Potential factors affecting semen quality in the Asian elephant (Elephas maximus)

Non-targeted proteomic analysis of Asian elephant (Elephas maximus) seminal plasma using an in-solution digestion technique and liquid chromatography tandem-mass spectrometry

Seminal plasma proteins have recently been reported to play a significant role as valuable materials for understanding male reproductive biology, identifying causes of fertility problems, and developing reproductive biomarkers. Proteomic analysis of seminal plasma holds promise in advancing the understanding of male Asian elephant reproductive biology. This study aims to explore seminal plasma proteins of Asian elephants and their probable functions to provide fundamental information about male reproduction in this species. The protein solution from pooled seminal plasma from 10 bulls (a total of 33 ejaculates) was digested into peptides and identified using LC-MS/MS. Out of 986 proteins, 597 were mapped and matched with 58 species in UniProt databases, including Elephas maximus. These mapped proteins were mostly involved in binding function, catalytic activity, cellular process, and metabolic process. Only 29 mapped proteins were recognized to be related in reproductive process, mainly associated in spermatogenesis and sperm capacitation. Additionally, several seminal plasma proteins related to fertility or semen quality in other mammals were also found in Asian elephant semen, such as keratin type I, aldose reductase, thrombospondon-1, fibronectin 1, platelet-activating factor acetyl hydrolase, mannosidase, and semenogelin-2. This discovery clearly reveals the beneficial protein profile in seminal plasma of the Asian elephant and serves as a crucial step in investigating infertility and poor semen quality in this valuable species.

Seasonal Effects on Body Condition and Characteristics of the Estrous Cycle in Captive Asian Elephants (Elephas maximus) in Thailand: A Retrospective Study

The aim of this study was to investigate the effects of season on the body condition score (BCS), the characteristics of the estrous cycle (luteal phase [LPL], follicular phase [FPL], estrous cycle [ECL] lengths, and the start of the luteal phase [SLP] and follicular phase [SFP]), and progesterone levels (baseline and peak) of eight captive Asian elephants (Elephas maximus) in Thailand. From 2014 to 2019, blood samples were collected weekly for serum progesterone enzyme immunoassays (EIAs). Estrous cycles (n = 70), including the luteal and follicular phases, and BCS (n = 70) were recorded. Based on the BCS, the LPL, FPL, and ECL were assigned to the following two groups: normal (BCS = 3.0-4.0, n = 38) and overweight (BCS = 4.5-5.0, n = 32). The findings demonstrated that there was no difference in LPL between the groups. However, in the normal group, the ECL was one week longer (14.9 ± 1.7 vs. 13.9 ± 1.7 weeks; p < 0.05), and the FPL also tended to be one week longer (7.2 ± 1.7 vs. 6.4 ± 1.5 weeks; p = 0.06) than in the overweight group. The mean progesterone level during the rainy, hot, and cool seasons was not statistically different. Based on the yearly averaged BCS from three seasons, the baseline and peak levels of progesterone were classified into the normal (n = 16) and overweight (n = 12) groups. Females with a normal BCS tended to exhibit higher progesterone peak levels (p = 0.08). The majority of peaks appeared during the rainy season (53.57%). The BCS was highest during the hot (4.47) and rainy (4.38) seasons, but not during the cool (4.12) season. The LPL, FPL, and ECL were not affected by the season in which the luteal phase occurred. On the other hand, the rainy season had a significant effect on the SFP, resulting in a longer LPL (p < 0.05) and ECL (p = 0.01); both were the longest during the rainy season. In conclusion, the effects of season on BCS may be related to characteristics of the estrous cycle and peak progesterone levels. Ultimately, these findings provide ground knowledge to assist elephant managers and owners in planning breeding activities using seasonal effects and BCS measurements in tropical climates.

Serum Insulin-like Growth Factor-1 Is a Biomarker of Testosterone Production and Intact Acrosome in Asian Elephants (Elephas maximus)

Simple Summary

In Thailand, the low fertility rate of Asian elephants has been identified. Factors contributing to poor semen quality in the elephants are not fully understood. Insulin-like growth factor-1 (IGF-1) is related to male infertility. It plays an essential role in testicular development by stimulating cell proliferation, differentiation, and steroidogenesis. In addition, there is increasing evidence that IGF-1 plays a critical role in spermatogenesis. This may be conducive to finding the causes of poor sperm quality in Asian elephants (Elephas maximus). In the present study, we investigated the relationships among serum IGF-1, serum testosterone level, and semen parameters in seven elephant bulls. The findings suggest that serum IGF-1 concentration is likely to predict sperm quality like acrosome integrity. The further mechanism by which IGF-1 affects sperm quality requires further investigation.

