Contrasting genetic diversity patterns in two sister kelp species co‐distributed along the coast of Brittany, France

Abstract

We investigated patterns of genetic structure in two sister kelp species to explore how distribution width along the shore, zonation, latitudinal distribution and historical factors contribute to contrasting patterns of genetic diversity. We implemented a hierarchical sampling scheme to compare patterns of genetic diversity and structure in these two kelp species co-distributed along the coasts of Brittany (France) using a total of 12 microsatellites, nine for Laminaria hyperborea and 11 for Laminaria digitata, of which eight amplified in both species. The genetic diversity and connectivity of L. hyperborea populations were greater than those of L. digitata populations in accordance with the larger cross-shore distribution width along the coast and the greater depth occupied by L. hyperborea populations in contrast to L. digitata populations. In addition, marginal populations showed reduced genetic diversity and connectivity, which erased isolation-by-distance patterns in both species. As L. digitata encounters its southern range limit in southern Brittany (SBr) while L. hyperborea extends down to mid-Portugal, it was possible to distinguish the effect of habitat continuity from range edge effects. We found that L. digitata did not harbour high regional diversity at its southern edge, as expected in a typical rear edge, suggesting that refuges from the last glacial maximum for L. digitata were probably not located in SBr, but most likely further north. For both species, the highest levels of genetic diversity were found in the Iroise Sea and Morlaix Bay, the two regions in which they are being currently harvested. Preserving genetic diversity of these two foundation species in these areas should, thus, be a priority for the management of this resource in Brittany.

Genetic diversity of Saccharina latissima (Phaeophyceae) along a salinity gradient in the North Sea–Baltic Sea transition zone

“…However, the complex circulation patterns, including turbulent mixing, vertical eddies and daily switches of current direction in the study area did not allow for such an approach. More replicates (particularly across Skagerrak/Kattegat) could strengthen our IBD inferences, but they generally agree with previous findings for several macroalgae (Durrant et al 2014) and for kelps specifically (Assis et al 2013, Robuchon et al 2014). …”

Status, trends and drivers of kelp forests in Europe: an expert assessment

“…Brittany constitutes a mosaic of contrasting conditions, with the western and north-western regions being colder and less affected by climate change than the other three regions (DerrienCourtel et al 2013;Gallon et al 2014). The highest abundance of L. digitata and L. hyperborea is found in these two colder regions and correlates with higher genetic diversity, although a trend of decrease in these specieś abundance is revealed for some parts of the central European coasts for small isolated marginal populations (Billot et al 2003;Valero et al 2011;Couceiro et al 2013;Robuchon et al 2014). Signs of maladaptive response (alteration of meiosis) of L. digitata at its southern edge of its distribution (Southern Brittany) became apparent where genetic diversity has declined (Oppliger et al 2014).…”

The importance of phenotypic plasticity and local adaptation in driving intraspecific variability in thermal niches of marine macrophytes

“…While most studies do not effectively disentangle the underlying mechanisms, it is plausible to assume that adaptation plays an influential role. The fine scale genetic structuring observed for many species (Valero et al 2011, Robuchon et al 2014 suggests that adaptation may be favoured, while experimental evidence also indicates that developmental plasticity and carry over effects do not drive differences in thermal phenotype along environmental gradients in seaweeds (Hays 2007). Thus, central populations may be vulnerable to both gradual and acute warming trends.…”

“…Unlike many marine species that have large dispersal capacities, marine macrophytes generally exhibit restrictive dispersal with seaweed spores settling within a few metres of the parent alga (Dayton 1985, Schiel and Foster 1986, Santelices 1990, Kendrick and Walker 1991, 1995, Norton 1992 and seagrass pollen and seed dispersal often limited to the meadow in which the adult plant inhabits (Zipperle et al 2011, Kendrick et al 2012. This often results in highly structured distributions (Valero et al 2011, Nicastro et al 2013, Robuchon et al 2014, Assis et al 2015, Neiva et al 2015 and means local ecotypes may be a common characteristic (Gerard and Du Bois 1988) in marine macrophytes, with any associated population decline unable to be ameliorated by migration (Bennett et al 2015, Assis et al 2017, Molinos et al 2017). However, it should be noted that even within this group some species exhibit larger scale dispersal capacities that can result in a closer tracking of habitat as niches shift (Duarte et al 2013).…”