Biology subjects

Snorrason, S. S.

Publications and source records attributed to Snorrason, S. S..

6 recordsLinked to original sources

bioRxiv2025

Whole genome sequencing reveals how plasticity and genetic differentiation underlie sympatric morphs of Arctic charr

Salmonids have a remarkable ability to form sympatric morphs after postglacial colonization of freshwater lakes. These morphs often exhibit differences in morphology, feeding, and spawning behaviour. Here we explore the genetics of morph differentiation by establishing a high-quality, annotated reference genome for the Arctic charr and use this as a resource for population genomic analysis of morphs from two Norwegian and two Icelandic lakes. The four lakes represent the spectrum of genetic differentiation between morphs from one lake with no genetic differentiation between morphs, implying phenotypic plasticity only, to two lakes with locus-specific genetic differentiation, implying incomplete reproductive isolation, and one lake with strong genome-wide divergence consistent with complete reproductive isolation. As many as 12 putative inversions ranging from 0.45 to 3.25 Mbp in size segregated among the four morphs present in one lake, Thingvallavatn, and these contributed significantly to the genetic differentiation among morphs. None of the putative inversions was found in any of the other lakes, but there were cases of partial haplotype sharing in similar morph contrasts in other lakes. The results are consistent with a highly polygenic basis of morph differentiation with limited genetic parallelism between lakes. The results support a model where morph differentiation is usually first established due to phenotypic plasticity that results in niche expansion and separation, followed by gradual development of reproductive isolation and locus-specific differentiation and eventually complete reproductive isolation and genome-wide divergence. A major explanation for salmonids ability to diversify into multiple sympatric morphs is likely the genome complexity caused by their ancient whole genome duplication that enhances evolvability.

evolutionary biology↗

bioRxiv2024

Variation of tooth traits in ecologically specialized and sympatric morphs

Differences in dentition between species relate to feeding specialisations, as examples of tetrapod dentition variation show clearly. The association of tooth traits and ecological opportunties in non-mammalian vertebrates is less studied. We examined variation in dental traits in four sympatric morphs of Arctic charr (Salvelinus alpinus) which differ in feeding specialisations, head and jaw bone morphology. We studied tooth numbers in six bones (dentary, maxilla, premaxilla, palatine, vomer and glossohyal) and tooth angles in one bone (maxilla). We found fluctuating asymmetry in tooth numbers and angles and that the allometry of tooth numbers varied by bone but not morphs. Tooth numbers differed by morphs in four bones (dentary, palatine, vomer and glossohyal). In general, the morphs defined as pelagic had more teeth, and this relates partially to changes in bone shape. There was a difference in maxilla tooth angle, with benthic morphs having teeth which were angled more inwards. Dentary and maxilla tooth number correlated moderately with bone shape, maxilla tooth angle and premaxilla tooth number did not. While it is currently unknown what tooth characteristics are ancestral vs derived in these populations, the marked differences in specific bones presents an opportunity to explore rapid evolution in dentition. Statement and DeclarationThe authors declare that they have no conflict of interest

evolutionary biology↗

bioRxiv2023

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

The diversity of functional feeding anatomy is particularly impressive in fishes and correlates with various interspecific ecological specializations. Intraspecific polymorphism can manifest in divergent feeding morphology and ecology, often along a benthic-pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism and in Lake Thingvallavatn, Iceland, four morphs of charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in six upper and lower jaw bones in adults of these four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and divergence along the benthic-pelagic axis. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic-pelagic axis in four bones (dentary, articular-angular, premaxilla and maxilla), as well as allometric shape differences between morphs in the dentary. Notably for the dentary, morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution.

evolutionary biology↗

bioRxiv2020

Multivariate distributions of behavioural, morphological, and ontogenetic traits in hybrids bring new insights into the divergence of sympatric Arctic charr morphs.

