Journal zyxwvutsr of Fish Biology zyxwvu (1 zyxwvutsrqp 99 zyxwvu 1) zyxwvut 39,649-659 Mitochondria1 DNA diversity among four sympatric morphs of Arctic charr, Salvelinus alpinus L., from Thingvallavatn, Iceland R. G. DANZMANN, M. M. FERGUSON, s. SK~LASON*, s. s. SNORRASONt AND D. L. G. NOAKES Department ofZoology. University of Guelph, Guelph, Ontario N l G zyxw 2 WI, Canada and ?Institute of Biology, University of Iceland, Grensasvegur 12, 108-Reykjavik, Iceland (Received 21 November 1990, Accepted zyxw I1 May 1991) Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were examined in progeny of four sympatric morphs of Arctic charr (Salvelinus alpinus L.) from Thingvallavatn, Iceland. The mtDNA analysis with 46 hexanucleotide restriction enzymes indicates that the Thingvallavatn morphs are very closely related. Sequence divergence was less than 0.2% between any of the five clones detected. Although not significant, the topology of the mtDNA UPGMA dendogram was similar to that from a previous allozyme survey. Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction. Key words: Arctic charr; salmonids; fish; mitochondrial DNA; genetics; zoogeography I. INTRODUCTION Four sympatric morphs of Arctic charr (Sulvelinus alpinus L.) occur in Thingvallavatn, a volcanic lake in southwestern Iceland. These have been charac- terized by differences in head and body morphology, growth rate, age and size at maturity, coloration, spawning times, and behaviour (Malmquist et al., 1985; Sandlund et al., 1987; Jonsson et ul., 1988; Malmquist, 1988; Sigurjonsdottir & Gunnarsson, 1989; Skulason et al., 1989u, b; Snorrason et al., 1989). The charrs can be divided into benthivore and pelagic morphotypes based primarily on differ- ences in head morphology. The benthivore morphotypes consist of small (SB) and large (LB) benthivore charr, while the pelagic morphotypes are composed of planktivorous (PL) and piscivorous (PI) charr. As their English designations suggest, these morphs have different feeding habits with the SB- and LB- charrs feeding primarily on Lyrnnuea peregru, an abundant gastropod on the littoral bottom of the lake. PI charr feed primarily on sticklebacks (Gasterosteus aculeatus L.) which are the only other fish species in the lake besides brown trout (Salmo trutta L.), while PL charr forage on an abundance of zooplankton. Heterochrony has been proposed as the primary mechanism leading to the pronounced differences in trophic morphology (Skulason et ul., 1989~). LB and SB charr presumably represent an arrest (paedomorphic juvenilization) of the ontogenetic development of the head, characterized by sub-terminal mouths and blunt snouts in the adults. PL and PI morphs have more differentiated head shapes than the embryonic phenotypes of the benthivore morphs and are characterized by terminal mouths in the adults. Based upon family studies, these differences appear *Present address: Hblar Agricultural College, Holar, Hjaltadel, 551 Saudarkrokur, Iceland. 649 0022-1112/91/011649+ 11 S03.00jO 0 1991 The Fisheries Society of the British Isles