Phototactic personality in fruit flies and its suppression by serotonin and white

Abstract

Drosophila typically move toward light (phototax positively) when startled. The various species of Drosophila exhibit some variation in their respective mean phototactic behaviors; however, it is not clear to what extent genetically identical individuals within each species behave idiosyncratically. Such behavioral individuality has indeed been observed in laboratory arthropods; however, the neurobiological factors underlying individual-to-individual behavioral differences are unknown. We developed "FlyVac," a high-throughput device for automatically assessing phototaxis in single animals in parallel. We observed surprising variability within every species and strain tested, including identically reared, isogenic strains. In an extreme example, a domesticated strain of Drosophila simulans harbored both strongly photopositive and strongly photonegative individuals. The particular behavior of an individual fly is not heritable and, because it persists for its lifetime, constitutes a model system for elucidating the molecular mechanisms of personality. Although all strains assayed had greater than expected variation (assuming binomial sampling), some had more than others, implying a genetic basis. Using genetics and pharmacology, we identified the metabolite transporter White and white-dependent serotonin as suppressors of phototactic personality. Because we observed behavioral idiosyncrasy in all experimental groups, we suspect it is present in most behaviors of most animals.ethology | stochasticity | bet-hedging | Ischnopterapion virens F ew debates in biology have generated broader interest than nature versus nurture. Not surprisingly, both heritable and environmental factors play significant roles in shaping an organism's traits. However, the precise contributions of genetic and environmental factors to complex traits, such as most behaviors, are poorly understood. Behavioral individuality, in the absence of genetic variation, has indeed been observed in the laboratory. Specifically, clonal pea aphids were shown to vary in their predator escape behavior, and these differences were maintained for at least 5 d (1). In another example, the naïve odor preference of fruit flies was highly variable across individuals (2). These experiments suggest that even when deterministic influences from genetics and environment are held constant, there is nevertheless considerable behavioral variability. Drosophila is an ideal model system to test whether individuals, matched both genetically and environmentally, possess unique behavioral personalities, and what genetic and neurobiological factors control the magnitude of this idiosyncrasy.To determine whether individuals are behaving idiosyncratically we need to measure the trial-to-trial variation in an individual's behavior and compare that to the variation between individuals. If we observe greater variability between individuals than within individuals (that cannot be explained by sampling error), this would constitute evidence for behavioral idiosyncrasy. This analysis req...

Systematic exploration of unsupervised methods for mapping behavior

“…The pairwise transition rates between clusters appeared to be idiosyncratic as well. These findings are consistent with behavioral individuality in Drosophila phototaxis (Kain et al 2012), locomotor handedness (Buchanan et al 2015) and thermal preference . However, the clear evidence of individuality in PCA 20 -GMM-SW cluster abundance distributions is notable when compared to the lack of signal of such individuality in the supervised classification results of Kain et al (2013).…”

Neuronal control of locomotor handedness in Drosophila

“…We measured the turn biases of hundreds of individual flies from seven different fly lines: Berlin-K (BK), Canton-S (CS), Cambridge-A (CA) (19), two lines of CS that were independently inbred for 10 generations, CA that was inbred for 10 generations (19), and w 1118 , the background line for many transgenic flies ( Fig. 1 E and F and Fig.…”

“…We examined whether disrupting the CC can alter a population's distribution of turn bias scores. First, we tested seven mutants that perturb central complex development and morphology (19). Of these, no-bridge, centralcomplex-deranged, and central-body-defect (cbd KS96 ) showed a significant increase in individual variation in turning compared with heterozygous controls (Fig.…”

Behavioral idiosyncrasy reveals genetic control of phenotypic variability

“…In medical genetics, many diseased states emerge beyond a phenotypic threshold, and high variability genotypes will produce a larger proportion of individuals exceeding that threshold than low variability genotypes, even if each genotypic class has the same mean. Although intragenotypic variability has been discussed in animal behavior, particularly in the context of the emergence of personality (10,17),…”