The ecology and physiology of fern gametophytes: A methodological synthesis

Abstract

All green plants alternate between the gametophyte and sporophyte life stages, but only seed‐free vascular plants (ferns and lycophytes) have independent, free‐living gametophytes. Fern and lycophyte gametophytes are significantly reduced in size and morphological complexity relative to their sporophytic counterparts and have often been overlooked in ecological and physiological studies. Understanding the ecological and physiological factors that directly impact this life stage is of critical importance because the ultimate existence of a sporophyte is dependent upon successful fertilization in the gametophyte generation. Furthermore, previous research has shown that the dual nature of the life cycle and the high dispersibility of spores can result in different geographic patterns between gametophytes and their respective sporophytes. This variation in distribution patterns likely exacerbates the separation of selective pressures acting on gametophyte and sporophyte generations, and can uniquely impact a species’ ecology and physiology. Here, we provide a review of historical and contemporary methodologies used to examine ecological and physiological aspects of fern gametophytes, as well as those that allow for comparisons between the two generations. We conclude by suggesting methodological approaches to answer currently outstanding questions. We hope that the information covered herein will serve as a guide to current researchers and stimulate future discoveries in fern gametophyte ecology and physiology.

Methodologies in gametophyte biology

“…They specifically focus on the advantages and limitations of laboratory and greenhouse studies, highlighting the potential field studies that become possible as fern gametophytes are unambiguously identified through DNA barcoding techniques. Quinlan et al (2022) provide an excellent example of how DNA barcoding and TD-PCR may be applied to address some of the broad ecological questions highlighted by Krieg and Chambers (2022). Focusing on a tree fern common in Taiwan, Alsophila podophylla Hook., Quinlan et al successfully examined phenological patterns.…”

“…However, with advances in DNA barcoding, as reviewed by Nitta and Chambers ( 2022 ), many of these studies may now be possible. Krieg and Chambers ( 2022 ) provide an overview of the historical research and previously employed methods used to study fern gametophyte ecology and physiology over the past century. They specifically focus on the advantages and limitations of laboratory and greenhouse studies, highlighting the potential field studies that become possible as fern gametophytes are unambiguously identified through DNA barcoding techniques.…”

“…Quinlan et al ( 2022 ) provide an excellent example of how DNA barcoding and TD‐PCR may be applied to address some of the broad ecological questions highlighted by Krieg and Chambers ( 2022 ). Focusing on a tree fern common in Taiwan, Alsophila podophylla Hook., Quinlan et al successfully examined phenological patterns.…”

“…A major question regarding gametophytes is how well they respond to stressful conditions like desiccation or freezing compared to sporophytes. As reviewed in Krieg and Chambers ( 2022 ), much of the previous work on fern gametophyte ecology has occurred in laboratory or greenhouse settings. Schneller and Farrar ( 2022 ) also highlight this in their study but provide a way to examine stress responses over time in natural, undisturbed habitats.…”

High‐speed video and plant ultrastructure define mechanisms of gametophyte dispersal

“…Dispersal of these various gametophytes is essential in determining the geographic distribution of plants. This is especially true for non‐seed plants; for instance, the distribution of bryophytes and ferns is influenced by both local and long‐distance dispersal, resulting in most families and genera having broad, multicontinental distributions (Smith et al, 2006 ; Medina et al, 2011 ; Patiño and Vanderpoorten, 2018 ; Krieg and Chambers, 2022 ). A deeper understanding of the mechanisms of gametophyte dispersal is necessary to assess current biogeographical patterns of plants at multiple taxonomic levels as well as future patterns under climate change, habitat destruction, and other human‐induced changes.…”