Individual, but not population asymmetries, are modulated by social environment and genotype in Drosophila melanogaster

Lateralised courtship behaviour and its impact on mating success in Ostrinia furnacalis (Lepidoptera: Crambidae)

Lateralisation is a well-established phenomenon observed in an increasing number of insect species. This study aims to obtain basic details on lateralisation in courtship and mating behaviour in Ostrinia furnacalis, the Asian corn borer. We conducted laboratory investigations to observe lateralisation in courtship and mating behaviours in adult O. furnacalis. Our goal was also to detect lateralised mating behaviour variations during sexual interactions and to elucidate how these variances might influence the mating success of males. Our findings reveal two distinct lateralised traits: male approaches from the right or left side of the female and the direction of male turning displays. Specifically, males approaching females from their right side predominantly exhibited left-biased 180° turning displays, while males approaching females from the left-side primarily displayed right-biased 180° turning displays. Notably, left-biased males, executing a 180° turn for end-to-end genital contact, initiated copulation with fewer attempts and began copulation earlier than their right-biased approaches with left-biased 180° turning displays. Furthermore, mating success was higher when males subsequently approached the right side of females during sexual encounters. Left-biased 180° turning males exhibited a higher number of successful mating interactions. These observations provide the first report on lateralisation in the reproductive behaviour of O. furnacalis under controlled laboratory conditions and hold promise for establishing reliable benchmarks for assessing and monitoring the quality of mass-produced individuals in pest control efforts.

Hybro chicks outperform Ross308 in a numerical-ordinal task. Cognitive and behavioral comparisons between 2 broiler strains of newborn domestic chicks (Gallus gallus)

Domestic chickens (Gallus gallus) are among those species subject to intensive selection for production. Among the most widely used broiler strains are the Ross308 and the Hybro. From the perspective of animal production, Ross308 were superior to Hybro in weight gain, final body mass, and feed conversion. Intensive selection is thought to also cause behavioral changes and to negatively affect cognitive abilities. Up to date, though, no evidence has been provided on broiler breeds. The aim of this study was to explore cognitive differences among Hybro and Ross308 chickens by assessing their ordinal-numerical abilities. Chicks learned learnt to find a food reward in the 4th container in a series of 10 identical and sagittally aligned containers. We designed a standard training procedure ensuring that all chicks received the same amount of training. The chicks underwent 2 tests: a sagittal and a fronto-parallel one. In the former test, the series was identical to that experienced during training. In the fronto-parallel test, the series was rotated by 90°, thus left-to-right oriented, to assess the capability of transferring the learnt rule with a novel spatial orientation. In the sagittal test, both chicken hybrids selected the 4th item above chance; interestingly the Hybro outperformed the Ross308 chicks. In the fronto-parallel test, both strains selected the 4th left and the 4th right container above chance; nevertheless, the Hybro chicks were more accurate. Our results support the hypothesis that intense selection for production can influence animal cognition and behavior, with implications on animal husbandry and welfare.

Subcortical life, evolution of flattened body, and constrained mating posture in the earwig Platylabia major (Insecta: Dermaptera: "Anisolabididae")

