Fern Gametophytes Exhibit Distinct Patterns of Niche Expansion and Convergence in Ecophysiological Functioning

ABSTRACT Ferns exhibit extraordinary ecological diversity, and their independent gametophyte and sporophyte stages make them distinct among other plant groups, yet the extent to which gametophyte and sporophyte ecology are coordinated is unknown. Here, we integrated spatial and climatic data to test the hypothesis that independent fern gametophytes occupy novel climatic niche space relative to their sporophytes. We also examined the physiological mechanisms in the gametophyte life stage that may underpin spatial patterns of fern ecology. We discovered that 57% of species examined have gametophytes that occupy novel climate niche space relative to their sporophytes and that this expansion occurs along specific axes of climate variation. We also discovered evidence of strong convergence in gametophyte ecophysiological function across broad environmental gradients. In particular, we found that gametophyte photosynthetic rate per mass was strongly linearly correlated to atmospheric water demand (e.g., potential evapotranspiration) and monotonically correlated to precipitation inputs. Taken together, these discoveries represent previously uncharacterized ecology and potential mechanisms that may drive spatial patterns of fern biodiversity.