Lasius Niger Research Articles

Differential responses to chemical cues correlate with task performance in ant foragers

Division of labor in social insects has been explained by response threshold models which are based on differential responses to task-specific stimuli. In the present study, we argue that other types of stimuli, such as location-related cues, which are correlated with but not directly linked to task performance, may be significant. Using the black garden ant Lasius niger as a model, we focused on three groups of workers that perform extranidal tasks: (1) scouts, which explore new and unmarked areas remote from the nest; (2) patrollers, which are not recruited by other ants, but nonetheless walk outside in the nest vicinity; and (3) recruits, which are temporary foragers whose exit is triggered by recruitment. We used standardized tests to investigate, in a context-independent way, whether differences in task performance by these three groups could be correlated to intrinsic differences in their responsiveness to trail pheromone or to nest-related stimuli such as the presence of nestmates or colony odor. Overall, we found that the task profile of workers was correlated neither with their tendency to explore unmarked areas nor with their social attraction to nestmates. Scouts showed a lower attraction to colony odor and lower scores of trail following than recruits. Conversely, recruits were more attracted to colony chemical cues and showed lower response threshold to trail pheromone. Patrollers displayed behaviors between those of recruits and scouts. Our study thus shows that differences in ant responsiveness to location-related cues and recruitment trails contribute to the regulation of extranidal tasks in ants. Work organization in insect societies has been explained by models of differential response thresholds to stimuli that are directly linked to the performance of specific tasks. However, the task performance of individuals could also depend on their responsiveness to social and location-related cues that are correlated but not directly linked to these tasks. Using standardized context-independent tests, we found that scout ants, which explore unknown areas, display a lower responsiveness to colony area marking and trail pheromone. Conversely, recruits, which forage outside the nest only during food exploitation, are the most attracted to nestmates, colony area marking and trail pheromone. Patrollers display intermediate levels of attraction. Location-related cues could therefore play a role in determining the level of task performance by ants and should be taken into consideration in threshold models of task allocation.

Распределение муравьев (Hymenoptera, Formicidae) в агроландшафте на Северо-Западе России

В агроландшафте на Северо-Западе России (на полях и их обочинах, опушках лесов и отдельных участках леса) отмечено 12 видов муравьев (Hymenoptera, Formicidae) из 4 родов. На полях различных сельскохозяйственных культур собрано 8 видов муравьев. Основу комплекса полевых видов составляют Myrmica rubra и Lasius niger – эвритопные виды, способные строить гнезда в земле.
 Обилие M. rubra и L. niger на возделываемых землях значительно ниже, чем в окружающих биотопах – на обочинах полей и опушках лесов.

Division of labour in the black garden ant (Lasius niger) leads to three distinct proteomes

Task specialization in social insects leads to striking intra-specific differences in behaviour, morphology, physiology and longevity, but the underlying mechanisms remain not yet fully understood. Adult colonies of black garden ants (Lasius niger) have a single queen fertilized by one or a small number of males. The inter-individual genetic variability is thus relatively low, making it easier to focus on the individual molecular differences linked to the division of labour. Mass spectrometry-based proteomics enabled us to highlight which biological functions create the difference between queens, foragers and nest-workers. The proteome of each caste reflected nicely their social role: e.g., reproduction for queens, pesticide resistance for foragers – that are the most exposed to environmental risk factors – and, interestingly, digestion for nest-workers, thus highlighting proteomic profiles differences even among workers. Furthermore, our exploratory approach suggests energy trade-off mechanisms – in connection with the theory of social immunity – that might explain the difference in longevity between queens and workers. This study brings evidence that proteomics is able to highlight the subtle mechanisms of molecular regulation induced by social organization.

Assessment of Hymenoptera and Non-Hymenoptera Insect Bite and Sting Allergy Among Patients of Tropical Region of West Bengal, India.

