Fig 1.
Isomorphic biphasic life cycle of Ulva.
Ulva cycles between two morphologically similar multicellular adult phases, a haploid gametophyte and a diploid sporophyte. Diploid sporophytes produce haploid zoospores that develop into gametophytes. Haploid gametophytes produce haploid gametes. When a “+” and “–” gamete fuse a zygote is formed, which develops into a diploid sporophyte.
Fig 2.
The graphs on the left (A, C) represent an U. compressa gametophyte, while the two graphs on the right (B, D) represent an U. compressa sporophyte. Fig 2A and 2B show the forward scatter by fluorescence, while Fig 2C and 2D represent the count of nuclei from 20,000 events. The sporophyte (B, D) has twice the fluorescence as the gametophyte (A, C), with the gametophyte mean fluorescence near 19,000 and the sporophyte mean fluorescence near 38,000.
Fig 3.
Map of Greenwich Bay (a subset of Narragansett Bay, Rhode Island).
This figure shows the relative proportion of gametophytes and sporophytes present at five sites in Greenwich Bay during the 2013 bloom-forming season. The sites are Warwick City Park (WCP), Oakland Beach Cove (OBC), Oakland Beach (OB), Sandy Point (SP), and Chepiwanoxet (CH). Pie chart sizes represent the relative number of individuals sampled.
Table 1.
Testing against the null model prediction of √2 gametophytes: 1 sporophyte by site and species.
The overabundant phase column indicates which phase was more abundant than predicted by the null model. Numbers in bold indicate significant (<0.05 values).
Table 2.
Table for the best-fit logistic regression with a binomial distribution and ploidy as the sindependent variable.
Model follows the form (1) (e.g. -2.480–1.130 * U. rigida– 0.946 * Oakland Beach + …). Numbers in bold indicate significant (< 0.05 values).
Fig 4.
The predicted probability of an individual being a gametophyte or sporophyte under different environmental conditions based on the model estimate.
Sporophytes are represented by one, while gametophytes are represented by zero. A value of one indicates 100 percent sporophyte abundance. Variables measured include Ulva biomass (g/0.08 m3) present at time of collection (4A), surface salinity values from the date collection (4B) and from two weeks prior to collection (4C). The upper line is U. compressa and the lower line is U. rigida. The shading indicates 95% confidence intervals.
Fig 5.
Growth of U. rigida and U. compressa gametophytes and sporophytes.
There are no significant differences in relative growth rate between ploidy levels in either species. Data are means ± one standard error.
Fig 6.
Cell area by species and ploidy for U. compressa and U. rigida.
Both species have significantly larger sporophyte cell area then gametophyte cell area. Data are means ± one standard error.