The magnitude of incubation temperature fluctuation affects the immunity of Chinese soft‐shelled turtle (Pelodiscus sinensis) hatchlings

We mimicked daily fluctuations in temperature to examine whether the magnitude of the incubation temperature fluctuation affected the immunity of Chinese soft‐shelled turtle (Pelodiscus sinensis) hatchlings. The control incubation temperature was 29℃. Two of the temperatures used (29℃ ± 3℃ and 29℃ ± 5℃) were within the optimal range of the turtle's constant incubation temperature, and one (29℃ ± 9℃) was outside of this range. Data on hatching success, incubation period, and weight of the turtle hatchlings were collected. The incubation period and hatchling weight were significantly affected by temperature fluctuation, whereas the hatching success was not. After two months, the effect of the temperature fluctuation on hatchling weight was much more pronounced. After challenging hatchlings with pathogens, the hatchlings from the extremely fluctuating incubation temperature group were feeble. To explore the molecular changes of immunity associated with incubation temperature, serum lysozyme, acid and alkaline phosphatase activities, and seven immune‐related genes were examined in two‐month‐old turtles. Before pathogen infection, serum lysozyme activities were lower in turtles that experienced fluctuating temperature, and serum acid and alkaline phosphatase activities were higher in turtles exposed at 29℃ ± 3℃ and 29℃ ± 5℃. After pathogen challenge, lysozyme responded to the pathogen infection in 12 h, and acid and alkaline phosphatase activities were lower at 12 and 48 h in all four groups. Although the expression of the seven immune‐related genes was not affected before the bacterial challenge, they were upregulated after the bacterial challenge in all four groups.