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

Abstract

Three genetically discrete morphs of Arctic charr in Loch Rannoch, Scotland originated from a recent divergence within the lake (in situ) (piscivore and benthivore morphs) and from secondary contact of two older lineages (ex situ; a planktivore-piscivore/ benthivore divergence). To test if the expression of traits with strong functional roles was linked to the age of the divergence, fin and gill anatomy, and dentition were quantified and compared across morphs. Five additional working hypotheses suggesting a rank order of trait expression amongst morphs were also tested. The planktivorous morph had more rays in the dorsal and pectoral fins, longer gill rakers (but not more) as well as a smaller gill cavity than the other two morphs.The piscivorous morph had more palatine teeth and longer teeth on the mandible, pre-maxillary and glossohyal bones, and a larger buccal cavity. These differences indicate a differential response to selection in these functional anatomical features most likely related to morph foraging specialisms. Notably, between-morph divergences in the expression of these traits were not simply linked to the length of divergence between morphs and have arisen equally quickly in the recent (in situ) divergence as they have in older, ex situ divergences.

Investigating the morphological and genetic divergence of arctic char (Salvelinus alpinus) populations in lakes of arctic Alaska

“…Further, in other regions with arctic char, lakes of similar ages exhibit genetically distinct populations. In Loch Rannoch, Scotland (~12 ka in age), divergent traits of genetically distinct char were not correlated with the age of lineage divergence; however, Loch Rannoch (surface area = 17 km 2 ; maximum depth = 134 m; Bryce et al, 2016) is also much larger than our study lakes. In Iceland, char populations in a series of lakes (~10 ka in age) exhibit varying degrees of phenotypic and genetic differentiation, and divergent morphs are likely due to sympatric divergence (Gislason et al, 1999).…”

“…Thus, it is important to understand whether polymorphic char types are genetically distinct and reproductively isolated. Genetic divergence among ecomorphs of char can arise either from differences in functional traits related to feeding ecology (e.g., jaw morphology or fin anatomy; Arbour et al., 2011; Bryce et al., 2016) or from differences in life histories (e.g., May‐McNally et al., 2015; Skúlason et al., 1996). The magnitude and consequences of genetic differences can vary among ecomorph types that diverge in sympatry and allopatry, with sympatric pairs potentially demonstrating higher levels of genetic differentiation than allopatric pairs (Praebel et al., 2016).…”

The role of Salvelinus in contemporary studies of evolution, trophic ecology and anthropogenic change

“…Thus, predation may have a strong structuring effect on fish populations in subarctic lake ecosystems. Salvelinus seem well suited to study the effects from predation as piscivory among charrs ranges from cannibalism, via intraspecific predation, to highly piscivorous species such as Lake charr populations (Amundsen, 2016;Bryce et al, 2016;Hansen et al, 2016a, b;Knudsen et al, 2016b).…”

“…Interestingly, in Scotland, Hooker et al (2016) describe a previously unknown sympatric divergence in S. alpinus into profundal macrobenthos-and plankton-feeding specialists which closely mirrors that reported by Knudsen and his colleagues in Norway . Bryce et al (2016) test if the degree of divergence of characters with a strong functional significance (dentition and respiratory capacity features) among three S. alpinus morphs in sympatry is predicted by the timing of genetic separation of populations. Surprisingly, they find that between-morph divergences in the expression of these traits are not simply linked to the length of time since divergence among morphs, with trait differences having arisen equally quickly in a recent (in situ) divergence as they have in older, ex situ divergences.…”

Evolvability under climate change: Bone development and shape plasticity are heritable and correspond with performance in Arctic charr (Salvelinus alpinus)

“…Among freshwater fishes, Arctic charr have the most extreme northern distribution, display a wide range of phenotypic variation, and are known to possess high levels of plasticity (Adams & Huntingford, 2002; Alexander & Adams, 2000; Jonsson & Jonsson, 2001; Klemetsen, 2010; Parsons et al, 2010, 2011). Phenotypic variation in this species is strongly linked to adaptive divergence (Adams et al, 1998; Skúlason et al, 1989; Snorrason et al, 1989), with variation in craniofacial and body‐shape traits having frequently been shown to correspond to feeding and swimming performance (Bryce et al, 2016; Kapralova et al, 2015; Skúlason et al, 1989). Therefore, Arctic charr are an ideal model to provide insights into how temperature changes may impact bone development and in turn adaptation in fishes.…”