West Bengal, India, is inhabited by abundance and variety of insects that triggers sensitization in some humans to inhalant allergens and/or insect stings/venoms. Lack of research on this topic prevented accurate diagnosis and proper follow-up treatments to patients suffering from insect-induced allergies. The aim of our study was to identify the allergy-causing insects and evaluate resulting sensitization among a study population in West Bengal, India. The skin prick test (SPT) evaluated sensitivity of 450 patients who sought treatment at the Allergy and Asthma Research Center from July 2017 to June 2018. Eight insect allergens were tested: Common Black Ant (Lasius niger, Linnaeus 1758), Fire Ant (Solenopsis invicta, Buren 1972), Honey Bee (Apis cerana indica, Fabricius 1798), Common Wasp (Vespula vulgaris, Linnaeus 1758), Mosquito (Aedes aegypti, Linnaeus in Hasselquist 1762), American Cockroach (Periplaneta americana, Linnaeus 1758), House Fly (Musca domestica, Linnaeus 1758), and Grasshopper (Gesonula punctifrons, Stal 1861). From a total of 450 patients evaluated, 370 patients had positive SPT reaction from at least one of the 8 insect allergens tested. Sensitivity to some Hymenoptera insects (common black ant, 87.62%; fire ant, 84.59%; and honey bee, 67.02%) was found in higher proportion than non-Hymenoptera group (mosquito, 66.67%; American cockroach, 33.33%; house fly, 10.41%; and grasshopper, 5.14%). There was significant difference in sensitivity among child, adolescent, and adult (P < 0.001). While female patients showed more sensitivity than males to SPT, the difference was statistically insignificant. In regards to occupation, farmers and bee keepers were most sensitive of field workers sensitive to Hymenoptera-derived allergens.

Body size variation of the ant Lasius niger along a metal pollution gradient

The phenotypic diversity of ant workers plays a fundamental role in their biology. In this study, we asked if the body size variation of monomorphic workers of the ant Lasius niger (Formicidae) responds adaptively to metal pollution in a post-mining metal-polluted area. Nest samples of workers were collected along a pollution gradient to calculate the within-colony variance in body size (expressed as maximum head width, HW). The results showed that the body size variation of L. niger was unrelated to the pollution index but demonstrated considerable variation between colonies even within the same study site. We suggest that the differences in morphological diversity between the colonies of L. niger could be shaped by colony personality traits, i.e., by colony-specific foraging and/or the feeding efficiency of nursing workers. The study supports previous findings, showing that morphological traits in Lasius ants are weakly related to environmental metal pollution.

Frequency of plant visits by the generalist ant Lasius niger depends on the surface microstructure of plant stems

The aim of this study was to analyze the visiting frequency of generalist ants to plants with different surface textures of their stems. We performed an experiment in which Lasius niger ants were attracted by sweet drops to flower stems of five plant species bearing different surface structures: Alchemilla mollis (wax projections and long tread-shaped trichomes), Lilium lancifolium (without wax, with ribbon-shaped trichomes and cuticular folds), Salvia nemorosa (without wax, with trichomes of various lengths and cuticular folds), Tulipa gesneriana (wax projections, no trichomes), and Paeonia lactiflora (neither of above surface features). As control samples, dry, smooth bamboo sticks were placed in the vicinity of experimental plant stems. Using cryo scanning electron microscopy, the micromorphology of stem surfaces was examined. The present study demonstrates that, on the one hand, ants avoid climbing wax-covered stems, if trichomes are lacking. On the other hand, some trichome-bearing stems having specific trichome micromorphologies were also ignored by ants. The strongest attractiveness was revealed in glossy stems and stems covered with soft/floppy trichomes. This experiment supports the hypothesis that when exposed to a diversity of plant stems in the field, generalist ants choose substrates where their locomotion is less hampered by obstacles or slipperiness of surface. Presumably, additional locomotory efforts needed to master climbing on “greasy” or “spiny” stems lead to an increase of costs-to-benefits ratio. However, since every type of stem surface was visited at least once during the experiment, it does not automatically mean that ants are not capable of walking on such challenging surfaces.

Private information conflict: Lasius niger ants prefer olfactory cues to route memory.

Foraging animals use a variety of information sources to navigate, such as memorised views or odours associated with a goal. Animals frequently use different information sources concurrently, to increase navigation accuracy or reliability. While much research has focussed on conflicts between individually learned (private) information and social information, conflicts between private information sources have been less broadly studied. Here, we investigate such a conflict by pitting route memory against associative odour cue learning in the ant Lasius niger. Ants were alternatingly trained to find a high-quality scented food source on one arm of a Y-maze, and a differently scented low-quality food source on the opposite arm. After training, ants were presented with a Y-maze in which the high- and low-quality-associated scents were presented on opposite arms than during training. The ants showed an extremely strong preferential reliance on the odour cues, with 100% of ants following the high-quality odour and thus moving towards the side associated with low-quality food. Further experiments demonstrated that ants also learn odour associations more rapidly, requiring only one visit to each odour-quality combination to form a reliable association. Side associations in the absence of odours, by contrast, required at least two visits to each side for reliable learning. While much attention has been focussed on visual route learning in insect navigation and decision-making, our results highlight the overwhelming importance of odour cues in insect path choice.

