Emergence and development of personality over the ontogeny of fish in absence of environmental stress factors
Animals typically display among-individual differences in behavior that are consistent over time (i.e., personality). These differences are often triggered by variable individual responses to environmental stress factors experienced during life, such as competition for resources and risk of predation. While the causes underlying animal personality are considered to be an issue of prime importance, it is still unknown whether personality emerges and develops over ontogeny if the main sources of behavioral differentiation are absent. Here, we tested whether personality emerged and was strengthened during the lifetime of Eastern mosquitofish (Gambusia holbrooki), once intraspecific competition and risk of predation were completely removed and genetic and maternal differences minimized. We found that individual differences in behavior were overall repeatable over ontogeny (i.e., personality was manifested). Personality was, however, not detectable in juvenile individuals but emerged during and after their sexual maturation. The emergence of personality was triggered by the decline in behavioral plasticity of individuals over ontogeny, while differences in behavior among individuals did not vary with age. Our results suggest that animal personality might be inevitable and emerge in fish under laboratory-controlled conditions even in absence of extrinsic factors that typically lead to behavioral differentiation. The decline of behavioral plasticity over lifetime might be a relevant mechanism for the development of personality in animals.
Increasing evidence suggests that animals have personality, that is, individuals consistently differ in behavior among each other (e.g., bold and shy or social and non-social individuals). Personality differences among animals should be, by definition, consistent over time and often caused by environmental challenges experienced early in life. In this study, we observed that personality differences were not present at juvenile age in social fish but emerged later in their life, despite the fact that environmental challenges (i.e., predation risk and competition for space, food, and mates) were absent. Personality differences strengthened over lifetime, resulting from declines in individual behavioral plasticity. Our results suggest that the decline in behavioral plasticity with age may represent a relevant mechanism for behavioral differentiation in animals, in agreement with evidences from the human literature on age-related loss in behavioral plasticity.
KeywordsBehavioral type Developmental plasticity Lifetime Gambusia Repeatability Temperament
- Ariani AP, Camassa MM, Wittmann KJ (2000) The dolinas of Torre Castiglione (Gulf of Tarent, Italy): environmental and faunistic aspects of a semi-hypogean water system. Mem Biospeol 27:1–14Google Scholar
- Baltes PB, Baltes MM (1993) Successful aging: perspectives from the behavioral sciences, vol 4. Cambridge University Press, CambridgeGoogle Scholar
- Bates D, Maechler M, Bolker B, Walker S (2014) lme4: linear mixed-effects models using Eigen and S4. R package version 1.1–5, https://cran.r-project.org/web/packages/lme4/index.html
- Bestion E, Teyssier A, Aubret F, Clobert J, Cote J (2014) Maternal exposure to predator scents: offspring phenotypic adjustment and dispersal. Proc R Soc B 281:–20140701Google Scholar
- Frederick JL (1997) Evaluation of fluorescent elastomer injection as a method for marking small fish. Bull Mar Sci 61:399–408Google Scholar
- Gorski JN, Dunn-Meynell AA, Hartman TG, Levin BE (2006) Postnatal environment overrides genetic and prenatal factors influencing offspring obesity and insulin resistance. Am J Physiol-Reg I 291:R768–R778Google Scholar
- Haake PW, Dean JM (1983) Age and growth of four Everglades fishes using otolith techniques. Technical Report SFRC83/03 South Florida Research Center, Everglades National Park Homestead, FLGoogle Scholar
- Kuznetsova A, Brockhoff PB, Christensen RHB (2016) lmerTest: tests in linear mixed effect models. R package version 2–6, https://cran.r-project.org/web/packages/lmerTest/index.html
- Pinheiro J, Bates D, DebRoy S, Sarkar D, R Core Team (2014) nlme: linear and nonlinear mixed effects models. R package version 3.1–118, http://CRAN.R-project.org/package=nlme
- R Core Team (2013) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria, https://www.r-project.org /
- Sogard SM (1997) Size-selective mortality in the juvenile stage of teleost fishes: a review. Bull Mar Sci 60:1129–1157Google Scholar