Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa

Abstract

By finding some important culture conditions as below, we succeeded in experimentally controlling the whole life history of a dioecious marine green alga, Bryopsis plumosa (Hudson) C. Agardh. In this study, we focused on the primary and secondary sex ratios (i.e. at inception and maturity) using these culture techniques. Gametogenesis was induced by culturing haploid gametophytes with Provasoli's enriched seawater (PES) medium under a 14:10 h light:dark cycle at 14 degrees C. Formed zygotes grew into diploid sporophytes, which were cultured for 3 months with PES medium under a 14:10 h light:nbsp;dark cycle at 18 degrees C. Then they were transferred into Schreiber medium and cultured under a 10:14 h light:dark cycle at 22 degrees C. Within 1 week, zoosporogenesis was observed. Zoospores were released within a couple of days. Each zoospore soon germinated and grew into a unisexual gametophyte. The primary sex ratio was examined in gametophytes that originated from a single sporophyte. The secondary sex ratio was studied in the field. Both were estimated as 1:1. Synchronized meiotic cell divisions might occur during zoosporogenesis dividing each sex-determining factor evenly among zoospores. Given the equal sex ratio at maturity, there seems to be no environmental factor that differentially affects the survival of male or female gametophytes in nature.

Temporal Variation in Isomorphic Phase and Sex Ratios of a Natural Population of Ulva Pertusa (Chlorophyta)1

“…Densities were expressed as the number of identified sporophytes or gametophytes per quadrat sampling unit and converted to the individual number · m −2 . To analyze the data on biphase and sex ratios, the two‐tailed binomial test was used (Togashi and Cox 2008). The null hypothesis tested was that both the gametophyte/sporophyte ratio and the sex ratio of gametophytes were equally likely to occur.…”

“…There are only limited data pertaining to seaweed sex ratios (see table 13.3 in De Wreede and Klinger 1988). In the case of green macroalga, 1:1 sex ratios of gametophytes have been observed in the natural population of Monostroma (Togashi et al 1997) and Bryopsis (Togashi and Cox 2008). However, these genera have a heteromorphic life history.…”

Evolution of gamete size in primitive taxa without mating types

“…In marine green algae, zygotes grow into diploid sporophytes that produce haploid zoospores through meiosis, each of which germinates into a new gametophyte. Also, the sex ratio of released zoospores has been suggested to be statistically 1:1 (Togashi and Cox 2008). This means that the number density of gametophytes in the next generation is given by…”

Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae

“…3B). Each diploid sporophyte that is developed from a survived zygote produces the same number of haploid zoospores with a 1:1 ratio of one mating type to another (35). Each zoospore germinates into an individual gametophyte of each sex that begins the life cycle in the next generation.…”