Abstract
Spore-producing organisms have small dispersal units enabling them to become widespread across continents. However, barriers to gene flow and cryptic speciation may exist. The common, haploid peatmoss Sphagnum magellanicum occurs in both the Northern and Southern hemisphere, and is commonly used as a model in studies of peatland ecology and peatmoss physiology. Even though it will likely act as a rich source in functional genomics studies in years to come, surprisingly little is known about levels of genetic variability and structuring in this species. Here, we assess for the first time how genetic variation in S. magellanicum is spatially structured across its full distribution range (Northern Hemisphere and South America). The morphologically similar species S. alaskense was included for comparison. In total, 195 plants were genotyped at 15 microsatellite loci. Sequences from two plastid loci (trnG and trnL) were obtained from 30 samples. Our results show that S. alaskense and almost all plants of S. magellanicum in the northern Pacific area are diploids and share the same gene pool. Haploid plants occur in South America, Europe, eastern North America, western North America, and southern Asia, and five genetically differentiated groups with different distribution ranges were found. Our results indicate that S. magellanicum consists of several distinct genetic groups, seemingly with little or no gene flow among them. Noteworthy, the geographical separation of diploids and haploids is strikingly similar to patterns found within other haploid Sphagnum species spanning the Northern Hemisphere. Our results confirm a genetic division between the Beringian and the Atlantic that seems to be a general pattern in Sphagnum taxa. The pattern of strong genetic population structuring throughout the distribution range of morphologically similar plants need to be considered in future functional genomic studies of S. magellanicum.
Highlights
Cosmopolitan species occurring at every continent and in all biomes are rare [1]
Fifty-nine of the S. magellanicum plants were diploid based on the observation that 50% or more of the microsatellite loci had two alleles [67]
With K = 3, the diploid formed one distinct genetic group, while haploid data were divided in two other groups
Summary
Cosmopolitan species occurring at every continent and in all biomes are rare [1]. In some organism groups, such as birds and spore-producing plants, species have wide distribution ranges covering many, if not all continents and biomes [1,2]. Spore-producing organisms, such as lichens and bryophytes, have microscopic dispersal units, generally less than 40 μm [8,9]. Spore-producing organisms typically have wide distribution ranges [11,12,13,14,15,16] that span multiple continents [11,14], sometimes including both the Northern and Southern Hemisphere [6,17]. Multiple founder events of remote islands seem common in sporeproducing plants [24,25], supporting the interpretation that long-distance dispersal occurs repeatedly
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