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Investigating the causes and consequences of niche partitioning in populations is a major goal in ecology and evolutionary biology. Previous studies have investigated genetic and environmentally induced variation in resource utility and their ecological implications. However, few studies have explored variability (non-genetic, stochastic variation) as a factor contributing to variation in resource utility. In this study, we studied the variability in foraging traits of Drosophila lutescens , a species of wild fruit fly. Using 70 iso-female lines from a single population, we observed two foraging traits, i.e., locomotive speed and resource preferences, in an “8”-shaped experimental arena containing different types of fruit juices. The mean locomotive speed and relative preference for orange juice over grape juice varied significantly among iso-female lines. Additionally, the degree of intraline variation (variability) was detected a fold-change of larger than 2-fold between the smallest line and the largest line. While the mean locomotive speed itself did not correlate with mean resource preferences, the variability of locomotive speed significantly correlated with that of resource preferences. These results suggest that the degree of variability within inbred lines for both locomotive activity and resource preference is potentially partly genetic and that a shared genetic basis may govern variability in these traits. The variability of a particular trait is considered to interact cooperatively with the variability of several other traits in creating phenotypic intraspecific variation within a population.

Collective behavior plays a vital role in detecting and evading predators, yet its neural and genetic underpinnings remain poorly understood. In Drosophila melanogaster , visual cues from conspecifics can alleviate freezing responses to threatening stimuli. Using a large-scale behavioral experiment combined with GWAS, we identify key loci, including Ptp99A and kirre , which are involved in visual neuron development and may influence visual responsiveness to conspecifics. Single-cell transcriptomics and functional assays confirm the modulatory roles of Ptp99A in gene expression in visual neurons and behavior. Furthermore, mixed-strain groups show enhanced freezing behavior compared to homogeneous groups, demonstrating a “diversity effect” where genetic diversity within groups induces flexible behavioral changes. Animal-computer interaction experiments using predatory spiders validate that variation in freezing durations among interactive individuals improves antipredator behavioral performance in fly groups. Agent-based simulations further support the hypothesis that behavioral synchronization among genetically diverse individuals improves group-level performance. We introduce genome-wide higher-level association study to find loci whose genetic diversity correlates with diversity effect, highlighting the potential roles of neuronal diversity. These findings demonstrate how genetic diversity fosters synergistic responses to threats, offering insights into the neural and genomic mechanisms underlying collective behavior in non-eusocial insects. Collective behavior plays an important role in predator evasion, but its neurogenetic basis is poorly understood. Here, Sato and Takahashi show that genetic diversity within groups of fruit flies enhances collective antipredator performance.

Many animals form mixed‐species groups. Interactions among individuals within a group often induce behavioral conformity, forming group‐level characteristics. However, mixed‐species groups are often studied with a focus on specific species, and it remains unclear whether conformity emerges or group‐level characteristics form in passive aggregations, such as insects patchily distributed on food sources. Here we focused on four sympatric Drosophila species, i.e., D. simulans, D. suzukii, D. lutescens, and D. takahashii, and revealed interspecific conformity in activity and the formation of group‐level characteristics. Within each species' solitary group, activity levels increased in other individuals when the focal individual began walking, indicating that activity conforms among individuals in all species. Experiments were conducted with D. lutescens in mixed groups that combined the other three species. Convergence in activity levels due to conformity was observed across all species. Interestingly, D. takahashii exhibited smaller behavioral changes in mixed groups than the other species. Conversely, D. lutescens showed the greatest change in activity levels when mixed with this species. These results suggest that D. takahashii exerts disproportionate influence on the formation of group‐level characteristics. Understanding intraspecific behavioral variation and intergroup variation may require considering the impact of such influential species within the same guild. Many animals form mixed‐species groups, but it remains unclear whether behavioral conformity and group‐level characteristics emerge in passive aggregations such as insects on shared food sources. Studying four sympatric Drosophila species revealed interspecific conformity in activity, with convergence of activity levels in mixed‐species groups and especially strong influence from D. takahashii, which induced large changes in D. lutescens. These results indicate that particular species can exert disproportionate effects on group‐level characteristics, highlighting the importance of species composition in understanding behavioral variation.

