Highly plastic resource allocation to growth and reproduction in females of an African annual fish

Phenotypic plasticity is an important mechanism to maximise fitness in unpredictable environments by fine-tuning phenotypes to a specific environmental setting. We used Nothobranchius furzeri, an African annual fish from temporary pools with erratic changes in habitat condition, to study changes in the allocation to growth and reproduction and to test the key trade-off between egg size and number. In an experimental setting, we quantitatively varied ration at two levels and over two time periods, including temporal switches in ration level. As predicted, female N.furzeri possessed the capacity for compensatory growth, which surprisingly came with no longer-term cost to fecundity. Females responded strongly to ration manipulation, with a pronounced decrease in fecundity associated with a low ration, even after accounting for body mass. Due to the unpredictability of offspring environment, we expected no adaptive change in oocyte size. However, females responded to the quality of their environment in accordance with an adaptive maternal effect, with females receiving a low ration producing larger eggs. Further, a switch in ration size in either direction was associated with a decrease in egg size. There was a trade-off between egg size and number in half of the treatments, but high variability in egg size among females made the relationship complex. Overall, N.furzeri females demonstrated high plasticity in both growth rate and fecundity parameters. Females appear able to track and respond adaptively to unpredictable changes in food availability in their environment.