Figure 15. Schematic representation of possible mechanism for the stress triggered germ cell apoptosis in Chinese fire-belly newt, Cynops orientalis.

(A) Potential pathways initiated by various stress in germ cell apoptosis. Cold exposure, cadmium exposure and heat exposure probably induced germ cell apoptosis via both extrinsic pathway and intrinsic pathway, but starvation likely only via extrinsic pathway. (B) Hypothesized sperm features and unique reproduction policy responsible for high occurrence of spermatid and sperm apoptosis. The nuclear morphology and mitochondria arrangement may be the physiological basis for observed high frequency of spermatid and sperm apoptosis, and a unique reproduction policy of newts may also account for this phenomenon.