Dispersal patterns of meiospores shape population spatial structure of saxicolous lichens

Abstract

4 Laboratorio analisi scientifica, Direzione ricerca e progetti cofinanziati, Soprintendenza per i beni e le attività culturali, Regione Autonoma Valle d'Aosta -Piazza Narbonne 3, 11100, Aosta, Italy AbstractRelationships between reproductive strategies and population spatial structure have been often suggested for lichens, but still not supported with experimental aerobiological data. For the first time, this study couples aerobiological investigations on meiospore dispersal by Caloplaca crenulatella (Nyl.) H. Olivier and Rhizocarpon geographicum (L.) DC. with the analysis of their local spatial patterns on the walls of a medieval castle in NW-Italy. During a two-year monitoring period carried out in the castle courtyard, a total of 169 polar diblastic spores, 20% of which were morphologically attributable to C. crenulatella, was detected in the mycoareosol, while muriform spores of R. geographicum were never found. Laboratory experiments confirmed that different dispersal patterns characterize the two species, the meiospores of R. geographicum being poorly discharged and only recovered at a short distance from the thalli, whereas those of C. crenulatella were more abundantly discharged, suspended and better dispersed by a moderate air flow. Such a difference was reflected on the castle walls by a random spatial pattern of C. crenulatella, while R. geographicum showed a clustered distribution. Different discharge rates and take-off limitations, possibly related to size differences between the spores, are not sufficient to explain the different colonization patterns and dynamics of the two species, and additional intrinsic and extrinsic factors likely drive the dispersal and establishment success. Nevertheless, information on the relationships between different dispersal patterns of the species and the local spatial structure of their populations may contribute to predict the recovery potential of lichen species exposed to habitat loss or disturbance, or encrusting monumental surfaces. Events of long-distance dispersal, favouring colonization of distant sites, followed by shortdistance dispersal, supporting a more local population expansion, were shown to explain the patchy lichen colonization in a former tree-less landscape (Gjerde et al. 2015). The productions of large asexual diaspores (isidia, soredia) and small sexually-generated meiospores are traditionally related to local and long distance dispersal, respectively (Hedenås et al. 2003;Leavitt & Lumbsch 2016). At the landscape scale, inferences from genetic population studies and spatial pattern analyses mostly supported this view, suggesting a tradeoff between a higher dispersal of meiospores, effective in landscapes with lower connectivity, and a higher establishment effectiveness of asexual diaspores in continuous landscapes (Ellis 2012). In-field measurements on diaspore dispersal generally showed short dispersal capabilities, but evidence on distributional ranges and phylogenetic studies suggested they are (2012) found a spatially structured pattern...

Differences in the sexual aposymbiotic phase of the reproductive cycles of Parmelina carporrhizans and P. quercina. Possible implications for their reproductive biology

“…Other studies have shown that species with spore sizes differing by one order of magnitude can have differences in ejection of two orders of magnitude, with those species with a smaller spore size ejecting more spores (Morando et al 2017). In contrast to the study of Morando et al (2017), we used two species of the same genus, which indicates that the reproductive strategies of genetically proximal species can differ substantially. Parmelina carporrhizans ejected upward fewer spores of greater size (and therefore with more reserve nutrients) and had a higher level of germination success in several culture media, while P. quercina ejected a greater number of smaller spores with lower germination success.…”

“…Our data suggest that P. carporrhizans and P. quercina could be used as models to test the "number-size theory" in lichens. Other studies have shown that species with spore sizes differing by one order of magnitude can have differences in ejection of two orders of magnitude, with those species with a smaller spore size ejecting more spores (Morando et al 2017). In contrast to the study of Morando et al (2017), we used two species of the same genus, which indicates that the reproductive strategies of genetically proximal species can differ substantially.…”

“…Sanders (2014) showed that in Calopadia puiggari macroconidia and photobiont cells were co-dispersed but that upon germination the fungus might grow away from the algal cells leaving them to form a free-living population. Apart from important but limited field observations, knowledge of lichen-forming fungal reproductive biology is still scarce for two reasons: their inability to successfully execute the complete reproductive cycle under in vitro conditions and the difficulty in tracing the reproductive propagules of most lichen species in nature (Schuster et al 1985; Ott 1987; Sanders 2014; Morando et al 2017). However, traceability of lichen spores could now be much easier thanks to the increased sensitivity of new methods developed by Eaton et al (2018) combining aerobiological traps with nested PCR protocols.…”

“…Johansson et al (2007) established a relationship between the age of trees and the size of spores of epiphytic lichens. Morando et al (2017) investigated the relationship between size and number of pores and spatial structure; they noted that discharge of fewer and larger spores could result in spore aggregation and reduced dispersion. As far as we know, no hypotheses in lichen-forming fungi have been proposed for the relationship between size and number of spores and germination success.…”

Diversity and functional traits of lichens in ultramafic areas: a literature‐based worldwide analysis integrated by field data at the regional scale

“…Following Giordani et al (2016, with refs therein), we selected traits associated with reproduction and ecophysiology (Table 3). Several traits play a decisive role in the phases of dispersal and establishment of new thalli: most of them include attributes related to morphological characteristics of the spores, such as their shape, number, dimension and color (Armstrong 1981; Morando et al 2017). Some eco-physiological functions, such as substrate colonization, evapotranspiration or photon absorption, are strictly related to lichen growth form (Palmqvist 2000), whereas some features (e.g.…”