Diverse stochasticity leads a colony of ants to optimal foraging

A mathematical model of garden ants (Lasius japonicus) is introduced herein to investigate the relationship between the distribution of the degree of stochasticity in following pheromone trails and the group foraging efficiency. Numerical simulations of the model indicate that depending on the systematic change of the feeding environment, the optimal distribution of stochasticity shifts from a mixture of almost deterministic and mildly stochastic ants to a contrasted mixture of almost deterministic ants and highly stochastic ants. In addition, the interaction between the stochasticity and the pheromone path regulates the dynamics of the foraging efficiency optimization. Stochasticity could strengthen the collective efficiency when the variance in the sensitivity to pheromone for ants is introduced in the model.

ВИДОВИЙ СКЛАД КОМАХ-НЕКРОБІОНТІВ НА ДІЛЯНКАХ З РІЗНИМИ ТИПАМИ ҐРУНТІВ В ОКОЛИЦЯХ МІСТА ХАРКОВА (УКРАЇНА)

On corpses of animals in areas with different soil types, 34 species of insects from three orders and 14 families were found, among which Coleoptera (24 species) and Diptera (7 species) were registrated as dominants. The species composition of insect-necrobionts did not differ from each other in areas with different soil types (faunistic similarity by index of Chekanovsky-Sørensen – 0.66–0.78). Typical necrobionts (more than 80% of the species composition of all insects) are represented by the majority of Diptera (Calliphora vomitoria, C. vicina, Cynomyia mortuorum, Lucilia caesar, L. sericata, Fannia scalaris, Sarcophaga carnaria) and Coleoptera (Hister impressus, Saprinus semistriatus, Necrophorus fossor, Silpha obscura, Oiceptoma thoracica, Creophilus maxillosus, Thanatophilus sinuatus, Th. rugosus, Staphylinus caesareus, Creophilus maxillosus, Philonthus nitidus, Ph. addendus, Dermestes undulatus, D. frischi, D. olivieri, D. erichsoni, D. murinus, Necrobia ruficollis, N. rufipes, N. violacea, Omosita colon), among which there are both typical necrophagous and entomophagous. These species are of most practical importance in forensic entomology. Some species of beetles (Adalia bipunctata, Onthophagus coenobita, Stomis pumicatus, Tachinus humeralis) and ants (Lasius niger, Myrmica ruginodis) identified during the course of study can be attributed to the random entomofauna of the corpses (about 20% of the species composition of all Insecta).

Modulation of trail laying in the ant Lasius neglectus (Hymenoptera: Formicidae) and its role in the collective selection of a food source

AbstractIn this study, we explored the feeding behaviour of the invasive garden ant Lasius neglectus. In particular, we investigated its ability to select the more profitable resource in a binary choice and its pheromonal trail marking. When facing a choice between two different energy sources, workers were rapidly recruited to the most profitable one, although both the speed of the recruitment and the number of ants varied considerably with the difference between the solutions. When facing two identical sources, workers were massively recruited onto one of the two in 80% of tests, whereas in the remaining 20% the workforce was split equally between the two. In the second experiment, we supplied a single food source and then assessed if the number of marks per ant was affected by solution concentration and direction of movement (nestward or foodward), and if it varied over time. Marking activity increased with solution concentration, was more intense in nestward‐moving ants, and decreased over time. All these effects, although significant, were not pronounced. However, the marking activity of the very first ants visiting the resource was more intense, and this seems to be sufficient to explain the collective selection of the most valuable resource. Finally, marks were not evenly distributed along the trail, but concentrated at some points. The behaviour of L. neglectus is partly comparable to that of Lasius niger, but appears to be more similar to that of other invasive ant species, suggesting a possible primary role of the marking behaviour in influencing the invasiveness of this species.

Phenotypic correlation between queen and worker brood care supports the role of maternal care in the evolution of eusociality.

