- The Social System of the Round-Eared Sengi(Macroscelides proboscideus) (2009)
- In the present study, I investigated the social system of the round-eared sengi (Macroscelides proboscideus), a small crepuscular mammal that lives in deserts and semi-deserts in Southern Africa. For studying the evolution of monogamy in this species, I determined the social organisation and male mate guarding in wild animals in the Goegap Nature Reserve, South Africa. Data were collected over three successive breeding seasons and one non-breeding season by radio-tracking and trapping over a period of 2.5 years. Additionally, extra-pair attempts of paired round-eared sengi males were studied under laboratory conditions using direct behavioural observations and morphological and physiological characteristics of males. In the field, the population was characterised by balanced adult sex ratios and by a lack in sexual dimorphism in body mass. Round-eared sengis lived in perennial territorial male-female-pairs. However, males maintained much larger areas than females that were sensitive to population density and the presence of neighbouring males. At higher density males used smaller areas than at lower population density, but the number of neighbouring males was fairly constant throughout the whole study. Male space use appeared to be primarily limited by the presence of neighbouring males. In contrast, females maintained smaller-sized territories despite changes in population density. Some paired males attempted to take over widowed females, but shifted back to their original home range following the intrusion of an un-paired male, possibly because of a low variation (about 10 %) in body mass. Female reproduced 2-3 litters during a long breeding season with an asynchronous birth interval between neighbouring females, favouring pre-copulatory and oestrus mate guarding. Males over-mark their females’ scent while following, possibly for concealing the females’ reproductive state and advertisement of the paired status, thereby decreasing the risk of intrusions by competitors. Mate guarding incurred costs, because, overall, males lost about 5 % of their body mass. On the individual level, male body mass loss was negatively related to the intensity of mate guarding during the pre-copulatory period. Furthermore, guarding was inversely correlated with male body mass in the pre-copulatory period and with the number of neighbouring males during oestrus, indicating that males vary their guarding effort in relation to their physical capabilities and the competitive environment. In addition, both sexes demonstrated promiscuous tendencies in the experimental study. Female sexual behaviour with male neighbours was positively related to the time neighbouring males spent in the females’ area and to male marking behaviour. Intruding males were attacked by resident males. Aggression experienced by intruding males was associated with body mass loss (about 4%) in these animals; the same was found for marking behaviour in the neighbouring area. Furthermore, glucocorticoid levels, determined from analyses of faeces and urine samples, positively correlated with male body mass loss and also with male marking behaviour of intruding males, indicating costs of this behaviour. In conclusion, pair-living is the predominant social organisation in round-eared sengis. Males suffered from a limited opportunity to monopolise more than a single female that may have resulted from females living solitarily in small exclusive territories, balanced adult sex ratios and a low variation in body mass between males. However, both sexes have promiscuous tendencies. Female reproduced asynchronously and advertised their reproductive status, so that males pursued two behavioural tactics: Males engage in mate guarding for ensuring paternity and also in extra-pair attempts with neighbouring females, possibly for increasing their reproductive success. Since both male tactics were energetic costly they may serve as honest signals of quality providing only higher quality males with the opportunity to enhance their reproductive success, which in turn may be advantageous for females in terms of genetic benefits.