Reduced genetic variability is known to adversely affect ejaculate quality in inbred lions (Panthera leo) physically isolated in the Ngorongoro Crater compared with outbred lions inhabiting the adjacent Serengeti Plains in East Africa. This study compared the histomorphology of testicular biopsies from these two lion populations. Ngorongoro Crater lions had fewer (P <0.05) seminiferous tubules with spermiogenesis and fewer (P <0.05) spermatids per seminiferous tubular cross-section than Serengeti Plains lions, although seminiferous tubular diameter did not differ (P > 0.05) between populations. Interstitial areas were greater (P <0.05) in Crater than in Plains lions, but no qualitative differences were evident, suggesting that proportionately less testicular area was occupied by seminiferous tubules in Crater lions. None of the lions in either population had evidence of testicular degeneration. Overall results suggest that inbred Crater lions have reduced spermiogenesis and less total seminiferous tubular area per testis. These data further support the premise that genetic homogeneity compromises reproductive traits in free-living, male African
L. Munson, J. L. Brown, M. Bush, C. Packer, D. Janssen, S. M. Reiziss and D. E. Wildt
J. L. Brown, M. Bush, C. Packer, A. E. Pusey, S. L. Monfort, S. J. O'Brien, D. L. Janssen and D. E. Wildt
Summary. Pituitary–gonadal function was examined in male lions free-ranging in the Serengeti Plains or geographically isolated in the Ngorongoro Crater of Tanzania. Lions were classified by age as adult (6·1–9·8 years), young adult (3·3–4·5 years) or prepubertal (1·4–1·6 years, Serengeti Plains only). Each animal was anaesthetized and then bled at 5-min intervals for 100 min before and 140 min after i.v. administration of saline or GnRH (1 μg/kg body weight). Basal serum LH and FSH concentrations were similar (P > 0·05) among age classes and between locations. In Serengeti Plains lions, net LH peak concentrations after GnRH were ∼ 25% greater (P < 0·05) in prepubertal than in either adult or young adult animals. GnRH-stimulated LH release was similar (P > 0·05) between adult and young adult lions, and these responses were similar (P > 0·05) to those measured in Ngorongoro Crater lions. Basal and GnRH-stimulated testosterone secretion was higher (P < 0·05) in adult than in young adult lions and lowest (P < 0·05) in prepubertal lions. Age-class differences in testosterone production were related directly to the concentrations of LH receptors in the testis (P < 0·05). Basal and GnRH-stimulated testosterone secretion and gonadotrophin receptor concentrations within age classes were similar (P > 0·05) between lions of the Serengeti Plains and Ngorongoro Crater. Lower motility and higher percentages of structurally abnormal spermatozoa were observed in electroejaculates of young adult compared to adult Serengeti Plains males (P < 0·05) and were associated with decreased steroidogenic activity. In contrast, there were no age-related differences in ejaculate characteristics of Ngorongoro Crater lions. Seminal quality in the Crater population was poor in adult and young adult animals and was unrelated to alterations in pituitary or testicular function. In summary, only seminal quality in adult male lions was affected by location, whereas age significantly affected both basal and GnRH-stimulated testosterone secretion and seminal quality (Serengeti Plains only) in sexually mature males. The striking seminal/endocrine differences among pride (breeding) males of different ages raises questions about the impact of age on individual reproductive performance in this species.
