Testis Size Variation and Its Environmental Correlates in Andrew's Toad (Bufo andrewsi)

Simple Summary Life-history theory includes that trade-offs between reproduction and survival are critical for organisms to adapt to different environments. Therefore, understanding how organisms adapt their reproductive investment can provide insights into the evolution of life history. Our results showed that the testes size of Bufo andrewsi significantly differed among populations. We found no geographic trends explaining the variability in testes size, as relative testes size did not vary with altitude and/or latitude. Although rainfall cannot directly affect testes size, the coefficient of variation of temperature showed effects on testes size, indicating declined male reproductive investment under environments with fluctuating temperature and thus highlighting important implications for amphibian conservation. Reproductive investments influenced by environmental conditions vary extensively among geographically distinct populations. However, investigations of patterns of intraspecific variation in male reproductive investments and the mechanisms shaping this variation in anurans remain scarce. Here, we focused on the variation in testis size in 14 populations of the Andrew's toad Bufo andrewsi, a species with weak dispersal ability but wide distribution in southwestern China, to establish whether male reproductive investment varies on an environmental gradient. Our analysis revealed a significant variation in relative testis size across populations, and a positive correlation between testis size and body condition. We, however, found no geographic trends explaining the variability in the testis size. The relative testis size did not increase with increasing latitude or altitude. We also found no relationship between relative testis size and rainfall, but a negative correlation with the coefficient of variation of temperature, with larger testes under stable environments. These findings suggest that the decreased male reproductive investment of this species may be a consequence of harsher or fluctuating environmental conditions.