Genetic variation in the moss Homalothecium lutescens in relation to habitat age and structure

Abstract

Relationships between genetic (allozyme) variation and landscape age and structure were investigated in 17 calcareous grassland demes of the moss Homalothecium lutescens (Hedw.) H. Rob. on the Baltic island of Öland. Mean within-deme gene diversity (H S = 0.152) was moderate compared with other bryophyte studies, and the between-deme proportion of the total diversity (G ST = 0.100, Jost's D = 0.011) was low but significantly different from zero. Clonal mixing, measured as the proportion of two adjacent shoots having different haplotypes, was relatively high (mean 0.32 over all demes). H S was higher in old grassland fragments, but negatively related to vascular plant species richness. Allelic richness (A) was positively associated with the area of old (≥ 280 years) grassland in the surroundings: although demes in old grasslands are genetically more variable than those in younger grasslands, proximity to large areas of old grassland may promote genetic variability even in younger grassland demes. The importance of management continuity for species diversity has been stressed in many earlier grassland studies. Here, we conclude that grassland fragments with a long history of grazing continuity are also positively associated with variability at within-species level, as exemplified by the bryophyte H. lutescens.Résumé : Dans dix-sept prairies calcaires de l'île d'Öland sur la Baltique, l'auteure a étudié les relations entre la variation génétique (allozyme) et l'âge, avec la structure des dèmes de la mousse Homalothecium lutescens (Hedw.) H. Rob. La variation génétique moyenne pour un dème donné (H S = 0,152) est modérée comparativement à d'autres études de bryophytes et la proportion de la variation totale entre dèmes (G ST = 0,100, Jost's D = 0,011) est faible, mais significativement différente de zéro. Le mélange clonal mesuré comme la proportion de deux tiges adjacentes ayant des haplotypes différents, est relativement élevée (moyenne de 0,32 pour l'ensemble des dèmes). La diversité génétique pour H S s'avère plus élevée dans les fragments de vieilles prairies, mais négativement reliée à la richesse en espèces de plantes vasculaires. La richesse allélique (A) montre une association positive reliée avec l'aire de la vieille prairie (≥ 280 ans) environnante : bien que les dèmes de la vieille prairie soient génétique-ment plus variables que celles des prairies plus jeunes, la proximité de grandes surfaces de vieilles prairies peut promouvoir la variabilité génétique, même dans les dèmes des prairies plus jeunes. On a déjà souligné l'importance de la continuité de l'aménagement pour la diversité des espèces dans des études antécédentes sur les prairies. L'auteure conclut que les fragments de prairies ayant connu une longue continuité de pâturage sont également associés avec de la variabilité à l'échelle intra spécifique, comme le montre la bryophyte H. lutescens. [Traduit par la Rédaction]

Production of diaspores at the landscape level regulates local colonization: an experiment with a spore‐dispersed moss

“…Surprisingly, there was no eff ect at the smallest scale (1 km), even when the actual number of occurrences of the species in the surrounding area was used as the explanatory variable. However, as noted in the introduction several other studies on genetic structure and occurrence patterns suggest more restricted dispersal at a landscape scale (Sn ä ll et al 2004a, Hutsem é kers et al 2013, Korpelainen et al 2013, Rosengren et al 2013. Initially, this appears to be counterintuitive since we know that there is a steep decline in deposition of diaspores (also shown for spores) from a point source (S ö derstr ö m and Jonsson 1989, Bullock and Clarke 2000, Roads and Longton 2003, Sundberg 2005, L ö nnell et al 2012.…”

“…Moreover, in a recent study of deposition patterns of Sphagnum spores, it was found that a connectivity of 200 km provided the best explanation for the deposition (Sundberg 2013). However, as noted in the introduction several other studies on genetic structure and occurrence patterns suggest more restricted dispersal at a landscape scale (Sn ä ll et al 2004a, Hutsem é kers et al 2013, Korpelainen et al 2013, Rosengren et al 2013. In light of the investigations suggesting good dispersal capacities, our result should not be altogether surprising, and it is even possible that we could have found a stronger relationship between colonization rates and extent of clay-dominated soils if we had implemented a design that allowed us to investigate even larger scales.…”

Surrounding landscape structures, rather than habitat age, drive genetic variation of typical calcareous grassland plant species

“…Central European calcareous grasslands represent local biodiversity hotspots due to their long existence, habitat diversity, and species richness (Steffan-Dewenter and Tscharntke 2002; Karlik and Poschlod 2009;Poschlod 2017). More precisely, they constitute valuable habitats for many specialised, rare, and endangered plant or insect species and are, therefore, considered as key areas for biodiversity conservation in agricultural landscapes (Raatikainen et al 2009;Rosengren et al 2013).…”

Rhytidium rugosum(Bryophyta) colonized Scandinavia from at least two glacial refugial source populations

“…Most probably haplotypes additional to these occurred in the lowlands during the early post‐glacial period. Genetic diversity in a population usually increases with time when a species is abundant and the connectivity among populations is good (Cronberg, ; Wang et al ., ; Rosengren et al ., ), but habitat fragmentation leading to small and isolated populations negatively affects their genetic diversity (Aguilar et al ., ). Thus, when the vegetation of the Swedish lowlands gradually closed, the three largest extant lowland populations of R. rugosum became smaller and increasingly isolated from each other and from those of the mountain range.…”