Search

Induction of spawning in catfish is well demonstrated in females while stimulation of spermiation in males seems difficult. This has led to least understanding of gene profile changes during testicular maturation. Expression of the factors after hormonal induction that control reproductive processes has become an intense research area in fish endocrinology. In view of this, de novo assemblies of testicular transcriptomes of the Asian catfish, Clarias batrachus and the African catfish, C. gariepinus, were performed to identify genes/factors involved in testicular maturation. For testicular induction, human chorionic gonadotropin (hCG) was administered in vivo to both the catfish species during active phase of reproduction. 1,68,071 and 1,26,232 assembled transcripts were obtained from C. batrachus and C. gariepinus testicular transcriptomes and were annotated using different databases. Further, in silico analysis suggested the presence of several transcripts that were involved in steroidogenesis and male reproduction. Comparison of transcriptomes of both species revealed the presence of certain unique genes related to reproduction differentially. Expression profiles after hCG induction in testis showed higher expression of certain steroidogenesis related genes such as star , cyp11b1 , cyp17a and cyp21a in both the species. Further, expression levels of crucial factors related to testis, such as dmrt1/2/3, were also found to be significantly higher after gonadotropin induction. However, amh , tgfα and dmrt4/5 expression levels were significantly low. Factors related to male reproduction i.e. , tekt1 , tekt2 , sox9 , spag1 , spata2 and spata7 were found to be differentially upregulated in hCG treated testicular tissues of both the species. Histology analysis indicated that the gonadotropin induction either short or long term is a better strategy to highlight expression profile changes during testicular maturation in teleost. • Testicular transcriptome sequencing of C. batrachus and C. gariepinus • Identification of testis-related genes and testicular histology analysis • Gonadotropin dependency of testis-related genes in both the species [ABSTRACT FROM AUTHOR]

The urogenital system of male squamates consists of the testis, testicular ducts, and sexual segment of the kidney. These structures undergo seasonal variation, and their morphology is variable across taxa. Despite multiple studies examining the morphology of the various components of the reproductive system, few studies have examined squamates in sympatry. The purpose of this study was to investigate the morphology and seasonal variation of the reproductive system in two taxa that are sympatric with one another, Anolis carolinensis and Sceloporus undulatus, from southeastern Louisiana. Specimens were collected monthly for an entire year and processed for histological and ultrastructural analysis. Both species have a single rete testis leading from the testis to the ductuli efferentes, which leads into the proximal portion of the epididymis. The rete testis consists of a simple squamous epithelium with irregularly shaped nuclei, the ductuli efferentes consists of a ciliated simple cuboidal epithelium, and the epididymis a pseudostratified columnar epithelium. No differences were observed in the morphology of the urogenital systems between taxa but phenological variation was observed in terms of the tissue development for reproduction. Anolis carolinensis has an extended active period and two separated periods of maximal activity evidenced by two peaks in the ductuli efferentes epithelial height and tubular diameter (March and July) whereas Sceloporus undulatus only had a single peak occurring in June. These results suggest that reproductive morphology may be conserved at taxonomic levels above family level, and reproductive activity may be constrained phylogenetically and is not solely dependent on environmental factors, at least in terms of geographic range, though it is acknowledged that microhabitats may play a major role in cyclicity of reproductive events. Future studies examining species at various taxonomic levels, as well as species in sympatry, will provide additional insight into hypotheses concerning abiotic factors and reproductive biology. [ABSTRACT FROM AUTHOR]

Roe deer are seasonal breeders with a complete yearly testicular cycle. The peak in reproductive activity is recorded during summer, the rutting period, with the highest levels of androgens and testicular weight. Melatonin plays a pivotal role in seasonal breeders by stimulating the hypothalamus–pituitary–gonads axis and acting locally; in different species, its synthesis within testes has been reported. The aim of this study was to evaluate the physiological melatonin pattern within roe deer testes by comparing data obtained from animals sampled during pre- and post-rut periods. Melatonin was quantified in testicular parenchyma, along with the genetic expression of enzymes involved in its local synthesis (AANAT and ASMT) and function (UCP1). Melatonin receptors, MT1-2, were quantified both at protein and gene expression levels. Finally, to assess changes in reproductive hormonal profiles, testicular dehydroepiandrosterone (DHEA) was quantified and used for a correlation analysis. Melatonin and AANAT were detected in all samples, without significant differences between pre- and post-rut periods. Despite DHEA levels confirming testicular involution during the post-rut period, no correlations appeared between such involution and melatonin pathways. This study represents the first report regarding melatonin synthesis in roe deer testes, opening the way for future prospective studies in the physiology of this species.