Many animals take advantage of the shaded, humid, and protected environments in subcortical spaces, i.e., thin spaces under the loosened bark of dead trees. Permanent inhabitants of subcortical spaces often show specialized morphologies, such as a miniaturized or dorsoventrally flattened body. However, the evolutionary consequences of these specialized morphologies on behavioral, ecological, and life-history traits have been little studied. We studied the mating biology and anatomy of Platylabia major (usually placed in the family Anisolabididae), which is an obligate inhabitant of subcortical spaces with a paper-like flattened body, and compared them with those of two thicker, spongiphorid earwigs, Nesogaster amoenus and Paralabellula curvicauda. Mating trials in various settings showed that Pl. major requires thin spaces sandwiched by two planes to accomplish genital coupling and insemination. In contrast, the thicker species, although also frequently found in subcortical spaces, could mate on a single horizontal plane due to the ability of the male to twist its abdomen through approximately 180°. Examination by micro-computed tomography and a reagent-based clearing technique revealed no substantive differences in the configuration of mid-abdominal musculature between the species. The dorsal and lateral muscles of Pl. major, which are almost parallel to the antero-posterior body axis for accommodation within the thin abdomen, seemed incapable of producing the power to twist the abdomen. The abdominal musculature conforms to a simple pattern in both male and female earwigs, which is repeated in each of the pregenital segments. We conclude that small differences in the range of motion of each abdominal segment can result in large differences in possible mating postures and positions. Surgical experiments also demonstrated that both right and left penises of Pl. major are competent and used for insemination with no lateral bias, as in most other earwigs with twin penises studied to date.

Asymmetric Presynaptic Depletion of Dopamine Neurons in a Drosophila Model of Parkinson's Disease

Parkinson's disease (PD) often displays a strong unilateral predominance in arising symptoms. PD is correlated with dopamine neuron (DAN) degeneration in the substantia nigra pars compacta (SNPC), and in many patients, DANs appear to be affected more severely on one hemisphere than the other. The reason for this asymmetric onset is far from being understood. Drosophila melanogaster has proven its merit to model molecular and cellular aspects of the development of PD. However, the cellular hallmark of the asymmetric degeneration of DANs in PD has not yet been described in Drosophila. We ectopically express human α-synuclein (hα-syn) together with presynaptically targeted syt::HA in single DANs that innervate the Antler (ATL), a symmetric neuropil located in the dorsomedial protocerebrum. We find that expression of hα-syn in DANs innervating the ATL yields asymmetric depletion of synaptic connectivity. Our study represents the first example of unilateral predominance in an invertebrate model of PD and will pave the way to the investigation of unilateral predominance in the development of neurodegenerative diseases in the genetically versatile invertebrate model Drosophila.

Laterality in the Damaraland Mole-Rat: Insights from a Eusocial Mammal

Lateralization is the functional control of certain behaviors in the brain being processed by either the left or right hemisphere. Behavioral asymmetries can occur at an individual and population level, although population-level lateralization is less common amongst solitary species, whereas social species can benefit more from aligning and coordinating their activities. We assessed laterality (individual and population) through turning biases in the eusocial Damaraland mole rat, Fukomys damarensis. We considered factors such as breeding status (queen or subordinate), environment (wild-caught or captive), sex (male or female), colony and body mass. All individuals together demonstrated significant left-turning biases, which was also significant at the population level. Wild-caught animals were more strongly lateralized, had a wider spread over a laterality index and lacked the population-level left-turning bias as compared to captive mole rats. Subordinate animals were more lateralized than queens, demonstrating social status differences in turning biases for social mole rats. This emphasizes the importance of animal handling and context when measuring and interpreting behavioral asymmetries.

Functional Asymmetries Routing the Mating Behavior of the Rusty Grain Beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

Simple Summary

We evaluated the behavioral asymmetries of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) males during courtship and mating with potential mates. The highest proportion of males showed left-biased approaches towards females, and turned 180° to their left. Right-biased males (i.e., approaching mates from the right and then turning 180°) were fewer than left-biased males. A low percentage of males approaching from the front and back side achieved successful mating. Left-biased-approaching males had a significantly shorter copula duration in comparison with other males. Left-biased males performed shorter copulation attempts and copula in comparison to right-biased males. This research contributes to understand the role of lateralization in the beetle family Laemophloeidae.

