Male mating strategies in the African elephant
Pioneering work combining behavioural, ranging, physiological and genetic analyses produces surprising results Henrik Rasmussen has been studying reproductive strategies in bulls since 1999 as part of STE's research project in Samburu. He joined STE in 1999 and completed his M. Sc. thesis from Aarhus University in 2001. In 2006 he finished his D.Phil. thesis on “Reproductive Tactics in Male African savannah Elephant (Loxodonta africana)” from Oxford University. He is currently working with STE on the GPS radio collaring program as well as continuing his research on reproductive tactics and spatial ecology of bulls.
In his doctoral thesis Henrik investigated aspects of the reproductive strategy of bulls. Using a multidisciplinary approach he combined data on behavior, endocrinology, GPS tracking and DNA micro- satellite analysis to evaluate differences between alternative conditional dependent reproductive tactics in bull elephants (pdf files on his scientific publications and his complete D.Phil. thesis is available from the STE website.)
Results from his research showed for the first time special reproductively active periods in younger non-musth bulls and distinctly different reproductive tactics in younger and older bulls.
As part of his thesis he investigated the correlation between behavioral indicators and physiological parameters in free-ranging bulls in collaboration with Dr. Andre Ganswindt from the German Primate Centre in Goettingen.
A combined analysis of male sex and stress hormones (androgens and glucocorticoid) 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 stress levels were not seen in musth bulls but were seen in reproductively active non-musth bulls. Behavioral changes and onset of musth signals occurred after an initial change in androgen levels suggesting that sex steroids may play a role in activating sexually active periods as well as activation of the musth tactic within sexually active periods.
The first study of genetic paternity in free-ranging African elephants, again conducted as part of his thesis work showed that the youngest (non-musth) bull to sire offspring was only 21 years although 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. Hence reproduction is not monopolized by bulls in musth, although skewed towards older males. This part of his research with STE was conducted in collaboration with Dr. George Wittemyer (University of Berkeley) and Dr. John Okello from the Wildlife Genetics Project (Makerere University, Uganda, and University of Copenhagen, Denmark) and Iain Douglas-Hamilton.
After finishing his thesis in March 2006 he has been working with Save the Elephants GPS tracking program and have carried out a number of GPS collaring operations at different locations in Kenya as well as other parts of the African continent. Henrik is currently working with the elephant GPS tracking project in Marsabit funded by People and Parks Support. This project, implemented by Save the Elephants in collaboration with KWS, contributes to the overall strategic studies conducted by KWS to provide baseline data on human and wildlife land-use and interactions within the Marsabit forest and surrounding areas. The results will be used for developing better land-use planning and mitigate human-wildlife conflicts in the area. The long-term aims are to facilitate a land-use development that will support the needs for both sustainable human economic development as well as conserving wildlife and the existing biodiversity in the area.
In his doctoral thesis Henrik investigated aspects of the reproductive strategy of bulls. Using a multidisciplinary approach he combined data on behavior, endocrinology, GPS tracking and DNA micro- satellite analysis to evaluate differences between alternative conditional dependent reproductive tactics in bull elephants (pdf files on his scientific publications and his complete D.Phil. thesis is available from the STE website.)
Results from his research showed for the first time special reproductively active periods in younger non-musth bulls and distinctly different reproductive tactics in younger and older bulls.
As part of his thesis he investigated the correlation between behavioral indicators and physiological parameters in free-ranging bulls in collaboration with Dr. Andre Ganswindt from the German Primate Centre in Goettingen.
A combined analysis of male sex and stress hormones (androgens and glucocorticoid) 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 stress levels were not seen in musth bulls but were seen in reproductively active non-musth bulls. Behavioral changes and onset of musth signals occurred after an initial change in androgen levels suggesting that sex steroids may play a role in activating sexually active periods as well as activation of the musth tactic within sexually active periods.
The first study of genetic paternity in free-ranging African elephants, again conducted as part of his thesis work showed that the youngest (non-musth) bull to sire offspring was only 21 years although 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. Hence reproduction is not monopolized by bulls in musth, although skewed towards older males. This part of his research with STE was conducted in collaboration with Dr. George Wittemyer (University of Berkeley) and Dr. John Okello from the Wildlife Genetics Project (Makerere University, Uganda, and University of Copenhagen, Denmark) and Iain Douglas-Hamilton.
After finishing his thesis in March 2006 he has been working with Save the Elephants GPS tracking program and have carried out a number of GPS collaring operations at different locations in Kenya as well as other parts of the African continent. Henrik is currently working with the elephant GPS tracking project in Marsabit funded by People and Parks Support. This project, implemented by Save the Elephants in collaboration with KWS, contributes to the overall strategic studies conducted by KWS to provide baseline data on human and wildlife land-use and interactions within the Marsabit forest and surrounding areas. The results will be used for developing better land-use planning and mitigate human-wildlife conflicts in the area. The long-term aims are to facilitate a land-use development that will support the needs for both sustainable human economic development as well as conserving wildlife and the existing biodiversity in the area.