The roe deer (Capreolus capreolus) represents a spontaneous model of testicular inactivation: During winter, bucks show a suspension of spermatogenesis that starts again in spring and peaks during the breeding season (July–August). The underlying mechanisms to the regulation of the cyclic testicular changes are still not fully clear but seem to be imputable to the spermatogenic cell line since other testicular cell populations remain stable without apoptotic phenomena. The aim of the study was to investigate apoptosis, gelatinases (MMP2 and 9), their inhibiting factors (TIMP 1-2), and two isoforms of vascular endothelial growth factor (VEGF121 and 165) with its receptors (VEGFR1-2) in testes collected during pre- and post-rut periods, and to correlate them with testicular weight (TW) and testosterone (TEST). Testes from 18 adult sexually mature bucks were collected in Bologna Apennines (Italy). Samples were weighed and parenchyma collected. Radioimmunoassay, real-time PCR, and zymography were performed. The results showed a post-rut decrease in TW and TEST and an increase in proMMP2, also highlighting a correlation between the gelatinases and the testicular functionality. The VEGF pattern did not show modifications nor correlation with TW and TEST. Overall, gelatinases and their inhibitors, described herein for the first time in roe deer testes, seem to play an important role in the testicular cycle.

We investigated whether circannual rhythms underlying annual testis maturation and moult cycles are independent of duration and frequency of the light period and circadian clock control in nonphotoperiodic spotted munia. Birds were subjected to an aberrant light-dark (LD) cycle (3.5 h L:3.5 h D; T7, where T is the period length of the LD cycle) and continuous light (LL, 24 h L:0 h D), with controls on 12 h L:12 h D (T24, 24 h LD cycle).We measured the behavioural activity pattern of the birds and 24 h mRNA oscillations of circadian clock genes (bmal1, clock, per2, cry1, cry2) in the hypothalamus, the putative site of seasonal timing. Diurnal munia were rhythmic in behaviour with the period of the activity-rest cycle matched to T7 and T24, and became behaviourally arrhythmic with activity scattered throughout 24 h under LL. Similarly, exposure to 3.5 h L:3.5 h D and LL caused arrhythmicity in 24 h clock gene expression, suggesting disruption of internal circadian timing at the transcriptional level; a significant rhythmwas found under 12 h L:12 h D. During an exposure of 80 weeks, munia showed two to three cycles of testis maturation and wing primaries moult under all photoperiods, although with a longer period under 12L:12D. Thus, the frequency of light period under 3.5 h L:3.5 h D or LL disrupted circadian clock gene cycles, but did not affect the generation of circannual testis and moult cycles. We conclude that the prevailing light environment and hypothalamic circadian gene cycles do not exert direct control on the timing of the annual reproductive cycle in spotted munia, suggesting independent generation of the circadian and circannual rhythms in seasonally breeding species. [ABSTRACT FROM AUTHOR]

Seasonal reproductive cycles of most birds are regulated by photoperiod via neuroendocrine control. Gonadotropin-inhibitory hormone (GnIH) in the hypothalamus has been reported to act as neuroendocrine integrator of photoperiodic cues. In this study, both captive and field investigations were carried out to understand the effects of photoperiod and seasonality on GnIH expression in subtropical tree sparrows. Monthly observations of GnIH mRNA and peptide expression in wild birds over a year revealed a significant increase in GnIH mRNA level and number of GnIH-ir neurons during the non-breeding season when compared with their expression in the breeding season. GnIH-ir neurons were found primarily in the paraventricular nucleus (PVN) with their fibers projecting into the median eminence and some other areas of the brain. In an 8 monthlong experiment, birds exposed to short days had higher GnIH expression compared with birds exposed to long days regardless of sampling month. Long-day birds with regressed testes had similar GnIH levels to short-day birds. Though the number of GnIH peptideexpressing neurons ran almost parallel to the levels of GnIH mRNA, they were inversely related to gonadal size in both sexes under natural and artificial photoperiodic conditions. These results clearly indicate an inhibitory role of GnIH in photoperiodic regulation of seasonal reproduction in the tree sparrow. [ABSTRACT FROM AUTHOR]

