Individuals differ. While seemingly trivial, this insight has nevertheless led to paradigm shifts, as three key fields of organismal biology have seen marked changes in key concepts over the past few decades. In animal behaviour, it has become increasingly recognised that behavioural differences among individuals can be stable over time and across contexts, giving rise to the concept of animal personalities. In ecology, attention has similarly shifted towards variation in the ecological niches occupied by species, populations and individuals, giving rise to the concept of niche specialisation or individual niche variation. In evolutionary biology, where individual variation has always been central, there is a growing awareness of the complex and dynamic ways in which individuals interact with the environment to produce unique phenotypes. Additionally, recent theoretical and empirical research suggests that fitness landscapes are not only complex, with multiple fitness peaks, but might even be more accurately described as constantly shifting 'fitness seascapes', where the fitness peak that an individual can reach - whether local or global - depends on its genotype and its interaction with the environment. Moreover, the previous distinction between ecological and evolutionary timescales is being replaced by a more integrative view that recognises that evolution can occur on ecological timeframes. These shifting perspectives over the past two decades underscore the need for a more integrated conceptual framework that transcends disciplines. While in behaviour, ecology and evolution, the concept of individualisation has contributed to major scientific progress, sufficient cross-fertilisation is still lacking. Here, we propose a new conceptual unification: the individualised niche. By merging the niche concept with the fitness concept, new explanatory power for both ecological and evolutionary processes emerges.

Many parasitoid wasps do not accumulate triacylglycerols (TAGs) as adults, yet recent studies have shown that they can convert sugars into fatty acids (FAs) and TAGs. Whether lipogenesis is fitness-relevant, and which fatty acid synthase (FAS) genes mediate it, remain unclear. Using RNAi-mediated knockdown and stable isotope labelling in the parasitic wasp Nasonia vitripennis, we demonstrate that the FAS gene Nvfas1 is required not only for TAG biosynthesis in females, but also for ovarian development and male pheromone production. Nvfas1 knockdown females exhibited significantly reduced de novo synthesis of TAGs and underdeveloped ovarioles with few or no mature oocytes. These females completely lost the ability to produce offspring, while their lifespan remained unaffected. In males, Nvfas1 knockdown led to a reduced de novo biosynthesis of the FA-derived sex pheromone. Our study provides the first evidence of a single FAS gene exerting such pleiotropic and far-reaching effects on both males and females of a parasitoid wasp. Although the absolute contribution of Nvfas1-mediated de novo FA and TAG synthesis is quantitatively minor, it is indispensable for reproductive success, highlighting the essential role of lipogenesis in the fitness of N. vitripennis.

BACKGROUND:Horizontal gene transfer (HGT) from bacteria can drive phenotypic innovation and adaptation in eukaryotes. Ants are likely carriers of HGT-derived genes, as they have repeatedly established mutualistic associations with vertically transmitted bacterial symbionts with direct access to the germline. However, the prevalence of HGT across ants and most other insects remains virtually unexplored. RESULTS:Here, we systematically investigated the genomes of over 160 species of ants and uncovered 497 protein-coding HGT events in 85 species, predominantly derived from intracellular symbionts. Among these, we identified several HGTs likely underpinning functional innovations, primarily by mediating immune-system adaptations or facilitating nutritional niche expansions. Several of these HGTs were conserved in sequence and synteny across multiple species, consistent with strong signatures of purifying selection over up to 40 million years. Functional and structural analysis of a horizontally acquired Xanthine-guanine phosphoribosyltransferase gene of Cardiocondyla ants reveals deep entrenchment of this protein in basic energy metabolism of the host, facilitated by the enzyme's substrate promiscuity. CONCLUSIONS:This study provides insights into the abundance and diversity of HGT from bacteria in the evolutionary history of ants. Furthermore, our comparative and functional analyses suggest that many of the horizontally acquired genes serve adaptive functions in ants, most prominently by expanding metabolic pathways or modulating immune responses.

