Reproductive ecology of the freshwater red alga Batrachospermum boryanum Sirodot in a temperature headwater stream

Abstract

Spatial distribution and abundance of Batrachospermum boryanum gametophytes within a headwater stream in Rhode Island, USA varied considerably over a period of two years due to significant changes in dominant substrata. However, periodicity of these plants was similar each year. Juvenile gametophytes were produced by the aseasonal annual 'chantransia' stage most abundantly in September and October. Macroscopic gametophytes appeared in November and attained a peak in development during late winter and spring, correlating with relative light penetration through the surrounding tree canopy. The ratio of female to male plants increased from 1: 1 in January to 4: 1 at the end of the growing season in June during both years. Spermatangia production was continuous throughout the growth period, averaging 26 000 mm -2; mean carpogonial density was 60 mm-2. Approximately 500 spermatia were released for each carpogonium present and the mean proportion of fertilized carpogonia was 22 % . Carposporophytes typically became detached and acted as dispersal agents, settling at 0.075 cm s-'. Current velocities in the stream varied from 10 to 50 cm s-and were calculated to carry the carposporophytes 5-35 m downstream. Monospores released by 'chantransia' upright filaments also added to population spread.

Gametogenesis, gametes and zygotes: An ecological perspective on sexual reproduction in the algae

“…Drebes, 1966;Vaulot & Chisholm, 1987;Armbrust, Chisholm & Olson, 1990). Photoperiod and total daily irradiance appear to determine the timing of gametophyte production in the freshwater red alga Batrachospermum boryanum Sirodot (Hambrook & Sheath, 1991).…”

“…Unfortunately, there are very few reports of the detailed spatial distribution of male and female plants (but see Hambrook & Sheath, 1991;Brawley, 1992), and we do not know how this distribution will affect fertilization success. Some indications are available from studies of invertebrates (Pennington, 1985;Yund, 1990), in which fertilization success decreased rapidly as a function of the distance of eggs from a spawning male.…”

“…Algae belonging to the Batrachospermales, Nemaliales, and Ceramiales potentially meet many of these requirements, and fertilization success has been studied in representatives of two of these orders. A mean proportion of 22% of carpogonia were fertilized in Batrachospermum boryanum (Batrachospermales) in a freshwater stream (Sheath & Hambrook, 1990;Hambrook & Sheath, 1991). These authors speculate that fertilization was enhanced because the non-motile spermatia were trapped in eddies downstream of rocks and carried through the fronds of the same female plants numerous times by these vortices.…”

“…A potential for polyspermy exists in Batrachospermum boryanum because 18% of trichogynes had more than one spermatium attached (Hambrook & Sheath, 1991).…”

Distribution and systematics ofBatrachospermum(Batrachospermales, Rhodophyta) in North America. 8b. SectionBatrachospermum: previously described species excludingBatrachospermum gelatinosum

“…In contrast, the range in carposporophyte number for the type specimen does not overlap with that of the North American populations (12-30 vs 1-10, respectively). This apparent difference may be due to such factors as population density and current velocity (Hambrook & Sheath, 1991).…”