Cooperative brood care by siblings, a defining feature of eusociality, is hypothesized to be evolutionarily derived from maternal care via shifts in the timing of the expression of genes underlying maternal care. If sibling and maternal care share a genetic basis, the two behaviors are expected to be genetically and phenotypically correlated. We tested this prediction in the black garden ant Lasius niger by quantifying the brood retrieval rate of queens and their first and later generation worker offspring. Brood retrieval rate of queens was positively phenotypically correlated with the brood retrieval rate of first generation but not with later generation workers. The difference between first and later generation workers could be due to the stronger similarity in care behavior provided by queens and first generation workers compared to later generations. Furthermore, we found that queen retrieval rate was positively correlated with colony productivity, suggesting that natural selection is acting on maternal care. Overall, our results support the idea of a shared genetic basis between maternal and sibling care as well as queen and worker traits more generally, which has implications for the role of intercaste correlations in the evolution of queen and worker traits and eusociality.

Small differences in learning speed for different food qualities can drive efficient collective foraging in ant colonies

Social insects frequently make important collective decisions, such as selecting the best food sources. Many collective decisions are achieved via communication, for example by differential recruitment depending on resource quality. However, even species which only rarely recruit can respond to a changing environment on a collective level by tracking food source quality. We hypothesised that an apparent collective decision to focus on the highest quality food source can be explained by differential learning of food qualities. Overall, ants may learn the location of higher quality food faster, with most ants finally congregating at the best food source. To test the effect of reward quality and motivation on learning in Lasius niger, we trained individual ants to find sucrose molarities of varying concentrations on one arm of a T-maze in spring and in autumn after 1 or 4 days of food deprivation. As predicted, ants learned fastest in spring and lowest in autumn, with reduced food deprivation leading to slower learning. Surprisingly, the effect of food quality and motivation on the learning speed was small. However, persistence rates varied dramatically: All ants in spring made all (6) return visits to all food qualities, in contrast to only 33% of ants in autumn after 1 day of food deprivation. Fitting the empirical findings into an agent-based model revealed that even a weak tendency of ants to memorise routes to high-quality food sources faster can result in ecologically sensible colony-level behaviour. This collective-seeming decision is non-interactive, and thus resembles an annealing process. Collective decisions of insects are often achieved via communication and/or other interactions between individuals. However, animals can also make collective decisions in the absence of communication. We show that foraging motivation and food quality can affect both route memory formation speed and the likelihood to return to the food source and thus mediate selective food exploitation. An agent-based model, implemented with our empirical findings, demonstrates that at the collective level even small differences in learning lead to ecologically sensible behaviour: mildly food-deprived colonies are selective for high-quality food while highly food-deprived colonies exploit all food sources equally. We therefore suggest that non-interactive factors such as individual learning and the foraging motivation of a colony can mediate or even drive group-level behaviour in a process resembling annealing. Instead of accounting collective behaviour exclusively to social interactions, a possible contribution of individual processes should also be considered.

Tasting the unexpected: disconfirmation of expectations leads to lower perceived food value in an invertebrate.

To make sensible decisions, both humans and other animals must compare the available options against a reference point-either other options or previous experience. Options of higher quality than the reference are considered good value. However, many perceptible attributes of options are value-neutral, such as flower scent. Nonetheless, such value-neutral differences may be part of an expectation. Can a mismatch between the expectation and experience of value-neutral attributes affect perceived value? Consumer psychology theory and results suggest it can. To test this in a non-human animal, we manipulated a value-neutral aspect of a food source-its taste-while keeping its absolute value-its sweetness-the same. Individual ants (Lasius niger) were allowed to drink either lemon- or rosemary-flavoured 1 M sucrose. After three successive visits to the food, we switched the taste in the last, fourth, visit to induce a disconfirmation of expectations. In control trials, ants received the same taste on all four visits. Disconfirmed ants showed lower food acceptance and laid less pheromone on the way back to the nest, even though the molarity of the food was unchanged. As ants recruit nest-mates via pheromone depositions, fewer depositions indicate that the ants valued the food less. Thus, an expectation of value-neutral attributes can influence the perceived value of a resource. Such influences of value-neutral variables on value perception may affect how animals interact with and exploit their environment, and may contribute to phenomena such as flower constancy.

