Effects of isolated-incubation embryos on the growth, development, social behavior, and locomotor performance of Rana zhenhaiensis tadpoles

Embryo-clustering incubation plays an important role in anti-predation, maintaining temperature balance between embryos, and promoting hatching synchrony for anurans. In this study, we investigated the effects of two hatching conditions(isolated-incubation and clustered-incubation) on the growth, development, social behavior, and locomotor performance of Rana zhenhaiensis tadpoles under laboratory conditions. Our results showed that both body length and the Gosner development stage of two-day-old hatchlings in a single-embryo treatment were significantly larger than those of the group-embryo treatment. The results of the ANCOVA(with body length as the covariate) analysis showed that both body width and body mass in the group-embryo treatment were significantly lower than those of the single-embryo treatment. For tadpole activity behavior, the occurrence frequency in the upper and middle water layers in the single-embryo treatments were significantly lower than those of the group-embryo treatment, whereas it was significantly greater in the single-embryo treatments than that of the group-embryo treatment in the lower water layers. The proportion of area occupied by tadpoles, the nearest neighbor distance, and the distance among individuals in the single-embryo treatment were both significantly greater than those of the group-embryo treatment, but the contact frequency between pairwise tadpoles was significantly lower than those of the group-embryo treatment. Regarding locomotor performance, we found that activity duration and activity frequency in the single-embryo treatment were significantly lower than those of the group-embryo treatment. These findings should provide valuable reference data on the growth and development of Rana zhenhaiensis, as well as other anuran species.