Monterey Bay Aquarium Research Institute
Marine Botany

Life History of Gracilariopsis lemanaeformis

develops from carpospore
releases tetraspores

The life history of Gracilariopsis is pretty run o' the mill for a red alga, but it's pretty darned nutty for most anything else. First thing to note is that there are three, yes three distinct life-history stages. Gracilariopsis is has an isomorphic life history. Isomorphic is greek for 'pain in the but to tell apart'. Let's start with the familiar male and female plants on the lower right in the figure above. Since they produce gametes, they are known as the gametophytes. The males and females are initially isomorphic, but the males produce spermatia (sperm with no flagellum), and the females produce eggs. The males release the spermatia into the water, and a lucky few bump into a female alga and fertilize the egg, which is still attached to the female. Now the zygote (fertilized egg) begins to divide and grow to form a ball of cells, and the female alga forms a protective wall of cells around it. This ball eventually matures and forms reproductive spores called carpospores, which escape the protective sheath through a small hole. You may not be shocked to learn that this bundle of cells that releases the carpospores is known as the carposporophyte. Each carpospore is capable of settling down on a rock and growing into a mature macroscopic alga that looks the same as the male and female algae. The carpospores grow instead to become the tetrasporophytes. As you may guess, the tetrasporophytes do indeed release tetraspores, and tetraspores do indeed come in groups of four. Each tetraspore that is released can mature into either a male or a female alga, and the cycle continues. For any chromosome counters around, the tetraspores come in groups of four as they are the product of meiosis. So the tetrasporophyte algae are diploid (two sets of chromosomes), the gametophytes that develop from the tetraspores are haploid (one set of chromosomes), and the carposporophyte that develops from the fertilized egg is diploid.

--Ben Hale 1999.

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Last updated: Feb. 05, 2009