1) Behaviour and speciation. I have a long-standing interest in the relationship between behavioural divergence and interfertility in populations of rodents, particularly those with interpopulation chromosomal variation. Some research questions. What mechanisms potentially promote/reduce gene flow among populations of striped mice? My focus initially had been to consider breeding and behaviour experiments between two different chromosomal forms of striped mice, situated 80km apart on the Highveld of South Africa, and compare the results with those of my earlier studies on geographically more distant populations (>900 km). Regardless of chromosomal differences, the closely-situated populations were behaviourally compatible but suffered hybrid failure compared to the more distant populations which never reproduced, highlighting the importance of geographic distance. In contrast, a subsequent the mate recognition system of striped mice supports a phylogenetic pattern, and not a geographic pattern, although environmental influences remain a confounding issue. The significance of this research has been the demonstration that genetic (behavioural) divergence is independent of chromosomal divergence, and ultimately contributes to our understanding of the biodiversity of southern African rodents.
Planned future and ongoing research. What extrinsic mechanisms (e.g. habitat type) restrict gene flow between populations? What intrinsic mechanisms (e.g. mate recognition signals; sociality) restrict gene flow? The aim is to target the areas where the 3 putative taxa of striped mice come in close contact and to study populations elsewhere within the range of these taxa. Thereafter, studies of habitat differences will be done at a macro-scale using GIS techniques and at a micro-scale. Behavioural tests (e.g. personality, sociality) will be conducted in captivity mainly and also in nature, drawing upon techniques developed in my other research.
2) Sociality and mating systems. The main research question - what factors determine within and between population variation in social organisation in striped mice? These studies focused mainly on a free-living population of striped mice in a semi-arid environment in Goegap Nature Reserve, in which a collaborator, Dr Carsten Schradin, and I established an ongoing project since 2001. Although we have not focussed much on grassland populations, these have served as suitable controls for the semi-arid population research. We described paternal care (occurrence, influence of prolactin) and a description of the social system and demography of this population; the striped mouse is the only known small African rodent to display paternal care in nature. Our studies have also considered the influence of habitat differences (semi-arid vs grassland) on social organisation, and the role of the father in the growth and survival of pups, and in the behavioural development (e.g. learning about novel food) in the young. Our studies have also considered the behaviour and physiology associated with huddling and basking in the semi-arid population, which showed the advantages of group-living because of energy savings obtained from huddling, and the importance of basking to kick-start thermoregulation and as a mechanism of social bonding.
Understanding behavioural plasticity has been a focus of my recent research. Some examples of completed research. 1) Individual females increased their home ranges to exploit protein-rich food during the breeding season, and returned to their original home ranges in the non-breeding season, reminiscent of the migratory behaviour of large mammals. 2) The dominance status of females influenced reproductive success in grassland striped mice: reproductive success was a function of the relative dominance status of neighbouring females, and was influenced by changes in neighbours and prior association between females (i.e. the dear enemy phenomenon). 3) Male mating strategy is governed proximate drivers (hormones and physiology) driven by population density, female sociality and environmental predictability.
Taken together, our results have shown that the success of striped mice is determined by their ability to adaptively respond to their particular habitat and their ability to respond to short-term environmental changes. Group-living in the arid areas is important for individual survival and reproductive success, and paternal care improves offspring survival and development. The significance of this research has been to show the occurrence population level variation in sociality, determined primarily by environmental factors and perhaps modulated by genetic differences.
Planned future and ongoing research. Future studies by Schradin will include experiments of the neuroendocrine mechanisms underlying social flexibility through, for example, experimental manipulations of sociality in free-living striped mice. Other studies will examine social flexibility in response to stochastic events (e.g. droughts). Our overall aim is to provide an integrated model of the ultimate and proximate causes of solitary and group living. This research has demonstrated the value and necessity for long term field studies.
3) Stereotypic behaviour. The main research question: why are striped mice so susceptible to the development of stereotypic behaviours (i.e. abnormal, repetitive behaviour)? In 2001, we showed a possible genetic basis for the transmission of stereotypic behaviours in striped mice. Subsequent research has shown that the susceptibility to develop stereotypic behaviours is related to its occurrence in the mother and not necessarily the father, indicating that the development of stereotypy may be more complex than initially assumed. Other studies have shown that stereotypic behaviour in striped mice is associated with increased reproductive output and that wild caught individuals are less susceptible to the development of stereotypic behaviour than captive born individuals. Overall, our research indicates that stereotypic behaviour develops spontaneously in captive striped mice and that there is likely to be artificial selection for stereotypy because of the greater reproductive success and genetic transmission of this behaviour. The significance of this research has been to provide a mechanism for stereotypy prevalence in captive striped mice and perhaps other species as well. In addition, my research addresses welfare issues of captive animals.