Abstract

The objective of this study was to find relationships among serum IGF-1, serum testosterone, seminal plasma IGF-1 concentrations and semen parameters in Asian elephants (Elephas maximus). A total of 17 ejaculates (one to three ejaculates/bull) were collected from seven captive elephant bulls by performing rectal massage. Before each ejaculation, blood samples were obtained for serum IGF-1 and testosterone assays. Subsequently, the semen characteristics of each ejaculate were evaluated. Mean serum IGF-1 concentration of elephant bulls was estimated as 326.3 ± 114.6 ng/mL (median, 286.2 ng/mL; range, 167.4–542.7 ng/mL). An increase in serum IGF-1 concentration was found to correlate with the percentage of spermatozoa with intact acrosomes. In addition, IGF-1 concentration was positively correlated with testosterone level. However, seminal IGF-1 concentrations could not be detected. In conclusion, our findings suggest that serum IGF-1 concentration is likely a biomarker of normal testicular functions, particularly spermatogenesis in elephants. Moreover, this commercial IGF-1 ELISA is eligible for analyzing serum IGF-1 concentration in Asian elephants.

Characterization of Longitudinal Testosterone, Cortisol, and Musth in Male Asian Elephants (Elephas maximus), Effects of Aging, and Adrenal Responses to Social Changes and Health Events

Simple Summary

The conservation of endangered species and sustainability of managed populations requires good health and welfare of individuals. Male elephants experience a biological phenomenon called “musth”, characterized by a suite of physiological and behavioral changes which serve to facilitate copulation between the sexes, but can also pose unique challenges under human care. This study characterized longitudinal patterns of circulating testosterone and cortisol in relation to musth in four adult Asian elephant bulls and assessed age-related effects on musth activity and adrenal responses to social changes and clinical health events. All bulls exhibited regular annual musth cycles, and there was no clear evidence of chronically elevated cortisol secretion outside of musth. Circulating cortisol covaried positively with testosterone and musth, highlighting intrinsic patterns that should be considered when evaluating the impact of changes on adrenal glucocorticoid activity. Testosterone decreased with age in sexually mature bulls, whereas age-related changes in cortisol varied across individuals, with the three older bulls showing the greatest rate of change during musth. Changes in cortisol were associated with treatment for Mycobacterium tuberculosis in two bulls, but not with activation of disease. In contrast to physiological factors, there was no evidence that social changes involving male herdmates impacted adrenal glucocorticoid activity in the short term. This study highlights the importance of longitudinal hormone monitoring to track changes in physiological function and identify factors that may influence welfare, which is important for making more informed decisions on how to manage male elephants under varying degrees of human care.

Abstract

The conservation of endangered species and sustainability of managed populations requires considerations to ensure the health and welfare of individuals. Male elephants experience a biological phenomenon called “musth”, which is characterized by increased testosterone production, temporal gland secretion and urine dribbling, heightened aggression and sexual behavior, and therefore can pose unique challenges for human safety and animal welfare. This study characterized longitudinal (9 to 22 years) patterns of circulating testosterone and cortisol in relation to musth in four adult Asian elephant bulls spanning ages from 12 to 54 years. Age-related effects on musth activity and adrenal responses to social changes and clinical health events were also examined. All bulls exhibited regular annual musth cycles. Circulating cortisol covaried positively with testosterone and musth, highlighting intrinsic patterns that should be considered when evaluating the impact of social, health, and environmental changes on adrenal glucocorticoid activity. Except for an end-of-life cortisol increase in one bull, there was no clear evidence of chronically elevated cortisol secretion outside of musth in any individual. Testosterone decreased with age in sexually mature bulls, whereas age-related changes in cortisol varied across individuals, with the three older bulls showing the greatest rate of change during musth versus inter-musth periods. In contrast to physiological factors, there was no evidence of social factors, such as addition of a new male and death of male herdmates, impacting adrenal glucocorticoid activity in these bulls in the short term. Changes in cortisol were associated with treatment for Mycobacterium tuberculosis (M. tb) in two bulls, increasing after start of treatment and decreasing with cessation of treatment, but were not clearly associated with activation of disease. This study highlights the importance of longitudinal hormone monitoring to track changes in physiological function and responses to social, health, and environmental change in elephant bulls, which is important for making more informed decisions on how to manage male elephants under varying degrees of human care to ensure welfare and safety.

