Behavioral idiosyncrasy reveals genetic control of phenotypic variability

“The nature of the forces influencing the evolution of alleles that affect variability has, more generally, been the focus of a rich theoretical literature explaining this phenomenon from a game theory perspective (36) or in terms of bet-hedging (37).”

“To that end, we performed an association study using a series of locusspecific mixed linear models (accounting for relatedness between lines and experimental block effect) and found 36 polymorphisms in 22 genes associated with variability in turning bias using a nominal P value (19, 21) of 5 × 10 (Fig.”

“Discussion In this study, we used a simple behavioral trait to show that individual genotypes vary considerably in their degree of intragenotypic variability (7, 15) and found that this variation is heritable.”

“This scenario should be particularly favored in fluctuating environments (38, 39).”

“The DGRP lines have been fully sequenced (19), allowing for genome-wide association mapping using the variability (i.”

“The nature of the forces influencing the evolution of alleles that affect variability has, more generally, been the focus of a rich theoretical literature explaining this phenomenon from a game theory perspective (36) or in terms of bet-hedging (37).”

“Within the central brain, Ten-a mutation causes midline fusion defects within the central complex), a brain structure implicated in sensory integration and locomotion (26).”

“Most recently, with the advent of genome-wide association studies, several groups (3, 4, 12, 13) have mapped quantitative trait loci affecting variance (vQTLs) by comparing phenotypic variances among individuals that share alleles.”

“Such research has revealed that several behaviors, including turn bias during navigation in a Y-maze, overall activity, and turn regularity, show significant genetic control of variation (Ayroles et al., 2015).”

“These results suggest the need for rigor in that multiple methods should be employed when applicable for testing host survival or validating gene candidate (Ayroles et al., 2015).”

“This is in addition to potentially facilitat-ingexploringthepoorlyunderstood genetic basisof sexualdimorphism (Rawlik et al. 2016), and loci which impact the variance of traits [rather than their central values (Ayroles et al. 2015)].”

“…has often been referred to as intra-genotypic variability (Metcalf & Ayroles, 2020; Bradshaw, 1965) or phenotypic variability (Abley et al. , 2021; Ayroles et al. , 2015; Willmore et al. , 2007), which is thought to be an emergent by-product of the developmental processes (Willmore et al. , 2007).”

“Turn bias variability has a complex genetic architecture involving many genes, particularly those involved in circuit development during pupation, including specifically teneurin-A (Ayroles et al., 2015) that encodes a protein involved in synaptic partner matching (Mosca, 2015).”

“As expected from animal and human studies, the time frame of days had little effect on the behavioral outcome ( Bell et al., 2009 ; Buchanan et al., 2015 ; Linneweber et al., 2020 ; Mischel, 1968 ; Pantoja et al., 2016 ; Ross, 1977 ; Schuett et al., 2011 ).”

“…repertoires, allowing researchers to better account for inborn variance or threshold effects in applications such as genetic mapping, behavioral manipulations, and neural perturbations (López-Alonso et al. 2014; Ayroles et al. 2015; Buchanan et al. 2015; Duistermars et al. 2018; Allen et al. 2015).”

“This is not a contradiction: in accordance with previous studies, we find that genetics merely bounds behavioural expression across individuals Ayroles et al. ( 2015 ); Linneweber et al. ( 2020 ).”

“Given recent work indicating that variation might be heritable (Ayroles et al., 2015; Herrera et al., 2022; Hill & Mulder, 2010; Jimenez-Gomez et al., 2011), selection for intraindividual trait variation is possible (Bruijning et al., 2020; Herrera, 2009; Metcalf & Ayroles, 2020), raising the…”

“In inbred lines of fruit flies, for example, systematic assessment of spontaneous locomotor behavior revealed that some lines have consistently elevated levels of intragenotypic variability amongst individuals (Ayroles et al., 2015).”

“…greater non-genetic variation (or less phenotypic robustness) than others (Waddington 1942; Whitlock and Fowler 1999; Ros et al. 2004; Hall et al. 2007; Hill et al. 2007; Ansel et al. 2008; Sangster et al. 2008; Shen et al. 2012; Ayroles et al. 2015; Morgante et al. 2015; Katsanos et al. 2017).”

“Only three studies to date have quantified the heritability of predictability in behavioral traits such as locomotor handedness in Drosophila (Ayroles et al.”

“Genetically identical Drosophila melanogaster flies display variability in their behaviors even when reared in identical environments [1–8] .”

