Phylogeography of Alpine populations of Rhytidium rugosum (Bryophyta) in a European context
Alp Botany
Phylogeography of Alpine populations of Rhytidium rugosum (Bryophyta) in a European context
Lars Hedena¨s 0 1
0 Department of Botany, Swedish Museum of Natural History , 50007, 104 05 Stockholm , Sweden
1 & Lars Hedena ̈s
The phylogeography and possible origins of the moss Rhytidium rugosum (Hedw.) Kindb. in the European Alps are studied based on information from the nuclear internal transcribed spacers 1 and 2 and a portion of the gene region for glyceraldehyde 3-phosphate dehydrogenase for 364 European specimens. Seventy-three Alps specimens were sampled from W Switzerland to W Austria, and were divided into four regional populations along a WestSouth-West (WSW) to East-North-East (ENE) gradient. These populations were compared with similar ones previously studied in other parts of Europe. The ENE-most Alps population, located ENE of the Adige break zone, deviates genetically from the other three. The two WSWmost populations of the Alps appear to be relatively isolated from most of the European populations outside the Alps, whereas the two ENE ones are similar to populations of northern Scandinavia. Populations in between the Alps and the Scandinavian mountain range deviate from those to the north and south, possibly due to low effective population sizes, earlier bottleneck events, or colonization from different source populations. Haplotype diversity and number of private haplotypes are marginally higher in the Alps than in Scandinavia. It is suggested that European Rhytidium originated from late glacial maximum refugia in (1) E-NE Europe, (2) in between the Late Glacial Maximum ice shields of Scandinavia and the Alps, and (3) S, SW, and W of the Swiss Alps. Those of the E Alps potentially originated mainly in E-NE Europe and those of the W Alps in the S, SW, and W.
Break zone; Haplotype; Intraspecific diversity; Private haplotype; Spore-dispersed plants
Introduction
Numerous investigations have focused on the post-glacial
colonization or phylogeographic patterns of different
portions of Europe, using molecular evidence
(e.g. Brochmann
et al. 2003; Hedena¨s 2015; Hewitt 2000; Jaarola et al. 1999;
Kyrkjeeide et al. 2014; Parducci et al. 2012; Taberlet et al.
1998)
. Several recent studies concerned plants, especially
flowering plants, in the European Alps (from here on called
‘the Alps’)
(e.g. Gugerli and Holderegger 2001;
Scho¨nswetter et al. 2005; Thiel-Egenter et al. 2011)
. Source
populations for late- to post-glacial colonization of the Alps
by plants occurred in glacial refugia in the lowlands, often
along the margins of the glaciated area, or on nunataks
within the ice shield, and the molecular evidence for such
refugia was summarized by Scho¨nswetter et al. (2005).
Many flowering plant species of the Alps seem not yet to
have colonized all potential habitats due to limited dispersal
abilities
(Dullinger et al. 2012; Scho¨nswetter et al. 2005)
.
Where environmental conditions hinder efficient dispersal
of species or intraspecific entities of different origins, break
zones are found where the turnover in species and/or
genotypes within species is markedly higher than elsewhere
(Thiel-Egenter et al. 2011)
. More break zones exist at the
species compared with the genotype level among flowering
plants, due to differences in dispersal potential between
species (dispersed by seeds) and genotypes (by pollen and
seeds). Two major break zones where species and genotype
patterns coincide occur around the Aoste valley in the west
and around the Adige valley in the east
(Thiel-Egenter et al.
2011)
.
In organisms like bryophytes and fungi, which disperse
by spores, sizes of dispersal units are usually in the lower
range of pollen grains. This means that the dispersal
potentials of both species and intraspecific entities are
similar to that of pollen in flowering plants. Spores below c.
20 lm are efficiently dispersed by wind
(Wilkinson et al.
2012)
and in open, windy environments with few or no trees
also small vegetative fragments are easily spread
(Flø and
Ha˚gvar 2013; Miller and Ambrose 1976)
. Phylogeographic
patterns of such organisms should thus be more similar to
those proposed for small organisms in a meta-community
perspective (De Meester 2011) than to the average flowering
plant species. Factors that could contribute to intraspecific
structure in spore-dispersed organisms include past or
present dispersal barriers, the ‘founder takes all’
densitydependent principle
(Waters et al. 2013)
, niche
specialization
(Buckley et al. 2013; Mikula´sˇkova´ et al. 2014)
, and
genetic drift in isolated populations (Frankham et al. 2002).
Based on these characteristics and processes, we can
hypothesize that break zones in spore-dispersed organisms,
both at the species and intraspecific levels, should likely
mirror those of genotypes within widespread vascular
plants.
The number of studies of spore-dispersed organisms that
cover large portions of the Alps and its surroundings wit (...truncated)