Prediction of the Ligands of the CYP9e Subfamily of Ant Cytochrome P450 with the ChEBI Ontologies of Chemical and Biological Characteristics

Cytochromes P450 are involved in the metabolism of various endogenous and exogenous compounds, and their role in the detoxification of xenobiotics has been extensively studied. CYP9e, one of the subfamilies of cytochromes P450, whose functions have been poorly studied, is amplified in the black garden ant Lasius niger. We have performed molecular modeling of 23 proteins of this family belonging to L. niger and other ant species, as well as molecular docking and virtual screening of suspected ligands. The substances used as ligands have been annotated with ChEBI ontologies to predict the chemical and biological properties of molecules forming complexes with CYP9e of ants. It has been shown that, among the ligands forming energetically favorable complexes, ChEBI ontologies of mycotoxins, phytotoxins, steroids, glycosides and terpenoids are overrepresented. Nevertheless, it has been demonstrated that in carrying out a large number of inaccurate simulations, the results of function predictions can be correlated with molecular docking and the evolutionary history of a protein family.

Voluntary switching in an invertebrate: The effect of cue and reward change.

When faced with multiple competing goals, individuals must decide which goal to attend to. Voluntary task switching is an important paradigm for testing cognitive flexibility and spontaneous decision-making when competing tasks are present. Of particular importance is the study of how reward affects task switching, as reward is perhaps the most commonly used tool for shaping both human and animal behavior. Recently, Fröber and Dreisbach (2016) demonstrated that it is not reward level per se, but reward change, which most strongly affects switching behavior in humans: Task switching was lowest when reward remained high and highest when reward is changed (increase or decrease), while the repetition of low reward showed intermediate switching levels. Here we replicate their experiment on individual foragers of the ant species Lasius niger. Using an adapted spontaneous alternation task, we find that ants' switching response in light of their immediate reward history is qualitatively identical to that of humans. In a second experiment, we show that some of this behavior can be explained by the cue change, rather than the rewards. However, patterns exist in the data which cue change cannot explain. The striking parallel in behavior between humans and insects raises questions about how reward shapes behavioral flexibility and stability in humans. (PsycINFO Database Record

When predator odour makes groups stronger: effects on behavioural and chemical adaptations in two termite species

1. Being able to detect a predator before any physical contact is crucial for individual survival. Predator presence can be detected thanks to several types of signal, such as chemical cues. Chemical signals are produced by predators for their protection against desiccation, for their communication, or possibly as a side‐effect of their activity. In insects, chemical communication plays a key role in diverse biological processes, including prey‐predator or plant‐insect interactions, courtship behaviour, and kin or species recognition.2. Cuticular hydrocarbons (CHCs) are specifically involved in recognition processes and social organisation (division of labour, caste ratios) in social insects. Here, the questions raised are whether termites can detect a predator with their cuticular compounds and whether the predator‐produced compounds can influence their prey.3. The responses of termites Reticulitermes grassei (Clément, 1978) and Reticulitermes flavipes (Kollar, 1837) to the presence of the cuticular compounds produced by a predator, the ant species Lasius niger (Linnaeus, 1758), were investigated. More specifically, the study quantified termite traits such as caste ratios, mortality rates, CHC profile homogeneity and aggressiveness of workers after 2 months' exposure to predator‐produced compounds.4. The results show that the predator odour did affect the aggressiveness of the native species R. grassei but not of the invasive R. flavipes. The caste ratios and the mortality rates were not affected for both species.5. Differences between species are discussed around the native or invasive status of each species, along with the role played by chemical cues on behavioural and chemical adaptations.

Synthesis of Insecticides from Selected Plant Materials

The quest on sustainable development has called for eco-friendly anthropogenic activities. Consequently, this research work looked into the synthesis of biodegradable fumigants from plant materials. With simple technologies, formulations with insecticidal properties were produced from Neem seeds, Garlic bulbs, Orange peels and Penny royal leaves. The formulations were prepared with the following combinations; Neem oil + Garlic extract (‘A’), Neem oil + Orange oil (‘B’), Neem oil + Penny royal (‘C’), Neem oil + Garlic extract + Orange oil + Penny royal (‘D’) and Garlic extract + Orange oil + Penny royal (‘E’). Mosquitoes (Culex spp. and Anopheles spp.), houseflies (Musca domestica) and black ants (Lasius niger) were used as test specimens for the formulations prepared. Formulation ‘A’ yielded the best insecticidal property killing mosquitoes in an average time of 1.78 ± 0.45 seconds, houseflies in 5.18 ± 0.43 seconds and black ants in 23.52 ± 0.54 seconds. The rest of the formulations produced varying results. A non-uniform performance pattern was realized when further studies were conducted on the effects of dose and distance on the potency of the formulations. A comparative study between formulation ‘A’ and a chemical insecticide revealed that, formulation ‘A’ was more potent that the chemical insecticide in killing test

