, and develops on the female gametophyte until the diploid spores are released. These spores grow into tetrasporophytes, and the cycle begins again! [10] The two drawings below show a carpogonial branch pre-fertilization and a carposporophyte growing on the female gametophyte.
sketch of carpogonial branchsketch of carposporophyte
This cycle can happen relatively quickly in laboratory conditions, on the order of a few months, but could take longer in vivo due to wave conditions, availability of space to settle, and difficulty for the male spermatia to find the trichogyne of the female procarps. Read more about the timing of the life-cycle on the growth-experiment page.

From my findings and looking through the Gilbert M. Smith Herbarium, it seems that all life stages of Antithamnion could be found at any time of year.


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References and Acknowledgements

© 2005 Charlotte Stevenson

Last updated: Feb. 05, 2009