Planned future and ongoing research. Projects include the behavioural motivation for stereotypy using economic models (e.g. demand functions, pay-off models), population differences in the prevalence and development of stereotypic behaviour, and a meta-analysis of the relationship between stereotypy and the outcome of other behavioural experiments (e.g. sociality). The overall aim of this research is to understand the mechanisms of stereotypy, particularly the gene x environment contributions to its development. Another aim is to assess the importance of stereotypic behaviour as part of a wider behavioural syndrome about individual variation in behaviour.
In summary, my research has shown that questions and experiments in one area can help explain findings or be used to generate hypotheses in other themes. Many populations of striped mice are used in my research programme, often from different habitat types (e.g. semi-arid, grassland, fynbos) and with different social structure (group-living, solitary, sex-specific sociality). One hypothesis that we are currently testing is whether differences in social systems result in population/taxon-specific mate recognition signals, which could reduce gene flow between different populations. In other studies, the results of captive studies show that striped mice from desert and grassland populations respond differently to stressors in captivity, which we hypothesise are due to population-specific differences in personality (e.g. behavioural syndrome), sociality, and brain function, which is related ultimately to habitat differences and genetic isolation.
I am an ethologist specializing in rodents. The striped mouse Rhabdomys spp. is the primary model for my research. Its generalised biology and widespread distribution in southern Africa makes it a suitable model to test the questions that I have asked. Broadly, I am interested in how rodents, particularly striped mice, respond to change, which has formed the basis of my research over the past decade. I have considered change at three levels: i) long-term evolutionary change; ii) short-term (e.g. seasonal) change; and iii) response to artificial environments (i.e. human induced change). This has resulted in three research themes, as discussed below.
Research context. In recent times, all life forms face continuous and rapid environmental change, either directly or indirectly attributable to human activities. Understanding how different organisms respond to these changes is topical and extensively researched. As a rodent biologist, I am interested in how rodents respond to these changes which is not well researched in South Africa. I am particularly interested in the behavioural resilience of rodent populations to change, which will tell us whether these populations can respond to change. Of course, animals that can respond flexibly to change are of particular interest. Change is not new however, and is a constant feature for all life. My studies are unique because my model allows me to test responses to change historically and currently. I am also interested in how newly-caught animals, or those bred for a few generations in captivity, respond to life in captivity, which has also become a reality for many animals, in for example, captive breeding, programmes. Since behavioural expression is underpinned by physiological processes and modulated by brain function, studying behavioural responses offers insights into how animals can respond adaptively to change.
Some of my students and collaborators have worked on other rodent taxa (e.g. the behavioural ecology of gerbils and otomyine rodents) and others on non-rodent taxa, including the social organisation of sengi, the behaviour of captive and free-living primates.
Publications since 2005. Full publication list available upon request.
Jones, M, van Lierop, M, Mason, G & Pillay, N. 2010. Increased reproductive output in stereotypic captive Rhabdomys females: potential implications for captive breeding. Applied Animal Behaviour Science 123: 63-69.
Schradin, C, Schmohl, G, R?, H, Schoepf, I, Treffler, S, Brenner, J, Bleeker, M, Schubert, M, K?, B, & Pillay, N. 2010. Female home range size is regulated by resource distribution and intraspecific competition: a long term field study. Animal Behaviour 79: 195-203.
Schubert, M, Schradin, C, R?, H, Pillay N, & Ribble, D. 2009. Male mate guarding in a socially monogamous mammal, the round-eared sengi: on costs and trade-offs. Behavioral Ecology and Sociobiology 64: 257-264.
Schubert, M, Pillay N, von Holst D, & Schradin, C. 2009. The round-eared sengi and the evolution of social monogamy: environmental parameters constrain males to live with a single female. Ethology 115: 972-985.
Schradin, C, Kinahan, , Pillay, N. 2009. Cooperative breeding in groups of synchronously mating females and evolution of large testes to avoid sperm depletion. Biology of Reproduction 81: 111-117.
Schubert, M, Pillay, N & Schradin, C. 2009. Parental and allo-parental care in a polygynous mammal. Journal of Mammalogy 90: 724?731.
