Evolutionary Ecology

To maximise fitness, individuals may apply different reproductive strategies. Such strategies could be phenotypically plastic and vary depending on the environment. For example, when resources are limited females often face a trade-off between investing in offspring quantity and quality, and how she balances this trade-off may depend on the environment. For phytophagous insects, and especially generalist insects, variation in host plant quality could have large effects on mating, reproduction and offspring performance. Here, we study if the polyphagous moth Spodoptera littoralis, which selects host plants through experience-based preference induction, also has a flexible allocation between egg weight and egg number as well as in temporal egg-laying behavior depending on larval host plant species. We found that S. littoralis has a canalized egg size and that an increased reproductive investment is made in egg quantity rather than egg quality. This increased investment depends on larval host plant species, probably reflecting parental condition. The constant egg weight may be due to physiological limitations or to limited possibilities to increase fitness through larger offspring size. We furthermore found that differences in onset of egg-laying is mainly due to differences in mating propensity between individuals raised on different host plant species. Thus, females do not seem to make a strategic reproductive investment in challenging environments. Instead, the low-quality host plant induces less and later reproduction, which could have consequences for population dynamics in the field.

The escape and radiate hypothesis predicts that once species have evolved aposematism, defended species can utilise more visually diverse visual backgrounds as they escape the need to be well camouflaged. This enables species to explore new ecological niches, resulting in increased diversification rates. To test this hypothesis escape component, we examined whether the background habitats of 12 nudibranch mollusc species differed among species depending on the presence and strength of chemical defences. We obtained a rich array of colour pattern statistics using Quantitative Colour Pattern Analysis (QCPA) to analyse backgrounds viewed through the eyes of a potential predator (triggerfish, Rhinecanthus aculeatus). Colour pattern analysis was done at viewing distances simulating an escalating predation sequence. We identified four latent factors comprising 17 non-correlated colour pattern parameters, which captured the among-species variability associated with differences in chemical defences. We found that chemically defended species, indeed, were found on visually distinct backgrounds with increased colour and luminance contrast, independent of viewing distance. However, we found no evidence for increased among-species background diversity coinciding with the presence and strength of chemical defences. Our results agree with the escape and radiate hypothesis, suggesting that potent chemical defences in Dorid nudibranchs coincide with spatiochromatic differences of visual background habitats perceived by potential predators. Lay SummaryAccording to the escape and radiate hypothesis, the ability to store potent chemical defences as protection from predators enables animals to be minimally dependent on matching visual backgrounds for camouflage. We found evidence supporting this hypothesis in 12 species of nudibranch molluscs. Aposematic species were found on visual backgrounds that differed consistently in appearance from the visual background of undefended cryptic species. However, we found no difference in the variability of visual backgrounds between species with or without chemical defences. This suggests that warning colouration in eastern Australian Dorid nudibranchs coincides with broadly generalisable spatiochromatic properties of visual backgrounds.

Understanding how plant-herbivore interactions can drive coevolution is a central goal of ecology and evolutionary biology. Of particular interest are the defenses produced by host plants/fungi and their impact on herbivore feeding strategies. In the immigrans-tripunctata radiation of Drosophila, mushroom-feeding species are classified as generalists, but their acceptable hosts include deadly Amanita species. In this study, we used behavioral assays to assess whether the mushroom-feeding species Drosophila guttifera is becoming a specialist and to characterize the impact of competition on host usage. We conducted feeding assays to confirm the presence of cyclopeptide toxin tolerance. We then completed host preference assays in female flies and larvae and did not find a preference for toxic mushrooms in either. Finally, we assessed the effect of competition on oviposition preference. We found that the presence of a competitors eggs on the preferred host was associated with the flies increasing the number of eggs laid on the toxic mushrooms. Our results suggest that an adaptation associated with specialized feeding behavior is not altering host usage and that competition plays a role in maintaining this trait. More broadly our work highlights how access to a low competition host resource helps to maintain adaptations with fitness costs.