Cities experience changes in abiotic factors, such as warming, increases in noise and light. These changes can lead to phenotypic changes. Several studies have revealed that altered environments change phenotypes in plants and animals in cities. However, limited studies have isolated evolutionary from nongenetic changes. Here, we analyzed the evolution of thermal tolerance and diurnal activity patterns in the urban population of the fruit pest, Drosophila suzukii. Urban and rural isofemale lines were reared under constant conditions. We compared the lower and upper thermal limits (CTmin and CTmax, respectively), and effects of temperature exposure on the thermal limits of urban and rural populations. Common garden experiments showed that urban populations exhibit a lower CTmin than rural populations, suggesting genetic difference in CTmin among populations. On the other hand, the difference in CTmax between urban and rural populations was not significant. Exposure to cold temperature did not affect CTmin in both urban and rural populations. In contrast, exposure to hot temperature increased CTmax especially in urban population, suggesting that urban populations evolved in response to urban heat. We also investigated the daily activity patterns of urban and rural populations and the effect of lifelong artificial light at night on daily activity. We found that night‐time light (dim light) reduced the total amount of activity compared to dark night condition. In addition, dim light at night altered the daily rhythm of activity and increased the activity rate at night. The effect of night light on total activity was less in urban than that in rural populations, suggesting that populations in cities evolved to mitigate decreased activity under night light. Our results showed that environmental temperature and artificial light at night evolutionarily and plastically influence ecologically important traits, such as temperature tolerance and diurnal activity. Our study examined the evolutionary and plastic changes in thermal tolerances and diurnal activity pattern in urban populations of Drosophila suzukii. Results revealed that urban populations get evolved in cold tolerance and ability to improve heat tolerance and night‐time light changes diurnal activity patterns. The evolutionary responses in urban populations could contribute to the survival in the urban environments.

Urbanization causes environmental changes like habitat loss, fragmentation, and pollution, which reduce biodiversity. Urban organisms face stressors, such as heat islands, air and water pollution, and anthropogenic noise, all of which can disrupt their development, behavior, and physiology. While some species adapt to urban environments, their responses and the role of evolution in urbanization are limited, as most studies focus on phenotypic traits. Artificial light at night (ALAN), a common urban stressor, disrupts behaviors and physiological processes, including circadian rhythms, sleep, and reproduction. The present study examined the effect of ALAN on body size, survival, activity rhythms, and gene expression in urban and rural strains of Drosophila suzukii in common garden experiments. ALAN reduced wing and thorax sizes regardless of sex and origin, decreased survival in rural populations, and increased it in urban populations. ALAN elevated overall activity, especially in the early night, while urban females displayed reduced sensitivity regarding activity and sleep. The circadian rhythm length was disrupted in rural populations but not in urban populations. Transcriptomic analysis revealed ALAN‐induced gene expression changes, particularly in urban females, with photoreceptor‐ and circadian rhythm‐related genes responding differently between urban and rural populations. These results indicate that urban populations have evolved adaptive mechanisms to counter ALAN's effects, likely mediated through gene regulation. This study highlights ALAN's impact on diverse traits and its potential for adaptive evolution in urban environments. Evolutionary adaptations in traits related to urban stress responses may enhance the ecological success of D. suzukii in urban habitats. Urbanization introduces stressors like artificial light at night (ALAN), which can disrupt physiology and behavior in urban wildlife. This study found that ALAN affected morphology, survival, activity rhythms, and gene expression in Drosophila suzukii, with urban populations showing signs of adaptive responses. The results suggest that urban environments may drive evolutionary changes through gene regulation to cope with light pollution.

Studying the mechanisms of the establishment of a population in a novel environment allows us to examine the process of local adaptations and subsequent range expansion. In a river system, detecting genetic or phenotypic differences between a freshwater and brackish water population could contribute to our understanding of the initial process of brackish water adaptation. Here, we investigated behavioural and gene expression responses to salt water in a freshwater and brackish water population of the freshwater snail, Semisulcospira reiniana . Although the individuals in brackish water exhibited significantly higher activity in saltwater than freshwater individuals just after sampling, the activity of freshwater individuals had increased in the second observation after rearing, suggesting that their salinity tolerance was plastic rather than genetic. We found 476 and 1002 differentially expressed genes across salinity conditions in the freshwater and brackish water populations, respectively. The major biological process involved in the salinity response of the freshwater population was the biosynthesis and metabolic processing of nitrogen-containing compounds, but that of the brackish water population was influenced by the chitin metabolic process. These results suggest that phenotypic plasticity induces adaptation to brackish water in the freshwater snail by modifying its physiological response to salinity.

