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

Abstract

Factors and mechanisms promoting resource-based radiation in animals still represent a main challenge to evolutionary biology. The modifications of phenotype tied with adaptive diversification may result from an environmentally related shift having occurred at the early stage of development. Here, we study the role of temperature dynamics on the reproductive sites in the early-life divergence and adaptive radiation of the salmonid fish Salvelinus malma dwelling in the Lake Kronotskoe basin (North-East Asia). Local sympatric charr ecomorphs demonstrate strict homing behaviour guiding the preordained distribution along tributaries and, hence, further development under different temperatures. We thoroughly assessed the annual temperature dynamics at the spawning grounds of each morph as compared to an ancestral anadromous morph. Then we carried out an experimental rearing of both under naturally diverging and uniformed temperatures. To compare the morphs’ development under the dynamically changing temperatures, we have designed a method based on calculating the accumulated heat by the Arrhenius equation. The proposed equation shows a strong predictive power and, at the same time, is not bias-susceptible when the developmental temperature approximates 0°C. The temperature was found to significantly affect the charrs’ early ontogeny, which underlies the divergence of developmental and growth rates between the morphs, as well as morph-specific ontogenetic adaptations to the spawning site’s temperatures. As opposed to the endemic morphs from Lake Kronotskoe, the anadromous S. malma, being unexposed to selection оn highly specific reproduction conditions, showed a wide temperature tolerance, Our findings demonstrate that the hatch, onset timing of external feeding, and size dissimilarities between the sympatric morphs reveal themselves during the development under contrast temperatures. As a result of the observed developmental disparities, the morphs occupy specific definitive foraging niches in the lake.

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

“…However, no particular impact was found directly in the jaw ossification among the groups. The same type of heterochronies has been previously revealed in the early development of sympatric salmonid morphs defined by specific adaptive features of head shape morphology (Esin et al, 2018;Esin, Markevich, Melnik, Zlenko, et al, 2021;Kapralova et al, 2015). This finding directly corresponds to the theory stating that asynchrony in the skeletal modules development could tune craniofacial morphogenesis and shaping (Mabee et al, 2000;Parsons et al, 2011).…”

“…The limnetic morph, as well as the experimentally CT-treated juveniles of the morph's ancestor differed from the benthivorous morph and the PTH-treated juveniles in the protruded snout, uplifted mouth, and enlarged pharingo-branchial area. At the same time, our sham-injected group did not differ significantly in ossification rate and head shape from the noninjected artificially reared juveniles, nor from wild Dolly Varden juveniles (Esin et al, 2018;Esin, Markevich, Melnik, Zlenko, et al, 2021).…”

“…Juveniles of S. malma , which are ancestral for these endemic morphs, were caught in the watercourse drained the opposite slope of the watershed range. To obtain early fry of the three groups of the same age after hatching, the benthivorous morph was sampled in mid‐September, the limnetic piscivorous morph ‐ in early October, and S. malma ‐ in late October (for more details please see Esin, Markevich, Melnik, Zlenko, et al, 2021).…”

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

“…The varied Lake Kronotskoe charrs show strict natal homing with some morphs spawning in tributaries and other morphs spawning within the lake (27). The morphs also exhibit differential annual windows for the timing of reproduction, which reinforces reproductive isolation and facilitates sympatric radiation (28).…”