Factors affecting formation of adventitious branches in the seaweeds Fucus vesiculosus and F. radicans

Abstract

Background In the brackish Baltic Sea, shedding of adventitious branches is central to asexual recruitment of new thalli in the brown algae Fucus vesiculosus and F. radicans . To test which factors influence the formation of adventitious branches in brackish and in more marine conditions, we sampled 29 Fucus sites in the Baltic Sea (salinity 3–11) and 18 sites from the Danish straits, Kattegat, Skagerrak, and the North Sea (salinity 15–35). Separately for each area, we used structural equation modelling to determine which of eight predictor factors (phosphate, nitrate, chlorophyll- a (as a proxy for turbidity), temperature, salinity, oxygen, grazing pressure, and thallus area) best explained observed numbers of adventitious branches. Results In more marine waters, high yearly average values of phosphate, salinity and turbidity had positive effects on the formation of adventitious branches. In brackish-waters, however, high numbers of adventitious branches were found in areas with low yearly average values of temperature, salinity and oxygen. Grazing intensity had no significant effect in either of the two study areas, contrasting findings from studies in other areas. In areas with both sexually and asexually reproducing Fucus individuals, clones had on average more adventitious branches than unique genotypes, although there was strong variation among clonal lineages. Conclusion This study is the first to investigate multiple potential drivers of formation of adventitious branches in natural populations of Fucus . Our results suggest that several different factors synergistically and antagonistically affect the growth of adventitious branches in a complex way, and that the same factor (salinity) can have opposing effects in different areas. Electronic supplementary material The online version of this article (10.1186/s12898-019-0239-7) contains supplementary material, which is available to authorized users.

Clones on the run: The genomics of a recently expanded partially clonal species

“…New clones are formed by shedding of adventitious branches, which reattach to the substratum and grow new individuals that are morphologically indistinguishable from sexually recruited individuals, including sexual organs (Tatarenkov et al, 2005). Adventitious branches that drop off and form new individuals asexually, are likely common in Fucus also outside the Baltic Sea (Kinnby et al, 2019), yet dominant clonal lineages do not form in core areas. This suggests that new clonal lineages remain sexually functional and are assimilated by recombination when surrounded by other sexually active individuals.…”

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

“…comm. ), alongside the frequent occurrence of adventitious branches (Kinnby et al, 2019 ) indicates that fragmentation and/or adventitious branches are credible methods. As the free‐living form has previously been presumed to be sterile (Bauch, 1954 ; Häyrén, 1949 ; Svedelius, 1901 ), the origin of clonal MLGs would therefore have to be either entirely or predominantly through clonal growth.…”

Clones on the run - the genomics of a recently expanded facultative asexual species

“…With extensive genomic data we are now able to answer the first question by showing that asexual reproduction is also present outside the Baltic Sea and cloning is an ancestral trait to the Baltic lineage of F. vesiculosus . It is already well-known that this species forms adventitious branches in both brackish and marine waters (59), but it has earlier been suggested that this was part of a wound-healing mechanism (60). Asexually recruited individuals are morphologically indistinguishable from sexually recruited individuals make clones only detectable using genetic markers, hence the occurrence of clones has been overlooked by biologists for centuries.…”