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

Abstract

BackgroundEstablishing populations in ecologically marginal habitats may require substantial phenotypic changes that come about through phenotypic plasticity, local adaptation, or both. West-Eberhard’s “plasticity-first” model suggests that plasticity allows for rapid colonisation of a new environment, followed by directional selection that develops local adaptation. Two predictions from this model are that (i) individuals of the original population have high enough plasticity to survive and reproduce in the marginal environment, and (ii) individuals of the marginal population show evidence of local adaptation. Individuals of the macroalga Fucus vesiculosus from the North Sea colonised the hyposaline (≥2–3‰) Baltic Sea less than 8000 years ago. The colonisation involved a switch from fully sexual to facultative asexual recruitment with release of adventitious branches that grow rhizoids and attach to the substratum. To test the predictions from the plasticity-first model we reciprocally transplanted F. vesiculosus from the original population (ambient salinity 24‰) and from the marginal population inside the Baltic Sea (ambient salinity 4‰). We also transplanted individuals of the Baltic endemic sister species F. radicans from 4 to 24‰. We assessed the degree of plasticity and local adaptation in growth and reproductive traits after 6 months by comparing the performance of individuals in 4 and 24‰.ResultsBranches of all individuals survived the 6 months period in both salinities, but grew better in their native salinity. Baltic Sea individuals more frequently developed asexual traits while North Sea individuals initiated formation of receptacles for sexual reproduction.ConclusionsMarine individuals of F. vesiculosus are highly plastic with respect to salinity and North Sea populations can survive the extreme hyposaline conditions of the Baltic Sea without selective mortality. Plasticity alone would thus allow for an initial establishment of this species inside the postglacial Baltic Sea at salinities where reproduction remains functional. Since establishment, the Baltic Sea populations have evolved adaptations to extreme hyposaline waters and have in addition evolved asexual recruitment that, however, tends to impede local adaptation. Overall, our results support the “plasticity-first” model for the initial colonisation of the Baltic Sea by Fucus vesiculosus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-017-0124-1) contains supplementary material, which is available to authorized users.

High climate velocity and population fragmentation may constrain climate‐driven range shift of the key habitat former Fucus vesiculosus

“…In addition, a closely related species F. radicans has evolved as an endemic species from F. vesiculosus inside the Baltic Sea (Ardehed et al., ; Bergström et al., ; Pereyra et al., ). Although genomic information about geographical differences in adaptive loci is lacking, there are indications of trait differences that suggest the presence of locally adapted populations along the Baltic Sea gradient in both these species (Johansson et al., ; Pearson, Kautsky, & Serrão, ; Serrão et al., ).…”

“…Fucus vesiculosus may disperse in several ways including short‐distance dispersal of gametes and zygotes to occasional long‐distance dispersal of dislodged and rafting buoyant sexually mature plants (Rothäusler, Corell, & Jormalainen, ; Thiel & Gutow, ). Also, dispersal on intermediate scales may occur through bed load transport of negatively buoyant plants and in some cases vegetative, adventitious branches (Johansson et al., ; Pereyra et al., ). Genetic studies indicate population structure on scales ranging from, in the extreme case 10 m, but more usually 1 km, which suggest relatively short dispersal distances (Muhlin, Engel, Stessel, Weatherbee, & Brawley, ; Tatarenkov, Jonsson, Kautsky, & Johannesson, ).…”

Tolerance to climate change of the clonally reproducing endemic Baltic seaweed, Fucus radicans: is phenotypic plasticity enough?

“…A previous study of Fucus radicans showed that this species grows better in the salinity of its current northern distributional range (4) than in the salinity of the Baltic Sea entrance (24), and the authors also reported variation in growth rate among ramets of the same clone (Johansson et al. ). Together with our results, this indicates that F. radicans is capable of phenotypic plasticity in growth with respect to salinity stress.…”

“…This has been proposed as an example of the so‐called plasticity‐first scenario for the establishment of a population in marginal habitats (Johansson et al. ). Furthermore, Baltic Sea fucoids have been shown to be phenotypically plastic for a number of other traits, such as phlorotannin production (Koivikko ), morphology (Sideman and Mathieson , Scott et al.…”

“…Furthermore, Johansson et al. () found among‐genotype variation in reaction norms (in the formation of adventitious branches) with respect to salinity (4 and 24; i.e., a genotype‐by‐environment interaction). This indicates the occurrence of genetic variation for plasticity, at least at salinities above those occurring in the current distribution range.…”