Thermal experience during embryogenesis contributes to the induction of dwarfism in whitefish Coregonus lavaretus

Abstract

Ecotype pairs provide well-suited model systems for study of intraspecific phenotypical diversification of animals. However, little is still known about the processes that account for the development of different forms and sizes within a species, particularly in teleosts. Here, embryos of a normal-growing ‘large’ form and a dwarf form of whitefish Coregonus lavaretus were incubated at two temperatures that are usually experienced at their own spawning sites (2°C for the normal and 6°C for the dwarf form). All fish were subjected to similar thermal treatment after hatching. The present data demonstrate for the first time that different thermal experience in embryonic life has lasting effects on body and muscle growth of this ecotype pair and contributes to the development of the dwarf form. Thus, juvenile fish of the regular form are much smaller and have less muscle mass when pre-hatching thermal conditions were similar to those typical for the spawning sites of the dwarf form (6°C) than when subjected to conditions of their own spawning sites (2°C). Surprisingly, fish of the dwarf form exhibit a similar pattern of response to thermal history (2°-fish much larger than 6°-fish), indicating that in their case, normal spawning site temperature (6°C) is indeed likely to act as a growth limiting factor. Results also demonstrate that the hypertrophic and hyperplastic muscle growth modes are similarly affected by thermal history. Immunolabelling experiments for Pax7, H3P and Mef2 provide evidence that the cellular mechanisms behind the increased growth rates after cold incubation in both ecotypes are increased proliferation and reduced differentiation rates of muscle precursor cells. This is of major significance to aspects of ecological and developmental biology and from the evolutionary perspective.

Phenotypic plasticity and epigenetics of fish: embryo temperature affects later-developing life-history traits

“…Differences in egg incubation temperature may contribute to this morph differentiation. Steinbacher et al (2017) revealed this by incubating embryos of a large and a dwarf form of C. lavaretus at 2° and 6°C, i.e. the typical temperature during embryogenesis of large and dwarf C. lavaretus in nature, respectively.…”

Thermal Effects on Ecological Traits of Salmonids

“…Two forms of European whitefish (Coregonus lavaretus) segregate vertically in Traunsee, Austria. The forms exhibit different metabolic adaptations and behavioural preferences for different temperatures [125]. In the lake, the two forms diverge by incubating embryos at either 2 • C or 6 • C, i.e., the typical temperature during embryogenesis of the two.…”