Haidar, M. A. | Search bioRxiv

bioRxiv2026

Increased variability and reduced phenotypic robustness in clonal Drosophila mercatorum

Quantitative genetics predicts that reducing genetic variability should reduce phenotypic variability, a common principle that underlies the widespread use of inbred, isogenic, and clonal animals in biomedical research. Yet extreme homozygosity can also expose recessive deleterious alleles and detoriate developmental buffering, potentially destabilizing rather than canalizing phenotypic outcomes. We tested this conflict directly in Drosophila mercatorum, a facultatively parthenogenic fly species in which pronuclear duplication results in fully homozygous, clonal offspring already after a single generation. Contrary to the expectation that genetic uniformity should reduce phenotypic variability, clonal parthenogenic flies showed changes in trait means, trait-dependent changes in interindividual variation, increased fluctuating asymmetry, and, most consistently, reduced behavioral and developmental canalization across a broad set of parameters. These effects on phenotypes spanned visually guided locomotion, circadian activity, wing morphology, bristle patterning, eye anatomy, brain volume, and serotonergic neuron numbers and were associated with reduced survival under environmental stress. Inbreeding of sexual D. mercatorum reproduced several of these phenotypic changes, whereas a single generation of outcrossing restored phenotypic robustness and the resulting F1 hybrids even exceeded the wild-type controls in several traits, consistent with a hybrid vigor effect. Together, these experiments identify loss of heterozygosity, rather than clonality per se, as the primary driver of developmental instability. Our findings show that genetic uniformity achieved through homozygosity can amplify stochastic phenotypic divergence by weakening developmental canalization, and suggest that the genetic context in which experimental standardization is achieved, especially heterozygosity, matters as much as the degree of genetic uniformity itself.

genetics↗

bioRxiv2023

Individuality across environmental context in Drosophila melanogaster

Over the past decade, several studies have demonstrated that idiosyncratic animal behaviors remain consistent over long time periods. The consistency of individually variable behaviors over time is often referred to as an animals individuality, or if consisting of multiple traits personality. However, most experimental studies have focused on individuality in a single, well-defined environmental context, whereas it is well-established from population studies that animal behavior is highly context-dependent. The person-situation debate in humans and decades of observations of animal individuality under intrinsically variable natural conditions raise the question of whether and to what extent animal behavior remains consistent across different situations, such as changing environmental contexts. For instance, one individual might be generally more visually guided than another, or rely only on one particular visual cue, or even on this very cue only in a specific environmental context. Here, we use a combination of both well-established and novel behavioral assays to demonstrate the relationship between individual behavior and variable environmental context under tightly controlled laboratory conditions in the model system Drosophila melanogaster. The consistency of three individual traits (termed exploration, attention, and anxiety) was investigated under changing environmental contexts (temperature, visual cues, arena shape), in both walking and flying flies. We find that individuality is highly context-dependent, but even under the most extreme environmental alterations tested, consistency of behavioral individuality always persisted in at least one of the traits. Furthermore, our quantification reveals a hierarchical order of environmental features influencing individuality. We confirmed this hierarchy using a generalized linear model and a hierarchical linear mixed model. In summary, our work demonstrates that, similar to humans, fly individuality persists across different contexts (albeit worse than across time), and individual differences shape behavior across variable environments. The presence of consistency across situations in flies makes the underlying developmental and functional mechanisms amenable to genetic dissection.

animal behavior and cognition↗