Elevated expression of ageing and immunity genes in queens of the black garden ant

Studies in model organisms have identified a variety of genes whose expression can be experimentally modulated to produce changes in longevity, but whether these genes are the same as those involved in natural variation in lifespan remains unclear. Social insects boast some of the largest lifespan differences known between plastic phenotypes, with queen and worker lifespans differing by an order of magnitude despite no systematic nucleotide sequence differences between them. The contrasting lifespans of queens and workers are thus the result of differences in gene expression. We used RNA sequencing of brains and legs in 1-day-old and 2-month-old individuals of the ant Lasius niger to determine whether genes with queen-biased expression are enriched for genes linked to ageing in model organisms. Because the great longevity of queens may require investment into immune processes, we also investigated whether queen-biased genes are enriched for genes with known roles in immunity. Queen-biased genes in legs were enriched for ageing genes and for genes associated with increasing rather than decreasing lifespan. Queen-biased genes in legs were also enriched for immune genes, but only in 1-day-old individuals, perhaps linked to the changing roles of workers with age. Intriguingly, the single most differentially expressed gene between 1-day-old queen and worker brains was an extra-cellular form of CuZn Superoxide Dismutase (SOD3), raising the possibility of an important role of anti-oxidant genes in modulating lifespan.

The Effects of Cervus nippon on Two Key Ecological Drivers Controlling Populations of Plebejus argus on Heaths: Larval Food Sources and Mutualistic Ants

This study investigated the effects of grazing by invasive sika deer, Cervus nippon on the abundance of the silver-studded blue butterfly Plebejus argus on a lowland heath system in the UK. Plebejus argus is a rare species whose UK stronghold is lowland heath, where it is dependent on a mutalistic relationship with species of Lasius niger ants. Cervus nippon is an invasive species but genetically and ecologically closely related to native red deer C. elaphus and so may have positive as well as negative ecological effects. This study examines the relationship between the incidence of C. nippon and the abundance of P. argus and tests the effect of deer i) directly via their impact on vegetation structure and composition, ii) indirectly their impact on the abundance of L. niger ants. Data were collected from 37 plots of heathland in Dorset, measuring 50 m by 50 Original Research Article Woodley and Diaz; ACRI, 12(1): 1-11, 2018; Article no.ACRI.39140 2 m which were differentially grazed by deer. The abundance of P. argus was found to be significantly higher in areas with high incidence of C. nippon and the best predictor of butterfly abundance was the abundance of L. niger ants rather than the abundance of butterfly larval food plants. We conclude that this result provides evidence for an important indirect impact of grazing via manipulating habitat suitability for a key mutualistic species.

Genomic Signatures of Selection between Urban and Rural Populations of Black Garden Ant Lasius niger

Black garden ant L. niger is known as a dominant species of urban ant fauna in Europe. Successful propagation of L. niger in transformed ecosystems was associated with behavioral traits in many surveys; however, molecular and genetic basis of such adaptation was never studied. In the present study, genomes of populations from the city of Moscow and natural habitats of Moscow oblast are compared. Pooled samples from rural and urban habitats are collected and sequenced with Illumina HiSeq. SNP frequency, Tajima’s D, and fixation index are estimated with PoPoolation and Popoolation2 software. SNP frequencies are significantly different in 64 genes according to Fisher’s exact test. Some of these genes are detected as affected by recent selection. Out of 64 genes, 26 encode retrotransposon proteins. The genes of immune response to viral and fungal infections, fatty acid synthases, and elements of the Hippo/Fat pathway have different SNP frequencies between populations. Certain retrotransposon genes also can be under selection. It is important to note that repressors and mediators of RNA polymerase II are significantly different between urban and rural populations of L. niger. These genes can influence retrotransposon mobility.