Testicular receptor 2 (TR2; also known as Nr2c1) is one of the first orphan nuclear receptors identified and known to regulate various physiological process with or without any ligand. In this study, we report the cloning of full length nr2c1 and its expression analysis during gonadal development, seasonal testicular cycle and after human chorionic gonadotropin (hCG) induction. In addition, in situ hybridization (ISH) was performed to localize nr2c1 transcripts in adult testis and whole catfish (1 day post hatch). Tissue distribution and gonadal ontogeny studies revealed high expression of nr2c1 in developing and adult testis. Early embryonic stage-wise expression of nr2c1 seems to emphasize its importance in cellular differentiation and development. Substantial expression of nr2c1 during pre-spawning phase and localization of nr2c1 transcripts in sperm/spermatids were observed. Significant upregulation after hCG induction indicate that nr2c1 is under the regulation of gonadotropins. Whole mount ISH analysis displayed nr2c1 expression in notochord indicating its role in normal vertebrate development. Taken together, our findings suggest that nr2c1 may have a plausible role in the testicular and embryonic development of catfish. [ABSTRACT FROM AUTHOR]

The objective of this study was to peruse the annular variations in testicular histomorphology and serum testosterone of guinea fowl (Numida meleagris) during different reproductive phases viz., resting, progression and peak breeding in Pakistan. Thirty healthy male birds were slaughtered: samples of testes were stained with H&E and histometric analysis was made with Image J®. Serum testosterone was measured by radioimmunoassay. Results revealed significantly (P<0.01) greater values of weight, volume, length, width, thickness and circumference of testes during peak breeding as compared to other phases. Histometric parameters like diameter of seminiferous tubules and its lumen, thickness of germinal epithelium and diameter of leydig cells showed significantly (P<0.01) higher values during peak breeding than other phases. Conversely, thickness of testicular capsule and percentage area of interstitial cells were significantly (P<0.01) higher during resting in contrast to progression and peak phases. Serum testosterone showed significantly (P<0.01) higher value (4.60±0.44) during peak breeding which declined significantly (P<0.01) in progression (1.73±0.19) and resting (0.62±0.07) phases. Moreover, all histomorphometric changes were positively correlated while percentage area of interstitial cells and thickness of testicular capsule were negative with hormonal profile during each phase. In conclusion, different reproductive phases influence annular testicular histomorphology and hormonal profile. Peak breeding activity of this bird is coincided with the increased steroid hormone synthesis under suitable circumstances. [ABSTRACT FROM AUTHOR]

The present study was carried out to analyze the differences in the activity of ultimobranchial gland (UBG) between male and female fresh water teleost Mastacembelus armatus during reproductive cycle. Considerable variations in the nuclear diameter of UBG cells and plasma calcitonin (CT) levels during different reproductive phases of testicular and ovarian cycle suggested that the activity of the UBG depends upon the sexual maturity of fishes. A positive correlation was observed between plasma CT and sex steroid levels and the gonadosomatic index in both sexes which further confirmed the involvement of UBG in the processes related to gonadal development in fishes irrespective of the sex. Sudden increase in the level of plasma CT and nuclear diameter of UBG cells after administration of 17 α-methyltestosterone in males and 17 β-estradiol in females during resting phase of the reproductive cycle clearly showed that UBG becomes hyperactive with increases in the level of sex steroids. Plasma calcium level was also found to be positively correlated with gonadal maturation in females. However no such change in plasma calcium level in relation to testicular cycle was observed. Thus it can be concluded that UBG becomes hyperactive during gonadal maturation but its role differs between male and female fishes. In females it may involved in both gonadal maturation and plasma calcium regulation while in males its involvement in calcium regulation was not justified. Variations in the level of CT during various phases of testicular cycle evidenced its involvement in gonadal maturation only. [ABSTRACT FROM AUTHOR]

