Scaling of processes shaping the clonal dynamics and genetic mosaic of seagrasses through temporal genetic monitoring

Abstract

Theoretically, the dynamics of clonal and genetic diversities of clonal plant populations are strongly influenced by the competition among clones and rate of seedling recruitment, but little empirical assessment has been made of such dynamics through temporal genetic surveys. We aimed to quantify 3 years of evolution in the clonal and genetic composition of Zostera marina meadows, comparing parameters describing clonal architecture and genetic diversity at nine microsatellite markers. Variations in clonal structure revealed a decrease in the evenness of ramet distribution among genets. This illustrates the increasing dominance of some clonal lineages (multilocus lineages, MLLs) in populations. Despite the persistence of these MLLs over time, genetic differentiation was much stronger in time than in space, at the local scale. Contrastingly with the short-term evolution of clonal architecture, the patterns of genetic structure and genetic diversity sensu stricto (that is, heterozygosity and allelic richness) were stable in time. These results suggest the coexistence of (i) a fine grained (at the scale of a 20 Â 30 m quadrat) stable core of persistent genets originating from an initial seedling recruitment and developing spatial dominance through clonal elongation; and (ii) a local (at the scale of the meadow) pool of transient genets subjected to annual turnover. This simultaneous occurrence of initial and repeated recruitment strategies highlights the different spatial scales at which distinct evolutionary drivers and mating systems (clonal competition, clonal growth, propagule dispersal and so on) operate to shape the dynamics of populations and the evolution of polymorphism in space and time. Keywords: clonality; seagrass; spatio-temporal genetic structure; Zostera marina INTRODUCTION Clonality is a life history trait widely distributed among taxa and habitats, particularly in photosynthetic organisms. Partially clonal organisms are characterized by a mixed system allowing the combination of two reproductive strategies: the production of new genetically identical modules through vegetative growth or fragmentation and the production of new genetic individuals through sexual recombination. As a consequence, their population dynamics and evolutionary trajectories are profoundly affected by their rate and mode of clonal reproduction. Populations of clonal plants are composed of genetic individuals, or genets occupying space and dispersing locally through the production of modular shoots, or ramets (Harper, 1977). As genets are able to persist through time and space, the composition and evolution of populations of clonal plants is largely affected by the level of intraspecific competition (Eriksson, 1989(Eriksson, , 1993Pan and Price, 2001;Travis and Hester, 2005).Depending on the turnover of genets and intensity of inter-genet competition for space, two extreme recruitment strategies have been defined (Eriksson, 1993): (i) the 'Initial Seedling Recruitment' (ISR) strategy, characterizing populations originating fro...

The importance of sampling design: spatial patterns and clonality in estimating the genetic diversity of coral reefs

“…Other studies that revealed paradoxical spatial patterns of genetic diversity (e.g., chaotic genetic patchiness; Johnson and Black 1982) may simply be revealing the underlying variance associated with small samples sizes (see Becheler et al 2010Becheler et al , 2013 for alternative explanations). For example, for the smallest sample size in Fig.…”

Species are hypotheses: avoid connectivity assessments based on pillars of sand

“…Fine-grained analysis of clonal lineage distribution in Zostera marina Linnaeus, 1753, revealed a large influence of clonality, leading to a mosaic pattern of genetic patchiness. This pattern is largely driven by patchy events of recolonization followed by the occupation of space through clonal spread, despite the likely occurrence of much larger scale effective migration (Becheler et al 2010(Becheler et al , 2014. The genetic concept of populations, based on panmixia, remains elusive in those partially clonal organisms.…”

Genetic temporal dynamics in restored wetlands: A case of a predominantly clonal species, Berula erecta (Huds.) Coville

“…We expected that restoration would result in an increase in vegetative multiplication of the species due to higher water levels after the restoration event compared to the pre-restoration stage. As a consequence, we expected a greater decline in clonal richness over time in restored wetlands vs. unrestored wetlands when comparing the two conditions over the same period of time (Becheler et al, 2014). Additionally, as vegetative propagation increases the probability of genotype survival over time, we hypothesised that genetic diversity would remain more stable in restored wetlands than in unrestored reference wetlands over time, even if clonality potentially increased over time in restored wetlands.…”

“…During a 3-year-long study, Becheler et al (2014) observed that select genets persisted and extended over time, whereas other genets were recruited each year. However, they only highlighted the stability of genetic diversity over the time scale of the study.…”

“…temporal variability in fecundity and higher elasticity of fecundity in short-lived species (Gomaa et al, 2011). Clonality, which is a very common method of plant colonisation, enhances genet longevity considerably, thereby rendering clonal plants as being potentially immortal (de Witte and Stocklin, 2010;Becheler et al, 2014). Clonal plants can compensate for partial losses in genetic variability due to disturbances and therefore can secure population persistence for long periods of time (de Witte and Stocklin, 2010).…”