Camouflage and warning signals are contrasted prey strategies reducing predator attack, which offer an excellent opportunity to study the evolutionary forces acting on prey appearance. Edible prey are often inconspicuous and escape predation by remaining undetected. Predators learn to find the most common ones, leading to apostatic selection (advantage to rare morphs) enhancing variation in cryptic prey. By contrast, defended prey are often conspicuous and escape predation by using warning colorations identifying them as unprofitable. Predators avoid the ones they are most familiar with, leading to positive frequency-dependence and warning signal uniformity. It is less clear, however, what happens when two morphs of the same species vary strongly in conspicuousness, and how to explain the maintenance of cryptic and conspicuous morphs within populations, in the case of profitable prey. Using the white and melanic morphs of the invasive Box Tree Moth (Cydalima perspectalis) presented at three different frequencies, we investigate whether a) caterpillars and adult moths are palatable for birds, b) the less conspicuous, melanic morph experiences lower predation rates and b) whether frequency-dependence balances morph frequencies. Our results suggest that the melanic morph enjoys a survival advantage owing to a lower visibility. However, our experiments show that, unexpectedly, the two color morphs experience opposite patterns of frequency-dependent predation, despite being both fully palatable to birds. The melanic morph is under apostatic selection, whereas the conspicuous, white morph is subject to positive frequency-dependence (safety in numbers). Our experiments also show some level of unpalatability in the caterpillars. These results offer novel insight into how predation triggers contrasting evolutionary patterns in a palatable, polymorphic species within two morphs that differ markedly in conspicuousness and within two different life stages. Lay summaryUnderstanding the factors influencing character variation in natural populations is a key question in evolutionary ecology. Predation is one of the main drivers of color evolution in prey communities and prey usually mitigate predation using camouflage or warning colors. Camouflage evolves because it lowers the probability of being detected by predators. Since predators are more efficient at finding prey which they are familiar with, prey which display a rare phenotype are favoured (negative frequency-dependent selection). By contrast, aposematism is defined by conspicuous appearance in toxic or otherwise unprofitable prey, and evolves because birds identify defended prey by learning to use their appearance as a warning signal. The most common signals are usually best identified and avoided (positive-frequency dependent selection). It is not clear, however, how these two forces combine when predators are facing cryptic and conspicuous morphs of the same species, and how to explain their coexistence. Here we investigate this question in a laboratory experiment, by presenting wild birds with a melanic and a white morph of the same moth. Unexpectedly, our results show that despite being both fully palatable to birds, the two color morphs are subject to very different types of selection depending on their frequencies. The melanic morph is favored when it is rare, the conspicuous white morph as it gets common. The simultaneous action of these forces may contribute to maintain color polymorphism in natural populations. We also show that caterpillars of this species are unpalatable and chemically defended, whereas adults are not, showing opposite strategies of predator defense in different life stages of the same species.

Density-dependent selection is an important factor shaping the evolution of life histories. In holometabolous insects, crowding in the larval and adult stages can have very different effects on key fitness components. While the nuanced effects of density-dependent selection through larval crowding in Drosophila melanogaster have been extensively studied for various life history traits, very few studies have investigated the effects of adult crowding in Drosophila. Moreover, these few studies were mostly conducted on large flies, derived from low larval density cultures, and typically treated the overall density of flies per culture container as an index of the strength of adult crowding. We hypothesized that the size of the adults should shape the impact of adult crowding, with small individuals experiencing less stress than large individuals when crowded. Consequently, the adverse fitness effects usually associated with adult crowding may not be observed for small individuals. We tested this hypothesis by subjecting flies of different sizes - regular-sized flies, and small flies derived via larval crowding or selection for rapid development to adulthood - to an episode of adult crowding and examining their mortality and fecundity. Thus, we explored the interactive effects between larval and adult crowding on key fitness components. Small body size enabled flies to handle adult crowding better, with significantly lower mortality under crowded conditions when compared to flies of large body size. Moreover, small flies showed a consistent pattern of increased fecundity upon adult crowding. This positive impact on fecundity was not observed when larger flies were crowded. It is clear from our study that the effects of adult crowding can be very nuanced and body size-specific, even to the extent of having a net beneficial effect on fitness components, contrary to previous belief.

