Variation in natural selection for growth and phlorotannins in the brown alga Fucus vesiculosus

Abstract

Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade‐offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past‐environment–current‐environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.

Seasonal variation of polyphenolics inAscophyllum nodosum(Phaeophyceae)

“…Similar conclusions were drawn in the study of Pavia et al (1999), which was done with A. nodosum collected in October 1992 and October 1993, in each case at two different study sites. Further investigations of polyphenol contents also demonstrated that yearto-year variations (Van Alstyne et al, 1999;Van Alstyne et al, 2001) occurred, and that differences in the habitat (Jormalainen & Honkanen, 2004), such as salinity, temperature, light intensity and ambient nutrients (Lu¨ning, 1985;Pavia & Brock, 2000;Pavia & Toth, 2000;Toth & Pavia, 2002;Jormalainen & Honkanen, 2004) play a role. The differences in the polyphenol content between our study and that of Ragan & Jensen (1978) may have been caused by different conditions at collection sites.…”

“…The concentration has been shown to depend on the season of harvesting (Ragan & Jensen, 1978;Ro¨nnberg & Ruokolahti, 1986;Peckol et al, 1996), the habitat (Jormalainen & Honkanen, 2004) and other extrinsic factors, e.g. light intensity and ambient nutrients (Pavia & Brock, 2000;Pavia & Toth, 2000;Toth & Pavia, 2002;Jormalainen & Honkanen, 2004;Svensson et al, 2007).…”

Use of hierarchical designs to detect scales of heterogeneity in the invasive species <em>Sargassum muticum</em>

“…between sites, can sometimes indicate that Sargassum muticum can have phenotypic adaptation to local environmental heterogeneity due to phenotypic plasticity and/or genetic differentiation. if different phenotypes are favoured in different environments, selection may either preserve genetic variation, assuming an insignificant gene flow, or lead to evolution plasticity (Jormalainen and Honkanen, 2004). this is an interesting consideration that should be further explored with reciprocal transplants of adult plants and zygotes, in order to determine whether genetic differentiation or phenotypic plasticity are the mechanisms driving such spatial variability.…”

Cosmeceuticals Derived from Bioactive Substances Found in Marine Algae

“…Most naturally occurring phenolic compounds are present as conjugates with mono-and polysaccharides, linked to one or more of the phenolic groups, and may also occur as functional derivatives such as esters and methyl esters. Phlorotannins (Figure 4a), a group of phenolic compounds which are restricted to polymers of phloroglucinol (1,3,5-trihydroxybenzene) (Figure 4b), have been indentified in several brown algal families such as Alariaceae, Fucaceae and Sargassaceae [43,44].…”