Publications

Some social animals can recognize and respond to the distress of group members. While well documented in mammals, such behaviour has also independently evolved in ants. To uncover the molecular basis of this social trait, we compared gene expression in the central and peripheral nervous system of Cataglyphis nigra workers differing in rescue propensity. RNA-seq of mushroom bodies, optic lobes, central brain and antennae revealed nine genes upregulated across all tissues of rescuers, including those encoding cytochrome P450-9e2 (CYP9E2) and arginase, and immune-related genes such as the defensin (DEFA) and serine protease snake (snk) genes. The mushroom bodies showed the strongest signal, including genes involved in juvenile hormone signalling, polyamine synthesis and immune function. These results suggest that the immune pathways and polyamine metabolism modulate social responsiveness or alarm-cue detection in ants. In contrast, morphological and physiological traits did not differ between rescuers and non-rescuers, indicating that rescue behaviour propensity is governed by the activity of the nervous system.

Fitness can vary between individuals of the same population for reasons related to nutrient acquisition during development, but also to the quality of the mating partners. We focus on ant queens of Cardiocondyla obscurior to investigate the effects of female and male morphology and sperm characteristics on productivity. We monitored queens for 12 weeks after egg production started as a proxy for lifetime productivity, and found that larger queens are more productive, as commonly found in other insects, producing more workers and winged males. Sperm viability, but not sperm length, was positively correlated with female-biased sex ratios, pointing to a better insemination rate. The high correlation between sperm viability, male body size, and mandible size suggests strong selection for larger and stronger males. However, male competition for access to unmated queens in the maternal colony may result in a trade-off between male size and developmental time in this species.

Ants have been proposed as good models to study ageing and the effects of extrinsic mortality because of their long lifespans and plasticity of ageing within species. We discuss how age-dependent extrinsic mortality might influence queen lifespan, and how the effect of age-independent extrinsic mortality needs further study, accounting for different density-dependence scenarios. Based on a critical review of the available demographic data, we discuss the selective forces underlying ant ageing. We discuss differences and similarities between the life-history strategy of ants and the reproductive strategies iteroparity and semelparity. We consider how late-life fitness gains for the “superorganism” select for a delay of actuarial, and reproductive senescence, and we suggest future research directions.

Fitness variation among individuals can be explained by both genetic and non-genetic factors, such as maternal age. Little is known about the genetic and non-genetic factors influencing fitness variation in ant queens. From queens of the ant Cardiocondyla obscurior exhibiting either high or low fertility, we set up genetic lines and found no correlation between maternal and daughter queen lifetime fertility or lifespan, indicating low heritability of life-history traits. However, differences in fertility suggest that developmental variation is influenced by the maternal environment or by mate quality. Finally, we found that maternal age, specifically the remaining reproductive output of the mother, had no effect on daughter fitness traits. This is coherent with the hypothesis that senescence in ant queens is selected against until very old ages because of late-life fitness gains.

Cooperative transport, defined as the coordinated effort of multiple individuals to move a single item, enables social animals to retrieve resources more efficiently and reduces the risk of exploitation by competitors. In this study, we provide the first detailed description of such a coordinated prey retrieval behavior in the invasive ant Anoplolepis gracilipes. We examined the influence of prey and colony size on the success of cooperative transport and investigated whether chemical cues, such as footprints of nestmates or workers of competing Diacamma rugosum ants, affected foraging decisions. Our results, using a Y-maze experimental setup, revealed that A. gracilipes does not modify its foraging behavior based on the presence or absence of chemical footprints. However, colonies exhibited fine-tuned cooperative transport, only once exhibiting a deadlock in 144 transport processes. The ants adjusted the number of workers involved according to prey weight, increasing retrieval speed. Nevertheless, lighter prey was still transported faster than heavier prey, even though fewer workers were involved in the transport. Lighter prey items and those carried by larger groups were more likely to be transported successfully, with most failures caused by navigation errors rather than insufficient workforce. Workers joined a transport typically positioning themselves at the front, aligned with the nest, rather than at alternative locations. Our findings highlight the efficiency and plasticity of cooperative transport, a coordinated behavior that likely confers the invasive A. gracilipes a significant competitive advantage over species lacking such sophisticated cooperative strategies.