Semen characteristics and second successful artificial insemination of Asian elephant (Elephas maximus) in Thailand

Background and Aim:

As the number of wild Asian elephants (Elephas maximus) continues to decline, maintaining healthy populations under human care is vital. Male fertility assessment is essential for understanding the reproductive status, which can help to uncover underlying problems and improve the rate of pregnancy success. The objectives of this study in Asian elephants were as follows: (1) To investigate the semen characteristics; (2) to compare the relative seminal vesicle size and semen characteristics; (3) to compare the semen characteristics between good-motile (>60% progressive motility) and poor-motile (<60% progressive motility) ejaculates; and (4) to investigate the pregnancy success rate after artificial insemination (AI) with combined chilled and frozen semen.

Materials and Methods:

In total, 153 ejaculates were collected by manual rectal stimulation from 25 bulls. The volume, pH, sperm concentration, progressive motility, viability, morphology, and membrane integrity were investigated in each ejaculate. Assessment of accessory sex glands was conducted using transrectal ultrasonography to compare the relative seminal vesicle size and semen characteristics, and the bulls were divided into two groups according to the size of the ampulla (<7 or ≥7 cm²). For the comparison of good and poor-motile ejaculates and semen characteristics, the samples were divided into two groups: Good-motile (>60% progressive motility) and poor-motile (<60% progressive motility) ejaculates. Semen ejaculates for AI were collected from three bulls. The estrous cycles of four females were monitored using an enzyme immunoassay. Seven AI attempts were conducted using frozen and/or chilled semen by endoscopic visualization. AI was repeated 1 day before the luteinizing hormone surge, on the day of the surge, and 1 day after the surge. Pregnancy was confirmed by monitoring the serum progesterone profile and the abdomen and mammary glands changes.

Results:

From 153 ejaculates, the mean±standard error values of progressive motility, semen volume, sperm concentration, pH, and viability were 40.18%±2.28%, 40.94±3.86 mL, 1,205.58±62.26×10⁶ sperm/mL, 7.50±0.10, and 56.17%±1.96%, respectively. Comparing ampulla size and semen characteristics revealed that the bulls with ampullae of ≥7 cm² yielded significantly larger volume ejaculates. However, there were no significant differences in sperm motility and concentration. The comparison of semen characteristics between good- and poor-motile ejaculates revealed that the former had significantly higher pH, viability, normal acrosomes, intact membranes, and normal head and tail morphology but often had a significantly lower volume and sperm concentration. From seven AI attempts in four females, one female had a confirmed pregnancy (14.3% pregnancy rate), and delivered a healthy live female baby weighing 128 kg at 21 months and 12 days of gestation. The baby is now 3 years old and in a healthy condition, with normally developing growth and behavior.

Conclusion:

The semen characteristics of Asian elephants can be used as the baseline reference for further applications. The ampullae size indicates semen quantity but not quality. Our success in producing an elephant calf from AI using frozen and chilled semen demonstrated that AI can be used as an alternative approach for the breeding management of Asian elephants. However, the semen of Asian elephants is of poor quality, especially in terms of membrane integrity; thus, the improvement in semen quality through intensive and careful management of elephant health and fertility remains a challenge for the future. Furthermore, a sperm bank should be established to develop sperm cryopreservation, which will be invaluable for improving the genetic diversity of the Asian elephant.

Non-Invasive Determination of Annual Fecal Cortisol, Androstenedione, and Testosterone Variations in a Herd of Male Asian Elephants (Elephas maximus) and Their Relation to Some Climatic Variables

Simple Summary

Studies of physiology, animal welfare, and behavior in endangered species are gaining more importance with the aim of contributing to their conservation, and studies that use non-invasive methods for hormonal determinations are especially valuable. In this study, feces were used to assess whether the adrenal and gonadal hormones showed variation in male Asian elephants in a 14-month period and to evaluate whether there were any influences of climatic variables with respect to hormonal secretion. We show here that the use of non-invasive methods to measure the levels of steroid hormones in Asian elephant feces allows us to obtain useful results without having to subject the animals to stressful activity or requiring specific training to obtain the samples. Additionally, this research provides a deeper understanding of endocrine regulation in captive Asian elephants (Elephas maximus) in order to enhance reproduction programs in captivity and conserve the species.

Abstract

The measurement of stress and reproductive hormones in wild animal species by non-invasive methods is of special interest. To assess whether the adrenal and gonadal hormones show annual variations in male Asian elephants (Elephas maximus) and to evaluate whether there is any influence of climatic variables on hormonal secretion, fecal samples were taken from a herd of 7 Asian elephants over a 14-month period to subsequently determine the concentrations of testosterone (T), androstenedione (A4), and cortisol (C) by a validated immunoassay technique. Data referring to three climatic variables in the place and period of study were collected, namely monthly mean values of temperature, humidity and rainfall. Levels of T and A4 showed two major increases in July (T: 1088.35 ± 131.04 ng/g; A4: 480.40 ± 50.86 ng/g) and October (T: 825.09 ± 31.60 ng/g; A4: 319.96 ± 32.69 ng/g) (p < 0.05). Our results show a secretion of fecal androgens dependent on temperature (T and A4), and humidity (T). Male musth was detected during the initial increases of T and A4 levels. The highest concentrations of C were observed in September (156.67 ± 60.89 ng/g) (p < 0.05), probably due to the stressful fights that occurred during the musth period. The observed results of the fecal levels of T, A4 and C were similar to those obtained by invasive methods. In conclusion, fecal secretion of the three hormones in these captive male Asian elephants showed variations related in some cases to different weather factors.