The evolution of visual traits in closely-related species living in sympatry is highly influenced by their ecological interactions: while sexual selection tends to promote the divergence of visual cues involved in mate choice, natural selection via predation may promote the convergence of dissuasive signals between prey species, especially in unpalatable or evasive prey. Here, we investigate the impact of sympatry on the evolution of the blue structural colouration in the wings of two closely-related Morpho butterfly species across several localities throughout Central and South America. Dorsal iridescence might affect mate choice and species recognition, which should promote its local divergence among species. However, the bright flashes and dynamic colour patterns produced by iridescence during flight might also increase survival by confusing predators and favouring escape. Such an effect might in turn lead to convergence in wing iridescence between evasive species occurring in sympatry, a phenomenon dubbed evasive mimicry. To test the effect of these putative antagonistic selective forces on visual cues evolution, we quantified the variation of the structural blue colour displayed at 13 different combinations of illumination/observation angles, on the wings of two closely-related Morpho species. We contrasted 10 sympatric and 11 allopatric locations and specifically compared the phenotypic distances between individuals from different species. Phenotypic distances between heterospecific pairs of individuals were significantly smaller in sympatry, consistent with the hypothesis of a local convergence of iridescence due to evasive mimicry. Interestingly, sexual dimorphism was found between males and females, suggesting that the trade-off between natural and sexual selection on the evolution of iridescence might differ between sexes. Our results suggest that local predation pressures may promote repeated evolutionary convergence of structural colouration between evasive prey species living in sympatry.

In the scenarios concerning the emergence and selection of spatiotemporal cognitive abilities in vagile plant-eating animals, there is always an implicit assumption: the distribution of plants does not change and ultimately shapes the cognitive abilities of the animals, hence their movement. Yet, if plant distribution patterns are likely to remain unchanged over short time periods, they may change over long time periods as a result of animal exploitation. In particular, animal movement can shape the environment by dispersing plant seeds. Using an agent-based model simulating the foraging behaviour of a seed disperser endowed with spatiotemporal knowledge of resource distribution, I investigated whether resource spatiotemporal patterns could be influenced by the level of cognition involved in foraging. This level of cognition represented how well resource location and phenology were predicted by the agent. I showed that seed dispersers could shape the long-term distribution of resources by materialising the routes repeatedly used by the agent with the newly recruited plants. This stemmed from the conjunction of two forces: competition for space between plants and a seed-dispersing agent moving from plant to plant based on spatiotemporal memory. In turn, resource landscape modifications affected the benefits of spatiotemporal memory. This could create eco-evolutionary feedback loops between animal spatiotemporal cognition and the distribution patterns of plant resources. Altogether, the results emphasise that foraging cognition is a cause and a consequence of resource heterogeneity.