Keywords: lion; GnRH; LH; testosterone; receptors; testis; spermatozoa
J. L. Brown, M. Bush, C. Packer, A. E. Pusey, S. L. Monfort, S. J. O'Brien, D. L. Janssen and D. E Wildt
Pituitary responses to gonadotrophin-releasing hormone (GnRH) and prolactin and steroid secretory profiles were examined in two populations of adult, female lions in the Serengeti (one outbred in the Serengeti Plains and one inbred in the Ngorongoro Crater) to determine whether reductions in genetic variability adversely affected endocrine function. GnRH-induced gonadotrophin secretion was also examined after adrenocorticotrophic hormone (ACTH) treatment to determine whether acute increases in serum cortisol altered pituitary function. Anaesthetized lions were administered (i) saline i.v. after 10 and 100 min of blood sampling; (ii) saline at 10 min and GnRH (1 μg kg−1 body weight) after 100 min; or (iii) ACTH (3 μg kg−1) at 10 min and GnRH after 100 min of sampling. Basal serum cortisol and basal and GnRH-induced gonadotrophin secretion were similar (P > 0.05) between females of the Ngorongoro Crater and Serengeti Plains. After ACTH, serum cortisol increased two-to threefold over baseline values and the response was unaffected (P > 0.05) by location. ACTH-induced increases in serum cortisol had no effect on subsequent basal or GnRH-stimulated luteinizing hormone (LH) or follicle-stimulating hormone (FSH) secretion. Overall mean serum progesterone concentrations ranged from 0.2 to 5.4 ng ml−1 with the exception of four females (two in the Serengeti and two in the Crater; progesterone range, 18.4–46.5 ng ml−1) that were presumed pregnant (three of these females were observed nursing cubs several weeks later). There were no differences (P > 0.05) between Serengeti and Crater lions in mean serum progesterone, oestradiol or prolactin concentrations, and hormone secretion was not influenced (P > 0.05) by GnRH or ACTH treatment. Although Ngorongoro Crater lions have decreased genetic variability, the reproductive–endocrine system of females appears functionally normal compared with outbred counterparts living in the Serengeti Plains. Furthermore, the acute rise in serum cortisol after ACTH administration in lions fails to alter subsequent GnRH-induced gonadotrophin release, suggesting that short-term changes in adrenal activity do not markedly affect pituitary responsiveness in this species.
J. L. Brown, D. E. Wildt, J. R. Raath, V. de Vos, J. G. Howard, D. L. Janssen, S. B. Citino and M. Bush
Summary. Pituitary, gonadal and adrenal activity were compared in free-living, adult African buffalo bulls during the breeding and nonbreeding seasons. Frequent blood samples were collected for 2 h from anaesthetized bulls treated intravenously with saline, gonadotrophin-releasing hormone (GnRH, 200 μg), human chorionic gonadotrophin (hCG, 10 000 i.u.) or adrenocorticotrophic hormone (ACTH, 1·5 mg). Electroejaculates also were collected from anaesthetized bulls during the breeding and nonbreeding seasons. Pretreatment testosterone concentrations among bulls varied more during the breeding (0·17–23·0 ng/ml) than the nonbreeding (0·15–2·21 ng/ml) season. The variation within the breeding season was attributed to 8 of 25 bulls producing higher (P < 0·05) serum testosterone (High-T; 16·28 ± 2·03 ng/ml) and testicular LH receptor (1·53 ± 0·22 fmol/mg testis) concentrations compared with their seasonal counterparts (Low-T; 0·95 ± 0·26 ng/ml; 0·38 ± 0·04 fmol/mg) or with all bulls during the nonbreeding season (0·90 ± 0·27 ng/ml; 0·31 ± 0·04 fmol/mg). The magnitude of GnRH- and hCG-induced increases in serum testosterone was similar (P > 0·05) between Low-T bulls and bulls during the nonbreeding season. In the High-T animals treated with GnRH or hCG, serum testosterone did not increase, suggesting that secretion was already maximal. Peak serum LH concentrations after GnRH were greater (P < 0·05) in bulls during the nonbreeding than the breeding season; FSH responses were similar (P > 0·05). ACTH treatment did not increase serum cortisol concentrations above the 2-fold increase measured in bulls treated with saline, hCG and GnRH (P > 0·05). Ejaculate volume, sperm motility and the proportion of morphologically normal spermatozoa were greater (P < 0·05) during the breeding than in the nonbreeding season, but the total number of spermatozoa/ejaculate was similar (P > 0·05). We suggest that season effects endocrine function and seminal quality in free-living, male African buffalo. During the breeding season some, but not all, adult bulls produce high circulating concentrations of testosterone associated with increased testicular LH receptor binding. These findings suggest that this species may experience selective gonadal suppression, perhaps related to differences in social status.
Keywords: buffalo; LH; FSH; testosterone; testis; gonadotrophin receptors; seasonality; spermatozoa
J. L. Brown, D. E. Wildt, J. R. Raath, V. de Vos, D. L. Janssen, S. B. Citino, J. G. Howard and M. Bush
Summary. Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April–May) and nonbreeding (September–October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 μg/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut. These data indicate that: (i) seminal quality in free-ranging impala undergoes seasonal changes coincident with alterations in testicular steroidogenic activity, and (ii) the increased testosterone secretion observed during rut is associated with increased testicular sensitivity to LH (via increased gonadotrophin receptors) rather than to increased circulating gonadotrophin concentrations or pituitary responsiveness to GnRH.
Keywords: impala; LH; FSH; testosterone; testis; receptors