We report here on the amplectic behavior of the Japanese treefrog (Hyla japonica) in microgravity. Treefrogs were exposed to 35 cycles of altered gravity, including ≈ 1.5 sec of G < 0.1 every 3 min and 15 sec, on the FreeFall “G.0” ride at Space World amusement park in Kitakyushu, Japan. During this period a pair of frogs spontaneously entered and maintained amplexus for 1 hr 20 min, before being removed from the ride. In freefall, the pair extended their hindlimbs in the characteristic posture of treefrogs in microgravity.

This is the first report of a vertebrate entering and sustaining a copulatory or amplectic posture under gravitational extremes, including true freefall. These observations bode well for the potential of anurans to breed in microgravity and to be used for biological research in space.