Characteristics of the seasonal development variation in the male reproductive system of Ranodon sibiricus
This study aimed to elucidate the reproductive strategy of Ranodon sibiricus,adapted to high-altitude and alpine environments,by examining seasonal developmental variations in the mature male reproductive system.One adult male was procured from the natural population of Ranodon sibiricus bimonthly for over a year.Data from eight individuals generated a continuous seasonal developmental profile of the male gonads.Using anatomical and histopathological methods,developmental variations in the male reproductive system across different seasons were detailed.These results indicate that the male gonadal developmental cycle of Ranodon sibiricus is segmented into reproductive,trophic,and hibernation periods.The reproductive period comprised spring phase Ⅰ,spring phase Ⅱ,and summer phase Ⅰ.In spring phase I,mature spermatozoa populate the testes;the gonadosomatic index(GSI)peaks annually at 5.93％and the fat body index(FBI)registers a yearly minimum of 0.06％,aligning with the onset of reproductive activity.By spring phase Ⅱ,all spermatozoa from the testes had transitioned to the vas deferens.Concurrently,the GSI dropped to an annual low of 0.49％,in anticipation of spermatozoa emissions,and the FBI increased slightly to 0.13％.During summer phase Ⅰ,spermatozoa are entirely evacuated from the vas deferens;the GSI slightly increases to 0.66％,indicating the commencement of another male gonad developmental cycle,and the FBI marginally increases to 0.14％.The trophic period is split between summer phase Ⅱ and autumn phase Ⅰ.Here,the seminiferous lobule is sequentially occupied by primary spermatogonia,secondary spermatogonia,primary spermatocytes,secondary spermatocytes,and spermatids.During this phase,the GSI increased to 1.62％and the FBI attained its yearly apex at 0.51％.The hibernation periods were categorized as autumn phase Ⅱ,winter phase Ⅰ,and winter phase Ⅱ.During this phase,mature spermatozoa developed in the testes.The GSI progressed from 1.87％to 3.75％,whereas the FBI decreased to 0.39％before increasing slightly to 0.45％,signifying the hibernation of the species and preparation for subsequent breeding.The findings revealed that adult male Ranodon sibiricus sperm matured annually.Males exhibit an annual breeding cycle that is characteristic of amphibians with discontinuous breeding cycles.Notably,male Ranodon sibiricus can engage in mating and spermatogenesis multiple times during the mating window(late April to late June)until sperm depletion.This study provides foundational knowledge in reproductive biology,which is vital for the scientific conservation of Ranodon sibiricus and advancements in artificial reproduction techniques.
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