Abstract Interdisciplinary research is widely acknowledged as a valuable means of knowledge production and as crucial for addressing complex scientific and societal problems. Interdisciplinary research takes many forms, and this article offers a novel case study of a distinctive form of interdisciplinarity, reflective interdisciplinarity. The article analyzes interdisciplinary research undertaken by philosophers of biology and empirically working biologists studying individualization. This kind of interdisciplinarity is reflective because biology is the target domain that philosophers of biology (and philosophically-minded biologists) reflect upon—as opposed to interdisciplinarity that occurs, for example, when insights from multiple distinct research domains are integrated. To analyze the case study, an analytic framework is developed that distinguishes four dimensions of interdisciplinarity: objects of interdisciplinary research, interdisciplinary research activities, communication of interdisciplinary results, and personal, institutional, and other conditions of interdisciplinary research. The case study shows, first, that reflective interdisciplinarity can involve interdependent, deeply immersive and cooperative interdisciplinary research processes (‘inquiry-embedded integration’) that include a form of knowledge-producing inquiry through which novel epistemic products emerge from joint commitments and goals, shared research questions, and intensive, collaborative discursive practices. The article adapts the notion of a plural subject in characterizing inquiry-embedded integration. Second, the analysis of the case study demonstrates how communicative choices, together with institutional and normative conditions, are partially constitutive of the interdisciplinary process. They shape the content of interdisciplinary products and play decisive roles in interdisciplinary activities such as knowledge integration. Finally, because the case study comprises the authors’ own research processes and publications, the analysis demonstrates that self-reflexive, qualitative analysis of interdisciplinary practice provides a valuable means of theorizing about interdisciplinarity with potential to offer transferable insights.

Abstract Cryptic species diversity, overlooked due to extreme morphological similarity, is a common phenomenon among ants. The “honeypot ant” genus Myrmecocystus (Wesmael, 1838; Formicinae: Lasiini) likely features multiple cryptic species, as previously suggested by phylogenetic studies based on ultraconserved elements (UCEs). Here, this work is expanded upon by examining 140 specimens and 2,508 UCE loci, with a particular focus on the M. mendax species complex from the southwestern USA and northern Mexico. Phylogenomic and population genomic analyses revealed five distinct M. mendax- like lineages and identified two potential cases of cryptic species diversity, one within samples matching the morphology of M. mendax and another within samples conforming to M. placodops . Most specimens morphologically identified as M. mendax formed a well-supported monophyletic group sister to M. melliger assigned individuals, with evidence for ongoing hybridization between both species in the Madrean Sky Islands along the USA-Mexico border. Patterns in the main M. mendax clade also suggest adaptive divergence across ecological gradients, warranting further investigation. Overall, these findings highlight the power of UCE-based genomic data in phylogenetic reconstructions and population genetic analyses to better resolve cryptic species diversity, and clarify complex evolutionary histories shaped by introgression and incomplete lineage sorting.

Glyphosate based herbicides (GBH) are worldwide one of the most widely used agrochemicals. This includes their application in combination with genetically engineered crops and in non-agricultural environments such as industrial or urban landscapes. Despite decades of widespread use and environmental contamination, ecotoxicological assessments of GBHs on non-target arthropods (NTAs) remain limited, particularly regarding oral exposure. To address this gap, we tested the effects of the GBH ETISSO (R) on two ant species, Camponotus maculatus and Cardiocondyla obscurior (Hymenoptera: Formicidae). Sub-colonies containing workers and larvae were orally exposed to test field-relevant test solutions containing 0.5%-10% GBH in 7.5-10% honey-water solutions for 21 days. GBH concentrations exceeding 7.2 g/L for C. maculatus and 3.6 g/L for C. obscurior led to significantly reduced food acceptance. Hence, starvation in combination with the toxicity led to a significantly increased mortality at those and higher concentrations. At lower, readily consumed concentrations, up to 32% of C. maculatus larvae exhibited development impairments, in the form of pupal malformation and the absence of the pupal cocoon while C. obscurior workers, exposed to GBH solutions during larval stages, showed altered morphological robustness. Thus, the GBH ETISSO (R) leads to significant disruptions of developmental processes in both species already at sublethal doses. Our study demonstrates for the first time, that sublethal GBH exposure in ant workers can negatively affect larval development, with potential long-term effects on colony maintenance and survival. Therefore, testing toxicity on adult workers only may be misleading for ants or social insects in general, as larvae appear more sensitive than adult workers. This is especially concerning since larvae may experience cumulative effects due to constant feeding by workers. Our study contributes to a better understanding of potential adverse effects through oral exposure of GBHs for non-target arthropods (NTAs). It also highlights the need to re-evaluate common testing schemes in particular when testing social insects that are key species for many terrestrial ecosystems. Our results challenge the widespread assumption that GBHs are non-toxic to terrestrial arthropods.

