Fish that are bred to be bolder or more shy show corresponding changes to their body shape and locomotion, suggesting that personality changes affect other seemingly unrelated traits. The findings could be useful in animal breeding, pest management and studies of complex human behaviors.
In a study performed by North Carolina State University researchers, zebrafish that were bred to be more bold -- quantified by the shorter amount of time they remained motionless when placed in new surroundings -- displayed a sleeker body shape and an ability to dart around the water more quickly when startled than those bred to be more shy.
Brian Langerhans, an assistant professor of biological sciences at NC State and a senior author on a paper describing the study, says the research could help scientists learn about the connectedness of what seem to be disconnected animal traits.
"Complex behaviors, like the behaviors we call 'personality' or 'temperament,' can be associated -- genetically correlated -- with other traits that one might think are independent of such behaviors, like body shape and swimming abilities," he said. "In other words, traits that seem unrelated may not be unrelated."
In the study, the researchers used zebrafish lines that had been selected to be bolder by breeding fish that stayed still for a maximum of 50 seconds after being introduced into new surroundings, while shy fish -- those that stayed still for more than 3 minutes when dropped into a new area -- were bred to create a shy line.
After just a few generations with these breeding regimens, the researchers began to see interesting changes to the different fish lines. Not only did a range of behaviors associated with stressful situations change, but bold fish lines also displayed a more elongate body with a larger tail region and generated higher velocity and acceleration during fast-start startle responses. Shy fish lines had less sleek bodies and slower startle responses.
"We think pleiotropy, or one gene affecting two or more phenotypes, may explain the correlation between personality and locomotion," Langerhans said. "On the other hand, the association between personality and body shape seems to reflect linkage disequilibrium that is not caused by pleiotropy or physical genetic linkage. That means these traits may owe their association to recurrent natural selection acting on combinations of traits -- being bolder and sleeker may help zebrafish survive to adulthood or to mate more successfully, resulting in fish tending to have those combinations of traits/genes."
Langerhans said that a major goal of his lab is to understand how organisms evolve integrated suites of traits, rather than thinking about traits in isolation.
"This is one of the first studies linking personality variation to these other types of traits, and I think many more will emerge in the coming years," Langerhans said.
The paper appears in the journal Animal Behaviour. NC State Ph.D. alumna Elizabeth Kern is the paper's lead author. NC State undergraduates Detric Robinson and Erika Gass co-authored the paper, as did John Godwin, a professor of biological sciences. Funding from the National Institutes of Health (1R21MH080500) and the National Science Foundation (DEB-0842364) powered the research.
Note to editors: An abstract of the paper follows.
Correlated evolution of personality, morphology and performance
Authors: Elizabeth M.A. Kern, Detric Robinson, Erika Gass, John Godwin and Brian Langerhans, North Carolina State University
Published: June 3, 2016, in Animal Behaviour
Abstract: Evolutionary change in one trait can elicit evolutionary changes in other traits due to genetic correlations. This constrains the independent evolution of traits and can lead to unpredicted ecological and evolutionary outcomes. Animals might frequently exhibit genetic associations among behavioral and morphological-physiological traits, because the physiological mechanisms behind animal personality can have broad multi-trait effects and because many selective agents influence the evolution of multiple types of traits. However, we currently know little about genetic correlations between animal personalities and non-behavioral traits. We tested for associations between personality, morphology, and locomotor performance by comparing zebrafish (Danio rerio) collected from the wild and then selectively bred for either a proactive or reactive stress coping style ("bold" or "shy" phenotypes). Based on adaptive hypotheses of correlational selection in the wild, we predicted that artificial selection for boldness would produce correlated evolutionary responses of larger caudal regions and higher fast-start escape performance (and the opposite for shyness). After 4-7 generations, morphology and locomotor performance differed between personality lines: bold zebrafish exhibited a larger caudal region and higher fast-start performance than fish in the shy line, matching predictions. Individual-level phenotypic correlations suggested that pleiotropy or physical gene linkage likely explained the correlated response of locomotor performance, while the correlated response of body shape may have reflected linkage disequilibrium, which is breaking down each generation in the lab. Our results indicate that evolution of personality can result in concomitant changes in morphology and whole-organism performance, and vice versa.