Reproductive Tactics Of Male African Savannah Elephants (Loxodonta Africana) (2005)

The present thesis investigates aspects of the reproductive strategy of male African savannah elephants (Loxodonata africana).




Rasmussen, H.B.

Date Published 2005-Rasmussen-PhD-Thesis-Reproductive-tactics-of-male-African-savannah-elephants

Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy at the University of Oxford Michaelmas Term 2005


The present thesis investigates aspects of the reproductive strategy of male African savannah elephants (Loxodonata africana). The existence of, and differences between alternative conditional dependent reproductive tactics are evaluated using a combination of behavioural, endocrinological and GPS tracking data and the age and tactic related success is measured using genetic paternity analysis. Hidden Markov Models were used as a probabilistic framework for analysing temporal changes in reproductively active and inactive periods based on shifts in association preferences of individuals. Distinct shifts between active and inactive periods were evident well before the onset of the aggressive reproductive tactic of musth, seen in older dominant males, hence providing the first quantitative evidence for the previously suggested sexually active periods in non-musth males. The link between hormones and reproductive status and tactics were investigated using a new technique for non-invasive faecal analysis of hormones. A combined analysis of androgens (Epiandrosterone) and glucocorticoid (3a,11-oxo-CM) hormones in relation to age, reproductive state and musth signals confirmed previously reported elevated levels of androgens during periods with temporal gland secretion and urine dribbling (Musth) but further showed that this increase is indeed linked to the presence of musth signals and not to the age of the individual. Androgen levels were generally increased during sexually active periods with a two-fold increase seen in active non-musth bulls and a four to six-fold increase in musth bulls. Contrary to expectations, increased glucocorticoids outputs were not seen in musth bulls but slightly elevated outputs were seen in active non-musth bulls. Brief peaks in glucocorticoids occurred immediately after physical fights and during periods of injuries. A general elevation of glucocorticoids was seen towards the end of the long dry season, a likely effect of ecological conditions. Behavioural changes and onset of musth signals occurred after an initial change in androgen levels suggesting that sex steroids may play an activiational role of sexually active periods as well as activation of the musth tactic within sexually active periods. Some evidence was found for increased androgen levels following encounters with receptive females, suggesting that such encounters may act as a “boosters vaccine” on androgen levels and hereby prolong active periods at times with high numbers of receptive females. Both musth and sexually active non-musth (SAN) bulls reduced their foraging and walked more than sexually inactive bulls. However musth bulls had a higher time specific investment in reproduction compared to SAN bulls with musth bulls doubling their daily walking distance compared to a 50% increase in SAN bulls. The (younger) non-musth bulls spent a larger part of the year sexually active (70%) compared to musth bulls (20%) hence SAN bulls have a tactic of prolonged low investment compared to the short and high investment seen in musth bulls, emphasising the need for evaluating the duration of reproductive bouts when comparing overall investments between tactics. The youngest (non-musth) bull to sire offspring was 21 years but older musth bulls above 35 years had a much higher age specific reproductive success compared to bulls below 30 years. However on a population level, bulls less than 30 years contributed 30% of the reproduction and 20-25% could be attributed to non-musth bulls.

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