Clonality, polyploidy and spatial population structure in Baltic Sea Fucus vesiculosus

Abstract

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.

Genetic characteristics influence the phenotype of marine macroalga Fucus vesiculosus (Phaeophyceae)

“…All collected thalli were also genotyped ( n = 115). For a detailed description of the microsatellite genotyping protocol, see Preston, Blomster, et al ( 2022 ) (including Supplementary Materials ). Microsatellite genotyping followed the aforementioned protocol exactly, although a brief summary is provided herein and in Table S1 .…”

“…Atypically for F. vesiculosus , the Baltic Sea distribution demonstrates facultative asexuality (Ardehed et al, 2016 ; Johannesson et al, 2011 ; Pereyra et al, 2013 ; Tatarenkov et al, 2005 ). Asexual reproduction, presumably by means of fragmentation and/or adventitious branches, is particularly pervasive within the free‐living form, although the prevalence of clonality is highly variable among populations (Preston, Blomster, et al, 2022 ). Accordingly, free‐living populations provide an ideal study system as they can consist of varying proportions of clones, either from single or multiple lineages, and unique multilocus genotypes (MLGs) (Preston, Blomster, et al, 2022 ).…”

“…are known to represent varying ploidy levels, with both allopolyploidy (hybridization between two or more related species) and autopolyploidy (multiplication of the whole genome of a single parent species) having been observed in natural populations (Coyer et al, 2006 ; Sjøtun et al, 2017 ). Recent investigations indicate that polyploidization may also occur within free‐living F. vesiculosus within the Baltic Sea (Preston, Blomster, et al, 2022 ). However, polyploidy in Fucus spp.…”

A review of reproduction in the seaweed genus Fucus (Ochrophyta, Fucales): Background for renewed consideration as a model organism

“…Recently, a study of attached (epilithic) and free-living (benthopleustophytic) forms of F. vesiculosus in the Baltic Sea revealed the presence of polyploidy (likely through autopolyploidy) throughout the majority of populations regardless of form with important implications in population structure (Preston et al, 2022).There is no direct evidence of sexual reproduction in the free-living form, which probably originated asexually via detached pieces of thalli aggregating in sheltered locations (Preston et al, 2022), and presumably without a functioning holdfast. Thus, the free-living form is at least 'ecad like'.…”

“…Although the free-living form was less genetically diverse than the attached, genetic diversity was still within expected limits for both forms and frequent asexual reproduction in the free-living form did not reduce the overall genetic variation in F. vesiculosus. Gene flow within and among the forms differed at various spatial scales, but the free-living populations were judged to be more unstable and at increased risk of local extinction (Preston et al, 2022).…”