Gonadal and Adrenal Hormone Patterns in African Lions (Panthera leo) of Diverse Age and Reproductive Success
Date
2017-01-26
Authors
Putman, Sarah
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Abstract
This study sought to gain a more thorough understanding of male and female African lion (Panthera leo) reproductive biology through non-invasive means. Compared to other felids housed in captivity, lions historically bred well. However, a 6-year period of low fecundity in the U.S. population was observed after the cessation of a breeding moratorium, so the North American African lion Species Survival Plan (SSP) requested assistance in identifying the cause. Additionally, wild lion populations are declining rapidly; thus, maintaining captive insurance populations and developing assisted reproductive technologies may be required to maintain genetic diversity and preserve the species. However, there is a dearth of basic information on lion reproductive biology, including puberty onset and the impact of stress on reproductive function, which led to this biomedical survey of animals of varying ages and reproductive success within the captive population. Twenty six males from 18 zoos ranging in age from < 1 mo – 16.0 yr, and 38 females from 19 zoos, ranging in age from < 1 mo – 13.8 yr, were included in this study. Gonadal and adrenal steroid hormone metabolites were monitored in feces collected from 20 males and 28 females, body weights measurements were obtained ~monthly from 11 males and 17 females, and urine samples were collected from six males for spermaturia evaluation. Specific objectives of this study were to: 1) utilize non-invasive hormone monitoring to identify age and seasonal changes in gonadal and adrenal activity; 2) assess hormonal fluctuations related to reproductive events, such as pregnancy and estrus, to characterize reproductive life history stages; 3) examine puberty onset using variation in hormone concentrations, reproductive events and body weight measurements in females, and changes in hormone concentrations, body weight and urinary sperm in males; and 4) obtain hormonal substantiation of contraceptive effects in female lions. There was an increase in fecal androgen metabolite concentrations (FAM) at 2.0 yr of age, indicating a shift from peripubertal to subadult androgen production. While subadults had similar FAM to adult males, they had not reached a full adult weight. Puberty occurred at an earlier age in captive than wild male lions; urinalysis for the presence of spermatozoa showed positive results in 83% of samples collected from males as young as 1.2 yr. Growth rates, based on body weight measurements, also was faster in captive individuals than wild counterparts. For females, longitudinal hormonal assessments showed that there were few age-related and no seasonality-related changes in ovarian steroid production after 0.9 yr. Based on fecal estrogen metabolites (FEM), 95% percent of individuals not treated with contraception were cycling normally; estrous cycle length averaged 17.5 ± 0.4 d, estrus was 4.4 ± 0.2 d and silent estrus was observed in 82% of females where behavioral observations were available. Pregnant luteal phases averaged 109.5 ± 1.0 d, while non-pregnant luteal phases were only 46.0 ± 1.2 d. In eight females treated gonadotropin-releasing hormone agonist (GnRH, Suprelorin) contraceptives, the return to cyclicity was variable; individuals treated with Suprelorin averaged ~4.0 yr. Similar to males, puberty onset occurred earlier in female lions; estrous cycles were observed as early as 1.1 yr, which may have been related to a faster rate of growth in captive versus wild cubs. Fecal glucocorticoid metabolite (FGM) concentrations did not vary by age or season in males or females; however, females that were treated with contraceptives exhibited significantly lower mean FGM during treatment compared to before or after treatment. All but one uncontracepted female was cycling normally during the study, so it appears that the decrease in reproductive output in the years following the breeding moratorium was not related to problems in gonadal or adrenal hormone function, but for some females may have been linked to previous hormone contraception use.
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Keywords
African lion, Endocrinology, Felid, Puberty, Contraception, Reproduction