Ecophysiological differentiation between life stages in filmy ferns (Hymenophyllaceae)

Abstract

Desiccation tolerance was a key trait that allowed plants to colonize land. However, little is known about the transition from desiccation tolerant non-vascular plants to desiccation sensitive vascular ones. Filmy ferns (Hymenophyllaceae) represent a useful system to investigate how water-stress strategies differ between non-vascular and vascular stages within a single organism because they have vascularized sporophytes and nonvascular gametophytes that are each capable of varying degrees of desiccation tolerance. To explore this, we surveyed sporophytes and gametophytes of 19 species (22 taxa including varieties) of filmy ferns on Moorea (French Polynesia) and used chlorophyll fluorescence to measure desiccation tolerance and light responses. We conducted phylogenetically informed analyses to identify differences in physiology between life stages and growth habits. Gametophytes had similar or less desiccation tolerance (ability to recover from 2 d desiccation at -86 MPa) and lower photosynthetic optima (maximum electron transport rate of photosystem II and light level at 95% of that rate) than sporophytes. Epiphytes were more tolerant of desiccation than terrestrial species in both generations. Despite their lack of greater physiological tolerances, gametophytes of several species occurred over a wider elevational range than conspecific sporophytes. Our results demonstrate that filmy fern gametophytes and sporophytes differ in their physiology and niche requirements, and point to the importance of microhabitat in shaping the evolution of water-use strategies in vascular plants.

Identifying cryptic fern gametophytes using DNA barcoding: A review

“…Other studies have also built upon previous DNA barcoding results to better understand fern ecology. Nitta et al (2020b) and Nitta et al (2021) both leveraged the DNA barcoding results of fern gametophytes on the islands of Mo'orea and Tahiti by Nitta et al (2017). Nitta et al (2020b) scored morphological traits including morphotype and presence of hairs, glands, and gemmae in the gametophytes surveyed by Nitta et al (2017), then included these trait data in a comparison of the functional community structure of terrestrial vs. epiphytic fern communities.…”

“…Additional studies of fern gametophyte morphological and physiological traits with species identified by DNA barcoding could provide even greater insight into the processes governing community assembly of epiphytic and terrestrial fern communities. Nitta et al (2021) took a unique approach that, to our knowledge, has not been used in any other study. To compare adaptations to water stress between terrestrial and epiphytic filmy ferns, they conducted desiccation tolerance assays on gametophytes of unknown species at the field station where they conducted their field survey, then later identified the individuals to species using DNA barcoding in the lab.…”

Identifying cryptic fern gametophytes using DNA barcoding: A review

“…Other studies have also built upon previous DNA barcoding results to better understand fern ecology. Nitta, Watkins, et al (2020) and Nitta et al (2021) both leveraged the DNA barcoding results of fern gametophytes on the islands of Moorea and Tahiti by Nitta et al (2017). Nitta, Watkins, et al (2020) scored morphological traits including morphotype and presence of hairs, glands, and gemmae in the gametophytes surveyed by Nitta et al (2017), then included these trait data in a comparison of the functional community structure of terrestrial vs. epiphytic fern communities.…”

“…Additional studies of fern gametophyte morphological and physiological traits with species identified by DNA barcoding could provide even greater insight into the processes governing community assembly of epiphytic and terrestrial fern communities. Nitta et al (2021) took a unique approach which we are not aware has been used by any other study: in order to compare adaptations to water stress between terrestrial and epiphytic filmy ferns, they conducted desiccation tolerance assays on gametophytes of unknown species at the field station where they conducted their field survey, then later identified the individuals to species using DNA barcoding in the lab. This resulted in rather skewed sampling numbers for some species (e.g., the most common species, Callistopteris apiifolia (Presl) Copel.…”

“…One of the most surprising results of this study was that the gametophytes of C. apiifolia, which had by far the broadest distribution compared to other species, were incapable of tolerating even slight amounts of desiccation. Rather, Nitta et al (2021) hypothesize that C. apiifolia gametophytes exploit small, well-protected microhabitats at the bases of rocks and trees to avoid desiccation and thus attain a broader geographic range than conspecific sporophytes. This points to the importance of microhabitat for understanding the distribution of fern gametophytes, which has also been supported by the finding of wide intraspecific variation in desiccation tolerance in vittarioid gametophytes mirroring variation in their environmental conditions (Stevens and Emery, 2015;Chambers and Emery, 2016;Chambers et al, 2017).…”