Genetic characteristics of populations can have substantial impacts on the adaptive potential of a species. Species are heterogeneous, often defined by variability at a range of scales including at the genetic, individual and population level. Using microsatellite genotyping, we characterize patterns underlying the genetic heterogeneity in marine macroalga Fucus vesiculosus, with a particular focus on two forms: attached and free‐living. Here we demonstrate that sympatric populations representing the two forms display marked differences in characteristics of reproduction and genetic diversity. Asexual reproduction was ubiquitous in the free‐living form despite being almost entirely absent in the attached form, while signals of polyploidy were common in both forms despite the distinct reproductive modes. Gene flow within and between the forms differed, with barriers to gene flow occurring between forms at various spatial scales due to the reproductive modes employed by individuals of each form. The divergent genetic characteristics of F. vesiculosus demonstrate that intraspecific differences can influence the properties of populations with consequential effects on the whole ecosystem. The differing genetic patterns and habitat requirements of the two forms define separate but closely associated ecological entities that will likely display divergent responses to future changes in environmental conditions.
Intraspecific variation is an important component of heterogeneity in biological systems that can manifest at the genotypic and phenotypic level. This study investigates the influence of genetic characteristics on the phenotype of free‐living Fucus vesiculosus using traditional morphological measures and microsatellite genotyping. Two sympatric morphotypes were observed to be significantly genetically and morphologically differentiated despite experiencing analogous local environmental conditions; indicating a genetic element to F. vesiculosus morphology. Additionally, the observed intraclonal variation established divergent morphology within some genets. This demonstrated that clonal lineages have the ability to alter morphological traits by either a plastic response or somatic mutations. We provide support for the potential occurrence of the Gigas effect (cellular/organ enlargement through genome duplication) in the Fucus genus, with polyploidization appearing to correlate with a general increase in the size of morphological features. Phenotypic traits, as designated by morphology within the study, of F. vesiculosus are partially controlled by the genetic characteristics of the thalli. This study suggests that largely asexually reproducing algal populations may have the potential to adapt to changing environmental conditions through genome changes or phenotypic plasticity.
Sequencing of a mitochondrial intergenic spacer and 23S subunit was used to investigate the phylogeographic patterns in Fucus vesiculosus. Samples originated from 21 sites spanning six subbasins of the Baltic Sea. We identify a putative ancestral mitochondrial haplotype that entered the Baltic Sea from the Atlantic, colonising extensively throughout the species’ distribution. The dominance of this haplotype is seen in the low overall haplotype diversity (H d = 0.29). Moreover, there is indication of few spatially aggregated patterns in the deeper demographic time scales (F ct = 0.040; F st = 0.049). Tajima’s D (−0.685, p-value 0.297) and Fu’s F S (0.267, p-value 0.591) showed no significant signals of extreme demographic changes. The Baltic Sea free-living Fucus is confirmed as F. vesiculosus or a closely related species. Haplotype diversities are comparable between forms (attached H d = 0.306; free-living H d = 0.268). The relatively short temporal scale for colonisation alongside low variance in the Fucus mitochondrial genome results in a rather panmictic structure across the Baltic Sea. Our data suggest that the mitochondrial intergenic spacer and 23S poorly describe the evolutionary dynamics of Fucus spp. in such a young, postglacial environment, yet this concatenated-barcode advances our understanding of the colonisation dynamics of F. vesiculosus over deeper demographic timescales.
Habitat complexity can boost biodiversity by providing a wide range of niches allowing species co-existence. Baltic Sea benthic communities are characterised by low species diversity. Thus the occurrence of the habitat forming macroalgaFucus vesiculosusmay influence benthic communities and promote diversity. Here we obtain biodiversity estimates through conventional and eDNA approaches for the benthic assemblages associated with free-livingFucusand the adjacent bare-sediment habitats at six sites from the Northern Baltic Proper and the Gulf of Finland. Free-livingF. vesiculosushabitats are heterogeneous with biodiversity estimates varying considerably among sites. The additional habitat complexity provided byF. vesiculosustends to improve taxa richness as a result of additional epifauna assemblages, although infaunal taxa richness and abundance is often reduced. Consequently the complex habitats provided by free-livingF. vesiculosusoften improves biodiversity, yet alters the composition of assemblages in soft sediment habitats and consequential ecosystem functioning. We emphasise the disparity in biodiversity estimates achieved when employing different biodiversity approaches. Biodiversity estimates were more similar within approaches compared to between habitat types, with each approach detecting exclusive taxa. We suggest that biodiversity estimates benefit from a multi-approach design where both conventional and eDNA approaches are employed in complement.
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