No evidence of evolutionary impact from size‐selective harvesting on epigenetic and reproductive molecular markers in zebrafish ( <scp> <i>Danio rerio</i> </scp> ) gonads

This study investigates whether size-selective harvesting induced heritable changes reflected in epigenetic and reproductive molecular markers in zebrafish (Danio rerio), thereby indicating potential evolutionary responses. We used an experimental harvest model where zebrafish populations were subjected to five generations of size-selective harvesting, followed by eight generations without harvesting in a controlled environment to examine evolutionarily fixed outcomes in response to harvest selection. We assumed the evolutionary adaptations to size-selection to have left a molecular legacy related to sexual development, as previous studies have shown that evolution of reproductive timing is a common response to size-selection. To that end, we examined the expression of specific genes related to sexual development, such as dmrt1 and cyp19a1a, and epigenetic markers, including dnmt1 and dnmt3b, in the gonads in those experimental lines selected for this study. Additionally, global DNA methylation patterns were analysed to explore potential long-term epigenetic changes associated with size-selection. The results revealed no significant differences in gene expression related to sexual development or epigenetics between the size-selected and control zebrafish lines in the gonads in the F13 generation, eight generations after size-selection stopped. Also, global DNA methylation patterns were similar across selection lines and sexes. These findings suggest that five generations of size-selective harvesting, followed by eight generations of maintenance reproduction without further selection, did not induce lasting epigenetic or molecular changes related to the target molecular markers of sexual development in the gonads of zebrafish. The no significant molecular responses to size-selective harvesting observed here, based on specific reproductive and epigenetic markers, differ from previous studies targeting other tissues such as brain and liver, highlighting that not all genes or processes necessarily respond to size-selection and underscoring the importance of marker-specific comparisons.