“New studies show that phenotypic variance is genetically controlled, and the variance itself is a quantitative trait [2-13].”

“However, differences in trait variance across different genotype classes have been observed in multiple phenotypes, including in human disease [3, 4], animal and plant developmental traits [5–9], and phenotypic plasticity in changing environments [10–12].”

“…ubiquity (Bolnick et al. , 2003; Des Roches et al. , 2018; Sih et al. , 2004)—arising even in the absence of genotypic or environmental variation (Ayroles et al. , 2015; de Bivort, 2025)— and impact on ecological and evolutionary processes (Cantwell-Jones et al. , 2024; Gamelon et al. , 2025;…”

“This can obscure the expressed phenotypic diversity and latent adaptive potential carried by a genotype [16–18].”

“Moreover, trait variance itself has been shown to be evolvable [12–14], further underscoring its potential evolutionary significance [15].”

“Evidence that variability of a trait is under gen - etic control (and therefore heritable) is mounting, with empirical studies of morphology (Dworkin and Gibson 2006; Debat et al. 2009; Turner et al. 2011) and behavior (Turner et al. 2013; Ayroles et al. 2015) supporting this.”

“Variance association studies have shown that some biomarkers affect the variability of traits (Ayroles et al., 2015; Nachman et al., 2003; Queitsch et al., 2002; Dumitrascu et al., 2019), and therefore in fl uence homeostasis.”

“…of these toolkits, screen experiments quantify the phenotypes of hundreds (Vitaterna et al., 1994), thousands (Kain et al., 2012), tens of thousands (Ayroles et al., 2015; Buchanan et al., 2015; Churgin et al., 2017) or even hundreds of thousands of individual animals (Robie et al., 2017).”

“The control of technical variation associated to animal handling is particularly relevant in studies of individual behaviour 1,5–7 , where variation in handling can translate into the measured inter-individual variation.”

“Crucially, different genotypes of the same species can still differ in how much and what kind of stochastic variation they show [3,44,45].”

“Because each skill is held fixed throughout a training or evaluation episode, we interpret it as a persistent exploratory strategy consistent with the locomotor handedness observed in individual flies (Buchanan et al., 2015; Ayroles et al., 2015; de Bivort et al., 2022).”

“Such variation shapes how populations respond to change and how their social structure forms [3, 11], yet how developmental noise becomes individual differences in decision-making is un-resolved at a mechanistic level [7, 12, 13].”

“Using a Y-maze assay ( Figure 1D ) that measures left-right choices that correlate with locomotor handedness in circling ( Buchanan et al., 2015 ), we measured the loco-motor handedness of flies in each of these lines three times weekly for 3 weeks.”

“High-368 throughput tracking revealed sparse but significant trait covariances that populate a multidimensional personality space, with the magnitude of intragenotypic variability modulated by genotype, behavioral domain, and environmental complexity (66, 86 – 88).”

“Many studies have reported vQTL associated with diverse phenotypes in Drosophila (Ayroles et al., 2015; Mackay & Lyman, 2005), in mice (Corty et al., 2018; Nachman et al., 2003), and in humans (Topless et al., 2015; Wei et al., 2017; Yang et al., 2012; Young et al., 2018).”

“…studied for phototactic preference ( Kain et al., 2012 ), temperature preference ( Kain et al., 2015 ), locomotor handedness ( Ayroles et al., 2015 ; Buchanan et al., 2015 ; de Bivort et al., 2022 ), object-fixated walking ( Linneweber et al., 2020 ), and odor preference ( Honegger et al., 2020 ).”

“…showing greater nongenetic variation (or less phenotypic robustness) than others (Waddington, 1942; Whitlock & Fowler, 1999; Ros et al ., 2004; Hall et al ., 2007; Hill et al ., 2007; Ansel et al ., 2008; Sangster et al ., 2008; Shen et al ., 2012; Ayroles et al ., 2015; Kat-sanos et al ., 2017).”

“In doing so, they drive repeatable non-genetic phenotypic variation in behavioral responses to serve as a bet hedging strategy (Vogt et al. 2008; Ayroles et al. 2015; Hiesinger and Hassan 2018; Honegger and de Bivort 2018).”

“…in methylation levels (p = 0.02), Minor methylation levels were obtained for samples S1, S2, S12 and S16 which might reflect individual variation between animals as they were exposed primarily to the same climate atmosphere (Bossdorf et al., 2005; Novak and Mack, 2005; Ayroles et al., 2015).”