Thermal Limits Across Development and Reproduction in the ditch shrimp Palaemon varians

Considering the current climate scenario, in which global warming is affecting ecosystems worldwide, it is imperative to determine the thermal tolerance of marine species to both present-day and future temperatures, particularly those inhabiting shallow-water environments, as these are expected to be the most exposed to environmental changes. Although several studies have addressed this topic, most overlook the fact that thermal tolerance may vary according to developmental stage and reproductive status, which may lead to underestimations of marine species vulnerability to thermal stress. The present study analysed the upper thermal limits of the ditch shrimp Palaemon varians across its entire developmental cycle (Zoea 1 to 5, postlarvae, and adults), as well as differences related to sex (males vs. females) and female reproductive status (immature, ovigerous, and spent), using Critical Thermal maximum (CTmax) assays. Results showed that early larval stages (Zoea 1- 3) and spent females displayed the lowest CTmax values, revealing that both early development and reproduction may constrain the thermal tolerance of this species. These stages may therefore represent critical bottlenecks for species survival under future global warming scenarios.