Abstract
To understand colonization processes, it is critical to fully assess the role of dispersal in shaping biogeographical patterns at the gene, individual, population, and community levels. We test two alternative hypotheses (H I and H II) for the colonization of disturbed sites by clonal plants, by analyzing intraspecific genetic variation in one and reproductive traits in two typical fen mosses with separate sexes and intermittent spore dispersal, comparing disturbed, early‐succession (limed) fens and late‐successional rich fens. H I suggests initial colonization of disturbed sites by diverse genotypes of which fewer remain in late‐successional fens and an initially balanced sex ratio that develops into a possibly skewed population sex ratio. H II suggests initial colonization by few genotypes and gradual accumulation of additional genotypes and an initially skewed sex ratio that alters into the species‐specific sex ratio, during succession. Under both scenarios, we expect enhanced sexual reproduction in late‐successional fens due to resource gains and decreased intermate distances when clones expand. We show that the intraspecific genetic diversity, assessed by two molecular markers, in Scorpidium cossonii was higher and the genetic variation among sites was smaller in disturbed than late‐successional rich fens. Sex ratio was balanced in S. cossonii and Campylium stellatum in disturbed fens and skewed in C. stellatum in late‐successional fens, thus supporting H I. In line with our prediction, sex expression incidence was higher in, and sporophytes were confined to, late‐succession compared to disturbed rich fens. Late‐successional S. cossonii sites had more within‐site patches with two or more genotypes, and both species displayed higher sex expression levels in late‐successional than in disturbed sites. We conclude that diverse genotypes and both sexes disperse efficiently to, and successfully colonize new sites, while patterns of genetic variation and sexual reproduction in late‐successional rich fens are gradually shaped by local conditions and interactions over extended time periods.
Highlights
Since nature is dynamic, organisms need to disperse, either back to places where they recently got extinct or to new areas that have become suitable due to local disturbances or changes in climate or other environmental factors (Clobert et al, 2012; Corlett & Westcott, 2013)
Scorpidium cossonii spores that colonize the unoccupied limed fens represent the overall genetic variation in the spore rain of the study region, and the sampled shoots represent this spore rain after chance effects and environmental filtering during establishment
If the sexes differ in habitat requirements, one sex may prevail if the environment gradually changes during succession (Bisang et al, 2019; Stark et al, 2005)
Summary
Organisms need to disperse, either back to places where they recently got extinct or to new areas that have become suitable due to local disturbances or changes in climate or other environmental factors (Clobert et al, 2012; Corlett & Westcott, 2013). Hypothesis I: Many different genotypes establish on the exposed surfaces at disturbed sites, after which some genotypes gradually disappear and only those best adapted to the local conditions will remain This hypothesis suggests that the study species will have a higher site-level genetic diversity and, under conditions of unlimited dispersal, will be genetically more homogeneous across sites of limed fens than across sites of natural rich fens. The chance for male and female plants to meet increases when clones expand and intermix during habitat succession, which is expected to result in higher fertilization success and sporophyte production (Bisang et al, 2004), as long as it is not counteracted by sex-differential processes during succession To test these hypotheses, we examined haplotype and nucleotide diversity and distribution of genetic variation in S. cossonii, and sex expression and sex ratio in S. cossonii and C. stellatum, in disturbed limed and natural rich fens, representing early- and late-successional environments. We ask whether within-and between-site patterns of intraspecific genetic variation, sex ratios, and frequencies of sex expression in the study species agree with either of the hypotheses for recruitment of clonal plants in disturbed sites
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