Mokotjomela, TM, Schwaibold, U & Pillay, N. 2009. Does the ice rat Otomys sloggetti robertsi contribute to habitat change in Lesotho? Acta Oecologica 35: 437-443.
Schradin, C, Scantlebury, M, Pillay, N & Koenig, B. 2009. Testosterone levels in dominant sociable males are lower than in solitary roamers: physiological differences between three male reproductive tactics in a sociably flexible mammal. American Naturalist 173: 376-388.
Pillay, N & Kinahan, . 2009. Mating strategy predicts the occurrence of the Bruce effect in the vlei rat Otomys irroratus. Behaviour 146: 139-151.
Jones, M, van Lierop, M & Pillay, N. 2008. All a mother s fault? Transmission of stereotypy in striped mice Rhabdomys. Applied Animal Behaviour Science 115: 82-89.
Lotter, T & Pillay, N. 2008. Reproduction and postnatal development of the bushveld gerbil Gerbilliscus (formerly Tatera) leucogaster. Mammalian Biology 430-437.
Rymer, T, Schradin, C & Pillay, N. 2008. Social transmission of information about novel food in two populations of the African striped mouse Rhabdomys pumilio. Animal Behaviour 76: 1297-1304.
Gustavsen, CR, Pillay, N. & Heller, RS. 2008. An immunohistochemical study of the endocrine pancreas of the African ice rat, Otomys sloggetti robertsi. Acta histochemica 110: 265-348.
Kinahan, & Pillay, N. 2008. Does differential exploitation of folivory promote coexistence in an African savanna granivorous rodent community? Journal of Mammalogy 89:132?137.
Kinahan, & Pillay, N. 2008. Dominance status influences female reproductive strategy in a territorial African rodent Rhabdomys pumilio. Behavioral Ecology and Sociobiology 62:579?587.
Rymer, T, Kinahan, & Pillay, N. 2007. Fur characteristics of the African ice rat Otomys sloggetti robertsi: modifications for an alpine existence. Journal of Thermal Biology 32: 428-432.
Schradin, C, Krackow, S, Schubert, M, Keller, C, Schradin, B & Pillay, N. 2007. Regulation of activity in desert-living striped mice: the importance of basking. Ethology 113: 606-614.
Hinze, A & Pillay, N. 2006. Life in an African alpine habitat: diurnal activity patterns of the ice rat, Otomys sloggetti robertsi. Arctic Antarctic and Alpine Research 38: 540-546.
Hinze, A, Pillay, N & Grab, S. 2006. The burrow system of the African ice rat Otomys sloggetti robertsi. Mammalian Biology 71 (6): 356-365.
Aenmey, T.K., Tierney, S.M., Pillay, N., Schwarz, M.P. 2006. Nesting biology of an African allodapine bee Braunsapis vitrea: female biased sex allocation in the absence of worker-like behavioural castes. Ethology Ecology and Evolution 18: 205-220.
Pillay, N, Eborall, J & Ganem, G. 2006. Divergence of mate recognition in the African striped mouse (Rhabdomys). Behavioral Ecology 17: 757-764.
Schwaibold, U & Pillay, N. 2006. Behavioral strategies of the African ice rat Otomys sloggetti robertsi in the cold. Physiology and Behavior 88: 567-574.
Schradin, C, Schubert, M and Pillay, N. 2006. Winter huddling groups in the striped mouse. Canadian Journal of Zoology 84: 693-698.
Schradin, C & Pillay, N. 2006. Female striped mice (Rhabdomys pumilio) change their home ranges in response to seasonal variation in food availability. Behavioral Ecology 17: 452-458.
Scantlebury, M., Bennett, N., Speakman, J., Pillay, N. & Schradin, C. 2006. The energetics of huddling in group-living African four-striped field mice Rhabdomys pumilio. Functional Ecology 20: 166-173.
Mullin, SK, Pillay, N & Taylor, PJ. 2005. The taxonomy of the African water rat Dasymys (Rodentia: Muridae) reflects the geographic and palaeoclimatic history of Africa. South African Journal of Science 10: 117-124.
Schradin, C & Pillay, N. 2005. Demography of the striped mouse (Rhabdomys pumilio) in the succulent karoo. Mammalian Biology 70: 84-92.
Schradin, C & Pillay, N. 2005. Intraspecific variation in the spatial and social organization of the African striped mouse. Journal of Mammalogy 86: 99-107.
Schradin, C & Pillay, N. 2005. The influence of the father on offspring development in the striped mouse. Behavioral Ecology 16: 450-455.