Interspecific interactions in nature often revolve around the acquisition of nutrients. Depending on the organisms metabolic requirements, competition for specific essential nutrients may occur, which selects for increased abilities to monopolize, consume and store these nutrients. Lipid scavengers are organisms that rely on exogenous lipid acquisition as they lack the ability to synthesize fatty acids de novo or in sufficient quantity. Most parasitoid insects are lipid scavengers: they obtain all required lipids by feeding on their hosts as larvae. Here we study the nutritional ecology of competitive interactions between native Nasonia vitripennis and introduced Tachinaephagus zealandicus. While the former was already known to lack lipogenesis, we show that T. zealandicus also relies on host lipids. The interactions between the two species were studied using competition experiments, in which oviposition of T. zealandicus on a host was followed by multiparasitism by N. vitripennis. The outcome of competition was determined by the duration of the time lag between oviposition events. N. vitripennis was superior when arriving 3 days after oviposition by T. zealandicus. In contrast, 9 days after oviposition of T. zealandicus we observed complete reversal, and no N. vitripennis offspring were able to develop. Only when N. vitripennis laid eggs 15 days after T. zealandicus oviposition, both species could emerge from the same host. However, N. vitripennis realizes only 10% of its potential fitness at this time point because prior parasitization by the gregarious T. zealandicus compartmentalizes the host resources, limiting the spread of N. vitripennis venom. This study shows that successful reproduction of N. vitripennis at 15 days was achieved by hyperparasitizing, a capability that provides a fitness benefit to N. vitripennis, as it extends the time window that hosts are available for parasitization. Choice tests with hosts at different time intervals after T. zealandicus oviposition revealed a partial mismatch in N. vitripennis females between competition avoidance and offspring performance, which may be linked to the limited co-evolutionary time between native and introduced species. We discuss our results in the context of nutritional ecology and, specifically, the role of lipids in ecological interactions.

Although organ systems evolve in response to many intrinsic and extrinsic factors, frequently one factor has a dominating influence. For example, mouthpart shape and mechanics are thought to correlate strongly with aspects of the diet. Within insects, this paradigm of a shape-diet connection is advocated for decades but the relationship has so far never been quantified and is mostly based on qualitative observations. Orthoptera (grasshoppers, crickets, and allies) are a prominent case, for which mandible shape and dietary preference are thought to correlate strongly and even lead to predictions of feeding preferences. Here, we analysed mandible shape, biting efficiency, and their potential correlation with dietary categories in a phylogenetic framework for a broad sampling of several hundred extant Orthoptera covering nearly all families. The mandibular mechanical advantage was used as a descriptor of gnathal edge shape and bite force transmission efficiency. We aimed to understand how mandible shape is linked to biting efficiency and diet, and how these traits are influenced by phylogeny and allometry. The investigation reveals that feeding ecology is not the unequivocal predictor of mandible shape that it was assumed to be. There is a strong phylogenetic signal suggesting that phylogenetic history does have a much more prevalent influence on gnathal edge shape and distal mechanical advantage, than, e.g., feeding guilds or the efficiency of the force transmission to the food. Being ancestrally phytophagous, Orthoptera evolved in an environment with abundant food sources so that selective pressures leading to more specialized mouthpart shapes and force transmission efficiencies were low.

Butterflies often show adaptive phenotypic plasticity where environmental cues during early stages are used to produce a phenotype that maximizes fitness in the environment experienced by adults. Many tropical satyrine butterflies (Nymphalidae: Satyrinae) are seasonally polyphenic and produce distinct wet- and dry-season form adults providing tight environment-phenotype matching in seasonal environments. Dry-season forms, which are expressed in the dry season, can be induced in the laboratory by growing larvae at low temperatures or on poor food quality. Since both these factors also tend to reduce larval growth rate, larval growth rate may be an internal cue that translates the environmental cues into the expression of phenotypes. If this is the case, we predict that slower-growing larvae would be more likely to develop a dry-season phenotype. To test this hypothesis, we measured both larval growth rate and adult phenotype (eyespot size and wing shape) of individuals of the common evening brown butterfly (Melanitis leda), reared at various temperatures and on various host-plant species. We found that among treatments, larvae with lower growth rates (low temperature, particular host plants) were more likely to develop dry-season phenotypes (small eyespots, falcate wing tips), but within treatments, larval growth rate was mainly linked to wing shape, not eyespot size. These relationships tended to be stronger for males than females as males showed a wider range of eyespot sizes and wing shapes. Overall, only plasticity in wing shape appears to be (partly) mediated by larval growth, and in a sex-specific manner.

