Developmental temperature induces consistent patterns of plasticity in lower, but not upper, critical thermal limits in threespine stickleback (Gasterosteus aculeatus)

Abstract Developmental plasticity, where early-life environmental cues shape developmental trajectories with lasting impact into adulthood, may play an important role in determining how species respond to changing thermal environments. We used marine threespine stickleback ( Gasterosteus aculeatus ) to investigate whether temperature experienced during embryonic development has persistent effects on critical thermal limits as adults. Egg clutches from six families of pure marine F2s were split across three developmental temperatures (12 °C, 15.5 °C, and 22 °C), transitioned to 15.5 °C once hatched, and reared to adulthood under common-garden conditions, before being assayed for critical thermal minimum (CT min ) and maximum (CT max ). Developmental temperature was found to have significant, persistent effects on CT min , where the direction of change tracked rearing temperature (i.e., CT min decreased as early life temperature decreased). While the extent of change (i.e., slope of reaction norm) and inherent values (i.e., height of reaction norm) varied across families, all families shared the same trend. In contrast, the effect of developmental temperature on CT max was minimal, with inconsistent patterns across families. The ability of marine stickleback to lower their CT min through developmental plasticity may help maintain phenotype-environment match under changing conditions; however, this will depend on congruence between early life and adult environments.