Horizontal Gene transfer (HGT) from bacteria has often led to Horizontal Gene Acquisition (HGA), subsequently contributing to phenotypic innovation. Ants are interesting potential targets for HGA because they host many mutualistic associations with vertically transmitted symbionts, but the overall prevalence of HGA across the ants and other insect lineages remains virtually unexplored. Here, we systematically screened the genomes of 163 ant species and identified 497 HGA events of protein-coding genes, predominantly derived from intracellular symbionts, in 85 species belonging to eight subfamilies. Apart from convergent horizontal transfers of Wolbachia-derived ankyrin repeat proteins into the genomes of 45 ant species, we identified dozens of other HGAs that likely offered adaptive innovations of phenotypic functions, primarily mediating immune-system adaptations or facilitating nutritional niche expansions. We provide in-depth characterizations of multiple clade- and species-specific HGAs, some as old as 40 MY, consistent with strong evolutionary conservation. Our study is the first of its kind in ants and considerably expands our general appreciation of the evolutionary significance of HGA from bacteria to eukaryotes.

DNA methylation has been proposed as an epigenetic driver of phenotypic plasticity in social insects, yet experimental evidence remains limited. Even less is known about the role of epigenetic mechanisms underlying behavioural and social polymorphism. We quantified CpG methylation for the socially polymorphic harvester ant Pogonomyrmex californicus across larvae, pupae, workers and queens using Oxford Nanopore Technologies (ONT) sequencing. These results were compared against the current gold standard whole-genome bisulfite sequencing (WGBS). Methylation sites were highly correlated between WGBS and ONT, validating the use of ONT for high-throughput epigenomic profiling. Genome-wide methylation was low (~3%), consistent with findings in other (Hymenoptera: Formicidae), and highly clustered within gene bodies, especially exons, while introns, intergenic DNA, promoters and transposable elements were hypo-methylated. Gene body methylation (GBM) correlated positively with gene expression in queens, corroborating previous reports for other insects, suggesting a conserved regulatory role for DNA methylation in insects. A comparison between developmental stages revealed significant stage-specific differences in GBM frequencies. Workers and queens, although from different populations, shared a substantial core of methylated loci enriched for olfactory-receptor activity and biosynthetic pathways, processes that are central to caste-specific behaviour and physiology. These shared methylation signatures, coupled with stage-dependent variability, highlight DNA methylation as a possible factor in developmental stages and caste differentiation. In the future, it is essential to disentangle the effects of caste and variation between populations. Our study establishes P. californicus as a powerful model for dissecting how epigenetic modifications interface with gene expression to generate developmental and complex social organization, which is largely unexplored.

Social insects vary considerably in their social organization both between and within species. In the California harvester ant, Pogonomyrmex californicus (Buckley 1867), colonies are commonly founded and headed by a single queen (haplometrosis, primary monogyny). However, in some populations in California (USA), unrelated queens cooperate not only during founding (pleometrosis) but throughout the life of the colony (primary polygyny). The genetic architecture and evolutionary dynamics of this complex social niche polymorphism (haplometrosis vs pleometrosis) have remained unknown. Here, we provide a first analysis of its genomic basis and evolutionary history using population genomics comparing individuals from a haplometrotic population to those from a pleometrotic population. We discovered a recently evolved (< 200 k years), 8 Mb non-recombining region segregating with the observed social niche polymorphism. This region shares several characteristics with supergenes underlying social polymorphisms in other socially polymorphic ant species. However, we also find remarkable differences from previously described social supergenes. Particularly, four additional genomic regions not in linkage with the supergene show signatures of a selective sweep in the pleometrotic population. Within these regions, we find for example genes crucial for epigenetic regulation via histone modification ( chameau ) and DNA methylation ( Dnmt1 ). These results suggest that social morph in this species is a polygenic trait involving a potential young supergene. Further studies targeting haplo- and pleometrotic individuals from a single population are however required to conclusively resolve whether these genetic differences underlie the alternative social phenotypes or have emerged through genetic drift.