Male age alone predicts paternity success under sperm competition when effects of age and past mating effort are experimentally separated

Older males often perform poorly under post-copulatory sexual selection. It is unclear, however, whether reproductive senescence is because of male age itself or the accumulated costs of the higher lifetime mating effort that is usually associated with male age. To date, very few studies have accounted for mating history and sperm storage when testing the effect of male age on sperm traits, and none test how age and past mating history influence paternity success under sperm competition. Here, we experimentally manipulate male mating history to tease apart its effects from that of age on ejaculate traits and paternity in the mosquitofish, Gambusia holbrooki. We found that old, naive males had more sperm than old, experienced males, while the reverse was true for young males. By contrast, neither male age nor mating history affected sperm velocity. Finally, using artificial insemination to experimentally control the number of sperm per male, we found that old males sired significantly more offspring than young males independently of their mating history. Our results highlight that the general pattern of male reproductive senescence described in many taxa may often be affected by two naturally confounding factors, male mating history and sperm age, rather than male age itself.

Effects of age on sperm quality metrics in endangered Mississippi gopher frogs (Lithobates sevosus) from captive populations used for controlled propagation and reintroduction efforts

A decline in sperm quality with age is a common prediction of senescence-based hypotheses and empirical studies. While widely studied across taxa, there is little known on the effect of ageing on sperm quality in amphibians, especially in captive populations used for controlled propagation and reintroduction efforts. Here, we investigated variation in sperm quality metrics (i.e., motility, concentration, and morphology) in the endangered Mississippi gopher frog (Lithobates sevosus) among males of three age categories using individuals from captive breeding populations housed at three different zoological institutions. Different aged males across the species expectant lifespan (1-9, 1-2, 3-4, and 8-9-year-old subcategories) were chosen in an attempt to identify an optimal breeding age relevant for captive breeding programs. Moreover, we explored and statistically controlled for potential differences in sperm quality which may be attributed to the type of induction hormones and source populations that differed among institutions. Results indicated that males of different ages did not differ in sperm motility or concentration. However, we did find that older males (8-9 years old) had significantly longer sperm than other age categories and younger males (1-2 years old) had significantly more atypical sperm than other age categories. Furthermore, we found no significant differences in any sperm quality metrics between the different induction hormones or source populations used at the different institutions. Within a captive breeding program, this information is especially valuable as our results indicate that males that have only recently sexually matured may not be ready to breed, while older males maintain sperm quality metrics presumably related to fertilization success.

Sperm motility, kinematics, morphometry and morphology over two seasons in free-ranging African elephants (Loxodonta africana)

This study aimed to address the lack of information on quantitative semen and sperm characteristics of free-ranging African elephants. Nineteen ejaculates were collected from 12 elephant bulls by means of electroejaculation in spring (Season 1, end of dry season, n=7) and in autumn (Season 2, end of rainy season, n=12). While most elephant cows are in oestrus in the rainy season, it is not evident whether sperm quality also improves during this period. Semen samples were assessed using computer-aided sperm analysis (CASA), brightfield microscopy and transmission electron microscopy. Seasonal differences and individual variation in sperm quality of bulls were apparent, with ejaculates collected during Season 2 revealing higher percentages for total motility, progressive motility, rapid-swimming spermatozoa and kinematic parameters compared with Season 1 (P<0.05). Although normal sperm morphology percentage was similar over the two seasons, more sperm tail defects were found in Season 2 (P<0.05). The baseline reference data and multivariate sperm parameter associations reported in this study can be used to predict elephant bull sperm quality and potential to fertilise. It is clear that CASA can detect subtle differences in sperm quality of African elephant ejaculates and should be the approach for future investigations.

Serological study on brucellosis in captive elephants (Elephas maximus) and stray dogs in North Thailand

Background and Aim:

Brucellosis is considered as an important zoonotic disease caused by various strains of Brucella in numerous host species. Although brucellosis has been reported in almost animal species, the relevance of brucellosis infection and diagnostic technique in Asian elephant (Elephas maximus) has been limited. The present serological investigation aimed to investigate the antibody response to Brucella abortus in captive Asian elephants in North Thailand. Moreover, further serological survey was also conducted to detect the antibody response to Brucella canis in stray dogs cohabiting the same area as the elephant herd.

