Spatial genetic structure of aquatic bryophytes in a connected lake system

Abstract

Using genetic markers, we investigated the genetic structure of three clonal aquatic moss species, Calliergon megalophyllum Mikut., Fontinalis antipyretica Hedw. and F. hypnoides Hartm. on two scales: among populations in a connected lake system (large-scale spatial genetic structure) and among individuals within populations (fine-scale spatial genetic structure). Mean genetic diversities per population were 0.138, 0.247 and 0.271, respectively, and total diversities equalled 0.223, 0.385 and 0.421, respectively. Relative differentiation levels (FST values of 0.173, 0.280 and 0.142, respectively) were significant but showed that there is a moderate amount of gene flow taking place within the lake system connected with narrow streams. Bayesian STRUCTURE analysis provided some indication that the direction of water flow influences population genetic structuring in the studied aquatic mosses. We propose that dispersal leading to gene flow in C. megalophyllum, F. antipyretica and F. hypnoides takes place both along water via connecting streams and by animal vectors, such as waterfowl. Nevertheless, the slight genetic structuring pattern along the direction of water flow suggests that dispersal of shoots or their fragments along water is a means of dispersal in these mosses. The absence of sexual reproduction and spores may have caused the observed spatial genetic structure within populations, including aggregations of similar genotypes (clones or closely related genotypes) at short distances in populations otherwise showing an isolation by distance effect. Regardless of the results pointing to the dominance of vegetative propagation, it is impossible to completely rule out the potential role of rare long-distance spore dispersal from areas where the species are fertile.

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.…”

Asexual reproduction and protonemal developmentin vitroinFontinalis antipyreticaHedw.

“…From their study on the role of hydrochory (passive dispersal by water) on spatial genetic structure in the aquatic moss Rhynchostegium riparioides, Hutsemekérs et al (2013) concluded that shoot fragments rather than spores are involved in local dispersal and that the 'extremely limited routine dispersal' by these unspecialized diaspores, 'coupled with discrete episodes of population extinctions and colonizations by spores', account for the absence of a downstream increase in genetic diversity (which would be expected from downstream migration of propagules alone). Even in three purely clonal species (including F. antipyretica), where a downstream increase in genetic diversity should be expected, Korpelainen et al (2013) found no relationship between genetic similarity and distance after a few hundred meters and concluded that rare events of upstream dispersal of gametophyte fragments by waterfowls may take place, although they could not rule out completely a potential role of rare longdistance spore dispersal from areas where the species were fertile.…”

“…If F. antipyretica does produce the same array of vegetative diaspores in the wild as observed in vitro, this would add a new, important, dimension to any study of the dispersal capacity of F. antipyretica and how this might affect spatial patterns of genetic structure and diversity in this aquatic species. Hitherto, such studies on F. antipyretica and other aquatic mosses (Korpelainen et al, 2013;Hutsemekérs et al, 2013) have assumed that these plants are able to disperse by spores and/or unspecialized vegetative propagules i.e. shoot fragments only.…”

“…exposure to air) as is the case for sporophytes, these, on a par with spores, might be air-rather than water-dispersed (Vitt & Glime, 1984). Thus not only shoot fragments transported upstream by animal vectors, but also air-transported protonemal gemmae and brood cells might have influenced the unexpected patterns of genetic diversity reported by Korpelainen et al (2013) in F. antipyretica.…”

Flooding and fragment size interact to determine survival and regrowth after fragmentation in two stoloniferous Trifolium species

“…Clonal species can quickly resprout from dormant meristems after clone fragmentation, by reallocating resources stored in the stolons and rhizomes to the sites of new leaf and root production (Klimesova and Klimes 2007). Apart from the negative effects of flooding-induced disturbance, flooding may also play an important role as a long-distance dispersal agent (Korpelainen et al 2013). Clonal fragments may be spread along the riverine systems during flooding events, thereby allowing plants to invade new habitats or already established populations.…”