Navigation is crucial for central-place foragers to locate food and return to the nest. Cataglyphis ants are renowned for their advanced navigation abilities, relying on landmark cues and path integration. This study aims to uncover the transcriptomic basis of exceptional spatial learning in the central nervous system of Cataglyphis niger. Ants navigated a maze with a food reward, and we examined expression changes linked to correct decisions in subsequent runs. Correct decisions correlated with expression changes in the optic lobes, but not the central brain, showing a downregulation of genes associated with sucrose response and Creb3l1. The latter gene is homologous to Drosophila crebA, which is essential for long-term memory formation. To understand how ants use distance information during path integration, we analyzed expression shifts associated with the last distance traveled. We uncovered a transcriptomic footprint in the central brain, but not in the optic lobes, with genes enriched for energy consumption and neurological functions, including neuronal projection development, synaptic target inhibition, and recognition processes. This suggests that transcriptional activity in the central brain is necessary for estimating distance traveled, which is crucial for path integration. Our study supports the distinct roles of different brain parts for navigation in Cataglyphis ants.

A key hypothesis for the occurrence of senescence is the decrease in selection strength due to the decrease in the proportion of newborns from parents attaining an advanced age – the so-called selection shadow. Strikingly, queens of social insects have long lifespans and reproductive senescence seems to be negligible. By lifelong tracking of 99 Cardiocondyla obscurior (Formicidae: Myrmicinae) ant colonies, we find that queens shift to the production of sexuals in late life regardless of their absolute lifespan or the number of workers present. Furthermore, RNAseq analyses of old queens past their peak of reproductive performance showed the development of massive pathology while queens were still fertile, leading to rapid death. We conclude that the evolution of superorganismality is accompanied by ‘continuusparity,’ a life history strategy that is distinct from other iteroparous and semelparous strategies across the tree of life, in that it combines continuous reproduction with a fitness peak late in life.

Evolutionary theories of ageing predict a reduction in selection efficiency with age, a so-called “selection shadow,” due to extrinsic mortality decreasing effective population size with age. Classic symptoms of ageing include a deterioration in transcriptional regulation and protein homeostasis. Understanding how ant queens defy the trade-off between fecundity and lifespan remains a major challenge for the evolutionary theory of ageing. It has often been discussed that the low extrinsic mortality of ant queens, that are generally well protected within the nest by workers and soldiers, should reduce the selection shadow acting on old queens. We tested this by comparing strength of selection acting on genes upregulated in young and old queens of the ant, Cardiocondyla obscurior. In support of a reduced selection shadow, we find old-biased genes to be under strong purifying selection. We also analyzed a gene coexpression network (GCN) with the aim to detect signs of ageing in the form of deteriorating regulation and proteostasis. We find no evidence for ageing. In fact, we detect higher connectivity in old queens indicating increased transcriptional regulation with age. Within the GCN, we discover five highly correlated modules that are upregulated with age. These old-biased modules regulate several antiageing mechanisms such as maintenance of proteostasis, transcriptional regulation, and stress response. We observe stronger purifying selection on central hub genes of these old-biased modules compared with young-biased modules. These results indicate a lack of transcriptional ageing in old C. obscurior queens, possibly facilitated by strong selection at old age and well-regulated antiageing mechanisms.

