Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans: in the field and after growth in a common-garden

Abstract

BackgroundMost species of brown macroalgae recruit exclusively sexually. However, Fucus radicans, a dominant species in the northern Baltic Sea, recruits new attached thalli both sexually and asexually. The level of asexual recruitment varies among populations from complete sexual recruitment to almost (> 90%) monoclonal populations. If phenotypic traits have substantial inherited variation, low levels of sexual activity will decrease population variation in these traits, which may affect function and resilience of the species. We assessed the level of inherited variation in nine phenotypic traits by comparing variation within and among three monoclonal groups and one group of unique multilocus genotypes (MLGs) sampled in the wild.ResultsOf the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.ConclusionsOur result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.

Reciprocal transplants support a plasticity-first scenario during colonisation of a large hyposaline basin by a marine macro alga

“…There is also support for local adaptation in other traits of Baltic Sea F. vesiculosus and F. radicans . For example, tolerance to emersion stress is lost in Baltic Sea populations following the switch to a more subtidal distribution [30], and a majority of genotypes in F. radicans have reduced tolerance to stress from desiccation and freezing [31]. Thus following the initial phase of establishment in the Baltic Sea supported by plasticity, the second phase involving selection towards increased fitness in hyposaline waters seems also to have extended the distribution of the F. vesiculosus lineage (including the F. radicans branch) to its current range margins in extremely low salinities (3–4‰).…”

Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment

“…Clones of F. radicans differ in inherited traits, such as tolerance to desiccation and freezing, and tolerance to grazing (as indicated by differences in phlorotannin content) (Johannesson et al. ). Thus, there is a basis for selection among clones, and opportunities for local adaptation of populations.…”

Increased resistance towards generalist herbivory in the new range of a habitat‐forming seaweed

“…Fucus vesiculosus produces polyphenolic secondary metabolites, phlorotannins, which can act as feeding deterrents against a number of herbivore species, including crustaceans (Targett and Arnold 1998, Amsler and Fairhead 2006, Jormalainen and Honkanen 2008. Phlorotannin production in F. vesiculosus and other fucoids is costly and show heritable genetic variation (Pavia et al 1999b, Jormalainen and Honkanen 2004, Jormalainen and Ramsay 2009, Johannesson et al 2012, thereby providing potential for defense evolution in response to changes in herbivore selection pressure.…”