Materials and Methods:

Serum samples were collected from 40 captive Asian elephants and submitted for serological analysis based on B. abortus antigen using Rose Bengal plate test (RBPT) in combination with ethylenediaminetetraacetic acid-tube agglutination test (EDTA-TAT) as a supplementary test and by commercial indirect enzyme-linked immunosorbent assay (iELISA). In addition, serum samples were also obtained from 16 stray dogs that live nearby the elephant-raising area and were tested using commercial Dot-ELISA based on B. canis antigen.

Results:

Serological analysis in captive Asian elephants showed 100% seronegative (40/40) from all serological tests response to B. abortus. For stray dogs, 12.5% (2/16) had a low positive reaction response to B. canis.

Conclusion:

The serological survey for brucellosis in Asian elephant was adapted and applied using RBPT, EDTA-TAT, and iELISA in the present study. For future evaluation, we recommended the use of a combination of serological tests with validation together with comparing by direct detection such as bacterial isolation to provide an appropriate brucellosis surveillance program in Asian elephants. In addition, the surveillance of stray dogs or multispecies habitation should be kept into considerations.

Influence of season, tourist activities and camp management on body condition, testicular and adrenal steroids, lipid profiles, and metabolic status in captive Asian elephant bulls in Thailand

We previously found relationships between body condition and physiological function affecting health and welfare of female tourist camp elephants in Thailand, and used that approach to conduct a similar study of bull elephants in the same camps (n = 13). A body condition score (BCS) was done every other month, and fecal glucocorticoid metabolite (FGM) concentrations were measured twice monthly for 1 year. Effects of season, camp management and tourist activity on lipid profiles [total cholesterol (TC), low density lipoproteins (LDL), high density lipoproteins (HDL), triglycerides (TG)] and metabolic factors [insulin, glucose, fructosamine, glucose to insulin ratio (G:I)] were determined and correlated to measures of body condition, testosterone and FGM. Positive correlations were found between BCS and TG, between FGM and TG, HDL and glucose, and between testosterone and HDL, whereas BCS and testosterone were negatively associated with the G:I. There was a significant positive relationship between FGM and testosterone. Elevated FGM concentrations were associated with altered lipid and metabolic profiles and were higher in winter compared to summer and rainy seasons. Insulin and glucose levels were higher, while the G:I was lowest in the winter season. Strong positive associations were found between TC and HDL, LDL and HDL and glucose, and glucose and insulin. By contrast, negative relationships were found between the G:I and HDL and glucose, and between insulin and G:I. Differences also were found between High and Low tourist season months for FGM, insulin, and G:I. Last, there was notable variation among the camps in measured parameters, which together with tourist season effects suggests camp management may affect physiological function and welfare; some negatively like feeding high calorie treats, others positively, like exercise. Last, compared to females, bull elephants appear to be in better physical health based on normal BCSs, lower insulin levels and higher G:I ratios.

Reproductive senescence: new perspectives in the wild

According to recent empirical studies, reproductive senescence, the decline in reproductive success with increasing age, seems to be nearly ubiquitous in the wild. However, a clear understanding of the evolutionary causes and consequences of reproductive senescence is still lacking and requires new and integrative approaches. After identifying the sequential and complex nature of female reproductive senescence, we show that the relative contributions of physiological decline and alterations in the efficiency of parental care to reproductive senescence remain unknown and need to be assessed in the light of current evolutionary theories of ageing. We demonstrate that, although reproductive senescence is generally studied only from the female viewpoint, age-specific female reproductive success strongly depends on male-female interactions. Thus, a reduction in male fertilization efficiency with increasing age has detrimental consequences for female fitness. Lastly, we call for investigations of the role of environmental conditions on reproductive senescence, which could provide salient insights into the underlying sex-specific mechanisms of reproductive success. We suggest that embracing such directions should allow building new bridges between reproductive senescence and the study of sperm competition, parental care, mate choice and environmental conditions.

