Temporal Germ Cell Development Strategy during Mixed Spermatogenesis within the Male Mediterranean Gecko, Hemidactylus turcicus (Reptilia: Gekkonidae)
The testes of Hemidactylus turcicus are composed of seminiferous tubules lined with continuous germinal epithelia in which multiple germ cell morphologies can be found during the active months of sperm development. Spermatogenesis is quiescent during September, with only spermatogonia A and spermatogonia B present in the seminiferous epithelia and minimal mitotic activity is observed. Recrudescence begins in October and the early stages of spermatogenesis progress through November. The onset of spermiation is observed in December and continues through August with the heaviest sperm release occurring in June and July. Multiple generations of late elongated spermatids are found in association with early mitotic and meiotic cells during the months of December–August. This temporal germ cell development strategy is similar to that described in other squamates and anamniotes and is different from the spatial development exhibited by birds and mammals, in which germ cell populations collectively progress through the stages of spermatogenesis. The reptilian temporal model of germ cell development within a structurally amniotic testis leads to two hypotheses in character evolution: birds and mammals exhibit convergence of germ cell development strategy, or the spatial development strategy is a synapomorphy in amniotes, and reptiles represent an evolutionary reversal to the strategy employed by anamniotes. These findings, along with present and future data, may allow for more concrete phylogenetic analyses by creating more characters for phylogenetic matrices and may prove to be useful in future histopathological studies.Abstract
Germ cell types found within seminiferous tubules of Hemidactylus turcicus. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PL, pre-leptotene spermatocyte; LP, leptotene spermatocyte; ZY, zygotene spermatocyte; PA, pachytene spermatocyte; DI, diplotene spermatocyte; M1, meiosis I; M2, meiosis II; ss, secondary spermatocyte; S1, step 1 spermatid; S2, step 2 spermatid; S3, step 3 spermatid; S4, step 4 spermatid; S5, step 5 spermatid; S6, step 6 spermatid; S7, step 7 spermatid; MS, mature sperm.
(A) Variation in seminiferous tubule diameter and (B) variation in germinal epithelial height during the entire calendar year of the male Mediterranean Gecko, Hemidactylus turcicus. Values represented on these graphs are means ± 1 standard error. Different superscripts indicate significant differences (P ≤ 0.05; Dunn-Sidak multiple range test).
(A) The cell types observed in the September seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; white arrow, Sertoli cell. (B) The cell types observed in the October seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PL, pre-leptotene spermatocyte; LP, leptotene spermatocyte; ZY, zygotene spermatocyte; VA, vacuole. (C) The cell types observed in the November seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PL, pre-leptotene spermatocyte; LP, leptotene spermatocyte; PA, pachytene spermatocyte; DI, diplotene spermatocyte; ZY, zygotene spermatocyte; S1, step 1 spermatid. (D) The cell types present in the December seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; SS, secondary spermatocyte; S1, step 1 spermatid; S4, step 4 spermatid; S5, step 5 spermatid; MS, mature sperm.
(A) The cell types observed in the January seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PA, pachytene spermatocyte; DI, diplotene spermatocyte; M1, meiosis I; M2, meiosis II; S1, step 1 spermatid; S7, step 7 spermatid; MS, mature sperm. (B) The cell types observed in the February seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PL, pre-leptotene spermatocyte; LP, leptotene spermatocyte; SS, secondary spermatocyte; S1, step 1 spermatid; S5, step 5 spermatid; S6, step 6 spermatid; MS, mature sperm; *, apparent vacuole as a product of the dehydration process. (C) The cell types observed in the March seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; DI, diplotene spermatocyte; M1, meiosis I; M2, meiosis II; S1, step 1 spermatid; S5, step 5 spermatid; S6, step 6 spermatid; MS, mature sperm. (D) The cell types observed in the April seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PL, pre-leptotene spermatocyte; LP, leptotene spermatocyte; ZY, zygotene spermatocyte; S1, step 1 spermatid; S2, step 2 spermatid; S4, step 4 spermatid; S6, step 6 spermatid; S7, step 7 spermatid; MS, mature sperm.
(A) The cell types observed in the May seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; S1, step 1 spermatid; S3, step 3 spermatid; S5, step 5 spermatid; S6, step 6 spermatid; S7, step 7 spermatid; MS, mature sperm. (B) The cell types observed in the June seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; SS, secondary spermatocyte; S1, step 1 spermatid; S2, step 2 spermatid; S6, step 6 spermatid; S7, step 7 spermatid; MS, mature sperm. (C) The cell types observed in the July seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; PA, pachytene spermatocyte; SS, secondary spermatocyte; S1, step 1 spermatid; S3, step 3 spermatid; S7, step 7 spermatid; MS, mature sperm; SC, Sertoli cell nucleus. (D) The cell types observed in the August seminiferous epithelia. Bar = 20 µm. SpA, spermatogonia A; SpB, spermatogonia B; S5, step 5 spermatid; S6, step 6 spermatid; MS, mature sperm.
Contributor Notes
Associate Editor: S. A. Schaefer.