Reproductive Biology of Sceloporus consobrinus (Phrynosomatidae): Male Germ Cell Development and Reproductive Cycle Comparisons within Spiny Lizards
Reproductive cycles of lizards have long been studied in both field and laboratory scenarios. However, comparisons of spermatogenic cycles and germ cell development strategies in different populations across a large geographic range have yet to be explored. The purpose of this study is to A) describe the spermatogenic cycle and germ cell development strategy of a population of Sceloporus consobrinus in southeast Louisiana, B) compare this cycle to a more northern population of this species, and C) compare the reproductive cycles of species within Sceloporus (N = 21). In S. consobrinus from Louisiana, recrudescence begins in the fall (October and November), and the peak of spermatogenesis is reached the following spring/summer (May, June, July). This spermatogenic cycle is similar to that of a more northern population of S. consobrinus from Missouri. Within the genus Sceloporus, there are two seasonal patterns of spermatogenesis: initiation of spermatogenesis in the summer/fall and initiation of spermatogenesis in the spring. In both summer/fall and spring spermatogenic patterns, spermiogenesis occurs in the spring and may continue into the summer. The seasonal timing of recrudescence is an extremely plastic trait that has evolved multiple times throughout the Sceloporus clade. However, there appears to be an association of summer/fall and spring recrudescence with latitude. Tropical populations have a higher frequency of spring recrudescence and temperate populations have a higher frequency of summer/fall recrudescence.Abstract
Cross-section of the testis in Sceloporus consobrinus showing the seminiferous tubules (St) and surrounding tunica albuginea (Ta). Scale = 100 μm.
Germ cell types found within the seminiferous epithelium of Sceloporus consobrinus. Spermatogonia A (SpA), Spermatogonia B (SpB), Pre-leptotene (PL), Leptotene (LP), Zygotene (ZY), Pachytene (PA), Diplotene (DI), Meiosis I (M1), Secondary spermatocyte (SS), Meiosis II (M2), Step 1 spermatid (S1), Step 2 spermatid (S2), Step 3 spermatid (S3), Step 4 spermatid (S4), Step 5 spermatid (S5), Step 6 spermatid (S6), Step 7 spermatid (S7), mature spermatozoon (MS). Scale = 10 μm.
Cross-section of seminiferous tubules of Sceloporus consobrinus during A) March, B) April, C) May, and D) June. Germ cell types include spermatogonia (Sp), meiotic cells (Me), spermiogenic cells (Ss), and mature spermatozoa (Ms). Basal lamina (black arrowhead). Scale = 50 μm.
Cross-section of seminiferous tubules of Sceloporus consobrinus during the months of A) July, B) August, C) September, and D) October. Germ cell types include spermatogonia (Sp), meiotic cells (Me), spermiogenic cells (Ss), and mature spermatozoa (Ms). Basal lamina (black arrowhead). Scale = 50 μm.
Cross-section of seminiferous tubules showing individual variation found during November in Sceloporus consobrinus. A) Individual only exhibiting spermatogonia (Sp) and early meiotic cells (Me). B) Individual exhibiting spermatogonia (Sp) and late meiotic cells (Me). C) Individual exhibiting spermatogonia (Sp), meiotic cells (Me), and spermiogenic cells (Ss). Basal lamina (black arrowhead). Scale = 50 μm.
Reproductive cycles in the Sceloporus genus. A) Fall spermatogenesis showing spermatogenic cycles (top), ± 1-month variation (middle) with gray bars showing a ± 1-month deviation, and spermatogenic cycle overlap (bottom) with red bars demonstrating areas of overlap between the reproductive cycles of the various species. B) Spring spermatogenesis showing spermatogenic cycles (top), ±1-month variation (middle) with gray bars showing a ± 1-month deviation, and spermatogenic cycle overlap (bottom) with red bars demonstrating areas of overlap between the reproductive cycles of the various species.
Character optimization of spermatogenic cycle, region inhabited, and parity mode across the molecular and morphological hypothesis proposed by Wiens and Reeder (1997) and the purely molecular hypothesis proposed by Leaché (2010).
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