What are social niches, and how do they arise and change? Our first goal in the present article is to clarify the concept of an individualized social niche and to distinguish it from related concepts, such as a social environment and a social role. We argue that focal individuals are integral parts of individualized social niches and that social interactions with conspecifics are further core elements of social niches. Our second goal in the present article is to characterize three types of processes-social niche construction, conformance, and choice (social NC3 processes)-that explain how individualized social niches originate and change. Our approach brings together studies of behavior, ecology, and evolution and integrates social niches into the broader concept of an individualized ecological niche. We show how clarifying the concept of a social niche and recognizing the differences between the three social NC3 processes enhance and stimulate empirical research.

Transposable elements (TEs) are found in virtually every eukaryotic genome and are important for generating de novo genetic variation. However, outside of costly and time-consuming whole-genome sequencing approaches, the set of available methods to study TE polymorphisms in non-model species is very limited. The Transposon Display (TD) is a simple yet effective technique to characterize polymorphisms across samples by identifying amplified fragment length polymorphisms using primers targeting specific TE families. So far, this technique has almost exclusively been used in plants. Here, we present an optimized TD protocol for insect species with small genomes such as ants (ca. 200-600 Mb). We characterized TE polymorphisms between two distinct genetic lineages of the invasive ant Cardiocondyla obscurior, as well as between neighboring populations of the New World lineage. We found active LTR/Ty3 retrotransposons, that contributed to the genetic diversification of populations in this species.

Recent efforts in a range of scientific fields have emphasised research and methods concerning individual differences and individualisation. This article brings together various scientific disciplines—ecology, evolution, and animal behaviour; medicine and psychiatry; public health and sport/exercise science; sociology; psychology; economics and management science—and presents their research on individualisation. We then clarify the concept of individualisation as it appears in the disciplinary casework by distinguishing three kinds of individualisation studied in and across these disciplines: IndividualisationONE as creating/changing individual differences (the process that generates differences between individuals: intrapopulation or intraspecific variation/heterogeneity); IndividualisationTWO as individualising applications (the tailoring or customising of something—information, treatment, a product or service, etc.—for an individual or specific group of individuals); and IndividualisationTHREE as social changes influencing autonomy, risk, and responsibilities (the process discussed under the rubric of sociological individualisation theory). Moreover, we analyse conceptual links between individualisation and individuality, and characterise different sorts of individuality that the disciplines study. This paper aims to promote interdisciplinary research concerning individualisation by establishing a common conceptual-theoretical basis, while leaving room for disciplinary differences.

Ants (Formicidae) are ubiquitous in terrestrial ecosystems, including agricultural areas and forests. They are important for soil movement, decomposition, nutrient cycling, pollination, predation, scavenging and seed dispersal. Furthermore, they serve as a crucial food source for various wildlife. However, ants are no part of current ecotoxicity testing. Here, we systematically analyze whether and how ants can be exposed to active substances from plant protection products (PPPs) or genetically modified plants (GMPs). Like other arthropods, ants can be exposed via direct contact with PPPs after application, inhalation, uptake of contaminated drinking water or diet. For plant incorporated protectants (PIPs) expressed by GMPs, dietary exposure is the only relevant exposure route. Ants exhibit a diverse dietary spectrum, including plant material, honey dew collection, fungal cultivation, scavenging, and predation. Notably, foraging for dead or weakened arthropods, e.g., treated pest organisms, represents a significant exposure route because such food may be readily available in large amounts after spraying a field. Arthropods, alive or deceased, serve as the dominant protein source for numerous ant species, essential for larval development and the egg production of the queen(s). Consequently, exposure routes, via contaminated food items, can jeopardize entire ant colonies if it reaches the queen. However, effects arising from contaminated prey are not routinely assessed, neither for non-social nor for social insects such as the honey bee, which collects only nectar and pollen and is intensively tested in the assessment of PPPs. We conclude that ecotoxicity testing in ants would fill a gap and support the assessment of biodiversity effects. To achieve this, we recommend further research to explore the exposure of the different castes and developmental stages of ants in greater detail and to develop protocols allowing for ecological risk assessments of PPPs and PIPs via dietary uptake. This comprehensive approach will contribute significantly to our understanding of the potential consequences of PPP and GMP exposure to non-target ants.