We carried out three choice experiments with 6116 nocturnal lepidopteran individuals (95 species, 7 families, 32 075 counts), each replicated 105 times during the seasons of 2 years. Moths were released indoors at the centre of a 10 × 10 m area with different lamps placed at each corner. In experiment 1, lamps emitted ultraviolet (UV) (peak at 365 nm), blue (450 nm), green (520 nm) or cool white (450 and 520 nm) radiation. In experiment 2, UV was replaced by red (640 nm). In experiment 3, we used UV and three mixed radiation lamps of different emission intensities (365–520 nm). We applied a linear mixed effect model to test for differences in attraction to the light sources. Among all counts, 12.2% (males) and 9.2% (females) were attracted to a lamp. Among the lamp counts, 84% were made at the UV lamp in experiment 1. In experiment 2, 63% of the counts were made at the blue lamp. In experiment 3, most counts were made at the strongest mixed radiation lamp (31%), and the UV lamp (28%). Patterns were generally similar across Lepidopteran families, and for both sexes. Moths are clearly preferentially attracted to short-wave radiation. Even small quantities of UV radiation, emitted, for example, by metal halide lamps and certain mercury vapour tubes, will disproportionately contribute to light pollution. Since blue light also attracts moths strongly, lamps with a low proportion of blue light should be given priority in lighting planning.

Ecological theories predict that assembly processes shape communities so that co-existing species may either be functionally more dissimilar ("divergence") or more similar ("convergence") than expected by chance. Two important factors that are rarely considered in combination are spatial scale and successional stage. Our aim is to identify different functional patterns during succession across spatial scales and to discuss the likely underlying assembly processes. We expect to find convergence due to environmental filtering at early succession, especially at the largest scales, and a tendency towards divergence driven by competitive interactions as succession unfolds and at smaller spatial scales. Location:Protected Landscape Area “Bohemian Karst”, Czech Republic. We studied three succession stages (two, eight and 55 years after abandonment). Each field was sampled using 40 1-m2 quadrats containing 100 pins in a regular grid. We analysed trait dispersion at several combinations of grain and extent and characterised trait similarity using phylogeny and four traits: specific leaf area, leaf dry matter content, height, and seed mass analysed individually and combined using Gower distance (multi-trait dissimilarity). In the youngest field, three of the traits individually and the multi-trait dissimilarity showed convergence regardless of scale. Phylogeny showed convergence at most spatial scales of the youngest stage. The other two fields showed greater divergence predominantly in the oldest field at the smallest spatial scale. The results are mainly congruent with theoretical expectations and provide a valuable example of directional changes from trait convergence to divergence along succession. The scale-invariant convergence in the early stages of succession seems to be the result of environmental filtering and weaker competitive exclusion. At later stages and particularly at smaller scales, divergence becomes more common, likely because competition limits the trait similarity of species. These results highlight the importance of predictable (non-random) changes in ecological succession.

From the forest edge to the forest interior, a small-scale gradient in the microclimate exists. Little is known about its influence on the abundance, diversity and morphological traits of insects in Amazonian forests, a major component of global terrestrial diversity. Our study investigates these traits in Arctiinae and Geometridae moths at the interior and the edge of a Peruvian lowland rainforest (Panguana field station, Puerto Inca Province). A total of 1286 Arctiinae and 2012 Geometridae specimens were collected, sorted according to DNA barcodes and identified using relevant type material. Moths’ assemblages at the forest edge differed significantly in their composition. At the forest edge, small-sized taxa (Lithosiini, Sterrhinae, Geometrinae) were less abundant whereas larger-sized Arctiini were more abundant. Moths were significantly larger at the forest edge than inside the forest, and these differences hold at subfamily and tribal level, possibly reflecting moth mobility, and abiotic conditions of habitats: larger moths might better tolerate desiccating conditions than smaller moths. A larger proportion of females was found at the forest edge, probably due to differences in the dispersal activity among sexes and/or in the tolerance to desiccation due to size. Our results revealed the edge effect on two rich herbivorous taxa in the Amazon basin. We provide a fully illustrated catalogue of all species as a baseline for further study and conservation purposes.