Abstract

The rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), is a serious secondary pest of stored and processed food commodities. In the present study, we investigated the lateralization of males during courtship and mating, attempting to understand if it can be linked with a high likelihood of successful copulation. Most males exhibited left-biased (41%) approaches towards females, and turned 180° to their left, with 37% mating success. Right-biased males (i.e., approaching from the right and then turning 180°) were fewer than left-biased ones; 26% out of 34% managed to copulate with females. Only 9% out of 13% and 7% out of 11% of the back side- and front side-approaching males succeeded in mating, respectively. Directional asymmetries in approaching a potential mate, as well as the laterality of side-biased turning 180°, significantly affected male copulation success, with left-biased males achieving higher mating success if compared to right-biased males. Copula duration was significantly lower for left-biased-approaching males (1668.0 s) over the others (i.e., 1808.1, 1767.9 and 1746.9 for right-biased, front and back side-males, respectively). Left-biased males performed shorter copulation attempts and copula compared to right-biased males. Overall, our study adds basic knowledge to the lateralized behavioral displays during courtship and copula of C. ferrugineus.

Visual Field Analysis: A reliable method to score left and right eye use using automated tracking

Brain and behavioural asymmetries have been documented in various taxa. Many of these asymmetries involve preferential left and right eye use. However, measuring eye use through manual frame-by-frame analyses from video recordings is laborious and may lead to biases. Recent progress in technology has allowed the development of accurate tracking techniques for measuring animal behaviour. Amongst these techniques, DeepLabCut, a Python-based tracking toolbox using transfer learning with deep neural networks, offers the possibility to track different body parts with unprecedented accuracy. Exploiting the potentialities of DeepLabCut, we developed Visual Field Analysis, an additional open-source application for extracting eye use data. To our knowledge, this is the first application that can automatically quantify left-right preferences in eye use. Here we test the performance of our application in measuring preferential eye use in young domestic chicks. The comparison with manual scoring methods revealed a near perfect correlation in the measures of eye use obtained by Visual Field Analysis. With our application, eye use can be analysed reliably, objectively and at a fine scale in different experimental paradigms.

Precise Quantification of Behavioral Individuality From 80 Million Decisions Across 183,000 Flies

Individual animals behave differently from each other. This variability is a component of personality and arises even when genetics and environment are held constant. Discovering the biological mechanisms underlying behavioral variability depends on efficiently measuring individual behavioral bias, a requirement that is facilitated by automated, high-throughput experiments. We compiled a large data set of individual locomotor behavior measures, acquired from over 183,000 fruit flies walking in Y-shaped mazes. With this data set we first conducted a "computational ethology natural history" study to quantify the distribution of individual behavioral biases with unprecedented precision and examine correlations between behavioral measures with high power. We discovered a slight, but highly significant, left-bias in spontaneous locomotor decision-making. We then used the data to evaluate standing hypotheses about biological mechanisms affecting behavioral variability, specifically: the neuromodulator serotonin and its precursor transporter, heterogametic sex, and temperature. We found a variety of significant effects associated with each of these mechanisms that were behavior-dependent. This indicates that the relationship between biological mechanisms and behavioral variability may be highly context dependent. Going forward, automation of behavioral experiments will likely be essential in teasing out the complex causality of individuality.

Behavioral Neuroscience in the Era of Genomics: Tools and Lessons for Analyzing High-Dimensional Datasets

Behavioral neuroscience underwent a technology-driven revolution with the emergence of machine-vision and machine-learning technologies. These technological advances facilitated the generation of high-resolution, high-throughput capture and analysis of complex behaviors. Therefore, behavioral neuroscience is becoming a data-rich field. While behavioral researchers use advanced computational tools to analyze the resulting datasets, the search for robust and standardized analysis tools is still ongoing. At the same time, the field of genomics exploded with a plethora of technologies which enabled the generation of massive datasets. This growth of genomics data drove the emergence of powerful computational approaches to analyze these data. Here, we discuss the composition of a large behavioral dataset, and the differences and similarities between behavioral and genomics data. We then give examples of genomics-related tools that might be of use for behavioral analysis and discuss concepts that might emerge when considering the two fields together.