Eusocial Hymenoptera have the highest recombination rates among all multicellular animals studied so far, but it is unclear why this is and how this affects the biology of individual species. A high-resolution linkage map for the antCardiocondyla obscuriorcorroborates genome-wide high recombination rates reported for ants (8.1 cM/Mb). However, recombination is locally suppressed in regions that are enriched with TEs, that have strong haplotype divergence, or that show signatures of epistatic selection inC. obscurior. The results do not support the hypotheses that high recombination rates are linked to phenotypic plasticity or to modulating selection efficiency. Instead, genetic diversity and the frequency of structural variants correlate positively with local recombination rates, potentially compensating for the low levels of genetic variation expected in haplodiploid social Hymenoptera with low effective population size. Ultimately, the data show that recombination contributes to within-population polymorphism and to the divergence of the lineages withinC. obscurior.

Attracting and securing potential mating partners is of fundamental importance for reproduction. Therefore, signaling sexual attractiveness is expected to be tightly coordinated in communication systems synchronizing senders and receivers. Chemical signaling has permeated through all taxa of life as the earliest and most widespread form of communication and is particularly prevalent in insects. However, it has been notoriously difficult to decipher how exactly information related to sexual signaling is encoded in complex chemical profiles. Similarly, our knowledge of the genetic basis of sexual signaling is very limited and usually restricted to a few case studies with comparably simple pheromonal communication mechanisms. The present study jointly addresses these two knowledge gaps by characterizing two fatty acid synthase genes that most likely evolved by tandem gene duplication and that simultaneously impact sexual attractiveness and complex chemical surface profiles in parasitic wasps. Gene knockdown in female wasps dramatically reduces their sexual attractiveness coinciding with a drastic decrease in male courtship and copulation behavior. Concordantly, we found a striking shift of methyl-branching patterns in the female surface pheromonal compounds, which we subsequently demonstrate to be the main cause for the greatly reduced male mating response. Intriguingly, this suggests a potential coding mechanism for sexual attractiveness mediated by specific methyl-branching patterns in complex cuticular hydrocarbon (CHC) profiles. So far, the genetic underpinnings of methyl-branched CHCs are not well understood despite their high potential for encoding information. Our study sheds light on how biologically relevant information can be encoded in complex chemical profiles and on the genetic basis of sexual attractiveness.

Distinctive chemical signatures have the potential to serve as discriminatory cues for olfactory recognition mechanisms. Cuticular hydrocarbon (CHC) profiles are among the most prominent chemical signatures in insects that can be highly diverse even among closely related species and between populations with similar ecology. Particularly within the major insect order Hymenoptera, CHC profiles are characterized by high complexity and variation with the potential to evolve rapidly. In this study, we found two very distinct CHC chemotypes distinguishing sympatric colonies of the African carpenter ant Camponotus maculatus (Hymenoptera: Formicinae). These chemotypic differences were mainly detected on the surface profiles of eggs produced by either queens or isolated worker groups. In one chemotype, queen- and worker-laid eggs are very similar. This is largely contrasted by the other chemotype, where queen-laid eggs clearly differ from worker-laid eggs with several prominent queen-exclusive compounds. However, workers display a stable behavior of discriminating against and selectively disposing of worker-laid eggs i.e., worker policing, independent of egg chemotype. Furthermore, genetic barcoding of workers revealed a clear separation between colonies characterized by producing these two distinct egg chemotypes, which may indicate that these colonies belong to a cryptic species complex. Interestingly, worker policing behaviour appears to be evolutionarily conserved, despite the strikingly different egg surface profiles.