Lipid and protein oxidation levels in spermatozoa and seminal plasma of Asian Elephants (Elephas maximus) and their relationship with semen parameters

Peroxidation damage to spermatozoa and seminal plasma has an important role in sperm quality. Thus, the objective of this study was to determine the levels of lipid and protein oxidation in spermatozoa and seminal plasma of Asian elephants (Elephas maximus) with varying percentage of progressive motility. Lipid and protein oxidation was measured by the thiobarbituric acid-reactive species (TBARS) assay and the 2, 4-dinitrophenylhydrazine (DNPH) carbonyl groups assay, respectively. Fresh semen samples were collected from Asian elephants and classified according to the percentage of motile spermatozoa into good (>60%) and poor (≤20%) motility. Results revealed that seminal plasma malondialdehyde (MDA) and seminal plasma protein carbonyls (PCs) were significantly higher in poor motility than in good motility (p < .05). The MDA and PC levels in seminal plasma were negatively correlated with the percentages of progressive motility (p < .05). In addition, the negative correlation between sperm concentration and seminal plasma MDA level was investigated (p < .05). The sperm viability was also negatively correlated with sperm PC level (p < .05). This study indicated that lipid and protein oxidation has deleterious effect on semen quality of Asian elephants.

Differential testosterone response to GnRH-induced LH release before and after musth in adult Asian elephant (Elephas maximus) bulls

Bull elephants exhibit marked increases in testosterone secretion during musth, and studies have shown a heightened sensitivity of the testis to GnRH-stimulated testosterone production in musth compared to nonmusth males. However, activity of the hypothalamo-pituitary-gonadal axis before or soon after musth has not been studied in detail. The aim of this study was to evaluate LH and testosterone responses to GnRH challenge in nine adult Asian elephant (Elephas maximus) bulls during three periods relative to musth: premusth, postmusth, and nonmusth. Bulls were administered 80 μg of a GnRH agonist, and blood was collected before and after injection to monitor serum hormone concentrations. The same bulls were injected with saline 2 weeks before each GnRH challenge and monitored using the same blood collection protocol. All bulls responded to GnRH, but not saline, with an increase in LH and testosterone during all three periods. The mean peak LH (1.76 ± 0.19 ng/mL; P < 0.001) and testosterone (6.71 ± 1.62 ng/mL; P = 0.019) concentrations after GnRH were higher than the respective baselines (0.57 ± 0.07 ng/mL, 3.05 ± 0.60 ng/mL). Although basal- and GnRH-induced LH secretion were similar across the stages, evaluation of the area under the curve in GnRH-treated bulls indicated that the testosterone response was greatest during premusth (2.84 ± 0.76 area units; P = 0.019) compared to postmusth (2.02 ± 0.63 area units), and nonmusth (2.01 ± 0.46 area units). This confirms earlier reports that GnRH stimulates LH release and subsequent testosterone production in bull elephants. Furthermore, although the hypothalamo-pituitary-gonadal axis is active throughout the year, the testis appears to be more responsive to LH in terms of testosterone production in the period leading up to musth, compared to the nonmusth and postmusth periods. This heightened sensitivity, perhaps as a result of LH receptor up-regulation, may prime the testis for maximal testosterone production, leading to the physiological and behavioral changes associated with musth.

Interplay of male traits, male mating strategies and female mate choice in the Asian elephant, Elephas maximus

Elaborate male traits with no apparent adaptive value may have evolved through female mate discrimination. Tusks are an elaborate male-only trait in the Asian elephant that could potentially influence female mate choice. We examined the effect of male body size, tusk possession and musth status on female mate choice in an Asian elephant population. Large/musth males received positive responses from oestrous females towards courtship significantly more often than did small/non-musth males. Young, tusked non-musth males attempted courtship significantly more often than their tuskless peers, and received more positive responses (though statistically insignificant) than did tuskless males. A positive response did not necessarily translate into mating because of mate-guarding by a dominant male. Female elephants appear to choose mates based primarily on traits such as musth that signal direct fertility benefits through increased sperm received than for traits such as tusks that may signal only indirect fitness benefits.

Lactotransferrin in Asian elephant (Elephas maximus) seminal plasma correlates with semen quality

Asian elephants (Elephas maximus) have highly variable ejaculate quality within individuals, greatly reducing the efficacy of artificial insemination and making it difficult to devise a sperm cryopreservation protocol for this endangered species. Because seminal plasma influences sperm function and physiology, including sperm motility, the objectives of this study were to characterize the chemistry and protein profiles of Asian elephant seminal plasma and to determine the relationships between seminal plasma components and semen quality. Ejaculates exhibiting good sperm motility (≥65%) expressed higher percentages of spermatozoa with normal morphology (80.3±13.0 vs. 44.9±30.8%) and positive Spermac staining (51.9±14.5 vs. 7.5±14.4%), in addition to higher total volume (135.1±89.6 vs. 88.8±73.1 ml) and lower sperm concentration (473.0±511.2 vs. 1313.8±764.7×10⁶ cells ml⁻¹) compared to ejaculates exhibiting poor sperm motility (≤10%; P<0.05). Comparison of seminal plasma from ejaculates with good versus poor sperm motility revealed significant differences in concentrations of creatine phosphokinase, alanine aminotransferase, phosphorus, sodium, chloride, magnesium, and glucose. These observations suggest seminal plasma influences semen quality in elephants. One- and two-dimensional (2D) gel electrophoresis revealed largely similar compositional profiles of seminal plasma proteins between good and poor motility ejaculates. However, a protein of ∼80 kDa was abundant in 85% of ejaculates with good motility, and was absent in 90% of poor motility ejaculates (P<0.05). We used mass spectrometry to identify this protein as lactotransferrin, and immunoblot analysis to confirm this identification. Together, these findings lay a functional foundation for understanding the contributions of seminal plasma in the regulation of Asian elephant sperm motility, and for improving semen collection and storage in this endangered species.