1Phenotypic evolution in sympatric species can be strongly impacted by species interactions, either mutualistic or antagonistic, which may favour local phenotypic divergence or convergence. Interspecific sexual interactions between sympatric species has been shown to favour phenotypic divergence of traits used as sexual cues for example. Those traits may also be involved in local adaptation or in other types of species interactions resulting in complex evolution of traits shared by sympatric species. Here we focus on mimicry and study how reproductive interference may impair phenotypic convergence between species with various levels of defences. We use a deterministic model assuming two sympatric species and where individuals can display two different warning colour patterns. This eco-evolutionary model explores how ecological interactions shape phenotypic evolution within sympatric species. We investigate the effect of (1) the opposing density-dependent selections exerted on colour patterns by predation and reproductive behaviour, and (2) the impact of relative species and phenotype abundances on the fitness costs faced by each individual depending on their species and phenotype. Our model shows that reproductive interference may limit the convergent effect of mimetic interactions and may promote phenotypic divergence between Mullerian mimics. The divergent and convergent evolution of traits also strongly depends on the relative species and phenotype abundances and levels of trophic competition, highlighting how the eco-evolutionary feedbacks between phenotypic evolution and species abundances may result in strikingly different evolutionary routes.

O_LIInsects are core actors for the balance of many earth ecosystems, as well as an alternative source of food and feed with a low ecological footprint. A comprehensive understanding of their life history requires reliable tools. Body condition constitutes the amount of energy reserves available to a fitness trait after maintenance costs have been accounted for. Body condition is standardly estimated using Body Condition Indexes (BCIs) in vertebrates. In insects the relevance of BCIs is frequently questioned on the basis that they might not accurately reflect neither energy reserves nor fitness.. However, to date no study has tested whether the very concept of body condition is relevant in insects, i.e. whether BCIs accurately reflect the relative energy reserves allocated to fitness traits. C_LIO_LIWe propose that the relevance of using BCIs in insects depends on whether their structural size has a fitness cost. If on the contrary insects only benefit from a larger body size, a simple measurement of body size or mass will predict fitness, but not a BCI. We experimentally manipulated food availability at the larval and adult stage and used total fecundity of females as a fitness proxy of Tenebrio molitor, an important model in physiology, ecology and evolution, and one of the first insects to be considered as a source of food and feed. C_LIO_LIOur results support three key assumptions of the relevance of BCIs in insects: (i) a valid BCI correlated with energy reserves corrected for a given size (i.e. relative energy reserves) and not with absolute measures of energy reserves; (ii) both structural size and body condition positively predict different components of fitness; and, (iii) the effect of body condition was dependent on resource availability, whereby its effect was only apparent and large when food was unrestricted at the larval stage and restricted at the adult stage. C_LIO_LIOverall we demonstrate the relevance of using BCIs in insects. Their use should be generalized to improve fitness readouts in evolution, ecological and physiological studies, as well as improve their husbandry for commercial purposes. C_LI

Since the classic work of E.B. Ford, alternate hypotheses have focused on explaining eyespot variation in the Meadow Brown butterfly strictly as a genetic polymorphism and the role of temperature in this classic example of natural selection has therefore been overlooked. Here we use large and continuous field collections from three sites in the UK to examine the effect of field temperature on total eyespot variation using the same presence/absence scoring as Ford. We show that higher developmental temperatures in the field lead to the disappearance of the spots visible while the butterfly is at rest, explaining Fords original observation that hindwing spotting declines across the season as temperatures increase. Analysis of wing damage supports the historical hypothesis that hindwing spots confuse aerial predators. However, as hindwing spotting declines over the season, a trade-off is suggested between their role in deflecting predators early in the season and their later developmental cost. In contrast, the large forewing eyespot is always present, scales with forewing length and its variation is best explained by day of the year rather than developmental temperature. As this large forewing spot is thought to be involved in startling predators, its constant presence is therefore likely required for defence. We model annual total spot variation with phenological data from the UK and derive predictions as to how spot patterns will continue to change under increasing summer temperatures, predicting that spotting will continue to decrease both across a single season and year or year as our climate warms. Summary statementWe show that a long-held example of genetic polymorphism, eyespot variation is the Meadow Brown butterfly, is correlated with field temperature during butterfly development.

