Testis asymmetry in the dark-spotted frog Rana nigromaculata

The left and right testes often differ in size, and testis asymmetry is particularly well studied in birds. The compensation hypothesis states that asymmetry in testes mass covaries with male quality. We tested this idea in the dark-spotted frog Rana nigromaculata, a species where large males have a mating advantage over small males. The left testes were significantly larger than the right testes. Larger and older males tended to have relatively larger testes, but did not show a higher degree of testis asymmetry than younger males. A negative correlation between male body size and testis asymmetry is in line with the hypothesis that the right testis has a compensatory role when the left testis is malfunctioning.