Biological Journal of the Linnean Society, 2003, 78, 43–49. With 3 figures © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78, 43–49 43 Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean Society of London, 2003 78 Original Article EPIGENETIC REGULATION OF TROPHIC MORPHOLOGYC. E. ADAMS ET AL. *Corresponding author. E-mail: C.Adams@bio.gla.ac.uk Epigenetic regulation of trophic morphology through feeding behaviour in Arctic charr, Salvelinus alpinus COLIN E. ADAMS*, CHRIS WOLTERING and GAVIN ALEXANDER Fish Biology Group, University Field Station, Institute of Biomedical and Life Sciences, University of Glasgow, Rowardennan, Loch Lomond, Glasgow G63 0AW, Scotland, UK Received 11 December 2001; accepted for publication 13 August 2002 Several models of speciation suggest that in species that are phenotypically plastic, selection can act on phenotypic variation that is environmentally induced in the earliest stages of divergence. One trait that could be subject to this process is foraging behaviour, where discrete foraging strategies are common. One species which is highly plastic in the expression of phenotype, the Arctic charr, Salvelinus alpinus (L.), is characterized by discrete variation in the anatomy of the head and mouthparts. These traits have been shown to have a functional significance, but the expres- sion of which is thought to be at least partly phenotypically plastic. Here we test the hypothesis that foraging behav- iour may regulate the anatomy of the head and mouthparts in Arctic charr. In a dyad experiment, size-matched pairs of fish from a mixed family group were fed a diet of either Mysis (a hard-bodied shrimp) or Chironomid larvae. Nine morphometric measures of head dimensions that describe wild trophic morphs were measured at the start of the experiment and 24 weeks later. Principal component scores of size-corrected morphometric measures showed highly significant differences between fish exposed to the two diets. Univariate ANOVA analysis of the head morphometric variables showed that fish fed on Chironomids developed longer, wider jaws, longer heads and a larger eye for a given body length than did those fish fed upon Mysis. We conclude that foraging anatomy in Arctic charr is phenotypically plastic and that variation in foraging behaviour that results in feeding specialization in the wild could induce vari- ation in head anatomy. This in turn could reinforce foraging specialization. Very rapid epigenetic divergence into distinct feeding morphs (as demonstrated here) would allow selection to act at more than one mode and thus could promote rapid evolutionary divergence, initially prior to genetic segregation, in species which are highly plastic. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78, 43–49. ADDITIONAL KEYWORDS: environmental regulation – evolution – phenotypic plasticity – speciation. INTRODUCTION Several models have shown that diversifying evolu- tionary forces operating at the very earliest stages of speciation could act on phenotypic variation that is environmentally induced in a single gene pool, i.e. epigenetic variation (West-Eberhard, 1989, 1998; Wimberger, 1994, Skúlason, Snorrason & Jónsson, 1999). This occurs when the gene pool has the ability to produce more than one discrete, alternative pheno- type for a given characteristic; that is, where the pop- ulation is phenotypically plastic. When this occurs, selection may be able to operate on two or more dis- crete phenotypes simultaneously resulting in diver- gence (West-Eberhard, 1989). An important element of these models is that phenotypic divergence may occur prior to any genetic segregation (West-Eberhard, 1986, 1989, 1998; Wimberger, 1994; Skúlason et al., 1999). The type of phenotypic variation on which these epigenetic evolutionary mechanisms are most likely to act initially is variation in behaviour. A likely candi- date for selection to act upon is foraging behaviour, because of the possibility of alternative strategies for successful foraging and its potential effects on fitness (see West-Eberhard, 1989; Wimberger, 1994; Skúlason et al., 1999). In nature, the existence of more than one discrete Downloaded from https://academic.oup.com/biolinnean/article-abstract/78/1/43/2639749 by guest on 05 June 2020