Environmental and Molecular Modulation of Motor Individuality in Larval Zebrafish

Innate behavioral biases such as human handedness are a ubiquitous form of inter-individual variation that are not strictly hardwired into the genome and are influenced by diverse internal and external cues. Yet, genetic and environmental factors modulating behavioral variation remain poorly understood, especially in vertebrates. To identify genetic and environmental factors that influence behavioral variation, we take advantage of larval zebrafish light-search behavior. During light-search, individuals preferentially turn in leftward or rightward loops, in which directional bias is sustained and non-heritable. Our previous work has shown that bias is maintained by a habenula-rostral PT circuit and genes associated with Notch signaling. Here we use a medium-throughput recording strategy and unbiased analysis to show that significant individual to individual variation exists in wildtype larval zebrafish turning preference. We classify stable left, right, and unbiased turning types, with most individuals exhibiting a directional preference. We show unbiased behavior is not due to a loss of photo-responsiveness but reduced persistence in same-direction turning. Raising larvae at elevated temperature selectively reduces the leftward turning type and impacts rostral PT neurons, specifically. Exposure to conspecifics, variable salinity, environmental enrichment, and physical disturbance does not significantly impact inter-individual turning bias. Pharmacological manipulation of Notch signaling disrupts habenula development and turn bias individuality in a dose dependent manner, establishing a direct role of Notch signaling. Last, a mutant allele of a known Notch pathway affecter gene, gsx2, disrupts turn bias individuality, implicating that brain regions independent of the previously established habenula-rostral PT likely contribute to inter-individual variation. These results establish that larval zebrafish is a powerful vertebrate model for inter-individual variation with established neural targets showing sensitivity to specific environmental and gene signaling disruptions. Our results provide new insight into how variation is generated in the vertebrate nervous system.

Random or handedness? Use of laterally paired penises in Nala earwigs (Insecta: Dermaptera: Labiduridae)

Animals can show bias in their use of laterally paired organs that do not have any conspicuous anatomical differentiation between the right and left organs. Like right handedness in humans, males of the giant earwig Labidura riparia (Labiduridae: Labidurinae) preferentially (~90%) use the right one of their laterally paired penises for copulation. To elucidate the evolutionary origin of this lateralization, patterns of penis use were examined for the related species of the genus Nala (Labiduridae: Nalinae). In multiple populations and broods of both Nala lividipes and Nala nepalensis, males that were ready to use the right or left penis were equally frequent, providing a striking contrast to Labidura. Surgical ablation of one of the two penises revealed that both penises are functionally competent in N. lividipes. Nevertheless, each male almost consistently used only one of the paired penises, either the right or the left one. Changes in penis use were estimated to occur only once per 64–143 days per male. The present study is the first report of individual-level lateralization for animal genitalia that do not show any conspicuous anatomical differentiation between the right and left organs. Possible advantages of lateralization are discussed in relationship to co-evolution of the genitalia between the sexes.

Stability and individual variability of social attachment in imprinting

Filial imprinting has become a model for understanding memory, learning and social behaviour in neonate animals. This mechanism allows the youngs of precocial bird species to learn the characteristics of conspicuous visual stimuli and display affiliative response to them. Although longer exposures to an object produce stronger preferences for it afterwards, this relation is not linear. Sometimes, chicks even prefer to approach novel rather than familiar objects. To date, little is known about how filial preferences develop across time. This study aimed to investigate filial preferences for familiar and novel imprinting objects over time. After hatching, chicks were individually placed in an arena where stimuli were displayed on two opposite screens. Using an automated setup, the duration of exposure and the type of stimuli were manipulated while the time spent at the imprinting stimulus was monitored across 6 days. We showed that prolonged exposure (3 days vs 1 day) to a stimulus produced robust filial imprinting preferences. Interestingly, with a shorter exposure (1 day), animals re-evaluated their filial preferences in functions of their spontaneous preferences and past experiences. Our study suggests that predispositions influence learning when the imprinting memories are not fully consolidated, driving animal preferences toward more predisposed stimuli.

