Photographic analysis of field-monitored fern gametophyte development and response to environmental stress

Abstract

Premise: Ferns differ from seed plants in possessing a life cycle that includes a small, free-living, seemingly vulnerable gametophyte stage in which sexual reproduction occurs. Most research on the response of fern gametophytes to environmental stress has been conducted on gametophytes grown in culture or harvested from natural habitats and subsequently manipulated and tested in laboratory experiments. We present a fixed-distance photographic methodology for monitoring longevity of gametophytes and their response to environmental stress in natural, undisturbed habitats over their life spans. Methods: We present methodology for non-invasive monitoring of growth and development in response to environmental factors, using programmed, fixed-distance photography, coupled with computer analyses allowing qualitative and quantitative comparisons. We tracked growth rates and stress responses of individual gametophyte plants to seasonal changes in a temperate climate. Results: Gametophytes and young sporophytes survived freezing and drought in temperate habitats, as we document through photographs and growth measurements. Gametophyte growth was suspended during the cold season and resumed the following spring. Individual gametophytes survived for up to nearly three years with retention of the ability to produce sporophytes. Discussion: Life histories of fern gametophytes in temperate habitats are more similar to those in tropical habitats than previous research has suggested. They survive and maintain reproductive capacity over several growing seasons, allowing extended opportunity for outbreeding. The application of photographic monitoring of additional species and habitats has great potential for a more complete understanding of the ecology of reproduction in homosporous vascular plants.