DOI: 10.5061/dryad.w9ghx3fxf
title: An ulvophycean marine green alga produces large parthenogenetic isogametes as predicted by the gamete dynamics model for the evolution of anisogamy

description: In eukaryotes, the gamete size difference between the two sexes
 (anisogamy) evolved from gametes of equal size in both mating types
 (isogamy). The gamete dynamics (GD) model for anisogamy evolution combines
 gamete limitation and competition and predicts that, if gametes of both
 mating types can develop parthenogenetically (i.e. without fusing with the
 opposite mating type), large isogamy can evolve under gamete-limited
 conditions. Ulvophycean marine green algae that have been claimed to
 exhibit various gametic systems from isogamy to anisogamy are important
 models for testing such theories. However, in most previous papers,
 whether a species is isogamous or anisogamous has not been examined
 statistically. Caution is necessary regarding claims of slight anisogamy
 because of gamete size variation. We reveal (i) that the gametic system of
 Struvea okamurae is large isogamy using a generalized linear mixed model
 (GLMM), which accounted for the variation of gamete size among individual
 gametophytes, and (ii) that gametes of this alga can actually develop
 parthenogenetically, contrary to a previous report. Its habitat
 environments and protracted duration of gamete release suggest that this
 alga might experience gamete-limited conditions. S. okamurae
 seems to produce large parthenogenetic isogametes following GD model
 predictions, as an adaptation to deep waters.
description: We collected gametophytes and sporophytes of <em>Struvea
 okamurae</em> in early spring (March 2020) at a depth of about 3 m
 off the coast of Ginoza, Okinawa, Japan (26°47’N, 127°78’E) (figure 1),
 and established the uni-algal culture strains of these gametophytes (So-4,
 So-6, So-14, So-21, and So-27) and sporophyte (So-1) using a
 protoplast-formation method. Protoplasts were cultured in 1/4
 concentration Provasoli’s enriched seawater (PES) medium [20] at 22°C
 under a long day condition (14 h: 10 h = light: dark) and ca. 15 μmol
 photons ·m<sup>-2</sup> · s<sup>-1</sup> in a
 culture chamber (LH-220S; NK system, Osaka, Japan). We isolated
 gametophyte/sporophyte <em>Struvea</em> plants developed from
 a protoplast individually into 12 well plastic plates (IWAKI, Tokyo,
 Japan) and induced gametogenesis/zoosporogenesis under an eutrophic
 condition by changing the medium. We estimated the
 volume of <em>S. okamurae</em> gametes more accurately than
 previous studies on other ulvophycean species by eliminating the error due
 to discrepancies between the calculation of biovolume based on geometric
 approximation and that based on real shapes. Some gametes were fixed with
 1% glutaraldehyde immediately after they were released. We observed them
 on a cover glass coated with poly-L-lysine (0.01 w/v%) and took a
 micrograph of each gamete using a differential interference microscope
 (Axio Imager A1; Zeiss, Oberkochen, Germany). We obtained successive
 vertical cross-sections through each pear-shaped gamete using the
 micrograph, calculated the volumes of each section with 1-pixel height,
 and summed the volumes of all sections.
description: # An ulvophycean marine green alga produces large parthenogenetic
 isogametes as predicted by the gamete dynamics model for the evolution of
 anisogamy
 [https://doi.org/10.5061/dryad.w9ghx3fxf](https://doi.org/10.5061/dryad.w9ghx3fxf) The data set includes the time until gamete release and the volume of gametes with the genotype and sex of gametophytes. The uploaded Excel file consists of two sheets for the time until gamete release and the volume of gametes. From our crossing tests, we determined that strains with So-4, So-27, So-1.1.1c1, and So-1.1.2b1 genotypes have one mating type (labelled type A) and that strains with So-6, So-14, So-21, So-1.1.4a3, and So-1.1.4b4 genotypes have the other mating type (labelled type B). The unit of the time until gamete release and that of the gamete volume is "hour (h)" and "cubic micrometer (um^3)", respectively. ### Change log **27-Sept-2024:** We uploaded the R script file that we used to analyze the data. The data on the time until gametes were released were moved to a separate file.