Genetic, endocrine and transgenerational effects of thermal stress on germinative cells in rainbow trout (Oncorhynchus mykiss)

Author(s)

Arno Juliano Butzge

• Document type: Doctoral Thesis
• Press: Botucatu. 2021-09-23.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2020-05-31
• Advisor: Claudio Oliveira; Ricardo Shohei Hattori

Abstract

In fish, exposure to high temperatures can affect the proliferation, differentiation or even survival of germ cells, compromising fertility and the reproductive capacity of the species. There is also evidence of epigenetic changes that may eventually be transmitted to the next generations, determining the survival and adaptive capacity of animals submitted to constant changing environments. The aim of this work was to elucidate the regulatory (molecular and endocrine) mechanisms and transgenerational effects involved in the maintenance and differentiation of germ cells in rainbow trout (Oncorhynchus mykiss) subjected to thermal stress. For this purpose, the effects of exposure to high temperatures during parr stages were initially evaluated on adult gonads, by comparing reproductive parameters and gamete quality. Then, these gametes were used in crosses, in order to compare the performance of respective offspring (WT) in relation to control group (CT), upon exposure to thermal stress. Finally, in vitro experiments with juvenile testis from the same progenies were performed with the purpose to find a relationship between thermal tolerance and the susceptibility to cortisol, the main stress hormone. The results of the first section demonstrated that the thermal stress clearly affected more the males than females, wherein deleterious effects were detected on testis development, fecundity, sperm motility and morphology, and also on embryo development. Surprisingly, in spite of those negative impacts, the progeny derived from stressed males subjected to the similar stressful conditions as their parents showed superior survival and growth, which demonstrate that thermal stress in parental fish can somehow confer thermotolerance in the offspring after a single generation. A similar performance was observed using progenies derived from three-year-old males, which points to constitutive alterations in spermatogonial stem cells. In vitro analysis revealed a lower susceptibility to cortisol in WT in relation to CT group, which suggests that the first may have a higher capacity to buffer the effects of stress. The remaining gene transcription analysis - which were interrupted due to COVID-19 pandemic - may elucidate the molecular aspects involved in the acquisition of high temperature tolerance. In conclusion, this study demonstrates that thermal stress during juvenile stages can induce permanent effects on essential reproductive features at adult stage and also modulate the adaptive capacity of the respective progeny, when they are exposed to similar conditions as those of their parents. These findings add a new dimension on the impacts of climate change in fish, but at the same time indicate the existence of mechanisms that allow animals to overcome the changing environment, given that the survival of next generations, even restricted, are ensured. As for commercially important species, the approach used in this study can contribute to the development of strains displaying higher resilience to particular environmental conditions. (AU)

• FAPESP's process: 19/02950-2 - Genetic, endocrine and transgenerational effects of thermal stress on germinative cells in Rainbow Trout (Oncorhynchus mykiss)
• Grantee: Arno Juliano Butzge
• Support Opportunities: Scholarships in Brazil - Doctorate