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

Abstract

The North Sea-Baltic Sea transition zone constitutes a boundary area for the kelp species Saccharina latissima due to a strong salinity gradient operating in the area. Furthermore, the existence of S. latissima there, along Danish waters, is fairly patchy as hard bottom is scarce. In this study, patterns of genetic diversity of S. latissima populations were evaluated along the salinity gradient area of Danish waters (here designated brackish) and were compared to reference sites (here designated marine) outside the gradient area, using microsatellite markers. The results showed that the S. latissima populations were structured into two clusters corresponding to brackish versus marine sites, and that gene flow was reduced both between clusters and between populations within clusters. In addition, results provided empirical evidence that marginal populations of S. latissima in the salinity gradient area exhibited a distinct genetic structure when compared to marine ones. Brackish populations were less diverse, more related, and showed increased differentiation over distance compared to marine populations. The isolation of the brackish S. latissima populations within the salinity gradient area of Danish waters in conjunction with their general low genetic diversity makes these populations vulnerable to ongoing environmental and climate change, predicted to result in declining salinity in the Baltic Sea area that may alter the future distribution and performance of S. latissima in the area.

Fine-scale population genetic structure of sugar kelp,Saccharina latissima(Laminariales, Phaeophyceae), in eastern Maine, USA

“…across broad spatial scales. For example, kelp population comparisons across greater geographic distances in the North and Baltic Seas, as well as in Chinese and Japanese waters, exhibited genetic differentiation an order of magnitude larger (F ST > 0.1) than those observed in the present study (Liu et al 2012; Nielsen et al 2016). Small but significant population structuring, however, was still evident across the small spatial scale in eastern Maine waters, including among individuals in the major embayments of Penobscot, Frenchman, and Cobscook Bays.…”

“…In addition, two loci used in the present study were monomorphic across populations. Using the same markers, most individual kelp populations in European waters exhibited larger allelic richness and heterozygosity, irrespective of geographic location (Nielsen et al 2016; Paulino et al 2016). The only previously sampled European population, at these markers, to exhibit somewhat similar heterozygosities to those in the present study was found in the more isolated Vejle Fjord in Denmark (H o = 0.318, H e = 0.358), which was within the North Sea-Baltic salinity transition zone and characterized by a small population size and limited connectivity (Nielsen et al 2016).…”

“…Using the same markers, most individual kelp populations in European waters exhibited larger allelic richness and heterozygosity, irrespective of geographic location (Nielsen et al 2016; Paulino et al 2016). The only previously sampled European population, at these markers, to exhibit somewhat similar heterozygosities to those in the present study was found in the more isolated Vejle Fjord in Denmark (H o = 0.318, H e = 0.358), which was within the North Sea-Baltic salinity transition zone and characterized by a small population size and limited connectivity (Nielsen et al 2016). Less genetic diversity was also detected in some populations of other algal species, including the kelp Laminaria digitata (Hudson) J.V.Lamouroux and the red alga Gigartina skottsbergii Setchell & N.L.Gardner, which were either spatially isolated by habitat discontinuities or in marginal zones of their geographic distribution, and exhibited significant, recent bottleneck effects (Billot et al 2003; Faugeron et al 2004; Robuchon et al 2014).…”

“…PCR was conducted in 15 µl volumes using 2 µl of DNA template, 1 × Promega GoTaq Flexi PCR buffer (Promega, Madison, WI, USA), 1.5–2.5 mM MgCl 2 , 0.2 µg/µl bovine serum albumin, 0.28 mM dNTPs, 0.1–0.3 µM of each primer, and 0.2 U GoTaq Flexi DNA polymerase. Multiplex PCRs were conducted following guidelines in Nielsen et al 2016, except different fluorescent dyes were used to label either the forward or reverse primer: 1) SLN319 (FAM-labeled), SLN320 (FAM), SLN34 (HEX), and SLN35 (HEX), 2) SLN58 (FAM) and SLN62 (HEX), and 3) SLN32 (NED) and SLN36 (HEX). Other loci were used individually in PCR reactions, including SLN54 (HEX), SLN314 (FAM), SLN510 (FAM), and SLN511 (HEX).…”

“…To this end, the purpose of the present study was to characterize the fine-scale population genetic structure of sugar kelp in eastern Maine. Recently, twelve polymorphic microsatellite loci were identified in S. latissima and used to characterize the genetic population structure along a salinity gradient in the North Sea-Baltic transition zone (Nielsen et al 2016). To our knowledge, however, these loci have not been assessed in boreal, northwest Atlantic populations, which also represents an opportunity to further evaluate the genetic diversity of this species.…”