Extensive genetic differentiation between recently evolved sympatric Arctic charr morphs.

Area of Science:

• Evolutionary biology
• Genomics
• Ecology

Background:

• Diverse ecological niches drive adaptation and trophic specialization in freshwater fish radiations.
• Salmonids, particularly the *Salvelinus* genus, exhibit remarkable phenotypic diversity and polymorphism.
• Arctic charr (*Salvelinus alpinus*) in Iceland display sympatric polymorphism, with four distinct morphs in Lake Þingvallavatn.

Purpose of the Study:

• To investigate the genetic relatedness and differentiation among Arctic charr morphs in Lake Þingvallavatn.
• To identify genetic markers associated with ecological divergence.
• To understand the role of genetics in the adaptive radiation of Arctic charr.

Main Methods:

• RNA-sequencing to identify variable sites in three Arctic charr morphs.
• Genotyping of 22 population samples to verify genetic variants.
• Gene Ontology (GO) analyses to infer functional differences between morphs.

Main Results:

• Significant genetic differences were found between Arctic charr morphs.
• The two benthic morphs (small benthic and large benthic) were genetically more similar than the planktivorous morph.
• Markers with high differentiation were distributed across linkage groups, suggesting ancient genetic separation. The piscivorous morph showed less genetic distinction.
• GO analyses indicated functional differences in collagen metabolism, odontogenesis, and sensory systems between planktivorous and benthic morphs.

Conclusions:

• The genetic separation among Arctic charr morphs suggests a degree of reproductive isolation.
• Ancient and pervasive genetic divergence underlies the observed polymorphism.
• Further research is needed to elucidate gene flow and the precise nature of reproductive barriers between morphs.