Effect of cooled storage on quality and DNA integrity of Asian elephant (Elephas maximus) spermatozoa

Artificial insemination (AI) is a potentially useful tool for breeding captive elephants because it facilitates efforts to minimise inbreeding. However, cooled storage of elephant semen markedly reduces fertility. This study compared the effects on semen-quality parameters, including sperm DNA fragmentation, of storing elephant semen at 4°C or 15°C in a commonly-used diluent (TEST) or a diluent developed to protect against sperm DNA damage (BullMax). Storing elephant semen for >24 h in either extender at either temperature resulted in decreases in sperm motility, viability, acrosome integrity and DNA integrity (P < 0.05); the decrease in motility was especially rapid. A subjective impression of circular sperm movement in TEST was confirmed by a higher curvilinear velocity and amplitude of lateral head displacement, but lower straight-line velocity and linearity than in BullMax. Initial percentages of spermatozoa with fragmented DNA (%SDF) did not differ between extenders or temperatures, but the rate of increase in %SDF during a 48-h incubation at 37°C was higher in TEST than in BullMax (P < 0.05). In conclusion, BullMax allows more linear movement and better preserves DNA stability of stored elephant spermatozoa than TEST. Sperm DNA stability during incubation at 37°C is a promising, discriminative parameter for selecting semen storage conditions of bulls for elephant AI.

Freezing African elephant semen as a new population management tool

BACKGROUND

The captive elephant population is not self-sustaining and with a limited number of breeding bulls, its genetic diversity is in decline. One way to overcome this is to import young and healthy animals from the wild. We introduce here a more sustainable alternative method - importation of semen from wild bulls without removing them from their natural habitat. Due to the logistics involved, the only practical option would be to transport cryopreserved sperm. Despite some early reports on African elephant semen cryopreservation, the utility of this new population management tool has not been evaluated.

METHODOLOGY/PRINCIPAL FINDINGS

Semen was collected by electroejaculation from 14 wild African savanna elephant (Loxodonta africana) bulls and cryopreserved using the directional freezing technique. Sperm treatments evaluated included the need for centrifugation, the use of hen or quail yolk, the concentration of glycerol (3%, 5% or 7%) in the extender, and maintenance of motility over time after thawing. Our results suggest that dilution in an extender containing hen yolk and 7% glycerol after centrifugation best preserved post-thaw sperm motility when compared to all other treatments (P≤0.012 for all). Using this approach we were able to achieve after thawing (mean ± SD) 54.6±3.9% motility, 85.3±2.4% acrosome integrity, and 86.8±4.6% normal morphology with no decrease in motility over 1 h incubation at 37°C. Sperm cryopreserved during this study has already lead to a pregnancy of a captive female elephant following artificial insemination.

CONCLUSIONS/SIGNIFICANCE

With working techniques for artificial insemination and sperm cryopreservation of both African and Asian elephants in hand, population managers can now enrich captive or isolated wild elephant populations without removing valuable individuals from their natural habitat.

Characteristics of high-quality Asian elephant (Elephas maximus) ejaculates and in vitro sperm quality after prolonged chilled storage and directional freezing

The in vitro quality of spermatozoa from one elephant (Elephas maximus) was examined after chilled storage and directional freezing (DF). High-quality, non-contaminated ejaculates (77.6 ± 6.0% progressive motility, 3.9 ± 1.5 µg creatinine mL–1 raw semen, 2.7 ± 0.6% detached heads) were cryopreserved after 0 (0hStor), 12 (12hStor) and 24 h (24hStor) of chilled storage. At 0 h and 6 h post-thawing, total motility, plasma membrane integrity, acrosome integrity, mitochondrial activity and normal morphology were similar (P > 0.05) across treatments. In contrast, progressive motility, rapid velocity and several kinematic parameters were lower (P < 0.05) for 24Stor compared with 0hStor at 0 h post-thaw. By 6 h post-thaw, amplitude of lateral head displacement and velocity parameters (average pathway, straight-line and curvilinear velocity) were lower (P < 0.05) for 24hStor compared with 0hStor and 12hStor. DNA integrity was high and remained unchanged (P > 0.05) across all groups and processing stages (1.6 ± 0.6% of cells contained fragmented DNA). Results indicate that DF after up to 12 h of chilled storage results in a post-thaw sperm population of acceptable quality for artificial insemination. These findings have implications for the cryopreservation of sex-sorted spermatozoa, which typically undergo more than 12 h of chilled storage prior to sorting and preservation.

