Divergent survival and reproductive trajectories across three generations of warming in a small tropical cyclopoid copepod

Short-lived, small tropical ectotherms may experience temperatures near their upper limits for several generations, yet risk assessments often rely on short-term exposure and responses within a single generation. Whether survival, body size and reproduction respond in parallel to sustained warming across multiple generations is unclear, which limits predictions of ecological consequences. We exposed five replicate lineages of the small tropical cyclopoid copepod Dioithona rigida to constant 28, 30, 32 or 34 °C for three generations. Survival to adulthood was on average 52.6% lower at 32-34 °C than at 28-30 °C, with no significant change across generations. In contrast, body size decreased and clutch size and nauplii production increased across generations at all temperatures, indicating a generation-related shift largely independent of temperature. Temperature differences in reproduction appeared only in F3, with smaller clutches at 32-34 °C and lower nauplii production at 34 °C. Fewer individuals reaching adulthood could reduce the number of reproducing adults and the supply of copepods to fish and shrimp larvae in tropical coastal food webs.