Reproduction, salamander, siren, spermatogenesis


I investigated the seasonal testicular histology and acystic lobular spermatogenesis in the Western Lesser Siren, Siren intermedia nettingi, from periodic sampling of this salamander over a span of 21 yr (1994-2015) in northeastern Arkansas. My results include the following general findings: 1) the largest testicular lobules occurred primarily in January-February during spermiogenesis and spermatozoa maturation; 2) lobular regression and spermatogenic cell recrudescence were underway by late March; 3) proliferation of secondary spermatogonia in lobules was prominent in May; 4) transformation of secondary spermatogonia into primary spermatocytes occurred by mid-July, and these cells became larger in diameter through increased nuclear size and by being heavy laden with lipid droplets, 5) lobular diameters gradually increased through the expansion of lobular luminal open space in July-August, and 6) lobular size continued to increase in October-December with lumina containing numerous secondary spermatocytes. Specifically, my primary objective in this part of a long-term study was to present histologically, for the first time, the annual testicular cycle in this species along with an explanation of the unique cellular complexities of acystic lobular spermatogenesis, a process which this sirenid species shares with another genus (Pseudobranchus) within the salamander family Sirenidae. No other vertebrates of any kind possess this type of spermatogenesis.