Figure 1.

Experimental design and two potential scenarios of transgenerational acclimation. Breeding design conducted three times (a) according to treatment design (Table 1) of wild caught and laboratory bred (parental and offspring) three‐spined sticklebacks from Kiel (KIE, 20 PSU), Thyborøn (THY, 33 PSU) and Nynäshamn (NYN, 6 PSU). The first generation (wild caught) is kept at its native salinity, and the second generation (G1, parental) is exposed to different salinities from the adult stage onwards for five months. The third generation (G2, offspring) is introduced to the respective salinity upon fertilization. Letters refer to control (C, native salinity) and treatment (T, foreign salinity) of parents and offspring, respectively (e.g., T‐C refers to parents in treatment and offspring in control condition). Within the breeding design, group 1 and group 2 were analyzed separately. Assuming the foreign environment of group 2 is challenging, we expect two potential scenarios for group 2 (b, c). Adaptive transgenerational plasticity (TGP) (b) occurs when fitness is highest if environments of parents and offspring match, while carry‐over effects (c) lead to the accumulation of negative effects over generations, leaving offspring of control parents with higher fitness. As foreign environments might also affect offspring condition positively, the sign of the effect could also be reversed