Studying the development of fitness related traits in hybrids from populations diverging in sympatry is a fundamental approach to understand the processes of speciation. However, such traits are often affected by covariance structures that complicate the comprehension of these processes, especially because the interactive relationships between traits of different nature (e.g. morphology, behaviour, life-history) remain largely unknown in this context. In a common garden setup, we conducted an extensive examination of phenotypic traits suspected to be involved in the divergence of two recently evolved morphs of Arctic charr (Salvelinus alpinus), and investigated the consequences of potential patterns of trait covariance on the phenotype of their hybrids. We observed differences among morphs in overall phenotypic variance and in trait correlations. Phenotypic contrainsts also tended to be reduced in the hybrids, which corroborates the narrative of hybridization facilitating adaptive divergence by relaxing trait covariance. However, the hybrids were associated with reduced phenotypic variance at different scales (i.e. at the scale of the entire P matrix and in different parts of the multivariate space), and we identified stronger correlations between several ontogenetic and morphological traits in the hybrids than in both morphs. These findings suggest a limited potential for hybridization to generate phenotypic novelty, and emphasise the need for multivariate approaches conciliating ontogenetic, morphological and behavioural processes to study the processes of adaptive divergence and speciation.

evolutionary biology↗

bioRxiv2020

Animal personality adds complexity to the processes of adaptive divergence and speciation.

Divergent selection is a powerful driver of speciation and has been widely studied in relation to the physical characters of organisms. Because evolution of behavioural traits may contribute to evolutionary processes, we explored how consistent variation in behaviours may affect the process of adaptive divergence and speciation. We studied whether two sympatric morphs of Arctic charr (Salvelinus alpinus) have recently evolved genetically-based differences in personality that conform to their respective ecological niches, and whether these differences contribute to reproductive isolation by generating maladaptive hybrid behaviours. Studying three aspects of behavioural variation (average trait value, consistent individual differences and trait covariance), we assessed the sociality and risk-taking propensity of hybrid and pure-morph offspring reared in common conditions. Contrary to expectations, the two morphs did not differ in the average values of these traits but showed different behavioural syndromes (trait covariances). While the hybrids did not differ from either morph in their average behavioural responses, they showed less individual consistency in these behaviours and a different set of behavioural syndromes. Differences between morphs and their hybrids in other behavioural aspects than their average behavioural responses suggest that our understanding of speciation processes can benefit from an integrative view of behavioural variation.

evolutionary biology↗

bioRxiv2018

Extensive genetic divergence between recently evolved sympatric Arctic charr morphs

The availability of diverse ecological niches can promote adaptation of trophic specializations and related traits, as has been repeatedly observed in evolutionary radiations of freshwater fish. The role of genetics, environment and history in ecologically driven divergence and adaptation, can be studied on adaptive radiations or populations showing ecological polymorphism. Salmonids, especially the Salvelinus genus, are renowned for both phenotypic diversity and polymorphism. Arctic charr (Salvelinus alpinus) invaded Icelandic streams during the glacial retreat (about 10,000 years ago) and exhibits many instances of sympatric polymorphism. Particularly well studied are the four morphs in Lake Thingvallavatn in Iceland. The small benthic (SB), large benthic (LB), planktivorous (PL) and piscivorous (PI) charr differ in many regards, including size, form and life history traits. To investigate relatedness and genomic differentiation between morphs we identified variable sites from RNA-sequencing data from three of those morphs, and verified 22 variants in population samples. The data reveal genetic differences between the morphs, with the two benthic morphs being more similar and the PL-charr more genetically different. The markers with high differentiation map to all linkage groups, suggesting ancient and pervasive genetic separation of these three morphs. Furthermore, GO analyses suggest differences in collagen metabolism, odontogenesis and sensory systems between PL-charr and the benthic morphs. Genotyping in population samples from all four morphs confirms the genetic separation and indicates that the PI-charr are less genetically distinct than the other three morphs. The genetic separation of the other three morphs indicates certain degree of reproductive isolation. The extent of gene flow between the morphs and the nature of reproductive barriers between them remain to be elucidated.

evolutionary biology↗