Paired fruit flies synchronize behavior: Uncovering social interactions in Drosophila melanogaster

Social behaviors are ubiquitous and crucial to an animal's survival and success. The behaviors an animal performs in a social setting are affected by internal factors, inputs from the environment, and interactions with others. To quantify social behaviors, we need to measure both the stochastic nature of the behavior of isolated individuals and how this behavioral repertoire changes as a function of the environment and interactions between individuals. We probed the behavior of male and female fruit flies in a circular arena as individuals and within all possible pairings. By combining measurements of the animals' position in the arena with an unsupervised analysis of their behaviors, we define the effects of position in the environment and the presence of a partner on locomotion, grooming, singing, and other behaviors that make up an animal's repertoire. We find that geometric context tunes behavioral preference, pairs of animals synchronize their behavioral preferences across shared trials, and paired individuals display signatures of behavioral mimicry.

Frequency-specific modification of locomotor components by the white gene in Drosophila melanogaster adult flies

The classic eye-color gene white (w) in Drosophila melanogaster (fruitfly) has unexpected behavioral consequences. How w affects locomotion of adult flies is largely unknown. Here, we show that a mutant allele (w¹¹¹⁸ ) selectively increases locomotor components at relatively high frequencies (> 0.1 Hz). The w¹¹¹⁸ flies had reduced transcripts of w⁺ from the 5' end of the gene. Male flies of w¹¹¹⁸ walked continuously in circular arenas while the wildtype Canton-S walked intermittently. Through careful control of genetic and cytoplasmic backgrounds, we found that the w¹¹¹⁸ locus was associated with continuous walking. w¹¹¹⁸ -carrying male flies showed increased median values of path length per second (PPS) and 5-min path length compared with w⁺ -carrying males. Additionally, flies carrying 2-4 genomic copies of mini-white⁺ (mw⁺ ) in the w¹¹¹⁸ background showed suppressed median PPSs and decreased 5-min path length compared with controls, and the suppression was dependent on the copy number of mw⁺ . Analysis of the time-series (i.e., PPSs over time) by Fourier transform indicated that w¹¹¹⁸ was associated with increased locomotor components at relatively high frequencies (> 0.1 Hz). The addition of multiple genomic copies of mw⁺ (2-4 copies) suppressed the high-frequency components. Lastly, the downregulation of w⁺ in neurons but not glial cells resulted in increased high-frequency components. We concluded that mutation of w modified the locomotion in adult flies by selectively increasing high-frequency locomotor components.

Does Brain Lateralization Affect the Performance in Binary Choice Tasks? A Study in the Animal Model Danio rerio

Researchers in behavioral neuroscience commonly observe the behavior of animal subjects in the presence of two alternative stimuli. However, this type of binary choice introduces a potential confound related to side biases. Understanding whether subjects exhibit this bias, and the origin of it (pre-existent or acquired throughout the experimental sessions), is particularly important to interpreting the results. Here, we tested the hypothesis according to which brain lateralization may influence the emergence of side biases in a well-known model of neuroscience, the zebrafish. As a measure of lateralization, individuals were observed in their spontaneous tendencies to monitor a potential predator with either the left or the right eye. Subjects also underwent an operant conditioning task requiring discrimination between two colors placed on the left–right axis. Although the low performance exhibited in the operant conditioning task prevents firm conclusions from being drawn, a positive correlation was found between the direction of lateralization and the tendency to select the stimulus presented on one specific side (e.g., right). The choice for this preferred side did not change throughout the experimental sessions, meaning that this side bias was not the result of the prolonged training. Overall, our study calls for a wider investigation of pre-existing lateralization biases in animal models to set up methodological counterstrategies to test individuals that do not properly work in a binary choice task with stimuli arranged on the left–right axis.