Lake Thingvdllavatn aupports four trophic morphs of Arctic charr, Salvelinus alpinus (L. j; two of the morphs are benthic (small and large benthivorous charr) one exploits pelagic waters iplanktivorous charr) and the fourth is found in both habitats (piscivorous charr). T h r morphological variation among these morphs was analysed by use of principal component analysis and canonical discriminant analysis. T h e brnthic morphs have a short lower j a w and lorig pcctoral fins. T h e benthic fish also have fewer gillrakrrs than the other morphs. Small and large bcnthivorous charrs attain scxual maturity from 2 and 6 years of age, and at fork lengths from 7 and 22 cm, respectively.Small benthivorous charr retain their juvenile parr marks as adults, h a w bcigr ventral rolours, and are frequently melanizcd under the lower jaw. Planktivorous and piscivorous charr attain scxual maturity from 4 and 6 years ofage, k o m fork lengths of 15 and 23 cm, respectively. This phcnotypic polymorphism is associated with habitat utilization and diet of the fish, and has probably arisen within the lake systrrn ttiniugh diversification and nichr specialization. 'l'hr pelagic morphs apparently stem from a singlr population, and arc possibly diversified through conditional niche shifts which affect ontogeny. Juveniles reaching a body length of 23 cm may changr from zooplankton ti] fish feeding. Asymptotic length increases thereby from 20.5 r m in planktiv(irous charr to 30.2 c m in piscivorous charr. 'The benthic morphs appear to represent scparatc populations. although both feed chiefly on the gastropod Igrnnaen perqra. 'l'heir co-cxistencc seems t o he facilitated by size drpendcnt constraints on habitat use. The small morph (asymptotic length 13.3 c m ) exploit t h r interstitial crevices in the lava block substratum. whereas thr largc morph (asymptotic length 55.4 c m ] live epibcnthically.
ADDI'I'IONAL KEY LVOKUS:arowth rarchabivat use Trophic morphology ~ life historycompetitivc c h r r g e n c r -5 1
R. 2004. Rapidly changing life history during invasion. Á/ Oikos 106: 138 Á/150.The fish species vendace (Coregonus albula ) invaded the sub-arctic Pasvik watercourse during the second half of the 1980s, and became the dominant pelagic species in the upstream part of the watercourse within a few years. Life history traits of the pioneer population of vendace in Pasvik were recorded from 1991 Á/2000. A rapid increase in population density in the upstream part of the watercourse was accompanied by decreased growth rates, decreased fecundity and a reduced size at first maturation. The downstream part of the watercourse showed a similar, but delayed, change in life history traits compared to the upstream part. The study documents great life history variability of a non-native fish species entering a new environment. We discuss two coacting explanations for the observed patterns: (i) a density dependent response mediated by food depletion; and (ii) a pioneer strategy that allocates resources to favour reproduction at early developmental stages with a high number of offspring, trading off growth and size of offspring.
Combining morphological and genetic analysis, we compared patterns of diversification within and between morphs among sympatric European whitefish (Coregonus lavaretus L.) populations in Lake Femund, Norway. Seven external populations, from potential colonization routes into Lake Femund were included. We found that deep‐, shallow‐, river‐ and bay spawning populations are distinct morphs in Lake Femund. Within morphs, populations range from being similar genetically (Fst = 0–0.005) among deep‐spawning populations to being highly differentiated (Fst = 0.153) between bay‐spawning populations. Between morphs, genetic differences ranged from a low (Fst = 0.008–0.022) between deep‐ and shallow‐spawning populations to high difference (Fst = 0.125–0.143) between shallow‐ and bay‐spawning populations. A higher proportion of molecular variance was seen among (3.9%) than within morphs (2.8%). The adaptive gene combinations behind the four morphs seem to have originated within the lake, although the lake could have been colonized from more than one source population.
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