Monterey Bay Aquarium Research Institute
Marine Botany

Chondracanthus exasperatus life history

The life histories of all red algae are fairly complex, and that of C. exasperatus is certainly no exception.  It may be useful to look at a quick run down of the basic life history of the Rhodophyta, specifically those in the subclass Florideophyceae, before delving into the specifics of C. exasperatus'.  If you would like to skip this introduction, please feel free to jump right to the  life history of our star, C. exasperatus.

Simplified life history of a typical Florideophyceae

life history diagram  This diagram depicts a simplified version of the Florideophyceae life history.   It is a triphasic life history, indicating three distinct phases: the gametophyte, the carposporophyte, and the tetrasporophyte.  The male and female gamete-producing reproductive organs are the spermatangium and carpogonium respectively, and both develop from the gametophyte.   There are no flagellated cells in any of the Rhodophyta, thus when the spermatia are produced and released by the spermatangium, they are carried passively by water currents to the trichogyne, or reproductive hair, located on the carpogonium.   The membranes fuse and the male nucleus travels down to the base of the carpogonium, where it fuses with the female nucleus.  This type of fertilization is called oogamy, because it involves the fusion of a larger, nonmotile egg cell with a smaller, motile sperm cell.  The fertilized carposporangia, still on the female gametophyte, then produces gonimoblast filaments, which in turn produce carposporangia and carpospores.  These carpospores, when released, settle and grow into the tetrasporophyte, which in many cases is indistinguishable from the gametophyte.  This situation is termed an isomorphic life history.     The tetrasporophyte is the site of meiosis, more specifically the tetrasporangia where haploid tetraspores are produced.   These tetraspores are released, settle, and grow into the gametophyte, completing the basic red algal life history (Lee, 1980).

Life History of our star, C. exasperatus
Most of what is known about this story is based on general studies of the Gigartina family, which C. exasperatus  was originally a part of.   Species specific life histories have only been determined for one member of this family, Chondrus crispus.  The germination of spores and their early stages of development has been investigated specifically for C. exasperatus and other members of the old Gigartina family.   Recent work by the Hommersand group to reclassify the Gigartinaceae order have led to new investigations of the specific life histories of its members.  Not only has G. exasperatus been reclassified as Chondrocanthus exasperatus, but further specifics of this life history have been determined.   So lets go....

In the beginning, there were the gametes and, since C. exasperatus is dioecious, these were each located on their own male or female gametophyte.....

drawing of spermatangiumThe spermatium are spherical and oblong, and each is formed in its own spermatangia cell.   These, in turn, are produced on spermatangial mother cells, which branch off from the male gametophyte.   The spermatangia are commonly colorless and found partially embedded in extensive patches on the male gametophyte (Ho Kim, 1976)....  
 spermatangium

 

 

When the spermatium are released, they take with them a mucilage sheath which will aid them later in adhering to the female trichogyne.  As these cells are unflagellated, they must rely on water currents to passively carry them to the female egg.  This condition of a small, motile sperm traveling to a larger, nonmotile egg cell is known as oogamy (Dixon, 1973).
 
   carpogonium

 

The female reproductive organ is the carpogonium.  It consists of an elongated, gelatinous tip, called the trichogyne, and an inflated basal region.   The carpogonium has two nuclei, one in the trichogyne, which disintegrates after fertilization, and the other in the base, which is the reproductive nuclei.  The carpogonium is located at the end of the three-celled carpogonial branch, originally formed from inner cortical cells, which, in turn, arises from the supporting cell.  This cell is very large and also serves as the auxiliary cell  once the cell is fertilized.  The carpogonial branch is curved bringing the auxiliary cell towards the carpogonium in a formation called a procarp, all of which is typically colorless (Dixon, 1973).

fertilizationFertilization begins with the fusion of the spermatium to the trichogyne.  The cell walls of each dissolve, and the male nucleus moves down into the basal portion of the carpogonium where it fuses with the female nucleus (karyogamy).  After fertilization, pit plug develops separating the carposporangial base from the trichogyne.   The supporting cell becomes the auxiliary cell and serves a vegetative role in development.  In the base, the nucleus begins to differentiate and produces about two dozen gonimoblast filaments "initials" extending in all directions.  Only those facing inward develop fully into gonimoblast filaments, and these cells are round (Ho Kim, 1976).   Carposporangia develop out from almost all of the complete gonimoblast filaments and have diploid carpospores at their tips. This is the carposporophyte stage.

carposporophyte
An envelope of cells develops from the cortex and medulla to surround the carposporophyte, and the entire structure is known as thecystocarp.  It is an interesting structure as the envelope is haploid and the internal carposporophyte is diploid.  These cystocarps are pushed out from the thallus and housed in the wart-like papillae so characteristic of C. exasperatus. There is only one cystocarp per papillae (Ho Kim, 1976).

 

 

gametophytetetrasporophyte

 

The carpospores are released, settle, and develop into the diploid tetrasporophyte.  It is not possible to differentiate the nonreproductive tetrasporophyte from the gametophyte except by very careful chemical analysis, and so this life history is termed isomorphic.
 
 
 
 
 

 

cruciate tetrasporeThe tetrasporophyte develops tetrasporangia from cells in primary filaments within the cortex, which lie adjacent to or embedded in the medulla.  These serve as the site of meiosis and produce four tetraspores.  Each of these is divided as if by a cross, a structure termed cruciate.  

Finally, these tetraspores are released through pores in the cell wall (Ho Kim, 1976).  They are distributed passively by water currents, settle, and grow into the gametophyte, beginning the life cycle all over again!

 

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Last modified: 3/18/99
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