High air humidity is sufficient for successful egg incubation and early post-embryonic development in the marbled crayfish (Procambarus virginalis)

Severe weather events, such as long-term droughts, are challenging for many freshwater species. To survive drought, freshwater crayfish tend to inhabit shelters or burrows where they can remain in contact with water or high humidity environments. However, it is not known whether embryogenesis or post-embryonic development can occur without free standing water. To address this question, three experiments were conducted using artificial burrows with high air humidity and using marbled crayfish (Procambarus virginalis Lyko, 2017) as a model species. Marbled crayfish are capable of parthenogenetic reproduction, burrow extensively and are able to travel long distances over land. In the first experiment, ovigerous females were transferred to simulated burrows without free water, but with high air humidity. A control group of females were kept in burrows with free water. Successful hatching was achieved in both groups. In the second experiment, ovigerous females were transferred to simulated burrows with no free water but high air humidity and post-embryonic development were observed. Following successful hatching, offspring moulted to the second developmental stage (stage 2 juveniles). Stage 2 juveniles remained viable without free water for 20 days, but further development was not observed. However, when some of these stage 2 juveniles were placed back into fully aquatic conditions (experiment 3), they moulted to stage 3 within 4 to 8 days. These results demonstrated the ability of marbled crayfish to undergo terminal phases of embryogenesis, including hatching, as well as early post-embryonic development under high air humidity conditions only. Post-embryonic development was suspended in the absence of free water, and successfully resumed when re-immersed. This similar ability to tolerate drought-like conditions during post-embryonic development may also occur in other crayfish species, especially primary burrowers. This unprecedented life history trait may be crucial for inhabiting ecosystems with rapidly changing water regimes. In drying climates, it may confer advantages on some crayfish species (including some invasive species) over others.