Abstract: The maturation inducing hormone, 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP) is required for the meiotic maturation and is produced from the precursor 17α-hydroxyprogesterone by the enzyme 20β-hydroxysteroid dehydrogenase (20β-HSD) in several teleosts. Central role of 20β-HSD in ovarian cycle and final oocyte maturation is well studied when compared to spermatogenesis. In the present study, we investigated the localization and expression of 20β-HSD in testicular cycle and gonadotropin induced sperm maturation. During testicular ontogeny, 20β-HSD expression was detectable at 50 and 100days post-hatch (dph), while the expression was high at 150dph. In testicular cycle, highest levels of mRNA and protein of 20β-HSD were observed during spawning phase. Intraperitoneal injection of human chorionic gonadotropin (hCG) to prespawning catfish elevated both 20β-HSD transcripts and protein levels when compared to saline treated controls in a time-dependent manner. Serum 17α,20β-DP levels, measured during different phases of testicular cycle as well as following the treatment of hCG, showed a positive correlation with the expression of 20β-HSD. Immunolocalization revealed the presence of 20β-HSD protein predominantly in interstitial cells and spermatogonia/spermatocytes while 20β-HSD was undetectable in haploid cells (spermatids/sperm). These results together with high expression during spawning phase of testicular cycle and after hCG treatment in the prespawning catfish suggests a pivotal role for 20β-HSD during testicular recrudescence leading to sperm maturation. Further studies using various fish models on testicular 20β-HSD may provide interesting details to understand its importance in teleostean spermatogenesis. [Copyright &y& Elsevier]

The article focuses on a study involving the observation of the reproductive cycle of the Okinawa rail (Gallirallus okinawae) in the wild. It describes the Okinawa rail as an almost flightless bird that is endemic to the northern part of Okinawa Island in Japan which has seen a decline in its wild populations caused by habitat loss and predation. Under the study, the testes and ovaries of 50 wild Okinawa rails have been examined postmortem. Findings recommend the use of female Okinawa rails in and after the second breeding season and of adult males to ensure effective captive breeding pairs.

Abstract: A full-length cDNA encoding 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) was cloned from testis of air-breathing catfish, Clarias gariepinus which showed high sequence homology to zebrafish and eel. The open reading frame of 11β-HSD2 was then transfected to COS-7 cells, which converted 11β-hydroxytestosterone (11-OHT) to 11-ketotestosterone (11-KT). Using NAD+, 11β-HSD2 from testicular microsomes oxidized 11-OHT with apparent K m 56±4nM and V max 55±6pmol/h/mgprotein values. Tissue distribution analysis revealed prominent expression in testis, anterior kidney, liver and gills. Expression of 11β-HSD2 in testis and serum levels of 11-KT were high in the prespawning phase. Administration of human chorionic gonadotropin (hCG) during prespawning and resting phases revealed initial rise in 11β-HSD2 transcript at 4h followed by gradual increase at 8h, 12h and peaking at 24h, only in testis of prespawning phase. Rate of conversion of 11-OHT to 11-KT by testicular microsomes during different testicular phases and after hCG administration corroborated well with the expression of 11β-HSD2. Ontogeny study indicated that this enzyme is expressed during testicular development. Thus the spatio-temporal expression supported with putative dehydrogenase activity and circulating 11-KT levels clearly suggest a major role for 11β-HSD2 during testicular differentiation and seasonal testicular cycle in catfish. [Copyright &y& Elsevier]

Abstract: Complementary DNAs encoding steroidogenic acute regulatory protein (StAR) have been isolated from different fish species, yet the relevance of StAR during gonadal cycle and more importantly in final oocyte maturation has not been assessed so far. A cDNA encoding StAR was isolated from the ovarian follicles of air-breathing catfish, Clarias gariepinus. Catfish StAR exhibited 55 to 72% identity at nucleotide level with other vertebrate orthologs. RT-PCR analysis of tissue distribution pattern demonstrated the presence of StAR mRNA in various tissues including gonads, kidney, liver, brain and intestine of catfish. Real-time RT-PCR analysis revealed high expression of StAR mRNA in the pre-spawning phase of ovary while it was low in preparatory, spawning and regressed phases. In testis, maximum expression was noticed during the preparatory phase. During human chorionic gonadotropin (hCG)-induced oocyte maturation, both in vitro and in vivo, StAR mRNA levels were augmented by 2 h and then declined gradually to reach basal levels by 12 h as that of saline-treated controls. Taken together, high level of expression during hCG-induced oocyte maturation vis-à-vis in spawning suggests a role for StAR, in addition to the steroidogenic enzyme genes in final oocyte maturation. [Copyright &y& Elsevier]

