Ambient temperature as a factor contributing to the developmental divergence in sympatric salmonids

Phylogenomic analysis of the Lake Kronotskoe species flock of Dolly Varden charr reveals genetic and developmental signatures of sympatric radiation

Recent adaptive radiations provide evolutionary case studies, which provide the context to parse the relationship between genomic variation and the origins of distinct phenotypes. Sympatric radiations of the charr complex (genus Salvelinus) present a trove for phylogenetics as charrs have repeatedly diversified into multiple morphs with distinct feeding specializations. However, species flocks normally comprise only two to three lineages. Dolly Varden charr inhabiting Lake Kronotske represent the most extensive radiation described for the charr genus, containing at least seven lineages, each with defining morphological and ecological traits. Here, we perform the first genome-wide analysis of this species flock to parse the foundations of adaptive change. Our data support distinct, reproductively isolated lineages with little evidence of hybridization. We also find that specific selection on thyroid signaling and craniofacial genes forms a genomic basis for the radiation. Thyroid hormone is further implicated in subsequent lineage partitioning events. These results delineate a clear genetic basis for the diversification of specialized lineages, and highlight the role of developmental mechanisms in shaping the forms generated during adaptive radiation.

Bone calcification rate as a factor of craniofacial transformations in salmonid fish: Insights from an experiment with hormonal treatment of calcium metabolism

Adaptation to different environments can be achieved by physiological shifts throughout development. Hormonal regulators shape the physiological and morphological traits of the evolving animals making them fit for the particular ecological surroundings. We hypothesized that the artificially induced hypersynthesis of calcitonin and parathyroid hormone mutually influencing calcium metabolism could affect bone formation during early ontogeny in fish imitating the heterochrony in craniofacial ossification in natural adaptive morphs. Conducting an experiment, we found that the long-standing treatment of salmonid juveniles with high doses of both hormones irreversibly shifts the corresponding hormone status for a period well beyond the time scale for total degradation of the injected hormone. The hormones program the ossification of the jaw suspension bones and neurocranial elements in a specific manner affecting the jaws position and pharingo-branchial area stretching. These morphological shifts resemble the adaptive variants found in sympatric pelagic and demersal morphs of salmonids. We conclude that solitary deviations in the regulators of calcium metabolism could determine functional morphological traits via transformations in skeletal development.