—In the homosporous fern Ceratopteris richardii, sex is not determined chromosomally. Rather, hermaphroditic gametophytes produce a hormone called antheridiogen, which induces maleness in undifferentiated gametophytes. The percentage of males increases with increasing density of gametophytes, presumably due to the cumulative effect of antheridiogen from multiple hermaphrodites.
Some have argued that antheridiogen lessens competition between gametophytes. Such competition is expected to be most intense between hermaphrodites given that they support zygote, embryo, and sporophyte growth. Therefore, it is predicted that at lower nutrient levels, the effect of antheridiogen in inducing male gametophytes is greater than at higher nutrient levels.
To test this hypothesis, C. richardii spores were sown over a range of densities (0.52/cm2 to 5.2/cm2) in four nutrient-level treatments (100, 50, 25, 12.5 percent of full-strength nutrient agar). Gametophytes were grown for four weeks at 28 degrees Celsius with a photoperiod of 14 L: 10 D. An ANCOVA found an overall positive relationship between gametophyte density and percentage of male gametophytes. However, the relationship between gametophyte density and percentage of male gametophytes did not differ among nutrient levels. Nutrient levels had no effect on the rate of male induction by antheridiogen. A post-hoc power analysis showed that the experimental power was 97%.
