Investigations into gametophyte morphology and population sex ratios through direct comparisons between laboratory-grown and field-grown fern gametophytes

Most previous studies on fern gametophytes have been conducted under laboratory conditions, leading some to question whether data from these studies accurately reflect gametophytes in nature. Our study compares laboratory cultured and field grown fern gametophytes of the same species. Results indicate few significant differences in morphology between laboratory cultured gametophytes and their field grown counterparts. The most consistent difference observed was the formation of archegonia and rhizoids on the dorsal surface of agar cultured gametophytes. Through alteration of laboratory growth conditions involving light orientation and relative humidity, dorsal archegonia were observed to result from translucence of the agar medium and high humidity within agar culture dishes. Both conditions yield a lowered differential between dorsal and ventral gametophyte surfaces relative to gametophytes on natural substrates. Our studies confirm the utility of studying gametophyte morphology in the laboratory. Characteristics of development, mature form, hairs, gametangial structure, etc. are sufficiently conserved to use in systematic studies and in field identification. By modifying culture conditions, the anomalous occurrence of archegonia on the dorsal surface can be reversed to produce gametophyte morphology in the laboratory that very closely resembles the morphology of gametophytes of the same species grown in nature.;The use of laboratory cultures to predict breeding systems in nature raises the question of whether or not conclusions drawn from these studies accurately reflect what is occurring in nature. Some previous studies have found differences in sex ratios between laboratory and field populations. We speculated that these differences were not necessarily a result of laboratory culture conditions, but instead result from the way in which spores are typically sown onto culture media. Laboratory cultures are generally inoculated onto culture media in a single sowing of spores, whereas field populations may receive several successive innoculations of spores over the duration of spore release from source sporophytes. In order to replicate the multiple spore introductions of natural populations, we added spores to our laboratory cultures over a period of ten days, then determined sex ratios of the resulting populations. Results indicate that staggering the application of the spores onto the medium results in elevated male:female ratios that more accurately reflects the sex ratios of field populations. Other factors such as soil vs. agar medium and heterogeneous vs. flat media surfaces also increased the number of male gametophytes. Our results indicate that changes in standard laboratory protocol may be required to produce culture populations that accurately reflect sex ratios found in nature.