Enriching the captive elephant population genetic pool through artificial insemination with frozen-thawed semen collected in the wild

The first successful AI in an elephant was reported in 1998, using fresh semen. Since then almost 40 calves have been produced through AI in both Asian and African elephants worldwide. Following these successes, with the objective of enriching the captive population with genetic material from the wild, we evaluated the possibility of using frozen-thawed semen collected from wild bulls for AI in captivity. Semen, collected from a 36-yr-old wild African savanna elephant (Loxodonta africana) in South Africa was frozen using the directional freezing technique. This frozen-thawed semen was used for four inseminations over two consecutive days, two before and two after ovulation, in a 26-yr-old female African savanna elephant in Austria. Insemination dose of 1200 × 10(6) cells per AI with 61% motility resulted in pregnancy, which was confirmed through ultrasound examination 75, 110 and 141 days after the AI procedure. This represents the first successful AI using wild bull frozen-thawed semen in elephants. The incorporation of AI with frozen-thawed semen into the assisted reproduction toolbox opens the way to preserve and transport semen between distant individuals in captivity or, as was done in this study, between wild and captive populations, without the need to transport stressed or potentially disease-carrying animals or to remove animals from the wild. In addition, cryopreserved spermatozoa, in combination with AI, are useful methods to extend the reproductive lifespan of individuals beyond their biological lifespan and an important tool for genetic diversity management and phenotype selection in these endangered mammals.

Are old males still good males and can females tell the difference? Do hidden advantages of mating with old males off-set costs related to fertility, or are we missing something else?

Sperm function generally declines with male age. Paradoxically, females of many species still choose to mate with old males rather than young males. Females choosing old mates may suffer reduced fertilization rates and an increased incidence of birth defects in offspring, lowering fitness which may in turn lead to conflict between the sexes. This apparent paradox has generated much interest from theorists, but whether this paradox presents in nature remains equivocal. Empirical studies have found mixed support for both a decline in fertility with male age and age-based female mate preference. Here, we examine recent evidence for this paradox, identify confounding variables, highlight areas that deserve further investigation, and suggest avenues for future research.

Breed and seasonal variations in the testicular morphometry, gonadal and extragonadal sperm reserves of the barred plymouth rock and Nigerian indigenous breeds of the domestic fowl

Breed and seasonal influence on testicular morphometry, Gonadal Sperm Reserves (GSR), Extragonadal Sperm Reserves (ESR) was investigated in the barred Plymouth rock and the Nigerian indigenous breeds of the domestic fowl. Twenty sexually matured birds per breed were studied in the four seasons of the year. Breed significantly (p<0.01) influenced the body weight (2.11 +/- 0.05 vs. 1.58 +/- 0.02), paired testes weight (21.92 +/- 1.46 vs. 12.43 +/- 0.91) and all other morphometric parameters with the barred Plymouth Rock showing superiority over the Nigerian indigenous breed. The GSR, ESR and their efficiencies (GSR/g, ESR/g) were highly and significantly (p<0.01) higher in the barred Plymouth rock. Season neither significantly (P>0.05) influenced the testicular morphometric parameters, GSR, ESR nor gonadal sperm reserve/gram testis (GSR/g). The higher numerical differences observed in morphometric parameters, GSR and ESR during the early and late dry seasons suggested that the dry season favors sperm production, hence sperm reserve potentials. The testicular weight was significantly (p<0.001) correlated not only to the body weight (r = 0.63) but to paired Tunica albuginea (= 0.98, p<0.001) and paired epididymal weight (r = 0.69, p<0.001). There was also a significant (p<0.001) and positive correlation between the testicular weight and GSR (r = 0.84, p<0.001). The GSR/g (r = 0.77; p<0.001) ESR (r = 0.86; p<0.001) and ESR/g (r = 0.50, p<0.001). Based on these observations it is concluded that genetic improvement of the Nigerian indigenous breed of the domestic fowl can be carried out by increasing their body weight, hence, testicular weight through crossbreeding with the heavier barred Plymouth rock to achieve improved sperm production and reserve for year round artificial insemination.