Zur Kurzanzeige

Male migration and alpha male takeovers in crested macaques, Macaca nigra

dc.contributor.advisorEngelhardt, Antje Dr.
dc.contributor.authorMarty, Pascal
dc.date.accessioned2015-05-26T08:22:08Z
dc.date.available2015-05-26T08:22:08Z
dc.date.issued2015-05-26
dc.identifier.urihttp://hdl.handle.net/11858/00-1735-0000-0022-5FF4-3
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-5089
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-5089
dc.language.isoengde
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/3.0/
dc.subject.ddc570de
dc.titleMale migration and alpha male takeovers in crested macaques, Macaca nigrade
dc.typedoctoralThesisde
dc.contributor.refereeFischer, Julia Prof. Dr.
dc.date.examination2015-04-24
dc.description.abstractengIn gregarious living mammals, males are often forced to leave their natal group as a consequence of selective pressures from within group competition and inbreeding avoidance. A successful natal dispersal increases a male´s chance to get access to unrelated mating partners and therefore enhances his reproductive success. Males may further increase their mating success by consecutive migrations into groups with more favourable conditions, allowing better access to fertile females. In socially living mammals, however, access to fertile females is often restricted to high ranking males such that the top dominant male reaps the highest benefits. Dispersal and the subsequent achievement of a high dominance rank are therefore essential events for a male to achieve high reproductive success and ultimately increase his fitness. During their dispersal and the attempt to achieve top dominance, males face various threats and often have to bear high costs. During the transition period between two social groups, males often face an increased predation risk and aggressive acts from conspecifics, potentially leading to severe injuries or death. During the process of immigrating into a group, males often get injured as a consequence of challenges for higher ranking positions. Both the transition period and the immigration itself are assumed to be very stressful events for dispersing males. Short-term elevated stress hormone levels are expected to be adaptive, a prolonged physiological stress response however, might be detrimental and would add additional costs to the dispersal event. As a consequence of the combined costs, male dispersal and intrasexual competition are considered to be the main causes of the higher mortality observed in male than in female animals. As a result, males often face a trade-off between the reproductive benefits of dispersal and the achievement of the alpha position in a group on the one hand, and the corresponding costs on the other hand. Selection would favour males who can shift this trade-off in a more favourable direction by strategically increasing benefits and reducing costs. Condition-dependent plasticity would be expected in such strategies, assuming that males migrate under different physical conditions.  Despite the importance for a male’s fitness, surprisingly little is known about dispersal, dispersal strategies, and the achievement of the alpha male position. The aim of this thesis was therefore to shed light on strategies utilised by males to disperse and to achieve top dominance. I predicted that males would use condition-dependent strategies to migrate and achieve the top dominant position with minimal costs and maximum reproductive benefits. A second aim of this study was to investigate the impact of an often neglected potential cost: an elongated stress response. The dispersal from one group to another is likely to represent the most profound shift in social life and environment in an animal’s life. I therefore expected males to show an adaptive stress response during the transition period between two groups, and during the following immigration process. If this stress response is prolonged over an extended time period, physiological costs for the dispersing males would be expected. I studied crested macaques (Macaca nigra), an ideal study species to investigate cost- and benefit-dependent migrating strategies, as all males disperse from their natal group and are known to subsequently migrate between groups. As a result of a high male reproductive skew, inter-individual differences in reproductive benefits were expected between males whereby the alpha male reaps the greatest benefits by siring most infants.  I found immigrations in crested macaques to occur in clusters, with several males immigrating into a group around the same time. Males used two specific strategies to immigrate according to their physical condition. Males who immigrated into a group first (pioneers) were most often males with substantial fighting ability, regularly achieving the alpha male position in the new group. The majority of pioneers who achieved the alpha male position were young males who had just emigrated out of their natal group. They either challenged the resident alpha male, or opportunistically took over the alpha male position after the resident alpha male previously emigrated or was injured. These males delayed their natal dispersal in order to reach their maximal physical prime, giving them the best chance to win an upcoming challenge. By doing so, natal males were expected to avoid costs of dispersal as a sub-adult male, and at the same time, increased their reproductive benefits by achieving the alpha male position upon natal emigration.  After the arrival of a pioneer, males of lower fighting ability (followers) subsequently immigrated into the group, usually achieving a low rank. By following a male of high fighting ability, these males reduced costs by taking advantage of instabilities in the male hierarchy. Males of low fighting ability therefore used a low-risk, low-benefit strategy. In contrast, males of high fighting ability, who immigrated into a group as pioneers, were more likely to get injured upon immigration and therefore used a high-risk, high-benefit strategy.  Surprisingly, males did not show a stress response during the transition period between two social groups. During immigration, however, a stress response was detectable in which the variation between males was extensive. Differences in the magnitude were most pronounced between natal emigrating males and males who already experienced dispersal. More experienced males showed lower stress hormone levels. The stress response was generally short and assumed to be only adaptive. Thus, physiological costs according to stress are not expected for dispersing male crested macaques.  The observed dispersal strategies in crested macaques are directly linked to alpha male replacements and the attributes of the social system of this species in general. I predicted the migrating strategies of males with high fighting ability to be part of a positive feedback loop: as a result of a delayed natal dispersal, all alpha male takeovers were conducted from extra-group males. As a consequence, females are unable to prevent infanticide by using strategies such as paternity confusion. Females are then expected to favour the alpha male which is most likely to protect their future infants against other extra-group males. Male-male competition is intense as a consequence of the high reproductive skew, whereby selection would favour males with more pronounced weaponry. Weaponry, such as large canines, therefore then add costs to dispersal, leading to a delayed dispersal and takeovers from outside males.  In summary, this thesis provides substantial evidence for the use of condition-dependent strategies by male crested macaques to reduce the costs of dispersal and to increase their chances of obtaining maximal reproductive benefits in a new group. Condition-dependent behavioural plasticity allows males to successfully enter a social group, which is, in most mammals, a requirement to get access to unrelated females. These strategies are assumed to ultimately increase a male’s fitness. Although this is the first study to systematically investigate condition-dependent strategies according to the costs and benefits of dispersal, such strategies are expected in a variety of species as a result of the high costs of dispersal. As soon as reproductive benefits of dispersal are dependent on intrinsic factors, the evolution of condition-dependent strategies is expected. Accordingly, the implications of this thesis reach far beyond primates. de
dc.contributor.coRefereeHodges, Keith Prof. Dr.
dc.subject.engMigrationde
dc.subject.engDispersalde
dc.subject.engMacaca nigrade
dc.identifier.urnurn:nbn:de:gbv:7-11858/00-1735-0000-0022-5FF4-3-1
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de
dc.identifier.ppn826068219


Dateien

Thumbnail

Das Dokument erscheint in:

Zur Kurzanzeige