Under which humidity conditions are moss spores released? A comparison between species with perfect and specialized peristomes

Abstract

Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%–65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long‐distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long‐distance dispersal capacities, might be seen as a safe‐site strategy, forcing spores to land in appropriate (micro‐) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.

Microclimatic variation in tropical canopies: A glimpse into the processes of community assembly in epiphytic bryophyte communities

“…Peristome reduction is itself significantly associated with hygrochasy, i.e., the release of spores under wet conditions (Zanatta et al, 2018), further decreasing chances of long-distance dispersal but enhancing rates of establishment (Johansson et al, 2016).…”

To what extent are bryophytes efficient dispersers?

“…Peristome movements are essential to regulate the dispersal of spores and play an active role in closing and opening the mouth of the capsule depending on variation in air humidity and vibrations caused by wind turbulence (Johansson, Lönnell, Rannik, Sundberg, & Hylander, 2016;Johansson, Lönnell, Sundberg, & Hylander, 2014;Lönnell et al, 2015). Hygrochastic peristomes open-up upon increasing relative humidity, when high chances of rain hamper the chances of wind LDD, favouring SSD as a safe-site strategy in species from patchy and dynamic habitats (Medina & Estebanéz, 2014;Zanatta et al, 2018), in line with the dispersal limitations evidenced by the analysis of genetic structures. Xerochastic peristomes, in turn, open-up upon decreasing air humidity, which Johansson et al (2016) interpreted as an adaptive mechanism favouring the release of spores in the morning, when the heating from the sun creates upward air movements.…”

Evidence of endozoochory in upland geese Chloephaga picta and white‐bellied seedsnipes Attagis malouinus in sub‐Antarctic Chile

“…Bryophytes, as most land plants, are sessile organisms depending on biotic or abiotic vectors to disperse propagules to other areas. Their movement is made possible via wind dispersal facilitated by sexual reproduction morphological features such as exposed spores, tall sporophytes, or the production of a large number of spores (Barbé et al., 2016; Muñoz, 2004); or via water dispersal, such as gemma or splash cups (Glime, 2017a, 2017b; Zanatta et al., 2018). On the other hand, some species of the Splachnaceae family, such as Tayloria dubyi , have even been known to have sticky spores and brightly colored sporophytes that emit a strong odor, mimicking decomposing organic matter, to attract flies as potential dispersal vectors (Jofre et al., 2011).…”

“…Their movement is made possible via wind dispersal facilitated by sexual reproduction morphological features such as exposed spores, tall sporophytes, or the production of a large number of spores (Barbé et al, 2016;Muñoz, 2004); or via water dispersal, such as gemma or splash cups (Glime, 2017a(Glime, , 2017bZanatta et al, 2018).…”