Meadow-scale genetic structure in Posidonia oceanica

Abstract

Posidonia oceanica (L.) Delile meadows are long-lived systems that persist in the field for millennia. The age and size of single clones have not been clearly assessed, nor has the withinmeadow dispersal of sexual propagules and neighbourhood size. The present study describes the genetic structure of an ancient and large P. oceanica meadow, extending from 3 to 33 m depth, that has been analyzed utilizing 13 variable microsatellite loci. A total of 180 single shoots (ramets) was sampled in 21 areas selected at nodes of a 160 × 400 m grid superimposed on the meadow. For each area, shoots were collected at a reciprocal distance of 1 to 5 m. The number of distinct genotypes was assessed for each sampling area and mapped on the grid using a kriging technique. Neighbourhood size and meadow-scale gene flow were assessed by means of autocorrelation analysis. Data indicate that the meadow is composed of a number of distinct clones, some of which might be hundreds of years old. Different sample groups were identified within the meadow by means of a Bayesian approach. The pattern of genetic diversity is not always related to shoot density, but it increases in the deepest stand, where density is lower. Spatial autocorrelation analysis showed a significant correlation up to 70 or 40 m, considering all samples or only distinct genotypes, respectively. The P. oceanica meadow analyzed seems to result from initial recruitment events and active clonal growth of originally established genotypes.

Fish herbivory leads to shifts in seagrass Posidonia oceanica investments in sexual reproduction

“…This requires herbivore-free refuges to serve as source areas within the metapopulation (Arnaud-Haond et al 2007, Rozenfeld et al 2008. Deeper P. oceanica meadows, where herbivores do not forage (Tomás et al 2005) could serve as refuges from herbivory, and thus facilitate genetic flow, although low genetic flow seems to occur between shallow and deep meadows (Procaccini & Mazzella 1998, Migliaccio et al 2005). In addition, most unprotected, shallow meadows today have very low densities of Sarpa salpa and may also supply recruits to highly grazed meadows.…”

Comparison of ISSR and SSR markers for analysis of genetic diversity in the seagrass Posidonia oceanica

“…P. oceanica has a monoecious mating system and potentially long-range dispersal by floating fruits and detached vegetative fragments. Sexual reproduction occurs irregularly throughout the whole basin and very large clones, extending over more than 100 m, can be found within the meadows (Migliaccio et al 2005). P. oceanica meadows, like other seagrass ecosystems, are extremely sensitive to the moderate to high levels of disturbances often associated with highly human impacted coasts (Procaccini et al 2003).…”

“…Recent and significant advances in population genetics of P. oceanica have been made possible by the selection of highly polymorphic dinucleotide microsatellites (Alberto et al 2003). Data obtained with those markers changed the perception of P. oceanica as a species with low genetic variability by detecting, at least in some localities, very high levels of genetic diversity (Arnaud-Haond et al 2005, Migliaccio et al 2005.…”

Seed nutrient content and nutritional status of Posidonia oceanica seedlings in the northwestern Mediterranean Sea

“…Recruitment by seeds has been observed only occasionally in the field (Buia & Mazzella 1991, Balestri et al 1998b, Piazzi et al 1999, Diaz Almela et al 2008. Although densities as high as to 480 germinated seeds m -2 have been detected in favorable sites, available data indicate that only a few seedlings can initiate new patches (Balestri et al 1998b, Alberto et al 2003, Jover et al 2003, Migliaccio et al 2005, Balestri & Lardicci 2008, Diaz Almela et al 2008. It seems that newly established seedlings rely on seed C-based reserves for most of the 1st year (Balestri et al 1998b, Belzunce et al 2005), but subsequently a large proportion of them (ca.…”