Simple Summary: The roe deer is a small wild ruminant, very common in Europe and Asia; adult specimens are sexually active only during summer, in very short timeframes. Peculiarly, males, also known as bucks, produce spermatozoa only in this period, with a subsequent morph-functional testicular involution. In seasonal breeders, melatonin plays a pivotal role by converting light information and controlling the testicular hormonal function and, recently, its local production within testes has been described in other species. The aim of the present work was to study testicular melatonin and its synthesis pathway in roe deer during the pre-rut (June–July) and post-rut (August–September) periods, and correlate it with morph-functional testicular changes. Samples were opportunistically obtained from hunted specimens according to the local hunting calendar. The results also seem to suggest a local melatonin production in this species, but no correlations with testicular involution parameters were highlighted, probably due to the very short sampling timeframe. More studies are necessary to understand the role of melatonin in the testicular cycle and provide more information regarding the interesting reproductive physiology of this species. Roe deer are seasonal breeders with a complete yearly testicular cycle. The peak in reproductive activity is recorded during summer, the rutting period, with the highest levels of androgens and testicular weight. Melatonin plays a pivotal role in seasonal breeders by stimulating the hypothalamus–pituitary–gonads axis and acting locally; in different species, its synthesis within testes has been reported. The aim of this study was to evaluate the physiological melatonin pattern within roe deer testes by comparing data obtained from animals sampled during pre- and post-rut periods. Melatonin was quantified in testicular parenchyma, along with the genetic expression of enzymes involved in its local synthesis (AANAT and ASMT) and function (UCP1). Melatonin receptors, MT1-2, were quantified both at protein and gene expression levels. Finally, to assess changes in reproductive hormonal profiles, testicular dehydroepiandrosterone (DHEA) was quantified and used for a correlation analysis. Melatonin and AANAT were detected in all samples, without significant differences between pre- and post-rut periods. Despite DHEA levels confirming testicular involution during the post-rut period, no correlations appeared between such involution and melatonin pathways. This study represents the first report regarding melatonin synthesis in roe deer testes, opening the way for future prospective studies in the physiology of this species. [ABSTRACT FROM AUTHOR]

Simple Summary: The roe deer (Capreolus capreolus) is a wild, small ruminant common in Europe and Asia with a peculiar reproductive cycle. The adult male shows a complete suspension of spermatozoa production during the winter that start again in spring with the peak of sexual activity in summer (July–August). The physiological mechanism underlying such a cycle is yet to be clarified. The work aimed at the analysis of some molecules, like gelatinases (MMP) and vascular growth factor, physiologically involved in tissue remodeling, in roe deer samples collected before (June–July) and after (August–September) the rutting period. Samples were provided by hunters of the Bologna Apennines area (Italy) according to the regional hunting plan. The result showed a post-rut reduction of testicular weight and testosterone, indicative of testes involution, correlated with an increase in pro-MMP2, the latent gelatinase capable of sustaining spermatogenesis once activated. It can be assumed that gelatinases are involved in the testicular cycle and start accumulating after the rutting period to be then activated in preparation of the next reproductive season inducing spermatozoa development and migration. Future studies on this pathway during all seasonal testicular cycles will provide more information about the interesting reproductive physiology of roe deer. The roe deer (Capreolus capreolus) represents a spontaneous model of testicular inactivation: During winter, bucks show a suspension of spermatogenesis that starts again in spring and peaks during the breeding season (July–August). The underlying mechanisms to the regulation of the cyclic testicular changes are still not fully clear but seem to be imputable to the spermatogenic cell line since other testicular cell populations remain stable without apoptotic phenomena. The aim of the study was to investigate apoptosis, gelatinases (MMP2 and 9), their inhibiting factors (TIMP 1-2), and two isoforms of vascular endothelial growth factor (VEGF121 and 165) with its receptors (VEGFR1-2) in testes collected during pre- and post-rut periods, and to correlate them with testicular weight (TW) and testosterone (TEST). Testes from 18 adult sexually mature bucks were collected in Bologna Apennines (Italy). Samples were weighed and parenchyma collected. Radioimmunoassay, real-time PCR, and zymography were performed. The results showed a post-rut decrease in TW and TEST and an increase in proMMP2, also highlighting a correlation between the gelatinases and the testicular functionality. The VEGF pattern did not show modifications nor correlation with TW and TEST. Overall, gelatinases and their inhibitors, described herein for the first time in roe deer testes, seem to play an important role in the testicular cycle. [ABSTRACT FROM AUTHOR]

