Clonal structure and fertility in a sympatric population of the peat mosses Sphagnum rubellum and Sphagnum capillifolium

Abstract

Data from isozyme and leaf shape variation are combined to explore the clonal structure at a site where hybridization between Sphagnum rubellum and Sphagnum cupillifolium was previously indicated. Shoots of both species were sampled at 10-cm intervals along seven transects across different hummocks. Allelic data from 13 enzyme systems revealed 22 multilocus genotypes representing different clones, 18 being S. capiilifolim and 4 being S. nrbellum. The mean f SE and maximum clonal length were 35 f 8 cm and 160 cm, respectively. The sets of alleles found in the progeny of S. capillifolium were identical to the maternal complement of alleles in 78% of the material, indicating either self-fertilization or fertilization by a male with the same set of alleles at the screened loci. Outcrossing was detected in six cases. Patterns of differentiation and the hierarchical structuring of diversity among species, transects, a d clones were analysed with canonical variates analysis using stem-leaf characters. A stronger relative differentiation was found between transects than between species. Clones identified by electrophoresis were usually morphologically well defied. Hybridization was indicated by morphological characters, occasional misplaced alleles, and signs of developmental instability.RCsum4 : L'auteur a explod la structure clonale sur un site oh l'hybridation entre le Sphagnum rubellum et le Sphagnum capillifolium a d6jB &5 mentionn6e; 2i cette fin, ils ont regroup6 les donnhs isozymiques ainsi que celles de la variation morphologique des feuilles. Les tiges des deux espkes ont 6t6 Cchantillom6es h 10 cm d'intervalles, le long de sept transects passant par diffkrentes buttes. Les donall6liques venant de 13 systkmes eqmatiques r6vklent que 22 g6notypes B lieux multiples repdsentent diffkrents clones, 18 appartenant au S. capillifalium et 4 au S. nrbellum. La moyenne f l b e u r standard et la longeur maximale sont de 35 f 8 cm et 160 cm, respectivement. L'ensemble des allkles retrouv6s dans la pmg6nifure du S. capillifolium est identique au compl6ment maternel des all&les dans 78% du mathiel, ce qui indique qu'il y a soit auto-fkondation ou encore fertilisation par un mfile ayant le meme ensemble d'all&les au lieu 6tudi6. Des croisements ext6rieurs ont 6tt5 d6tectCs dans six cas. En appliquant l'analyse de variation canonique aux caractkres de la tige et des feuilles, l'auteur a analyst5 les patrons de differenciation et la structure hibrarchique de la diversit6 entre les esp&ces, les transects et les clones. Ils ont d6tectt5 une plus forte diffkenciation relative entre les transects qu'entre les espkes. Les clones identifibs par 6lectrophorhe sont gknbralement bien d6finis morphologiquement. L'hybridation est indiquh par les caractkres morphologiques, par des allkles occasionnellement d6placCs et par des signes de d6veloppement instable. Mots clds : allozymes, a d y s e d ' h g e s assist& par ordinateur, syst&me de croisement, structure clonale, Sphagnum rubeilm, Sphagnum capillifollium. [Traduit par la &laction] ln...

Sporophyte production and spore dispersal phenology in Sphagnum: the importance of summer moisture and patch characteristics

“…A suggestion is then that the area with 50% chance of sporophyte production over several years is an indication of mean clone size in dioecious Sphagnum species (range 0-8.9 dm 2 in the present study of which the highest figure is for S. rubellum). This then yields similar (or somewhat smaller) mean clone (= genet) sizes as Cronberg (1996a) showed for Sphagnum capillifolium and S. rubellum by isozyme studies.…”

“…Sjörs (1949), Jones (1986), and Soro et al (1999) provided strong evidence of successful Sphagnum colonizations by spores after long-distance dispersal, suggesting that regeneration by spores is important after disturbance and under reduced competition. The high level of genetic variation found within populations of most investigated sphagna suggests colonization by numerous individuals (Daniels 1982(Daniels , 1985Shaw and Srodon 1995;Cronberg 1996aCronberg , 1996bStenøien and Såstad 1999) and that this variation has a selective value along small-scale environmental gradients (Daniels 1985;Såstad et al 1999).…”

Ubiquitous genetic diversity in ISSR markers between and within populations of the asexually producing moss Pleurochaete squarrosa

“…It is widely known that, as a result of vegetative growth and dispersal, a single clone (genet) may cover large areas and constitute numerous patches (Appelgreen and Cronberg 1999). Studies carried out so far show that genetic variability also occurs in clonal species of bryophytes (Cronberg 1996(Cronberg , 2002Cronberg et al 2003;Shaw and Srodon 1995;Skotniki et al 1998Skotniki et al , 1999 but as a consequence of clonal growth, allelic frequencies observed in a population may be substantially different at each sampling site (Shaw 2000). In the clonal moss Sphagnum rubellum, for instance, the analysis of 100 shoots for 10 isozyme loci showed 7 different haplotypes, two of which, as an effect of clonal growth, covered a good 66% of the area colonised by the whole population (Shaw and Srodon 1995).…”

“…In addition, the high level of genetic variability detected in this moss also suggests that each genet has a rather small size (our unpublished observations indicate a clonal size of approximately 10-20 cm 2 ). Sexual reproduction, recruitment, and somatic mutation have been considered the main factors affecting the level and the amount of genetic variability in moss populations (Cronberg 1996(Cronberg , 2000(Cronberg , 2002Cronberg et al 2003;Skotnicki et al 1999;Van der Velde and Bijlsma 2003;Van der Velde et al 2001a, 2001b. However, reproduction in many bryophytes is largely or wholly asexual, because sporophytes are rarely or never produced, as in the case of P. squarrosa.…”

“…Genetic diversity in clonally growing moss species was also investigated, especially by employing enzymatic markers (Cronberg 1996(Cronberg , 2002Cronberg et al 2003;Shaw and Srodon 1995;Wyatt 1989) and several observations suggest that clonal growth greatly affects the genetic structure of moss populations, with gene diversity being generally low. In particular, the high frequency of single or few haplotypes in populations of clonal species seems to indicate that, in mosses, the effects of clonal growth on population structure are generally more noticeable than those of gene flow (Shaw 2000;Shaw and Srodon 1995).…”