The maternal match hypothesis predicts that maternal exposure to a stressor may help prepare offspring to cope with the same disturbance in later life. Although there is support for this hypothesis, the signals involved in non-genetic inheritance are unclear. In this study we tested how adult zebrafish exposure to diel cycles of thermal stress (27-36°C), hypoxia (20-85% dissolved oxygen), or the combined treatment affect maternal and embryonic levels of cortisol and heat shock proteins (HSPs). While parental exposure to the thermal, hypoxic, or combined treatment for 2 weeks did not affect whole-body cortisol levels, the combined exposure increased ovarian cortisol levels by 4-fold and reduced embryonic cortisol content by 60%. The combined treatment also elicited 3- and 19-fold increases in embryo transcripts involved in cortisol breakdown (11bhsd2) and export (abcb4), respectively. The thermal stress and combined exposure also elicited marked increases in ovary and embryo hsp70a (20- to 45-fold) and HSP70 (3- to 7-fold), and smaller increases in ovary and embryo hsp90aa and hsp47 (2- to 4-fold) and in embryo HSP90 and HSP47 (2- to 6-fold). In contrast, except for increases in ovary hsp90aa (2-fold) and embryo HSP90 (3-fold), the hypoxia treatment had little effect on HSP expression and transfer. Overall, while the embryonic deposition of HSPs largely paralleled the ovarian cellular stress response, the inverse relationship between ovary and embryo cortisol levels suggests barriers against cortisol deposition in response to environmental stressors. We conclude that the endocrine and cellular stress responses make stressor-specific and distinct contributions to non-genetic inheritance.

Predicted climate change-induced increases in heat waves and hypoxic events will have profound effects on fishes, yet the capacity of parents to alter offspring phenotype via non-genetic inheritance and buffer against these combined stressors is not clear. This study tested how prolonged adult zebrafish exposure to combined diel cycles of thermal stress and hypoxia affect offspring early survival and development, parental investment of cortisol and heat shock proteins (HSPs), larval offspring stress responses, and both parental and offspring heat and hypoxia tolerance. Parental exposure to the combined stressor did not affect fecundity, but increased mortality, produced smaller embryos, and delayed hatching. The combined treatment also reduced maternal deposition of cortisol and increased embryo hsf1, hsp70a, HSP70, hsp90aa, and HSP90 levels. In larvae, basal cortisol levels did not differ between treatments, but acute exposure to combined heat stress and hypoxia increased cortisol levels in control larvae with no effect on larvae from exposed parents. In contrast, whereas larval basal hsf1, hsp70a, and hsp90aa levels differed between parental treatments, the combined acute stressor elicited similar transcriptional responses across treatments. Moreover, the combined acute stressor only induced a marked increase in HSP47 levels in the larvae derived from exposed parents. Finally, combined hypoxia and elevated temperatures increased both thermal and hypoxia tolerance in adults and conferred an increase in offspring thermal but not hypoxia tolerance. These results demonstrate that intergenerational acclimation to combined thermal stress and hypoxia elicit complex carry-over effects on stress responsiveness and offspring tolerance with potential consequences for resilience.