Dependence of the carposporophyte on the maternal gametophyte in three ceramiacean algae (Rhodophyta), with respect to carposporophyte development, spore production and germination success

The reproductive performance of carposporophytes with various lengths of attached female branch was compared among three ceramiacean red algae, Antithamnion nipponicum, Ceramium boydenii and C. japonicum. The length of time prior to initiation of spore discharge was comparatively stable, but the number of spore discharge events fluctuated, regardless of the branch length attached to the carposporophyte. The total number of discharged spores and their size were both drastically reduced in A. nipponicum carposporophytes with female branches < 1 mm long, whereas in the two Ceramium species the size and number gradually decreased in carposporophytes with branches < 4 mm long. Carposporophytes that had been completely removed from the vegetative branches generally liberated the smallest and fewest carpospores and discharged spores only once; the accompanying young gonimolobes never grew larger. This Conspicuous reduction in spore size was observed even if carposporophytes were excised the day before spore discharge. The size of spores released from the excised carposporophytes was significantly reduced in the three different strains of C. japonicum, but the ratio of the total spore number to control decreased by 53-88%. Germlings from large spores discharged from an unexcised carposporophyte showed faster growth rates than germlings from small spores from an excised carposporophyte. Our results suggest that nutrients are Continuously supplied from gametophyte to carposporophyte until spore discharge and that carposporophytes cannot maintain the normal size and number of carpospores without remaining attached to a critical length of female branch, the length varying among taxa. The pathway for metabolite translocation and the significance of the association of carposporophyte with gametophyte are discussed.