Further Studies on Sperm Morphology of Japanese Salamanders, with Special Reference to Geographic and Individual Variation in Sperm Size

Abstract

Sperm shape and size of Hynobius takedai, H. lichenatus, H. retardatus, and H. stejnegeri were examined with light and scanning electron microscopy. Sperm shape is essentially identical with, and sperm length is within the range of, previously described hynobiid species. Remarkable geographic variations in sperm length were found in H. nebulosus and H. naevius of Kyushu, whereas sperm lengths in different populations of Cynops pyrrhogaster varied only slightly. Sperm length varied individually in all examined species, but the range of individual variations was limited as compared with the range of geographic variations. Interspecific variations in sperm length do not correlate with body size, testes size, clutch size, or egg diameter. Sperm size may be constrained by genome size, reproductive mode, phylogeny, etc., but the ralationships seems to be much more complicated in salamanders than in mammals, birds, or Drosophila.