ABSTRACT
Raghavendra Gadagkar1'2 and K. Chandrashekara1'3* 1Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560012, India, Email: ragh@ces.iisc.ernet.in evolutionary and Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, 560064, India 3Department of Entomology, University of Agricultural Sciences, GKVK Campus, Bangalore 560065, India
Phenotypic Plasticity and Behavioural Diversity
Phenotypic plasticity refers to the phenomenon by which the same genotype gives rise to different phenotypes due to environmental variations (Schlichting and Pigliucci 1990). Phenotypic plasticity and its various synonyms have been used with different shades of meaning. West-Eberhard (2003) uses the phrase "developmental plasticity" in the most possible inclusive manner. Phenotypic plasticity can be seen in every aspect of the phenotype, anatomy, morphology, physiology, life history and especially behaviour. Given that the phenotype is a product of the interaction between genes and environment, the existence of phenotypic plasticity is to be expected if the environment varies. That phenotypic plasticity helps organisms to cope with varying environments is also to be expected. The exact mechanisms of causation of phenotypic variation and its role in evolution are however the subject of much discussion (review in Schlichting and Pigliucci 1990, West-Eberhard 2003). In colonies of social insects, phenotypic plasticity takes on an altogether new significance. Because social insect colonies exhibit division of labour, differences between members of the colony are especially useful. While many social insects have
morphologically differentiated workers specialized in different tasks, in other social insects behavioural differences among morphologically similar individuals help accomplish division of labour. The proximate mechanism that generate behavioural variation among the members of social insect colonies is much debated (reviewed in Bourke and Franks 1995). And yet, there has been insufficient attempt to develop quantitative methods to measure the extent of behavioural variability and understand its distribution among different levels of biological organization in insect societies. Inspired by Lewontin's (1972) attempt to apportion human genetic diversity, here we develop the concept of behavioural diversity and attempt to apportion it between different hierarchical levels within an insect society. We first begin by describing the method used by Lewontin 1972, adapt it to the study of behavioural diversity, apply the adapted methodology to the primitively eusocial wasp Ropalidia marginata and discuss the implications of the results. Throughout this chapter we will use the phrase behavioural diversity as a proxy for phenotypic plasticity but of course it is obvious that behavioural diversity is one component of phenotypic plasticity.
