Social organisation and mating strategies of the fossa (Cryptoprocta ferox) in Kirindy Forest CFPF, Madagaskar
Final Report Abstract
Mammalian mating systems are closely related to the social organisation of a species, which in turn is determined by sex-specific selection pressures with respect to access to limited resources. In previous studies of solitary carnivores, mating systems have often been described based on social organisation or molecular evidence alone, due to difficulties of observing mating behaviour in far-ranging species with low population densities. In this study, we combined spatial data collected via GPS technology with detailed behavioural and genetic data on the fosa (Cryptoprocta ferox: Eupleridae), a medium-size solitary carnivore with a mating system characterised by prolonged polyandrous mating on traditional mating trees. The main aim of our research was to illuminate determinants of this unusual system with a specific focus on the underlying sex-specific reproductive strategies; thereby contributing new insights into our general understanding of the incentives of female polyandry, the operation of pre-copulatory female choice and male competitive tactics. A further focus of this project was to investigate the occurrence, patterns and consequences of male associations in this otherwise solitary species. From 2007 to 2010, we trapped, anaesthetised, sampled and took measurements of 33 fosas (24 males, 9 females) in Kirindy Forest/CNFEREF, Madagascar. Nine males and four females could be partially tracked simultaneously by means of GPS tags, which provided data on movement patterns, ranging area and degree of sociality. To investigate correlates and consequences of male association, we combined body acceleration data with spatial information of simultaneous tracking and stable isotope analyses of hair samples. Furthermore, we used genetic analyses based on 16 variable microsatellite markers to determine relatedness patterns in the population and specifically the degree of relatedness among associated males. During the seasonal mating periods of four successive years, we followed six oestrous females during their complete mating activity, collecting 540 hours of continuous observation including information on 316 copulations on four different mating trees. These data allowed elucidating determinants of male mating success, the degree of polyandry and patterns of female pre-copulatory choice. This combination of multiple methodological approaches yielded several major results. First, females ranged solitarily and showed indications of territoriality. Males had three times larger ranges (Ø 53.1 km2) than females (Ø 17.8 km2) and spatially overlapped extensively with females and males. Second, whereas some males ranged solitarily, 10 of 22 adult males were organised in temporally stable associations that were most often composed of littermates. Third, associated males differed from solitary males in that they were (1) 13% larger and 38% heavier at comparable age, (2) hunted cooperatively, (3) used larger prey types more often, and (4) had higher mating success. Associated males neither defended territories nor exclusive excess to oestrous females. Instead, their physical superiority appeared to be advantageous in terminating matings of rivals. Fourth, females dominated males regardless of their physical dissimilarity and actively sought polyandrous matings. Fifth, females indirectly chose physically superior, i.e. associated males, by enhancing male-male contest and temporally restricted intervention in its outcome. Hence, associated males gained two-fold benefit with respect to male and female mating strategies. Overall, these results allow four major conclusions concerning the fosa's social organisation and mating system. First, the species' basic social organisation can be characterised as solitary but a high proportion of males forms spatially and temporally synchronised social units. Second, associated males achieve higher body mass and size than solitary individuals, which is most likely fuelled by effective cooperative hunting. Third, male body mass and thereby a male's degree of sociality are major determinants of male mating success. Fourth, convenience polyandry can be excluded as the most likely driver in the system. Instead, this mating system appears to be ultimately explained by a combination of benefits from polyandry and the consequences of different subsistence strategies. This interplay of male sociality and female preference for superior competitors provides an important reference for future socio-ecological research.
Publications
- (2010) An unusual case of cooperative hunting in a solitary carnivore. Journal of Ethology 28: 379-383
Lührs ML, Dammhahn M
- Strength in numbers: males in a carnivore grow bigger when they associate and hunt cooperatively. Behavioral Ecology, Volume 24, Issue 1, 1 January 2013, Pages 21–28
Lührs ML, Dammhahn M, Kappeler PM
(See online at https://doi.org/10.1093/beheco/ars150)
