Recent evolution in Baltic Fucus vesiculosus: reduced tolerance to emersion stresses compared to intertidal (North Sea) populations

Abstract

The Baltic is a young, brackish and non-tidal sea, supporting an impoverished marine flora compared with adjacent open coastal areas. Populations of the normally intertidal brown alga Fucus vesiculosus L. are permanently submerged in the Baltic. We tested the hypothesis that these populations have evolved a reduced ability to withstand water-stresses caused by aerial exposure (desiccation and freezing), relative to adjacent intertidal populations in the North Sea. Desiccation and freezing tolerance were compared using chlorophyll fluorescence to monitor photosynthetic status during stress and recovery. To control for the influence of growth salinity on stress tolerance, the experimental material consisted of either adult algae cross-acclimated at Baltic and North Sea salinities (6.5 and 20 to 24 practical salinity units [psu], respectively), or juveniles from both populations grown in the Baltic from embryos (submersed, 6.5 psu). Baltic algae were less able to recover maximum photochemical yield (F v /F m ) after freezing at -15°C than North Sea algae, and neither acclimation (adults) or growth salinity (juveniles) accounted for between-population differences. During desiccation at 5°C, differences in the response of variable fluorescence (F v ), as well as in initial fluorescence (F 0 ) and F v during recovery, indicated that impaired photoprotective processes may contribute to the inability of Baltic algae to fully recover F v /F m after stress, in contrast to North Sea algae which displayed dynamic and rapidly recoverable reductions of F v /F m . Subsequent desiccation experiments during the summer (at 25°C) showed that, relative to North Sea algae, the effective photochemical yield (∆F/F m ') of Baltic algae started to decline at lower tissue-water content (TWC) and recovered less completely after a return to seawater. A critical TWC of ca 10% for Baltic populations was identified, below which ∆F/F m ' did not fully recover. In addition, Baltic algae were less able to regain initial TWC during recovery. These results indicate that, in ca 7500 yr since the recruitment of the present marine flora to the Baltic, F. vesiculosus has evolved reduced tolerance to emersion stresses compared to adjacent intertidal populations.

The effect of desiccation on the emission of volatile bromocarbons from two common temperate macroalgae

“…As environmental factors and history can play a role in determining F v /F m (Walz, 1998) care must be taken when comparing F v /F m results between studies. Our starting F v /F m values, nevertheless, compare well with previous studies which report F v /F m values for healthy F. vesiculosus and U. intestinalis samples of ∼ 0.7-0.8 (Lewis et al, 2001;Magnusson, 1997;Pearson et al, 2000).…”

The Future of Baltic Sea Populations: Local Extinction or Evolutionary Rescue?

“…In sand goby, a visual pigment has evolved by local adaptation to the stable but locally divergent light conditions in different parts of the Baltic Sea (Larmuseau et al 2010). Baltic populations of fucoid macroalgae have evolved clonality and decreased resistance to desiccation and temperature stress Pearson et al 2000;Lago-Leston et al 2010). Even regularly migrating species like herring show evidence of strong local adaptation among Baltic stocks (Gaggiotti et al 2009).…”

Convergent adaptation to a marginal habitat by homoploid hybrids and polyploid ecads in the seaweed genusFucus

“…Substantial intraspecific variation is common in Fv (Powell 1963) and is a necessary prerequisite for local adaptation to environments like the brackish Fsp (17) m-lF (5) Fv (14) Fsp ( (3-7 psu) Baltic Sea, where it is widely distributed and the only perennial fucoid . Moreover, Baltic Sea populations of Fv are permanently submerged in brackish water and, consequently, more tolerant of low salinity (Serrão et al 1996) and less tolerant of emersion stress (Pearson et al 2000). Recent genetic analysis also has revealed a common origin between Fv and the newly described Fucus radicans in the northern Baltic Sea (Bergström et al 2005).…”