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Hormonal variation and temporal dynamics of musth in Asian elephants (Elephas maximus) are associated with age, body condition and the social environment - PubMed

  • ️Sun Jan 01 2023

Hormonal variation and temporal dynamics of musth in Asian elephants (Elephas maximus) are associated with age, body condition and the social environment

Chase A LaDue et al. Conserv Physiol. 2023.

Abstract

The sustainability of endangered Asian elephants in human care is threatened in part by low breeding success and concerns over individual animal wellbeing. Male elephants have received less research attention compared to females, yet males deserve special consideration due to their unique reproductive biology (particularly the sexual state of "musth") and the complex interaction of physiological, environmental, and social pressures they face. We measured fecal androgen metabolites (FAMs), fecal glucocorticoid metabolites (FGMs), and fecal triiodothyronine metabolites (FT3s) collected weekly over approximately 12 months from 26 male Asian elephants housed in zoos across the US, hypothesizing that FAM, FGM, and FT3 concentrations would be associated with temporal correlates of musth and would vary further with intrinsic (musth status, age, body condition) and extrinsic (social environment) factors. The duration of each musth episode was positively associated with exposure to male conspecifics and negatively associated with body condition. Further, elevated FAM concentrations were associated with social exposure, age, and body condition, and FGM concentrations also varied with age and body condition. FT3 concentrations were not associated with any factor we measured. We also identified periods of lower FAM concentration than confirmed musth episodes (but still higher than baseline FAM concentrations) that we termed "elevated FAM episodes." The durations of these episodes were negatively correlated with exposure to other male elephants. Together, these results provide evidence that hormone profiles (including those that are predicted to change around musth) vary significantly between male Asian elephants in a way that may be attributed to intrinsic and extrinsic factors. Studies like these serve to enhance the sustainability of ex-situ populations by providing wildlife managers with information to enhance the health, welfare, and reproduction of threatened species like Asian elephants.

Keywords: androgens; glucocorticoids; health; musth; sustainability; thyroid hormones; welfare.

© The Author(s) 2023. Published by Oxford University Press and the Society for Experimental Biology.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1

Visual scale used by zoo staff to record BCS upon collection of each fecal sample. BCS was recorded from 1 (underweight) to 3 (ideal weight) to 5 (overweight) after inspection of ribs, pelvis, and backbone, based on descriptions from Pokharel et al. (2017). Illustrations by C. LaDue.

Figure 2
Figure 2

Example FAM profile demonstrating the parameters used to define a confirmed musth episode among Asian elephants in this study. Each point represents a sample, with the yellow shaded region defining the duration of a confirmed musth episode. Blue dashed line represents the UBT (the maximum FAM baseline value that remained within the range of iterative calculations of the overall mean FAM concentration plus 1.5 times the standard deviation), and green dotted line is the LBT (calculated by averaging the baseline FAM values and adding two times the baseline standard deviation). Points marked with red triangles indicate samples collected when a male elephant was exhibiting visible musth indicators (temporal gland secretions and/or urine dribbling).

Figure 3
Figure 3

Individual hormone profiles of representative male Asian elephants “D1” and “E2,” showing longitudinal concentrations of FAMs, FGMs and FT3. Circles represent individual fecal samples with solid lines connecting consecutive samples; orange shaded regions indicate confirmed musth episodes, and gray shaded regions show elevated FAM episodes. The UBT of FAM for each elephant is shown with the dashed line in the FAM panels.

Figure 4
Figure 4

Association between duration of elevated FAM and confirmed musth episodes in male Asian elephants (n = 26) and (a) average BCS and (b) average exposure to male conspecifics. Blue circles represent individual elevated FAM episodes, and orange triangles indicate individual confirmed musth episodes. Dashed blue lines and solid orange lines show linear regressions for elevated FAM episodes and confirmed musth episodes, respectively. BCS values were significantly associated with duration for confirmed musth episodes (P = 0.045) but not elevated musth episodes (P = 0.536). However, the duration of both elevated FAM episodes (P = 0.029) and confirmed musth episodes (P = 0.033) differed significantly with exposure to male conspecifics.

Figure 5
Figure 5

Variation of FAM concentrations in male Asian elephants (n = 26) in relation to age, BCS and musth status (non-musth, elevated FAM episode, confirmed musth episode). Points represent individual fecal samples, and lines show linear model prediction for each BCS score.

Figure 6
Figure 6

Variation of FGM concentrations in male Asian elephants (n = 26) in relation to age, BCS and musth status (non-musth, elevated FAM episode, confirmed musth episode). Points represent individual fecal samples, and lines show linear model prediction for each BCS score.

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