Elucidating the mechanism shaping the spatial variations of traits has long been a central concern of evolutionary biologists. Geographic clines of allele/morph frequencies along environmental gradients are suggested to be established and maintained by the balancing of two opposing evolutionary forces, namely selection that generates spatial differentiation in morph frequencies, and selection and/or stochastic factors that lead to the coexistence of multiple morphs within a population. Thus, testing for both selection and stochastic factors is necessary for a comprehensive understanding of the mechanism underlying clinal variation in morph/allele frequency in natural populations. Here, I identified the evolutionary forces responsible for clinal variation of color morph frequency in Ischnura senegalensis by comparing the population divergence of putatively neutral loci generated by high-throughput next-generation sequencing ( F STn ) with that of the putative color locus ( F STc ). No strong correlation was observed between F STn and F STc , suggesting that stochastic factors contribute less to color-locus population divergence. F STc was less than F STn between populations exposed to similar environmental conditions, but greater than F STn between populations exposed to different environmental conditions, suggesting that both balancing selection and divergent selection act on the color locus. Therefore, two antagonistic selection factors rather than stochastic and historical factors contribute to establishing the clinal variation of morph frequency in I. senegalensis .

One of the most important questions in evolutionary biology is how the spatial distribution of species is limited. Asymmetric gene flow from core populations is suggested to increase the number of poorly adapted immigrants in the populations at the range edge. Genetic load due to migration, i.e., migration load, should prevent adaptation to the local habitat, leading to decreases in distribution range via local extinction or the limiting range expansion. However, few experimental studies have examined the effects of immigration on fitness and natural selection within recipient populations. To investigate the influence of migration load on the evolution of distribution range, we performed field and laboratory observations as well as population transcriptomics for the common river snail, Semisulcospira reiniana . This species meets the conditions that migration from source populations can prevent local adaptation in a sink population because they inhabit the broader range of environments, including middle/upper reaches of a river and estuaries within a single river and they may be more vulnerable to being swept away by water currents due to lowered spontaneous (upward) locomotion activity. We found that river steepness was related to the lower distribution limit of S . reiniana , with a narrower distribution range in the steeper river. Population transcriptomic analysis showed that gene flow was heavily asymmetric from the upstream populations to downstream ones in the steep river, suggesting a greater migration load in the steep river. The number of genes putatively involved in adaptation to the local habitat was lower in the steep river than in the gentle river. Gene expression profiles suggested that individuals achieve better local adaptation in the gentle river. Laboratory experiments suggested that evolutionary differences in salinity tolerance among local populations were only found in the gentle river. Our results consistent with the hypothesis that migration load owing to asymmetric gene flow disturbs local adaptation and restricts the distribution range of river snails.

Although genetic diversity within a population is suggested to improve population-level fitness and productivity, the existence of these effects is controversial because empirical evidence for an ecological effect of genetic diversity and the underlying mechanisms is scarce and incomplete. Here, we show that the natural single-gene behavioural polymorphism (Rover and sitter) in Drosophila melanogaster has a positive effect on population fitness. Our simple numerical model predicted that the fitness of a polymorphic population would be higher than that expected with two monomorphic populations, but only under balancing selection. Moreover, this positive diversity effect of genetic polymorphism was attributable to a complementarity effect, rather than to a selection effect. Our empirical tests using the behavioural polymorphism in D. melanogaster clearly supported the model predictions. These results provide direct evidence for an ecological effect of genetic diversity on population fitness and its condition dependence.

A continuous spatial gradient in visible traits, which is called a cline, is a natural model system for quantifying the effects of selection and stochastic factors and their relative importance. Geographic clines in phenotypic traits also provide key insights into the evolutionary forces that lead to allopatric speciation in nature. Thus, the underlying mechanisms for establishing clines and their evolutionary consequences remain key topics in evolutionary biology. However, few experimental studies have confirmed the underlying mechanisms of geographic clines in morph/allele frequencies, probably because of the lack of understanding of the theoretical basis of geographic clines in polymorphisms and/or suitable comprehensive tests. Thus, I present a general review of the underlying mechanisms for establishing geographic clines in polymorphisms. I also provide a case study using the female dimorphic damselfly Ischnura senegalensis to illustrate a strategy that confirms the underlying mechanisms of geographic clines in morph frequencies. This review may help to address geographic clines in other polymorphic systems, as well as contribute to a comprehensive understanding of geographic clines in quantitative traits, and thus, their evolutionary consequences in nature.