Dormant and active ostracod communities in six rice fields of Yunnan, China

Ostracods have frequently been reported as part of the active faunas in the wet phase of rice fields, but knowledge on the dormant ostracods during the dry period of the rice cycle has been limited, hindering a comprehensive understanding of their adaptation to the rice field environment. In this study, we record 11 dormant ostracod species by incubating soil samples from six desiccated rice fields in Yunnan Province of southwestern China. The dormant ostracod community was dominated by species of the family Cyprididae, accompanied by members of Candonidae, Ilyocyprididae, and Notodromadidae. Our data provide unequivocal evidence for the presence of dormant ostracods from all the four families of the superfamily Cypridoidea in desiccated rice fields, verifying that these ostracods adapt to the rice fields by desiccation-resistant stage. Considering the usually shallow penetration depth of ostracods, the frequent discoveries of dormant ostracods in 2‒4 cm depth in the soil profile were probably the result of ploughing. Despite overlap in species composition, the dormant ostracod community differs from the active community sampled at the same sites more than four years ago. This suggests temporal changes of faunal composition, although the ecological memory of the dormant community containing multiple generations and the different seasonal windows represented by the two types of communities should also be considered. The emergence of adults within the first two weeks of the incubation experiment suggests the presence of dormant instars in the soil rather than resting eggs alone.