Mitochondrial DNA variation in Arctic charr (Salvelinus alpinus (L.)) morphs from Loch Rannoch, Scotland: evidence for allopatric and peripatric divergence

Abstract

Three ecologically and morphologically distinct forms of Arctic charr (Salvelinus alpinus L.) have been identified in Loch Rannoch, Scotland, whose evolutionary status and origins are incompletely understood. A study was made of restriction fragment length polymorphism (RFLPs) detected variation in the D-loop, ND1 and cytochrome b regions of the mitochondrial genome, encompassing [3500 bp. Eight RFLP haplotypes were identified that clustered into three distinct clans based on restriction differences and into four clans based on sequence differences. Significant differences in RFLP frequencies were found among all morph groups. The pelagic morph was highly divergent from the two benthic forms, with the benthic forms having variants from only one genetic clan while the pelagic was dominated by a single variant from another clan. The relative divergence observed among benthic and pelagic forms is *10 fold greater when nucleotide divergence among the haplotypes, as well as haplotype frequency differences, is taken into account. Sequence divergence between haplotypes in the two main clans is of a similar order to that between haplotypes in these clans and a charr from North America. In contrast, divergence among the two benthic morphs relates entirely to differences in haplotype frequencies. The study confirms the genetic distinctiveness of the pelagic and benthic forms as well as of the two benthic forms. It strongly supports previous evidence that the genetic divergence between the pelagic and benthic populations is allopatric in origin. Additionally, the results strongly suggest that the two benthic populations have undergone peripatric divergence through the sequential colonisation of the two basins by one lineage, followed by their spatial separation and reproductive isolation.

Divergent functional traits in three sympatric Arctic charr Salvelinus alpinus morphs are not coupled with the age of the lineage divergence

“…In general, the planktivore or the piscivore morphs tended to be the most divergent of the trophic traits reported here. There is strong evidence from neutral genetic markers that the planktivorous form diverged from the ancestral form of other two morphs before the postglacial invasion of Loch Rannoch by Arctic charr, and that the benthivorous and piscivorous morphs diverged in situ following invasion (Verspoor et al, 2010;Garduño-Paz et al, 2012). A logical expectation is that the degree of divergence in functional anatomy features might reflect the period of genetic divergence amongst groups (Hypothesis 1).…”

“…There are also clear genetic differences amongst them (Verspoor et al, 2010). This polymorphism represents one of the best-studied sympatric morph systems of Arctic charr (Klemetsen, 2010), and has been described fully elsewhere; thus only a brief summary is presented here.…”

“…In some lakes where such polymorphisms have been described, the morphs have arisen in sympatry (Gislason et al, 1999;Verspoor et al, 2010;Garduño-Paz et al, 2012), but this is not always be the case (see Garduño-Paz et al, 2012). There is significant evidence from Arctic charr of parallel, in situ divergences resulting in the emergence of similar ecological specialists occurring in different lake systems across the range of the species (Jonsson & Jonsson, 2001;Alekseyev et al, 2002;Adams et al, 2008).…”

“…The evidence of population genetics studies, using selectively neutral markers, is that the benthivorous and the piscivorous morphs have diverged relatively recently, and in situ in Loch Rannoch, whereas the planktivorous morph diverged earlier from the other two and in allopatry (Verspoor et al, 2010;Garduño-Paz et al, 2012).…”

Climate change and primary industries

“…sympatric divergence, although allopatric divergence of sympatric populations has been observed as well (e.g. Verspoor et al 2010). In the latter case, lakes have probably been colo-nised by different evolutionary lineages, i.e.…”