Bryopsis corticulans Life History
Bryopsis have found to be able to reproduce both sexually and asexually, though in various references, it has been said to only reproduce sexually without a sporangial life phase (no diploid sporophyte generation as discussed below). Despite the discrepencies in the literature, I have outlined both the entire sexual life cycle (as I seem to found a sporangial life phase in a tropical Bryopsis species, pictured above) and asexual reproduction.
In Bryopsis, the gametophyte (the macroscopic plant we commonly think of as Bryopsis) is much larger than the sporophyte and only has one set of chromosomes (haploid, 1N). * When it starts to reproduce, chloroplasts will aggregate at the base of a pinnae (branch) because the base of the pinnae will start to swell. This effectively forms a "plug" separating the cytoplasm in the pinnae from that in the main axis (thallus). This will effectively block off the transport of chloroplasts, nuclei and organelles to certain pinna by "pinching off" and isolating the pinna. These specialized pinna become the gametangia, the gamete-producing (gametogenesis) areas of the plant. Each gametangium will either produce either male or female haploid gametes. Both male and female gametangia are produced on the same parental plant (monoecious).*
Bryopsis is anisogamous, meaning that it produces motile gametes that are unequal in size (the female gamete is three times larger than the male). Both gametes are pear shaped and have to flagella of equal length (biflagellated). The male gamete has a giant mitochondrion, occupying a greater volume of the cytoplasm, whereas the female gamete has many small mitohondria and a larger chloroplast with an eyespot. *
The gametes are released into the ocean for external fertilization. Since Bryopsis is monoecious (both male and female gametangia on same parental plant), the male and female gametes are released at the same time and often times fertilization of gametes from the same parent will produce homothallic plants (where both gametes are from the same parent). Fertilization of the gametes will produce a diploid (two sets of chromosomes, 2N) zygote that will develop into either gametophytes (macrothalli, 1N) through meiosis and mitosis or a sporophyte (microthallus, 2N). *
The sporophyte looks nothing like the gametophyte. It looks like a creeping filamentous germling. Through mitosis and subsequent meiosis, the sporophyte produces and releases numerous haploid zoospores (spore with flagella) which develop into new gametophytes (approximately 50% male and 50% female). And thus the cycle starts again. *