Cooperation between kin and cooperation between non-kin often appear functionally similar, but the evolutionary mechanisms that drive the emergence of these two forms of cooperation can be dramatically different. The mechanisms responsible for non-kin cooperation, in particular, are not well established in an empirical context. To truly understand the emergence of non-kin cooperation, the fitness outcomes of cooperation should be compared with the alternate strategy of solitary living in the same environment. Ant populations that contain a mix of queens who found nests alone (monogyny), and cooperative unrelated ant queens who found nests together and remain together through colony development (primary polygyny), provide a useful natural context to make such a comparison. To estimate the reproductive costs for primary polygyny relative to solitary nest founding, we measured alate (reproductive) production for colonies in a mixed population of polygynous and monogynous California harvester ant colonies over a 2-year period. Colony-level reproductive output was not substantially higher in polygynous colonies compared to those with single queens, and consequent per-queen reproductive gain was significantly lower. Given that polygynous queens in this population are unrelated, nest sharing thus generates a significant annual and potentially lifetime cost for cooperative queens. Comparative measures of colony dynamics, however, suggest that polygynous colonies have a larger or more active workforce than monogynous colonies. Additionally, polygynous colonies may be more conservative than monogynous colonies in resource allocation towards reproduction. These results collectively suggest that primary polygyny generates annual reproductive fitness costs. However, polygynous colonies likely also shift life history strategies in ways that emphasize long-term survival and colony growth over immediate reproduction. Over time, this shift may mitigate the annual fitness costs of cooperation. Significance statement When things get difficult, it pays to work together. In some ant species, unrelated queens form long-term cooperative associations that share resources and a workforce within a single nest. The fitness consequences and evolutionary drivers of non-kin cooperation in this and other systems are unclear. We compared the reproductive investment and colony dynamics of single-queen and multi-queen California harvester ant colonies in a shared environment to directly compare the fitness of cooperative and non-cooperative queens. Our data suggest that cooperation not only lowers annual per-queen reproduction, but also produces a more robust colony that may recoup annual fitness losses by extending colony longevity.

Wolbachia is a genus of endosymbiotic bacteria that is widespread among arthropods. It is responsible for manipulating various host phenotypes and often affects their host's fitness. We used the generalist parasitoid wasp Nasonia vitripennis and its endosymbiont Wolbachia to test whether and how Wolbachia affects the fitness of N. vitripennis by comparing the host preference and parasitization rate of cured and uncured N. vitripennis lines. We reared four genotypes of wasps, each with Wolbachia infection or cured of infection, using two different host species, namely Calliphora vomitoria and Lucilia sericata , for 3–4 generations before measuring their host preference because rearing history has previously been shown to influence host preference in N . vitripennis . We found that all experimental groups significantly preferred C. vomitoria pupae. Neither rearing history nor Wolbachia infection altered N. vitripennis female's innate host preference. Furthermore, we investigated whether Wolbachia infection may affect Nasonia's parasitization rate, offspring production and sex ratio using parasitization assays of two wasp genotypes with and without Wolbachia infection. Our results show that uncured wasps have fitness costs of harbouring Wolbachia in terms of reduced parasitization rate and offspring production in one of the host genotypes and reduced proportion of female offspring in the second host genotype tested, highlighting the context‐dependency of host–endosymbiont relationships.

Depending on the reproductive strategy of a species, the same environmental barrier can affect gene flow differently. In this study, we analyzed the effects of a river on the gene flow of two ant species, one with wingless queens (Megaponera analis) and one with winged queens (Paltothyreus tarsatus), both with winged males. Colonies were sampled in the Comoe National Park, Cote d'Ivoire, from April to June, in 2017 and 2019. A detailed sociogenetic analysis corroborated monogyny and monandry for M. analis (74 of 78 colonies), including 29 colonies with evidence of recent fission events. In contrast, the sociobiological structure of P. tarsatus was more heterogeneous. Nine colonies were monogynous and monandrous, 14 colonies were either polygynous and / or polyandrous, and worker genotypes in seven colonies can only be explained by polygyny. For both species, we quantified gene flow between four sympatric subpopulations that are separated by the Comoe river. Comparisons of the different populations using two mitochondrial genes showed a clear substructure in M. analis, separating the respective river sides, while no substructure was found in P. tarsatus. Microsatellites, as likely neutral nuclear markers, showed, in contrast to mitochondrial DNA analyses, no significant substructure between any of the four subpopulations for both species. Even though microsatellites have been mostly replaced in population genetics by large-scale single nucleotide polymorphism analyses (e.g., based on restriction site associated DNA or whole genome sequencing), they are still the most efficient way to determine the social structure of social insect colonies based on thousands of samples (in our case, approx. 2000) or revealing atypical reproductive systems like genetic caste determination. These microsatellite analyses allowed us to show that gene flow in M. analis through wingless queens is restricted but compensated for by male dispersal on the nuclear DNA level. This underlines the importance of having at least one winged sexual alate in the reproductive strategy of social insects to allow for suf-ficient gene flow across minor environmental barriers.