Fauchea: life history
The life history of Fauchea is, like most red algae, one of the most complicated of all the living organisms. This alga experiences three distinct life phases:Gametophyte, Carposporophyte, and Tetrasporophyte; each with its own interesting quirks.
Click on any of the below images to visit that part of the life cycle
Let's start with the two gametophytes... The female and male gametophytes are, in general, fairly indistinguishable from each other. If you find a piece of Fauchea on the beach somewhere and don't see any bumps or bands on the thalli you are probably looking at a female or male. Since the spermatia are yellow or pale in color, the male gametophyte is often characterized as being paler than the other life stages. Thus, it may lack the brilliant iridescence. As I never found any males to speak of (that is, we never found spermatia), the image used will have to suffice, though the sex is undetermined. Both gametophytes, having derived from tetraspores, are haploid.
Female Fauchea??? Male Fauchea??
Our female has a rather complex reproductive structure. Within the thallus are evenly arranged carpogonial branches containing the egg cell and several additional cells needed for fertilization and production of the cystocarp.
At the base, and above the supporting cell are the carpogonia that contain the egg cells. Attached to the supporting cell are the auxiliary and auxiliary mother cells. The topmost cell of the carpogonial branch is the trichogyne, a specialized cell that some believe serves to catch the un-flagellated spermatia.
The male gametophyte on the other hand, is relatively simple. Scattered across the thallus are spermatangia, small cells that produce spermatia. Due to the inconspicuousness of these cells, few samples exist, and I was unable to find a male with spermatia. The fascinating part of the male, though, is that the spermatia lack flagella. They are mercy to the whims of the ocean. It's amazing that the Rhodophyta manage to reproduce at all.
Upon maturing, the male gametophytes release their spermatia. Reports differ on this, and since it hasn't been observed (to be best of my knowledge) there is know way to really know. The spermatia may be released in a mucus matrix or individually. Odds are the sliminess of Fauchea supports the first theory. Furthermore, what are the odds of a single sticklike cell (trichogyne) catching a single un-flagellated spermatia? My vote goes with the mucus matrix.
Fertilization occurs within the females thalli and the carposporophytes grow on the female. The auxiliary mother cell will become multi-cellular after fertilization. It is the sole location of nutritive support for the developing gonimoblast, or embryo, after fertilization. The auxiliary cell, lacking a nucleus, accepts the fertilized egg and will contain it as the embryo divides to form the carpospores. The cells surrounding the branch will begin to form the pericarp, the vegetative surrounding mass that serves to protect the developing carposporophyte. Within the pericarp, the carposporophyte produces dozens of carpospores. The cystocarp refers to the coupling of the pericarp and the carposporophyte. The bumps on the female below are cystocarps. The pericarp is the surface of the bumps while the carposporophyte is within.
The carposporophytes soon break open, releasing their carpospores. These diploid carpospores have been produced by the fertilization of the female ovum with a male spermatium. After meiosis, the carpospores are diploid. When the carpospores land on a substrate, they grow into tetrasporophytes. Tetraporophytes are distinguishble by their elongate and irregular banding.
The tetrasporophyte is diploid as well since it is simply a grown carpospore. As it matures it develops its nemathecia, the areas of banding seen in this image that contain the tetraspores.
The tetrasporophytes will produce tetraspores asexually, thus producing haploid spores. The division in Fauchea tetraspores is cruciate, meaning dividing on two perpendicular planes, and looks like this:
Each of these haploid tetraspores
will go on to make a female or male gametophyte, thus starting the cycle
anew. back to top
© 2003 Nicholas Vidargas