From individuals to populations : personality traits in southern dumpling squid (Euprymna tasmanica Pfeffer, 1884) and their life history correlates

Several major reviews have recently highlighted the interest amongst life scientists in understanding the ecological and evolutionary significance of animal personality traits (e.g., Wilson 1998; Gosling 2001; Sih et al. 2004a). The term personality trait as it is used here simply refers to consistent individual differences in an animal's behavioural style (as opposed to its discrete acts), and therefore, represent a potential suite of behavioural traits that can describe behavioural individuality in animals. Using personality descriptors such as shyness-boldness, activity, etc., has the advantage in that we can describe holistic, aggregate behaviour of animals that may be important for selection between individuals. Understanding how animal personalities interact with life history strategies may help explain how individuals make-up populations, an important issue in evolutionary and population ecology. While intuitively appealing, our knowledge of how intra-population individual differences in behaviour influence life histories is in its infancy (Wilson 1998). Cephalopods are well-known for their inter-individual variation in several key life history traits (e.g. growth and age-at-maturity), represent important commercial species in a number of worldwide fisheries, and also display complex individual behaviours (Sinn et al. 2001). Through a series of four experiments this project investigated personality traits in squid and their biological and ecological consequences. Four traits (shy-bold, activity, reactivity, and bury persistence) were identified across two ecologically important contexts in wild-caught adult squid. Trait expression was sex-independent, context-specific (i.e. bold squid in threat tests were not necessarily bold in feeding ones), and was related to body size and reproductive maturity. There was high individual variability in developmental processes associated with all traits, but some of this variation was partially explained by context, age, and developmental groups of squid. A quantitative genetic study was undertaken to describe the genetic structure of traits, in order to understand the potential for traits to respond to selection as well as provide a genotypic basis to understand potential fitness-related processes. In general, there were significant patterns of additive genetic variance for threat traits but not their feed counterparts, while age-related patterns of heritability indicated age-specific genetic expression for traits in both contexts. Reproductive experiments indicated no direct relationship between a female squid's personality and her short-term fitness, but an individual's levels of feeding boldness did have consequences for its subsequent success in mate pairings. Finally, a three year field study examined the frequencies of personality phenotypes across two populations in relation to density, body size, and sex ratios of squid within each population. Observations indicated differences between years and populations in mean change and patterns of frequencies of behavioural phenotypes, but these changes appeared to be independent of patterns in population body size and sex-ratio. This study is a first attempt to relate individualized behaviour to life history variables in a cephalopod mollusc, and the results should contribute to our knowledge of how individuals make up populations, a process that is of importance to a number of life sciences, including behavioural, population, fisheries and evolutionary ecology.