The rapid environmental changes challenge organisms that must cope with multiple changing factors. In this ecological context, phenotypic plasticity allows organisms to rapidly react. It can occur, both within- and across generations, as a response to environmental information or to environmental quality affecting individual somatic state. Information- and state-based plasticity have largely been investigated independently, which limits theoretical developments and empirical result interpretation. In this study, we investigate the interaction between these two types of plasticity in the context of anti-predator defences, using a two-generation laboratory experiment in the snail Physa acuta. Our results revealed that both types of plasticity participate in shaping the within- and transgenerational responses. Within a generation, the limited resource decreases the individuals somatic state but did not constrain the costly expression of defences. Across generations, the poor state of parents decreased the offspring state, which in turn decreased the absolute levels of their defences. The lower defences of offspring from low-resource parents were, however, compensated by a higher reproductive success. By illustrating the intimately intertwining between information- and state-based plasticity, our study calls for increased study integrating their complex interactions to improve research about the role of phenotypic plasticity in ecology and evolution.

Predators are thought to prey on individuals that are in poor physical condition, although the evidence supporting this is ambiguous. We tested if sick individuals where more predated using Drosophila melanogaster flies as manipulable preys. We asked whether hunting spiders, trapped from the wild, would selectively prey upon flies with compromised health (i.e. chronically infected or cancerous) versus healthy flies under laboratory conditions. Flies chronically infected with the bacterium Providencia rettgeri, a natural Drosophila pathogen, were not selectively preyed upon by jumping spiders. We strengthened and confirmed our finding with another hunting spider species, small wolf spiders. We discuss that this result supports the hypothesis that chronic infection is associated with reduced symptoms notably to avoid the potentially deadly consequences of host predation on pathogens. We then induced colon cancer in some of the flies and asked whether the presence of cancer led to selective predation; there is little evidence for this, even in vertebrates. As the cancer developed, the incidence of predation by jumping spiders on the afflicted flies increased. We conclude that disease can have different lethal consequences through predation, even in invertebrate species, and that cancer is a factor in selective predation. Our results may explain why early tumours, but not metastasized cancers, are commonly detected in organisms in the wild, as cancer bearing individuals are rapidly eliminated due to the strong selective pressure against them.

Plasticity can help populations cope with environmental changes namely by exploring different ecological niches. Addressing plasticity for nutritional responses in a range of fruit hosts potentially used by Drosophila may be essential in predicting the capacity of insects to colonize new environments or return to ancestral ones. Here we test for differences in oviposition performance, reproductive success and juvenile viability in different host fruits in the colonizing species Drosophila subobscura Collin, and compare them with those of the laboratory maintenance medium to which populations adapted for [~]150 generations. We question: does Drosophila subobscura show plasticity associated with different fruit hosts? Is performance better in the long-term maintenance (control) medium? We observed a higher fecundity, reproductive success and juvenile viability of flies maintained in the fruit media versus the control, but no differences between fruits. Our experiment shows that long-term lab populations of Drosophila subobscura can still assess environmental cues of new substrates allowing for flexible adaptive plasticity to occur through increased fecundity and reproductive success in fruit hosts relative to the control conditions. Importantly, this ability was not lost during long-term evolution in a benign, homogeneous environment. Furthermore, the high performance across fruits reinforces its status as a generalist species and further attests its potential to colonize different ecological settings.

Individuals can cooperate in groups to achieve greater fitness, but the contribution of each individual to the collective good may depend on group size and on strategies employed by other members. How environmental contexts influence selection for cooperation is currently poorly understood and lacks experimental evidence from systems exhibiting behavioural plasticity in collective acts. This study investigates group size dependent selection on collective chemical defence in a gregarious pine sawfly (Neodiprion sertifer). Larvae perform chemical defence by secreting a costly deterrent fluid while adopting a U-posture. By manipulating group size and the individuals ability to deploy the defensive fluid for the collective good, we show that survival against predation is higher in cooperative groups and that the benefits gained via collective defence are more pronounced in smaller groups. As predicted by theory, individuals participate less in collective defence in larger groups than in smaller ones. This lower contribution is not attributed to higher life-history costs from increased resource competition. Altogether, these results suggest that selection for cooperation in public goods is group size dependent, promoting cooperation in smaller groups whereas the relative fitness of freeloaders is higher in larger groups.