We describe the histological characteristics of the testis and spermatogenesis of the cave molly Poecilia mexicana, a viviparous teleost inhabiting a sulfur spring cave, Cueva del Azufre, in Tabasco, Southern Mexico. P. mexicana has elongate spermatogonial restricted testes with spermatogonia arranged in the testicular periphery. Germ cell development occurs within spermatocysts. As spermatogenesis proceeds, the spermatocysts move longitudinally from the periphery of the testis to the efferent duct system, where mature spermatozoa are released. The efferent duct system consists of short efferent duct branches connected to a main efferent duct, opened into the genital pore. Spermatogenesis consisted of the following stages: spermatogonia (A and B), spermatocytes (primary and secondary), spermatids, and spermatozoa. The spermatozoa are situated within spermatocysts, with their heads oriented toward the periphery and flagella toward the center. Once in the efferent duct system, mature spermatozoa are packaged as unencapsulated sperm bundles, that is, spermatozeugmata. We suggest that the histological characteristics of the testis and spermatogenesis of P. mexicana from the Cueva del Azufre, and the viviparous condition where the spermatozoa enter in the female without been in the water, have allowed them to invade sulfurous and/or subterranean environments in Southern Mexico, without requiring complex morphofunctional changes in the testis or the spermatogenetic process., (© 2019 Wiley Periodicals, Inc.)

The testicular histology and cytology of spermatogenesis inGraptemys pseudogeographica kohniiwere examined using specimens collected between July 1996 and May 2004 from counties in northeastern Arkansas. A histological examination of the testes and germ cell cytology indicates a postnuptial testicular cycle of spermatogenesis and a major fall spermiation event. The majority of the germ cell populations in May and June specimens are represented by resting spermatogonia, type A spermatogonia, type B spermatogonia, pre-leptotene spermatocytes, and numerous Sertoli cell nuclei near the basement membrane. The start of proliferation is evident as spermatogonia in metaphase are present near the basal lamina and many of these germ cells have entered meiosis in June seminiferous tubules. Major spermatogenic events occur in the June and July specimens and result in an increased height of the seminiferous epithelium and increased diameter of the seminiferous tubules. The germ cell population during this time is represented by spermatogonia (type A, B, and resting), hypertrophic cells, large populations of early primary spermatocytes, and early round spermatids. By September, the major germ cell population has progressed past meiosis with abundant round and early elongating spermatids dominating the seminiferous epithelium. October seminiferous epithelia are marked by a decreas in height and mature spermatozoa fill the luminal space. Round and elongating spermatids constitute the largest portion of the germ cell population. Following the spermiation event, the testes enter a period of quiescence that lasts till the next spermatogenic cycle, which begins in the subsequent spring. Based on the cytological development of the seminiferous tubules revealed by our study,Graptemys pseudogeographica kohniidemonstrates a temporal germ cell development strategy similar to other temperate reptiles. A single major generation of germ cells progresses through spermatogenesis each year resulting in a single spermiation event with sperm stored within the epididymis until the next spring mating season. [ABSTRACT FROM PUBLISHER]

The testicular histology and cytology of spermatogenesis in Graptemys pseudogeographica kohnii were examined using specimens collected between July 1996 and May 2004 from counties in northeastern Arkansas. A histological examination of the testes and germ cell cytology indicates a postnuptial testicular cycle of spermatogenesis and a major fall spermiation event. The majority of the germ cell populations in May and June specimens are represented by resting spermatogonia, type A spermatogonia, type B spermatogonia, pre-leptotene spermatocytes, and numerous Sertoli cell nuclei near the basement membrane. The start of proliferation is evident as spermatogonia in metaphase are present near the basal lamina and many of these germ cells have entered meiosis in June seminiferous tubules. Major spermatogenic events occur in the June and July specimens and result in an increased height of the seminiferous epithelium and increased diameter of the seminiferous tubules. The germ cell population during this time is represented by spermatogonia (type A, B, and resting), hypertrophic cells, large populations of early primary spermatocytes, and early round spermatids. By September, the major germ cell population has progressed past meiosis with abundant round and early elongating spermatids dominating the seminiferous epithelium. October seminiferous epithelia are marked by a decreas in height and mature spermatozoa fill the luminal space. Round and elongating spermatids constitute the largest portion of the germ cell population. Following the spermiation event, the testes enter a period of quiescence that lasts till the next spermatogenic cycle, which begins in the subsequent spring. Based on the cytological development of the seminiferous tubules revealed by our study, Graptemys pseudogeographica kohnii demonstrates a temporal germ cell development strategy similar to other temperate reptiles. A single major generation of germ cells progresses through spermatogenesis each year resulting in a single spermiation event with sperm stored within the epididymis until the next spring mating season.