The hypothesis of slow-fast syndromes predicts a correspondence between personality type and learning style; fast explorers would have a more proactive (fast but inflexible) learning style and slow explorers would be more reactive (slow but flexible) learners. Empirical evidence for this personality-cognition coupling remains inconclusive and heavily biased towards birds. Moreover, most studies did not examine the personality-cognition correlation when the cognitive task is discerning food quality, a scenario directly related to energy acquisition that underpins the evolution of slow-fast syndromes. In this study, we examined the exploration-cognition correlation in the context of avoidance learning in an opportunistic predator - the common sun skink Eutropis multifasciata. We quantified exploration tendencies of individuals in an unfamiliar environment and compared foraging behaviours when lizards associated prey colour and quality during the initial learning trials and subsequent reverse learning trials, where the prey colour-taste combinations were switched. We found that fast explorers were less choosy but more reactive foragers, whereas slow explorers exhibited the opposite learning style. Interestingly, there was no evidence for a learning speed-flexibility trade-off. Our findings are in contrast with conventional predictions and suggest that the two types of exploration-cognition coupling could be different viable responses to fast-changing environmental predictability.

In animal groups with dominance hierarchies, there often occurs a tug-of-war competition over resources and reproduction between dominants and subordinates, because neither is able to fully control the other. Consequently, individuals may mitigate within-group conflict, either by fighting others or by signalling their willingness to tolerate others. Nevertheless, how such a tolerance interaction evolves remains unclear. Here, we addressed this knowledge gap and tested the tug-of-war competition hypothesis, by investigating whether subordinates pay to stay in the group by helping dominants (pay-to-stay), and whether dominants pay costs by living with subordinates in the group (pay-from-staying). We used the burying beetles, Nicrophorus vespilloides, which compete with intra- and inter-specifics for valuable carcasses that are needed for reproduction. Multiple conspecifics can reproduce together through communal breeding, thereby enhancing benefits in terms of reproduction and resource defence against competitors. In communal associations, larger individuals are often dominant in carcass use and reproduction, whereas subordinates have restricted access to the carcass. Our findings show that cooperative subordinates paid costs by helping dominant breeders in carcass preparation in order to be tolerated (i.e. increased access towards the carcass) by dominant breeders, but subordinates did not increase their reproductive success by helping. Such tolerance was eliminated by a high interspecific competition with blowfly maggots. Our results also show that dominant males, but not dominant females, benefitted more from the presence of subordinates, partly due to a sex difference in the compensation strategy of dominants. Overall, our study demonstrates that a social tolerance occurring in situations with a tug-of-war competition could be a common strategy to resolve conflicts in animal societies.

Organisms must navigate complex interactions with host plants, microbial communities, and environmental cues to ensure their survival and reproductive success when adapting to novel environments. Host plant specialists can be used to study how these interactions affect fitness due to their ecological constraints. In specialist species, such as cactophilic Drosophila, it remains unclear how feeding preferences, nutritional value of the substrate, and microbial interactions collectively shape fitness outcomes. We used diverse laboratory media formulations to examine the fitness implications in Drosophila mettleri, a species that exclusively uses Saguaro cactus (Carnegiea gigantea) as its natural host plant. We found that D. mettleri did not preferentially feed on one medium compared to others, nor on C. gigantea supplemented media compared to controls. Microbial communities, especially on banana media with C. gigantea additives, appear to improve developmental success and can influence D. mettleri post-pupation success. Taken together, our results highlight the behavioral and environmental interplay between host plant substrate and microbial communities.